Comparative Study of Drought Stress Effects on Traditional and Modern Apple Cultivars

Cerium oxide nanoparticles alleviate drought stress in apple seedlings by regulating ion homeostasis, antioxidant defense, gene expression, and phytohormone balance

Drought stress is one of the most important environmental constraints that negatively affect the growth and production of crops worldwide. Recently, nanotechnology has been increasingly used to improve the tolerance of plants exposed to abiotic stresses such as drought. The present study was designed to investigate the moderating effect of cerium oxide nanoparticles (CeO2 NPs) on alleviating drought stress for the apple cv. 'Red Delicious' on M9 rootstock. Drought stress caused a significant increase in CAT, GPX, APX, and SOD enzyme activities compared to control plants. Drought decreased the content of macro and microelements, and the application of CeO2 NPs led to significant changes in the content of these elements in plants under drought stress. CeO2 NPs significantly reduced chlorophyll damage under high drought levels. In addition, they alleviated the damage caused by drought, which was shown by lower levels of MDA and EL. When these nanoparticles were used during drought stress, they greatly increased the production of abscisic acid and indole-3-acetic acid hormone. In response to drought stress, the expression of DREB1A and DREB1E genes increased. The use of CeO2 NPs in stressful and non-stressful conditions had a positive effect on improving the studied traits of the apple plants and enhancing nutrient levels. Taken together, the findings suggest that CeO2 NPs can be used as promising drought stress-reducing agents in apples. Therefore, understanding the mechanisms of abiotic stress in global horticulture and the role of nanoparticles is essential for developing improved, drought-tolerant crops and the adoption of measures to deal with changing climatic conditions.

Biochemical and gene expression profiling of five pear species under drought stress conditions

Drought is one of the crucial abiotic stresses which affects growth, development, and performance of pear trees. This research was performed to investigate responses of five pear species including Pyrus communis L., Pyrus boissieriana Bushe., Pyrus glabra Boiss., Pyrus syriaca Boiss., and Pyrus salicifolia Pall. to different levels of drought stress. The potted trees were irrigated with water volume of 100%, 60%, or 30% of field capacity (FC) during 90 days. Based on the visual observation, the plant growth was restