Dynamics of leaf and root growth: endogenous control versus environmental impact

Adsorption rate of uranium and thorium isotopes in soil and plants grown in a high background radiation area

An important method for measuring radionuclide activity is alpha spectrometry. Ten soil samples were collected from the studied area. The activity concentrations of 238U and 234U in the collected soil samples ranged between 135 and 218 Bq kg-1 and between 117 and 183 Bq kg-1, respectively. 232Th, 230Th and 228Th activity concentrations ranged between 101 and 339, between 122 and 234 and between 106 and 385 Bq kg-1, respectively. When calculating the amount of radionuclide transport across the food chain, assessment models usually employ a transfer factor. Through root uptake, U and Th are transferred from the soil to food plants. To monitor the movement of radionuclides from the uranium series in diverse environments, it may be possible to use the ratios of uranium and thorium isotopes. Uranium mobility in soil depends on different physicochemical, organic and enzymatic factors and mechanisms. The high mobility of uranium is the main reason for the accumulation of uranium in the soil at root level and the possibility of its transfer to plants. A group of plants were selected that are grown in this area and the population relies on them mainly to meet their food needs. The concentration and transfer factor values of uranium isotopes were the highest in roots as compared with leaves and stems. Uranium in plants accumulates in roots and is then transferred to leaves. The mobility of uranium in plant tissues is constrained because it frequently adsorbs cell wall components. As a result, concentrations are frequently higher in tissues located in lower parts of the plant, with root surfaces having the highest concentrations.

Testing the effect of semi-transparent spectrally selective thin film photovoltaics for agrivoltaic application: A multi-experimental and multi-specific approach

The integration of photovoltaic technologies within the agricultural framework, known as agrivoltaics, emerges as a promising and sustainable solution to meet the growing global demands for energy and food production. This innovative technology enables the simultaneous utilization of sunlight for both photovoltaics (PV) and photosynthesis. A key challenge in agrivoltaic research involves identifying technologies applicable to a wide range of plant species and diverse geographic regions. To address this challenge, we adopt a multi-experimental and multi-species approach to assess the viability of semi-transparent, spectrally selective thin-film silicon PV technology. Our findings demonstrate compatibility with crop production in controlled environments for both plants and algae. Notably, selective thin-film PV exhibits the potential to enhance crop yields and serves as a photo-protectant. We observe that plant and algal growth increases beneath the selective PV film when supplemented with appropriate diffuse light in the growth environment. Conversely, in situations where light intensity exceeds optimal levels for plant growth, the selective PV film provides a photo-protective effect. These results suggest potential supplementary benefits of employing this technology in regions characterized by excessive light irradiation, where it can contribute to healthy plant growth.

Tapping into the plasticity of plant architecture for increased stress resilience

Plant architecture develops post-embryonically and emerges from a dialogue between the developmental signals and environmental cues. Length and branching of the vegetative and reproductive tissues were the focus of improvement of plant performance from the early days of plant breeding. Current breeding priorities are changing, as we need to prioritize plant productivity under increasingly challenging environmental conditions. While it has been widely recognized that plant architecture changes in response to the environment, its contribution to plant productivity in the changing climate remains to be fully explored. This review will summarize prior discoveries of genetic control of plant architecture traits and their effect on plant performance under environmental stress. We review new tools in phenotyping that will guide future discoveries of genes contributing to plant architecture, its plasticity, and its contributions to stress resilience. Subsequently, we provide a perspective into how integrating the study of new species, modern phenotyping techniques, and modeling can lead to discovering new genetic targets underlying the plasticity of plant architecture and stress resilience. Altogether, this review provides a new perspective on the plasticity of plant architecture and how it can be harnessed for increased performance under environmental stress.

Salt Stress-Regulation of Root Water Uptake in a Whole-Plant and Diurnal Context

This review focuses on the regulation of root water uptake in plants which are exposed to salt stress. Root water uptake is not considered in isolation but is viewed in the context of other potential tolerance mechanisms of plants-tolerance mechanisms which relate to water relations and gas exchange. Plants spend between one third and half of their lives in the dark, and salt stress does not stop with sunset, nor does it start with sunrise. Surprisingly, how plants deal with salt stress during the dark has received hardly any attention, yet any growth response to salt stress over days, weeks, months and years is the integrative result of how plants perform during numerous, consecutive day/night cycles. As we will show, dealing with salt stress during the night is a prerequisite to coping with salt stress during the day. We hope to highlight with this review not so much what we know, but what we do not know; and this relates often to some rather basic questions.

Multi-nutrient stoichiometry of Chinese hickory (Carya cathayensis) saplings: plant organs vary in their response to nitrogen fertilization

Nitrogen (N) enrichment from excessive fertilization in managed forests affects biogeochemical cycles on multiple scales, but our knowledge of how N availability shifts multi-nutrient stoichiometries (including macronutrients: N, phosphorus, potassium, calcium, magnesium and micronutrients: manganese, iron and zinc) within and among organs (root, stem and leaf) remains limited. To understand the difference among organs in terms of multi-nutrient stoichiometric homeostasis responding to N fertilization, a six-level N supply experiment was conducted through a hydroponic system to examine stem growth, multi-nutrient concentrations and stoichiometric ratios in roots, stems and leaves of 2-year-old Chinese hickory (Carya cathayensis Sarg.) saplings. Results showed that N supply significantly enhanced leaf length, width, basal diameter and sapling height. Increasing the rates of N also significantly altered multi-nutrient concentrations in roots, stems and leaves. Macronutrients generally respond more positively than micronutrients within organs. Among organs, leaves and stems generally responded more actively to N supply than roots. The stoichiometric ratios of nutrients within different organs changed significantly with N supply, but their direction and degree of change varied by organ. Specifically, increased N supply reduced the ratios of both macronutrients and micronutrients to N in plant organs, while increased N supply elevated the ratios of P to other nutrients. With N fertilization, ratios of micronutrients decreased in leaves and stems and increased in roots. In particular, leaf N and stem Mn stoichiometries responded strongly to N availability, indicating stimulated N uptake but a decreased risk of Mn2+ accumulation to excessive N. Overall, Chinese hickory saplings responded positively to increasing N availability in terms of stem growth, but the multi-nutrient stoichiometric homeostasis was distinctively organ-dependent. These results are expected to enhance our understanding of N-induced changes in homeostasis of multiple nutrients at the organ level and may offer new insights into how plants adapt to increasing N fertilization.

Contribution of Fine Roots to Soil Organic Carbon Accumulation in Different Desert Communities in the Sangong River Basin

This study explored the relationship between soil organic carbon (SOC) and root distribution, with the aim of evaluating the carbon stocks and sequestration potential under five plant communities (Alhagi sparsifolia, Tamarix ramosissima, Reaumuria soongorica, Haloxylon ammodendron, and Phragmites communis) in an arid region, the Sangong River watershed desert ecosystem. Root biomass, ecological factors, and SOC in different layers of a 0-100 cm soil profile were investigated. The results demonstrated that almost all living fine root biomass (11.78-34.41 g/m²) and dead fine root biomass (5.64-15.45 g/m²) levels were highest in the 10-20 cm layer, except for the P. communis community, which showed the highest living and dead fine root biomass at a depth of 60-70 cm. Fine root biomass showed strong seasonal dynamics in the five communities from June to October. The biomass levels of the A. sparsifolia (138.31 g/m²) and H. ammodendron (229.73 g/m²) communities were highest in August, whereas those of the T. ramosissima (87.76 g/m²), R. soongorica (66.29 g/m²), and P. communis (148.31 g/m²) communities were highest in September. The SOC of the five communities displayed strong changes with increasing soil depth. The mean SOC value across all five communities was 77.36% at 0-30 cm. The highest SOC values of the A. sparsifolia (3.08 g/kg), T. ramosissima (2.35 g/kg), and R. soongorica (2.34 g/kg) communities were found in June, and the highest value of the H. ammodendron (2.25 and 2.31 g/kg, p > 0.05) community was found in June and September. The highest SOC values of the P. communis (1.88 g/kg) community were found in July. Fine root production and turnover rate were 50.67-486.92 g/m²/year and 1.25-1.98 times per year. The relationships among SOC, fine root biomass, and ecological factors (soil water content and soil bulk density) were significant for all five communities. Based on the results, higher soil water content and soil conductivity favored the decomposition of root litter and increased fine root turnover, thereby facilitating SOC formation. Higher pH and bulk density levels are not conducive to soil biological activity and SOC mineralization, leading to increased SOC levels in desert regions.

Metabolism and autophagy in plants - A perfect match

Autophagy is a eukaryotic cellular transport mechanism that delivers intracellular macromolecules, proteins, and even organelles to a lytic organelle (vacuole in yeast and plants/lysosome in animals) for degradation and nutrient recycling. The process is mediated by highly conserved Autophagy-Related (ATG) proteins. In plants, autophagy maintains cellular homeostasis under favorable conditions, guaranteeing normal plant growth and fitness. Severe stress such as nutrient starvation and plant senescence further induce it, thus ensuring plant survival under unfavorable conditions by providing nutrients through the removal of damaged or aged proteins, or organelles. In this article, we examine the interplay between metabolism and autophagy, focusing on the different aspects of this reciprocal relationship. We show that autophagy has a strong influence on a range of metabolic processes, whereas, at the same time, even single metabolites can activate autophagy. We highlight the involvement of ATG genes in metabolism, examine the role of the macronutrients carbon and nitrogen, as well as various micronutrients, and take a closer look at how the interaction between autophagy and metabolism impacts on plant phenotypes and yield.

Variations in Morphological Characters and Antioxidant Potential of Different Plant Parts of Four Ziziphus Mill. Species from the Cholistan

Genus Ziziphus (Z.) contains various important species in tropical and subtropical regions that are globally famous for their food and medicinal uses. However, no comprehensive study was available on the morphology and phytochemistry of Ziziphus species, mainly under different growth conditions, i.e., irrigated and desert (Cholistan). Therefore, this study was carried out to evaluate the morphological and phytochemical characteristics of Ziziphus species, i.e., Z. jujuba, Z. mauritiana, Z. spina-christi, and Z. nummularia, found in the irrigated and desert conditions. Our results revealed significant variations for most of the measured parameters, showing a large-scale diversity among Ziziphus species under irrigated and desert conditions. Specifically, Ziziphus species showed better morphology of all measured parameters of leaves and fruits under irrigated conditions compared to desert conditions, indicating that the optimum water availability in irrigated conditions improved the morphological parameters of Z. species. Meanwhile, among all Ziziphus species, the maximum leaf length (7.4 cm), leaf width (4.1 cm), leaf area (30.6 cm²), and leaf petiole length (1.3 cm) were observed for Z. jujuba, and the highest leaf dry weight (55.4%) was recorded for Z. mauritiana. Similarly, the highest fruit length (3.9 cm), fruit stalk length (1.5 cm), fruit diameter (3.6 cm), fruit width (3.8 cm), fruit area (66.1 cm²), seed length (2 cm), and seed diameter (1.1 cm) were measured for species Z. jujuba, while the maximum fruit dry weight (49.9%) and seed width (1.4 cm) were recorded for species Z. nummularia. Interestingly, compared to irrigated conditions, higher values of bioactive contents, i.e., phenol, flavonoid, and antioxidant activity, in fruits and leaves of Ziziphus species under desert conditions indicated the positive impact of desert climate on the phytochemistry of the Z. plants. Among Ziziphus species, Z. nummularia accumulated the maximum fruit phenols (304.4 mg GAE/100 g), leaf phenols (314.2 mg GAE/100 g), fruit flavonoids (123.7 mg QE/100 g), and leaf flavonoids (113.4 mg QE/100 g). Overall, this study demonstrated the significant morphological and phytochemical variations of the Ziziphus species under irrigated and desert conditions, which could be utilized for future studies to improve the production and medicinal potential of the Ziziphus, especially in desert areas.

Energy-Saving LED Light Affects the Efficiency of the Photosynthetic Apparatus and Carbohydrate Content in Gerbera jamesonii Bolus ex Hook. f. Axillary Shoots Multiplied In Vitro

An energy-saving light emitting diode (LED) system allows for adjustment of light quality, which affects plant development and metabolic processes in in vitro cultures. The study investigated the content of endogenous carbohydrates and the condition of the photosynthetic apparatus of Gerbera jamesonii Bolus ex Hook. f. Our aim was to analyze the effects of different LED light qualities-100% red light (R LED), 100% blue (B LED), a mixture of red and blue (7:3) (RB LED), and a fluorescent lamp as a control (Fl)-during the multiplication of axillary shoots. After 40 days, the culture measurements were performed using a non-invasive pulse amplitude modulation (PAM) fluorimeter. Sugar content was assessed with high performance liquid chromatography (HPLC). Two forms of free monosaccharides (glucose and fructose), two sugar alcohol derivatives (inositol and glycerol), and seven forms of free oligosaccharides were identified. Of those, glucose content was the highest. LEDs did not disturb the sugar metabolism in multiplied shoots. Their monosaccharides were three times more abundant than oligosaccharides; the same results were found in plants grown under control light. R light depleted the performance of the photosynthetic apparatus and caused its permanent damage. The RB LED spectrum ensured the most efficient non-photochemical quenching of the photosystem II (PS II) excitation state and high shoot quality.

Ageing affects microplastic toxicity over time: Effects of aged polycarbonate on germination, growth, and oxidative stress of Lepidium sativum

Plastic has been an environmental pollutant far longer than claimed by the first reports surfacing in 1979, meaning some plastic materials have been decaying in nature for decades. Nevertheless, the threat posed to biota is not fully understood, especially from aged microplastic. The question considered in this study was whether the adverse effects of new plastic differ from those of old plastic material. Therefore, the morphological and physiological effects on Lepidium sativum with exposure to both new and aged polycarbonate were considered against a known stressor leaching from polycarbonate with time, bisphenol-A. Exposure to new and short-term aged polycarbonate (up to 80 days) elicited the most severe effects such as germination inhibition, reduced seedling growth, decreased chlorophyll concentrations, and increased catalase activity. These adverse effects in L. sativum associated with polycarbonate exposure were reduced as a function of the ageing time applied to the polycarbonate. The chemical substances that lend new polycarbonate material its toxicity were likely leached with time during the ageing process. Based on the results obtained, temperature and humidity based artificial ageing significantly reduced the phytotoxicity of the microplastic particles.

Case Study Comparing Effects of Microplastic Derived from Bottle Caps Collected in Two Cities on Triticum aestivum (Wheat)

As plastic has become an integral component of daily life, microplastic has become a ubiquitous, unavoidable constituent of nearly all ecosystems. Besides monitoring the amount and distribution of microplastic in the environment, it is necessary to understand the possible direct effects, especially toxicity and how it is affected by environmental factors where it is discarded. The present study investigated how microplastic derived from high-density polyethylene bottle caps collected in two climatically different cities, i.e., Singapore (tropical rainforest climate) and Lahti, Finland (continental climate), affected the essential agricultural grain crop, Triticum aestivum (L.). Wheat seedlings were exposed to microplastic derived from these collected bottle caps, as well as new and artificially aged caps, for seven days. Morphological parameters, such as root and shoot length and oxidative stress development, were measured. Exposure to microplastic derived from the caps resulted in reduced seedling root and shoot lengths compared to the controls, as well as enhanced lipid peroxidation and catalase activity. With all parameters tested, microplastic derived from Lahti bottle caps exhibited more severe effects than Singapore, which was similar to that elicited by new microplastic. The Singapore microplastic had possibly leached its toxic substances before collection due to accelerated degradation promoted by the prevailing warmer climate conditions.

Developmental stochasticity and variation in floral phyllotaxis

Floral phyllotaxis is a relatively robust phenotype; trimerous and pentamerous arrangements are widely observed in monocots and core eudicots. Conversely, it also shows variability in some angiosperm clades such as 'ANA' grade (Amborellales, Nymphaeales, and Austrobaileyales), magnoliids, and Ranunculales. Regardless of the phylogenetic relationship, however, phyllotactic pattern formation appears to be a common process. What are the causes of the variability in floral phyllotaxis and how has the variation of floral phyllotaxis contributed to floral diversity? In this review, I summarize recent progress in studies on two related fields to develop answers to these questions. First, it is known that molecular and cellular stochasticity are inevitably found in biological systems, including plant development. Organisms deal with molecular stochasticity in several ways, such as dampening noise through gene networks or maintaining function through cellular redundancy. Recent studies on molecular and cellular stochasticity suggest that stochasticity is not always detrimental to plants and that it is also essential in development. Second, studies on vegetative and inflorescence phyllotaxis have shown that plants often exhibit variability and flexibility in phenotypes. Three types of phyllotaxis variations are observed, namely, fluctuation around the mean, transition between regular patterns, and a transient irregular organ arrangement called permutation. Computer models have demonstrated that stochasticity in the phyllotactic pattern formation plays a role in pattern transitions and irregularities. Variations are also found in the number and positioning of floral organs, although it is not known whether such variations provide any functional advantages. Two ways of diversification may be involved in angiosperm floral evolution: precise regulation of organ position and identity that leads to further specialization of organs and organ redundancy that leads to flexibility in floral phyllotaxis.

Does a trade-off between growth plasticity and resource conservatism mediate post-fire shrubland responses to rainfall seasonality?

Growth plasticity may allow fire-prone species to maximize their recovery rates during temporary, sporadic periods of rainfall availability in the post-fire environment. However, moisture-driven growth plasticity could be maladaptive in nutrient-limited environments that require tighter control of growth and resource use. We investigated whether a trade-off between plasticity and conservatism mediates growth responses to altered rainfall seasonality in neighbouring shrubland communities that occupy different soils. We monitored post-fire vegetation regrowth in two structurally similar, Mediterranean-type shrublands for 3 years. We investigated the effects of experimentally altered rainfall seasonality on post-fire species' growth rates. We found that moisture-driven growth plasticity was higher among species occupying the fertile soils of the renosterveld site relative to those occupying the nutrient-poor soils of the fynbos site. This resulted in higher overall responsiveness of post-fire recovery patterns in renosterveld to experimental shifts in rainfall seasonality. In post-fire shrubland communities, the trade-off between moisture-dependent growth plasticity and resource conservatism could be mediated by soil nutrient availability. Therefore, edaphic differences between structurally similar shrublands could lead to differences in their sensitivity to post-fire rainfall seasonality.

Robust Surface Reconstruction of Plant Leaves from 3D Point Clouds

The automation of plant phenotyping using 3D imaging techniques is indispensable. However, conventional methods for reconstructing the leaf surface from 3D point clouds have a trade-off between the accuracy of leaf surface reconstruction and the method's robustness against noise and missing points. To mitigate this trade-off, we developed a leaf surface reconstruction method that reduces the effects of noise and missing points while maintaining surface reconstruction accuracy by capturing two components of the leaf (the shape and distortion of that shape) separately using leaf-specific properties. This separation simplifies leaf surface reconstruction compared with conventional methods while increasing the robustness against noise and missing points. To evaluate the proposed method, we reconstructed the leaf surfaces from 3D point clouds of leaves acquired from two crop species (soybean and sugar beet) and compared the results with those of conventional methods. The result showed that the proposed method robustly reconstructed the leaf surfaces, despite the noise and missing points for two different leaf shapes. To evaluate the stability of the leaf surface reconstructions, we also calculated the leaf surface areas for 14 consecutive days of the target leaves. The result derived from the proposed method showed less variation of values and fewer outliers compared with the conventional methods.

Photosynthetically active radiation impacts significantly on root and cell hydraulics in barley (Hordeum vulgare L.)

Photosynthetically active radiation (PAR) affects transpirational water loss, yet we do not know through which mechanisms root water uptake is adjusted in parallel. Here, we exposed hydroponically grown barley plants to three levels of PAR [Normal (control), Low, High] and focused on the role which aquaporins (AQPs), apoplastic barriers (Casparian bands, suberin lamellae) and root morphology play in the adjustment of root hydraulic conductivity (Lp). Plants were analyzed when they were 14-18 days (d) old. Root and cell Lp, which involves AQP activity, was determined through exudation and cell pressure probe measurements, respectively. Gene expression of AQPs was analyzed through qPCR. The formation of apoplastic barriers was studied through staining of cross-sections. The rate of transpirational water loss per plant and unit leaf area increased in response to high-PAR and decreased in response to low-PAR treatments, both during day and night. Hydraulic conductivity in roots decreased significantly at organ and cell level in response to Low-PAR, and increased (organ) or did not change (cell level) in response to High-PAR. The formation of apoplastic barriers was little affected by PAR. Gene expression of AQPs tended to be highest in the Low-PAR treatment. Lateral roots, showing few apoplastic barriers, contributed the least in Low- and the most to root surface area in High-PAR plants. It is concluded that barley plants which experience changes in shoot transpirational water loss in response to PAR adjust root water uptake through changes in root Lp, and that these changes are mediated through altered AQP activity and root morphology.

Nitrogen application mitigates drought-induced metabolic changes in Alhagi sparsifolia seedlings by regulating nutrient and biomass allocation patterns

Groundwater and its associated nutrients sustain the establishment and persistence of phreatophytes. Rapid root elongation immediately after germination is vital for desert species to access deep water sources to avoid water-deficit stress. However, the growth strategy and responses to nutrients and water of young phreatophyte seedlings before their roots reach the water table are poorly understood, especially in the scenarios of nitrogen (N) deposition and drought. We investigated how simulated N deposition and drought affect the plasticity of Alhagi sparsifolia seedlings by multiple eco-physiological mechanisms. Seedlings were planted under drought-stressed or well-watered conditions and subjected to various levels of N addition (0, 3.0, 6.0, or 9.0 gN·m^-2 yr^-1). The amounts of N and water independently or interactively affected the photosynthetic traits, drought tolerance characteristics, morphological traits, biomass allocation strategy, and nutrient distribution patterns among the plant organs. Moreover, changes mediated by N addition at the leaf level reflected the drought acclimation of the seedlings, which may be related to biomass and nutrient partitioning between organs. The roots were found to be more sensitive to variation of the N:phosphorus (P) ratio, and greater proportions of biomass, N, and P were allocated to resource-acquiring organs (i.e., leaves and fine roots) than to other tissues. A. sparsifolia adopts numerous strategies to tolerate drought, and additional N input was crucial to enhance the growth of drought-stressed A. sparsifolia, which was mainly attributable to its positive impact on the N and P uptake capacity mediated by increased biomass allocation to the roots.

Maize Straw Strip Mulching as a Replacement for Plastic Film Mulching in Maize Production in a Semiarid Region

Straw strip mulching in maize (Zea mays L.) production is showing a positive effect with the increasing negative effects coming from crop straw and plastic film residues. Therefore, it is imperative to develop comprehensive utilization of straw, and promote the green development of agriculture in rainfed regions. A dryland field experiment was conducted in semiarid northwestern China in 2017 and 2018 and included three treatments: maize straw strip mulching with alternating strips of mulched and non-mulched soil (MSSM), and double ridge-furrow fully mulched soil with white or black plastic film (DRWP or DRBP, respectively). The results show that the interaction between mulching treatment and year significantly influenced maize silage yield, grain yield, biomass yield, aboveground plant water content at silage maize harvest stage, ears ha−1, kernels ear−1, and thousand kernel weight (p < 0.001, p = 0.002, p < 0.001, p < 0.001, p < 0.001, p < 0.001, p < 0.001, and p < 0.001, respectively). For silage, maize growth under straw strip mulching was greater than that of the double ridge mulching system. Silage yield of MSSM was significantly higher than that of DRWP and DRBP, but maize grain and biomass yields under MSSM were significantly lower those under DRWP and DRBP in 2017 and 2018. Compared with the double ridge mulching system, net economic return from silage with MSSM was significantly increased by 28.31% and 20.85% in 2017 and 2018, respectively, and net economic return from grain was 6.67% lower in 2017 and 2.34% higher in 2018. The MSSM treatment exhibited water-temperature coupling; the MSSM treatment significantly reduced soil temperature in the 0–25 cm soil layer by 1.23–2.14 °C and increased soil water storage in the 0–200 cm soil layer by 9.75 and 24.10 mm in 2017 and 2018, respectively, thereby delaying growth development of maize by about 13 days. Therefore, straw mulch can replace plastic film mulch and serve as an environmentally friendly cultivation method for maize in semiarid rainfed regions.

Consequences of removal of exotic species (eucalyptus) on carbon and nitrogen cycles in the soil-plant system in a secondary tropical Atlantic forest in Brazil with a dual-isotope approach

The impact of exotic species on heterogeneous native tropical forest requires the understanding on which temporal and spatial scales these processes take place. Functional tracers such as carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopic composition in the soil-plant system might help track the alterations induced by the exotic species. Thus, we assess the effects from the removal of the exotic species eucalyptus (Corymbia cytriodora) in an Atlantic forest Reserve, and eucalyptus removal on the alteration of the nutrient dynamics (carbon and nitrogen). The hypotheses were: (1) the eucalyptus permanence time altered δ¹³C and δ¹⁵N in leaves, soils and litter fractions (leaves, wood, flowers + fruits, and rest); and (2) eucalyptus removal furthered decomposition process of the soil organic matter. Hence, we determined the soil granulometry, the δ¹³C and δ¹⁵N in leaves, in the superficial soil layer, and litter in three sites: a secondary forest in the Atlantic forest, and other two sites where eucalyptus had been removed in different times: 12 and 3 months ago (M12 and M3, respectively). Litter samples presented intermediate δ¹³C and δ¹⁵N values in comparison with leaves and soil. In the M3, the greater δ¹³C values in both litter rest fraction and soil indicate the presence, cycling and soil incorporation of C, coming from the C₄ photosynthesis of grassy species (Poaceae). In the secondary forest, the soil δ¹⁵N values were twice higher, compared with the eucalyptus removal sites, revealing the negative influence from these exotic species upon the ecosystem N dynamics. In the M12, the leaves presented higher δ¹³C mean value and lower δ¹⁵N values, compared with those from the other sites. The difference of δ¹³C values in the litter fractions regarding the soil led to a greater fractioning of ¹³C in all sites, except the flower + fruit fractions in the secondary forest, and the rest fraction in the M3 site. We conclude that the permanence of this exotic species and the eucalyptus removal have altered the C and N isotopic and elemental compositions in the soil-plant system. Our results suggest there was organic matter decomposition in all litter fractions and in all sites. However, a greater organic matter decomposition process was observed in the M3 soil, possibly because of a more intense recent input of vegetal material, as well as the presence of grassy, easily-decomposing herbaceous species, only in this site. Therefore, the dual-isotope approach generated a more integrated picture of the impact on the ecosystem after removing eucalyptus in this secondary Atlantic forest, and could be regarded as an option for future eucalyptus removal studies.

Functional Traits, Morphology, and Herbage Production of Vernalised and Non-Vernalised Chicory cv. Choice (Cichorium intybus L.) in Response to Defoliation Frequency and Height

Chicory (Cichorium intybus L.) used in pastoral systems has the attributes required of a forage species to reduce animal urinary nitrogen loading to soil, increase milk production, and enhance milk fatty acid profile to improve pastoral farm systems for matching increasing global demand for dairy products and environmental standards of livestock systems. Greater adoption of chicory requires confidence in management decisions that can control risks to farm production, namely bolting after vernalisation or a decline in persistence of chicory swards, which have slowed its adoption in pastoral systems. We, therefore, measured functional traits, morphology and herbage production of chicory under irrigated field conditions before and after vernalisation in Canterbury, New Zealand. The experimental site was laid out in a complete randomized block design with four replications where two regrowth intervals and two defoliation heights were applied. Regrowth interval had a stronger influence over functional traits and herbage production than defoliation height, with more pronounced effects after vernalisation. Plants managed under shorter regrowth intervals had narrower roots with lower concentration of sugars than plants under longer intervals, which might compromise their longevity. In addition, plants managed under shorter intervals remained mostly vegetative with heavier and longer leaves, though with reduced photosynthetic capacity than those managed under longer intervals. The thermal time to initiate stem elongation in plants managed under longer intervals was ~274 growing degree-days, with a mean stem elongation rate increasing linearly at 1.4 ± 0.08 mm/growing degree-days. The key outcomes of this research quantify the growing degree-days to initiate stem elongation post vernalisation, which provides management directive for timing of defoliation of chicory in order to maintain feed quality for grazing livestock. Alternating frequent and infrequent defoliation regimes might be used to optimise vegetative growth, root reserves, and pasture persistence.

Appraisal of wheat genomics for gene discovery and breeding applications: a special emphasis on advances in Asia

We discussed the most recent efforts in wheat functional genomics to discover new genes and their deployment in breeding with special emphasis on advances in Asian countries. Wheat research community is making significant progress to bridge genotype-to-phenotype gap and then applying this knowledge in genetic improvement. The advances in genomics and phenomics have intrigued wheat researchers in Asia to make best use of this knowledge in gene and trait discovery. These advancements include, but not limited to, map-based gene cloning, translational genomics, gene mapping, association genetics, gene editing and genomic selection. We reviewed more than 57 homeologous genes discovered underpinning important traits and multiple strategies used for their discovery. Further, the complementary advancements in wheat phenomics and analytical approaches to understand the genetics of wheat adaptability, resilience to climate extremes and resistance to pest and diseases were discussed. The challenge to build a gold standard reference genome sequence of bread wheat is now achieved and several de novo reference sequences from the cultivars representing different gene pools will be available soon. New pan-genome sequencing resources of wheat will strengthen the foundation required for accelerated gene discovery and provide more opportunities to practice the knowledge-based breeding.

All roads lead to growth: imaging-based and biochemical methods to measure plant growth

Plant growth is a highly complex biological process that involves innumerable interconnected biochemical and signalling pathways. Many different techniques have been developed to measure growth, unravel the various processes that contribute to plant growth, and understand how a complex interaction between genotype and environment determines the growth phenotype. Despite this complexity, the term 'growth' is often simplified by researchers; depending on the method used for quantification, growth is viewed as an increase in plant or organ size, a change in cell architecture, or an increase in structural biomass. In this review, we summarise the cellular and molecular mechanisms underlying plant growth, highlight state-of-the-art imaging and non-imaging-based techniques to quantitatively measure growth, including a discussion of their advantages and drawbacks, and suggest a terminology for growth rates depending on the type of technique used.

Fluttering of growing leaves as a way to reach flatness: experimental evidence on Persea americana

Simple leaves show unexpected growth motions: the midrib of the leaves swings periodically in association with buckling events of the leaf blade, giving the impression that the leaves are fluttering. The quantitative kinematic analysis of this motion provides information about the respective growth between the main vein and the lamina. Our three-dimensional reconstruction of an avocado tree leaf shows that the conductor of the motion is the midrib, presenting continuous oscillations and inducing buckling events on the blade. The variations in the folding angle of the leaf show that the lamina is not passive: it responds to the deformation induced by the connection to the midrib to reach a globally flat state. We model this movement as an asymmetric growth of the midrib, which directs an inhomogeneous growth of the lamina, and we suggest how the transition from the folded state to the flat state is mechanically organized.

Genome-wide association mapping in a diverse spring barley collection reveals the presence of QTL hotspots and candidate genes for root and shoot architecture traits at seedling stage

BACKGROUND

Adaptation to drought-prone environments requires robust root architecture. Genotypes with a more vigorous root system have the potential to better adapt to soils with limited moisture content. However, root architecture is complex at both, phenotypic and genetic level. Customized mapping panels in combination with efficient screenings methods can resolve the underlying genetic factors of root traits.

RESULTS

A mapping panel of 233 spring barley genotypes was evaluated for root and shoot architecture traits under non-stress and osmotic stress. A genome-wide association study elucidated 65 involved genomic regions. Among them were 34 root-specific loci, eleven hotspots with associations to up to eight traits and twelve stress-specific loci. A list of candidate genes was established based on educated guess. Selected genes were tested for associated polymorphisms. By this, 14 genes were identified as promising candidates, ten remained suggestive and 15 were rejected. The data support the important role of flowering time genes, including HvPpd-H1, HvCry2, HvCO4 and HvPRR73. Moreover, seven root-related genes, HERK2, HvARF04, HvEXPB1, PIN5, PIN7, PME5 and WOX5 are confirmed as promising candidates. For the QTL with the highest allelic effect for root thickness and plant biomass a homologue of the Arabidopsis Trx-m3 was revealed as the most promising candidate.

CONCLUSIONS

This study provides a catalogue of hotspots for seedling growth, root and stress-specific genomic regions along with candidate genes for future potential incorporation in breeding attempts for enhanced yield potential, particularly in drought-prone environments. Root architecture is under polygenic control. The co-localization of well-known major genes for barley development and flowering time with QTL hotspots highlights their importance for seedling growth. Association analysis revealed the involvement of HvPpd-H1 in the development of the root system. The co-localization of root QTL with HERK2, HvARF04, HvEXPB1, PIN5, PIN7, PME5 and WOX5 represents a starting point to explore the roles of these genes in barley. Accordingly, the genes HvHOX2, HsfA2b, HvHAK2, and Dhn9, known to be involved in abiotic stress response, were located within stress-specific QTL regions and await future validation.

Night-Time Transpiration - Favouring Growth?

Plants grow and transpire water during the day and night. Recent work highlights the idea that night-time transpirational water loss is a consequence of allowing respiratory CO₂ to escape at sufficiently high rates through stomata. Respiration fuels night-time leaf expansion and requires carbohydrates produced during the day. As carbohydrate availability and growth are under the control of the plants' internal clock, so is night-time transpiration. The cost of night-time transpiration is that water is lost without carbon being gained, the benefit is a higher efficiency of taken up water for use in leaf expansion. This could provide a stress acclimation process.

Plant Phenotyping: Past, Present, and Future

A plant develops the dynamic phenotypes from the interaction of the plant with the environment. Understanding these processes that span plant's lifetime in a permanently changing environment is essential for the advancement of basic plant science and its translation into application including breeding and crop management. The plant research community was thus confronted with the need to accurately measure diverse traits of an increasingly large number of plants to help plants to adapt to resource-limiting environment and low-input agriculture. In this overview, we outline the development of plant phenotyping as a multidisciplinary field. We sketch the technological advancement that laid the foundation for the development of phenotyping centers and evaluate the upcoming challenges for further advancement of plant phenotyping specifically with respect to standardization of data acquisition and reusability. Finally, we describe the development of the plant phenotyping community as an essential step to integrate the community and effectively use the emerging synergies.

Plant Phenotyping: Past, Present, and Future

A plant develops the dynamic phenotypes from the interaction of the plant with the environment. Understanding these processes that span plant's lifetime in a permanently changing environment is essential for the advancement of basic plant science and its translation into application including breeding and crop management. The plant research community was thus confronted with the need to accurately measure diverse traits of an increasingly large number of plants to help plants to adapt to resource-limiting environment and low-input agriculture. In this overview, we outline the development of plant phenotyping as a multidisciplinary field. We sketch the technological advancement that laid the foundation for the development of phenotyping centers and evaluate the upcoming challenges for further advancement of plant phenotyping specifically with respect to standardization of data acquisition and reusability. Finally, we describe the development of the plant phenotyping community as an essential step to integrate the community and effectively use the emerging synergies.

Physiological Effects of Copper Oxide Nanoparticles and Arsenic on the Growth and Life Cycle of Rice ( Oryza sativa japonica 'Koshihikari')

A factorial study was conducted to evaluate the phytotoxicity of copper oxide nanoparticles (nCuO, 0.1-100 mg/L), arsenic (As, 0 and 10 mg/kg), and their interaction to rice plants ( Oryza sativa japonica 'Koshihikari') during the life cycle. No significant effect was observed on seed germination. The main effects of nCuO and As were observed on lengths and biomasses of seedling shoots and roots and on root branching. The interaction between nCuO and As also significantly influenced these parameters. nCuO addition increased Cu uptake in seedlings and generally improved seedling growth. With As addition, As was highly concentrated in roots and increased in shoots, and seedling growth was also inhibited. Additionally, nCuO and As had significant main and interaction effects on mature plant dry biomass, panicle number, total grain weight, average grain weight, and several other panicle parameters. Moreover, nCuO and As interacted to affect panicle emergence. nCuO also decreased As accumulation in dehusked grains. The accelerated heading stage by nCuO may help shorten the life cycle of rice plants, thereby reducing As accumulation in grains. This study is the first to examine the influence of nCuO in combination with As on the life cycle of rice plants.

Global analysis of an exponential model of cell proliferation for estimation of cell cycle duration in the root apical meristem of angiosperms

Background and Aims

Information on cell cycle duration (T) in the root apical meristem (RAM) provides insight into root growth, development and evolution. We have previously proposed a simple method for evaluating T based on the dynamics of root growth (V), the number of cells in the RAM (Nm) and the length of fully elongated cells (l), which we named the rate-of-cell-production (RCP) method. Here, a global analysis was performed to confirm the reliability of this method in a range of angiosperm species and to assess the advantages of this approach.

Methods

We measured V, Nm and l from live or fixed cleared primary roots of seedlings or adventitious roots of bulbs and used this information to estimate the average T values in 73 angiosperm species via the RCP method. The results were then compared with published data obtained using the classical but laborious and time-consuming 3H-thymidine method.

Key Results

In most species examined, the T values obtained by the RCP method were nearly identical to those obtained by the 3H-thymidine method.

Conclusions

The global analysis demonstrated that the relationship between the variables V, Nm and l in roots in the steady state of growth is correctly described by the equation T = (ln2 Nm l)V-1. Thus, the RCP method enables cell cycle duration in the RAM to be rapidly and accurately determined. This method can be performed using live or fixed roots for each individual cell type. The simplicity of the approach suggests that it will be widely used in phenomics, evolutionary ecology and other plant biology studies.

Diurnal variation in gas exchange and nonstructural carbohydrates throughout sugarcane development

Photosynthesis and growth are dependent on environmental conditions and plant developmental stages. However, it is still not clear how the environment and development influence the diurnal dynamics of nonstructural carbohydrates production and how they affect growth. This is particularly the case of C4 plants such as sugarcane (Saccharum spp.). Aiming to understand the dynamics of leaf gas exchange and nonstructural carbohydrates accumulation in different organs during diurnal cycles across the developmental stages, we evaluated these parameters in sugarcane plants in a 12-month field experiment. Our results show that during the first 3 months of development, light and vapour pressure deficit (VPD) were the primary drivers of photosynthesis, stomatal conductance and growth. After 6 months, in addition to light and VPD, drought, carbohydrate accumulation and the mechanisms possibly associated with water status maintenance were also likely to play a role in gas exchange and growth regulation. Carbohydrates vary throughout the day in all organs until Month 9, consistent with their use for growth during the night. At 12 months, sucrose is accumulated in all organs and starch had accumulated in leaves without any diurnal variation. Understanding of how photosynthesis and the dynamics of carbohydrates are controlled might lead to strategies that could increase sugarcane's biomass production.

Simulated nitrogen deposition affects stoichiometry of multiple elements in resource-acquiring plant organs in a seasonally dry subtropical forest

Increase of anthropogenic atmospheric nitrogen (N) deposition markedly influences biogeochemical cycles of elements in a wide range of ecosystems. However, our knowledge of how N deposition affects stoichiometry of plants in forests experiencing regular seasonal droughts remains limited. Using a 3-year (2013-2015) N-manipulative experiment, we examined the stoichiometric responses of ten mineral elements, including the most limiting elements (N and P) to plant growth, base cations (K, Ca, and Mg), and trace metal cations (Mn, Zn, Cu, Al, and Fe) in resource-acquiring organs (foliage vs. absorptive roots) of Pinus elliottii to N additions in both wet and dry seasons in a seasonally dry subtropical forest. Stoichiometric responses of both organs depended on rate of N addition (generally stronger under high rate) and season. N additions increased foliar [N] and decreased foliar [P] only in dry season and the relative changes in foliar N:P ratio were twice higher in dry than wet seasons, suggesting an aggravated P limitation in dry season. The stoichiometry of absorptive roots was more responsive to N additions than that of foliage, especially for the base cations. N additions increased [Mn] and decreased Fe:Mn ratio in both organs, indicating increased risk of Mn²⁺ toxicity to this tree species. Our results have implications for understanding the N-induced changes in nutrient limitation of forests influenced by seasonal drought, and highlight the contrasting stoichiometric responses of above- and below-ground resource-acquiring plant organs to N loading.

Circadian regulation of grapevine root and shoot growth and their modulation by photoperiod and temperature

Some plant species demonstrate a pronounced 24 h rhythm in fine root growth but the endogenous and exogenous factors that regulate these diel cycles are unclear. Photoperiod and temperature are known to interact with diel patterns in shoot growth but it is uncertain how these environmental factors are interrelated with below-ground growth. In this particular study, the fine root system of two grapevine species was monitored over a period of ten days with a high resolution scanner, under constant soil moisture and three different photoperiod regimes. Pronounced diel rhythms in shoot and root growth rates were apparent under a fixed 14 h photoperiod. Maximal root growth rate occurred 1-2 h prior to- and until 2 h after the onset of darkness. Subsequently, during the latter part of the dark period, root growth rate decreased and reached minimal values at the onset of the light period. Relative to 22 °C, exposure to a 30 °C air and soil temperature halved root growth but stimulated shoot growth. Notably, the shoot extension rate peak shifted from late afternoon to midnight at this higher temperature zone. When plants were exposed to a delayed photoperiod or progressively shortening photoperiod, the diel changes in root growth rate followed the same pattern as in the fixed photoperiod, regardless of whether the plant was in light or dark. This suggests that light was not the predominant trigger for stimulating root elongation. Conversely, shoot growth rates were not fixed to a clock, with minimum growth consistently at the completion of the dark period regardless of the time of day. In summary, fine root growth of grapevines was found to have a pronounced diel pattern and an endogenous circadian clock appears to orchestrate this rhythm. Soil temperature modified the amplitude of this pattern, but we argue here that, as evidenced from exhausted starch reserves within root tips by early morning, carbon supply from photosynthesis is also required to maintain maximum root growth.

Exogenous short-term silicon application regulates macro-nutrients, endogenous phytohormones, and protein expression in Oryza sativa L

BACKGROUND

Silicon (Si) has been known to regulate plant growth; however, the underlying mechanisms of short-term exogenous Si application on the regulation of calcium (Ca) and nitrogen (N), endogenous phytohormones, and expression of essential proteins have been little understood.

RESULTS

Exogenous Si application significantly increased Si content as compared to the control. Among Si treatments, 1.0 mM Si application showed increased phosphorus content as compared to other Si treatments (0.5, 2.0, and 4.0 mM). However, Ca accumulation was significantly reduced (1.8- to 2.0-fold) at the third-leaf stage in the control, whereas all Si treatments exhibited a dose-dependent increase in Ca as determined by radioisotope ⁴⁵Ca analysis. Similarly, the radioisotope ¹⁵N for nitrogen localization and uptake showed a varying but reduced response (ranging from 1.03-10.8%) to different Si concentrations as compared to ¹⁵N application alone. Physiologically active endogenous gibberellin (GA₁) was also significantly higher with exogenous Si (1.0 mM) as compared to GA₂₀ and the control plants. A similar response was noted for endogenous jasmonic and salicylic acid synthesis in rice plants with Si application. Proteomic analysis revealed the activation of several essential proteins, such as Fe-S precursor protein, putative thioredoxin, Ser/Thr phosphatase, glucose-6-phosphate isomerase (G6P), and importin alpha-1b (Imp3), with Si application. Among the most-expressed proteins, confirmatory gene expression analysis for G6P and Imp3 showed a similar response to those of the Si treatments.

CONCLUSIONS

In conclusion, the current results suggest that short-term exogenous Si can significantly regulate rice plant physiology by influencing Ca, N, endogenous phytohormones, and proteins, and that 1.0 mM Si application is more beneficial to plants than higher concentrations.

Non-destructive measurement of soybean leaf thickness via X-ray computed tomography allows the study of diel leaf growth rhythms in the third dimension

Present-day high-resolution leaf growth measurements provide exciting insights into diel (24-h) leaf growth rhythms and their control by the circadian clock, which match photosynthesis with oscillating environmental conditions. However, these methods are based on measurements of leaf area or elongation and neglect diel changes of leaf thickness. In contrast, the influence of various environmental stress factors to which leaves are exposed to during growth on the final leaf thickness has been studied extensively. Yet, these studies cannot elucidate how variation in leaf area and thickness are simultaneously regulated and influenced on smaller time scales. Only few methods are available to measure the thickness of young, growing leaves non-destructively. Therefore, we evaluated X-ray computed tomography to simultaneously and non-invasively record diel changes and growth of leaf thickness and area. Using conventional imaging and X-ray computed tomography leaf area, thickness and volume growth of young soybean leaves were simultaneously and non-destructively monitored at three cardinal time points during night and day for a period of 80 h under non-stressful growth conditions. Reference thickness measurements on paperboards were in good agreement to CT measurements. Comparison of CT with leaf mass data further proved the consistency of our method. Exploratory analysis showed that measurements were accurate enough for recording and analyzing relative diel changes of leaf thickness, which were considerably different to those of leaf area. Relative growth rates of leaf area were consistently positive and highest during 'nights', while diel changes in thickness fluctuated more and were temporarily negative, particularly during 'evenings'. The method is suitable for non-invasive, accurate monitoring of diel variation in leaf volume. Moreover, our results indicate that diel rhythms of leaf area and thickness show some similarity but are not tightly coupled. These differences could be due to both intrinsic control mechanisms and different sensitivities to environmental factors.

Genetic mapping of the LOBED LEAF 1 (ClLL1) gene to a 127.6-kb region in watermelon (Citrullus lanatus L.)

The lobed leaf character is a unique morphologic trait in crops, featuring many potential advantages for agricultural productivity. Although the majority of watermelon varieties feature lobed leaves, the genetic factors responsible for lobed leaf formation remain elusive. The F2:3 leaf shape segregating population offers the opportunity to study the underlying mechanism of lobed leaf formation in watermelon. Genetic analysis revealed that a single dominant allele (designated ClLL1) controlled the lobed leaf trait. A large-sized F3:4 population derived from F2:3 individuals was used to map ClLL1. A total of 5,966 reliable SNPs and indels were identified genome-wide via a combination of BSA and RNA-seq. Using the validated SNP and indel markers, the location of ClLL1 was narrowed down to a 127.6-kb region between markers W08314 and W07061, containing 23 putative ORFs. Expression analysis via qRT-PCR revealed differential expression patterns (fold-changes above 2-fold or below 0.5-fold) of three ORFs (ORF3, ORF11, and ORF18) between lobed and non-lobed leaf plants. Based on gene annotation and expression analysis, ORF18 (encoding an uncharacterized protein) and ORF22 (encoding a homeobox-leucine zipper-like protein) were considered as most likely candidate genes. Furthermore, sequence analysis revealed no polymorphisms in cDNA sequences of ORF18; however, two notable deletions were identified in ORF22. This study is the first report to map a leaf shape gene in watermelon and will facilitate cloning and functional characterization of ClLL1 in future studies.

Emission of Volatile Compounds from Apple Plants Infested with Pandemis heparana Larvae, Antennal Response of Conspecific Adults, and Preliminary Field Trial

This study investigated the volatile emission from apple (Malus x domestica Borkh., cv. Golden Delicious) foliage that was either intact, mechanically-damaged, or exposed to larval feeding by Pandemis heparana (Denis and Schiffermüller) (Lepidoptera: Tortricidae). Volatiles were collected by closed-loop-stripping-analysis and characterized by gas chromatography-mass spectrometry in three time periods: after 1 h and again 24 and 48 h later. Volatiles for all treatments also were monitored continuously over a 72-h period by the use of proton transfer reaction - time of flight-mass spectrometry (PTR-ToF-MS). In addition, the volatile samples were analyzed by gas chromatography-electroantennographic detection (GC-EAD) using male and female antennae of P. heparana. Twelve compounds were detected from intact foliage compared with 23 from mechanically-damaged, and 30 from P. heparana-infested foliage. Interestingly, six compounds were released only by P. heparana-infested foliage. The emission dynamics of many compounds measured by PTR-ToF-MS showed striking differences according to the timing of herbivory and the circadian cycle. For example, the emission of green leaf volatiles began shortly after the start of herbivory, and increased over time independently from the light-dark cycle. Conversely, the emission of terpenes and aromatic compounds showed a several-hour delay in response to herbivory, and followed a diurnal rhythm. Methanol was the only identified volatile showing a nocturnal rhythm. Consistent GC-EAD responses were found for sixteen compounds, including five aromatic ones. A field trial in Sweden demonstrated that benzyl alcohol, 2-phenylethanol, phenylacetonitrile, and indole lures placed in traps were not attractive to Pandemis spp. adults, but 2-phenylethanol and phenylacetonitrile when used in combination with acetic acid were attractive to both sexes.

Genomic Tools in Pearl Millet Breeding for Drought Tolerance: Status and Prospects

Pearl millet [Penisetum glaucum (L) R. Br.] is a hardy cereal crop grown in the arid and semiarid tropics where other cereals are likely to fail to produce economic yields due to drought and heat stresses. Adaptive evolution, a form of natural selection shaped the crop to grow and yield satisfactorily with limited moisture supply or under periodic water deficits in the soil. Drought tolerance is a complex polygenic trait that various morphological and physiological responses are controlled by 100s of genes and significantly influenced by the environment. The development of genomic tools will have enormous potential to improve the efficiency and precision of conventional breeding. The apparent independent domestication events, highly outcrossing nature and traditional cultivation in stressful environments maintained tremendous amount of polymorphism in pearl millet. This high polymorphism of the crop has been revealed by genome mapping that in turn stimulated the mapping and tagging of genomic regions controlling important traits such as drought tolerance. Mapping of a major QTL for terminal drought tolerance in independent populations envisaged the prospect for the development of molecular breeding in pearl millet. To accelerate genetic gains for drought tolerance targeted novel approaches such as establishment of marker-trait associations, genomic selection tools, genome sequence and genotyping-by-sequencing are still limited. Development and application of high throughput genomic tools need to be intensified to improve the breeding efficiency of pearl millet to minimize the impact of climate change on its production.

Response of wheat and pea seedlings on increase of bromine concentration in the growth medium

Biogeochemical cycles of bromine (Br) and its quantitative requirements for different plant species are still studied poorly. There is a need to examine Br pathways in plants and evaluate the factors important for Br accumulation in a plant. In the present work, the effects of different Br compounds on an uptake of Br by two plant species (wheat and pea) that tolerate Br differently (pea is more sensitive to Br compared with wheat) have been studied. The growth medium was spiked with either KBr or NaBr at concentrations 0, 10, 50 and 100 mg/L. Elemental analysis of the plants was performed using inductively coupled plasma optical emission spectrometry (ICP-OES) and ICP-MS analytical techniques after leaching of the samples with tetramethyl ammonium hydroxide at mild temperature (60 °C). The experimental results have shown that wheat and pea seedlings can accumulate rather large amounts of Br. An increase of Br concentration in a plant was not always directly proportional to the variations in the Br concentration in the growth medium. In wheat, the greater part of Br was accumulated during first 7 days. In pea, the uptake of Br lasted until the end of the experiment. Certain differences in the ability of plants to accumulate Br were observed when the plants were grown in a medium spiked with different Br compounds. In most cases, Br accumulation was higher in the leaves of the plants grown in the medium spiked with KBr. The same tendency was observed for another halogen, chlorine (Cl).

The impact of Polycomb group (PcG) and Trithorax group (TrxG) epigenetic factors in plant plasticity

Current advances indicate that epigenetic mechanisms play important roles in the regulatory networks involved in plant developmental responses to environmental conditions. Hence, understanding the role of such components becomes crucial to understanding the mechanisms underlying the plasticity and variability of plant traits, and thus the ecology and evolution of plant development. We now know that important components of phenotypic variation may result from heritable and reversible epigenetic mechanisms without genetic alterations. The epigenetic factors Polycomb group (PcG) and Trithorax group (TrxG) are involved in developmental processes that respond to environmental signals, playing important roles in plant plasticity. In this review, we discuss current knowledge of TrxG and PcG functions in different developmental processes in response to internal and environmental cues and we also integrate the emerging evidence concerning their function in plant plasticity. Many such plastic responses rely on meristematic cell behavior, including stem cell niche maintenance, cellular reprogramming, flowering and dormancy as well as stress memory. This information will help to determine how to integrate the role of epigenetic regulation into models of gene regulatory networks, which have mostly included transcriptional interactions underlying various aspects of plant development and its plastic response to environmental conditions.

Carbon partitioning in Arabidopsis thaliana is a dynamic process controlled by the plants metabolic status and its circadian clock

Plant growth involves the coordinated distribution of carbon resources both towards structural components and towards storage compounds that assure a steady carbon supply over the complete diurnal cycle. We used (14) CO2 labelling to track assimilated carbon in both source and sink tissues. Source tissues exhibit large variations in carbon allocation throughout the light period. The most prominent change was detected in partitioning towards starch, being low in the morning and more than double later in the day. Export into sink tissues showed reciprocal changes. Fewer and smaller changes in carbon allocation occurred in sink tissues where, in most respects, carbon was partitioned similarly, whether the sink leaf assimilated it through photosynthesis or imported it from source leaves. Mutants deficient in the production or remobilization of leaf starch exhibited major alterations in carbon allocation. Low-starch mutants that suffer from carbon starvation at night allocated much more carbon into neutral sugars and had higher rates of export than the wild type, partly because of the reduced allocation into starch, but also because of reduced allocation into structural components. Moreover, mutants deficient in the plant's circadian system showed considerable changes in their carbon partitioning pattern suggesting control by the circadian clock.

The significance of image compression in plant phenotyping applications

We are currently witnessing an increasingly higher throughput in image-based plant phenotyping experiments. The majority of imaging data are collected using complex automated procedures and are then post-processed to extract phenotyping-related information. In this article, we show that the image compression used in such procedures may compromise phenotyping results and this needs to be taken into account. We use three illuminating proof-of-concept experiments that demonstrate that compression (especially in the most common lossy JPEG form) affects measurements of plant traits and the errors introduced can be high. We also systematically explore how compression affects measurement fidelity, quantified as effects on image quality, as well as errors in extracted plant visual traits. To do so, we evaluate a variety of image-based phenotyping scenarios, including size and colour of shoots, leaf and root growth. To show that even visual impressions can be used to assess compression effects, we use root system images as examples. Overall, we find that compression has a considerable effect on several types of analyses (albeit visual or quantitative) and that proper care is necessary to ensure that this choice does not affect biological findings. In order to avoid or at least minimise introduced measurement errors, for each scenario, we derive recommendations and provide guidelines on how to identify suitable compression options in practice. We also find that certain compression choices can offer beneficial returns in terms of reducing the amount of data storage without compromising phenotyping results. This may enable even higher throughput experiments in the future.

Challenges and opportunities for quantifying roots and rhizosphere interactions through imaging and image analysis

The morphology of roots and root systems influences the efficiency by which plants acquire nutrients and water, anchor themselves and provide stability to the surrounding soil. Plant genotype and the biotic and abiotic environment significantly influence root morphology, growth and ultimately crop yield. The challenge for researchers interested in phenotyping root systems is, therefore, not just to measure roots and link their phenotype to the plant genotype, but also to understand how the growth of roots is influenced by their environment. This review discusses progress in quantifying root system parameters (e.g. in terms of size, shape and dynamics) using imaging and image analysis technologies and also discusses their potential for providing a better understanding of root:soil interactions. Significant progress has been made in image acquisition techniques, however trade-offs exist between sample throughput, sample size, image resolution and information gained. All of these factors impact on downstream image analysis processes. While there have been significant advances in computation power, limitations still exist in statistical processes involved in image analysis. Utilizing and combining different imaging systems, integrating measurements and image analysis where possible, and amalgamating data will allow researchers to gain a better understanding of root:soil interactions.

Nondestructive and intuitive determination of circadian chlorophyll rhythms in soybean leaves using multispectral imaging

The circadian clock, synchronized by daily cyclic environmental cues, regulates diverse aspects of plant growth and development and increases plant fitness. Even though much is known regarding the molecular mechanism of circadian clock, it remains challenging to quantify the temporal variation of major photosynthesis products as well as their metabolic output in higher plants in a real-time, nondestructive and intuitive manner. In order to reveal the spatial-temporal scenarios of photosynthesis and yield formation regulated by circadian clock, multispectral imaging technique has been employed for nondestructive determination of circadian chlorophyll rhythms in soybean leaves. By utilizing partial least square regression analysis, the determination coefficients R(2), 0.9483 for chlorophyll a and 0.8906 for chlorophyll b, were reached, respectively. The predicted chlorophyll contents extracted from multispectral data showed an approximately 24-h rhythm which could be entrained by external light conditions, consistent with the chlorophyll contents measured by chemical analyses. Visualization of chlorophyll map in each pixel offers an effective way to analyse spatial-temporal distribution of chlorophyll. Our results revealed the potentiality of multispectral imaging as a feasible nondestructive universal assay for examining clock function and robustness, as well as monitoring chlorophyll a and b and other biochemical components in plants.

Influences of environmental factors on leaf morphology of Chinese jujubes

Rainfall and temperature are the primary limiting factors for optimum quality and yield of cultivated jujube (Ziziphus jujuba Mill.). Adaptation to arid and cool environments has been and remains an important goal of many jujube improvement programs. This study summarized the survey results of 116 Chinese jujube varieties grown at 33 sites in China. The objective was to identify the environmental factors that influence leaf morphology, and the implications for breeding and introduction of new jujube varieties. Jujube leaf morphological traits were evaluated for their potential relationships with mean annual temperature (MAT) and mean annual precipitation (MAP). The results showed that many leaf morphological traits had a strong linear relationship with local precipitation and temperature. Longer veins per unit area (VLA) and reduced leaf area and leaf perimeter were typical of arid areas. VLA was inversely related to MAT and MAP at the centers of origin of jujube. There was a positive relationship between leaf shape (perimeter2/area) and both MAT and MAP. These results indicated that leaf vein traits of Chinese jujubes might have resulted from their adaptation to environmental factors in the course of long-term evolution. Principal component analysis allocated the 116 jujube varieties to three different groups, differentiated on the basis of morphological and physiological leaf characteristics. Jujube varieties from the Hebei, Shandong, Henan, southern Shanxi and central Shaanxi provinces were closely related, as were varieties from northwest Shanxi and northeast Shaanxi provinces, and varieties from the Gansu and Ningxia provinces. These close relationships were partially attributed to the frequent exchanges of varieties within each group. Leaf venation characteristics might be used as reference indices for jujube variety introduction between different locations.

Phytotyping(4D) : a light-field imaging system for non-invasive and accurate monitoring of spatio-temporal plant growth

Integrative studies of plant growth require spatially and temporally resolved information from high-throughput imaging systems. However, analysis and interpretation of conventional two-dimensional images is complicated by the three-dimensional nature of shoot architecture and by changes in leaf position over time, termed hyponasty. To solve this problem, Phytotyping(4D) uses a light-field camera that simultaneously provides a focus image and a depth image, which contains distance information about the object surface. Our automated pipeline segments the focus images, integrates depth information to reconstruct the three-dimensional architecture, and analyses time series to provide information about the relative expansion rate, the timing of leaf appearance, hyponastic movement, and shape for individual leaves and the whole rosette. Phytotyping(4D) was calibrated and validated using discs of known sizes, and plants tilted at various orientations. Information from this analysis was integrated into the pipeline to allow error assessment during routine operation. To illustrate the utility of Phytotyping(4D) , we compare diurnal changes in Arabidopsis thaliana wild-type Col-0 and the starchless pgm mutant. Compared to Col-0, pgm showed very low relative expansion rate in the second half of the night, a transiently increased relative expansion rate at the onset of light period, and smaller hyponastic movement including delayed movement after dusk, both at the level of the rosette and individual leaves. Our study introduces light-field camera systems as a tool to accurately measure morphological and growth-related features in plants.

Understanding circadian regulation of carbohydrate metabolism in Arabidopsis using mathematical models

C3 plants assimilate carbon by photosynthesis only during the day, but carbon resources are also required for growth and maintenance at night. To avoid carbon starvation, many plants store a part of photosynthetic carbon in starch during the day, and degrade it to supply sugars for growth at night. In Arabidopsis, starch accumulation in the day and degradation at night occur almost linearly, with the shape of this diel starch profile adaptively changing to allow continuous supply of sugar even in long-night conditions. The anticipation of dawn required to ensure linear consumption of starch to almost zero at dawn presumably requires the circadian clock. We review the links between carbon metabolism and the circadian clock, and mathematical models aimed at explaining the diel starch profile. These models can be considered in two classes, those that assume the level of available starch is sensed and the system ensures linearity of starch availability, and those in which sugar sensing is assumed, yielding linearity of starch availability as an emergent property of sucrose homeostasis. In the second class of model the feedback from starch metabolism to the circadian clock is considered to be essential for adaptive response to diverse photoperiods, consistent with recent empirical data demonstrating entrainment of the circadian clock by photosynthesis. Knowledge concerning the mechanisms regulating the dynamics of starch metabolism and sugar homeostasis in plants is required to develop new theories about the limitations of growth and biomass accumulation.

Diel growth patterns of young soybean (Glycine max) leaflets are synchronous throughout different positions on a plant

Leaf growth is controlled by various internal and external factors. Leaves of dicotyledonous plants show pronounced diel (24 h) growth patterns that are controlled by the circadian clock. To date, it is still uncertain whether diel leaf growth patterns remain constant throughout the development of a plant. In this study, we followed growth from the primary leaves to leaflets of the seventh trifoliate leaf of soybean (Glycine max) on the same plants with a recently developed imaging-based method under controlled conditions and at a high temporal resolution. We found that all leaflets displayed a consistent diel growth pattern with maximum growth towards the end of the night. In some leaves, growth maxima occurred somewhat later - at dawn - as long as the leaves were still in a very early developmental stage. Yet, overall, diel growth patterns of leaves from different positions within the canopy were highly synchronous. Therefore, the diel growth pattern of any leaf at a given point in time is representative for the overall diel growth pattern of the plant leaf canopy and a deviation from the normal diel growth pattern can indicate that the plant is currently facing stress.

What determines a leaf's shape?

The independent origin and evolution of leaves as small, simple microphylls or larger, more complex megaphylls in plants has shaped and influenced the natural composition of the environment. Significant contributions have come from megaphyllous leaves, characterized usually as flat, thin lamina entrenched with photosynthetic organelles and stomata, which serve as the basis of primary productivity. During the course of evolution, the megaphylls have attained complexity not only in size or venation patterns but also in shape. This has fascinated scientists worldwide, and research has progressed tremendously in understanding the concept of leaf shape determination. Here, we review these studies and discuss the various factors that contributed towards shaping the leaf; initiated as a small bulge on the periphery of the shoot apical meristem (SAM) followed by asymmetric outgrowth, expansion and maturation until final shape is achieved. We found that the underlying factors governing these processes are inherently genetic: PIN1 and KNOX1 are indicators of leaf initiation, HD-ZIPIII, KANADI, and YABBY specify leaf outgrowth while ANGUSTIFOLIA3 and GROWTH-REGULATING FACTOR5 control leaf expansion and maturation; besides, recent research has identified new players such as APUM23, known to specify leaf polarity. In addition to genetic control, environmental factors also play an important role during the final adjustment of leaf shape. This immense amount of information available will serve as the basis for studying and understanding innovative leaf morphologies viz. the pitchers of the carnivorous plant Nepenthes which have evolved to provide additional support to the plant survival in its nutrient-deficient habitat. In hindsight, formation of the pitcher tube in Nepenthes might involve the recruitment of similar genetic mechanisms that occur during sympetaly in Petunia.

Digital imaging approaches for phenotyping whole plant nitrogen and phosphorus response in Brachypodium distachyon

This work evaluates the phenotypic response of the model grass (Brachypodium distachyon (L.) P. Beauv.) to nitrogen and phosphorus nutrition using a combination of imaging techniques and destructive harvest of shoots and roots. Reference line Bd21-3 was grown in pots using 11 phosphorus and 11 nitrogen concentrations to establish a dose-response curve. Shoot biovolume and biomass, root length and biomass, and tissue phosphorus and nitrogen concentrations increased with nutrient concentration. Shoot biovolume, estimated by imaging, was highly correlated with dry weight (R(2) > 0.92) and both biovolume and growth rate responded strongly to nutrient availability. Higher nutrient supply increased nodal root length more than other root types. Photochemical efficiency was strongly reduced by low phosphorus concentrations as early as 1 week after germination, suggesting that this measurement may be suitable for high throughput screening of phosphorus response. In contrast, nitrogen concentration had little effect on photochemical efficiency. Changes in biovolume over time were used to compare growth rates of four accessions in response to nitrogen and phosphorus supply. We demonstrate that a time series image-based approach coupled with mathematical modeling provides higher resolution of genotypic response to nutrient supply than traditional destructive techniques and shows promise for high throughput screening and determination of genomic regions associated with superior nutrient use efficiency.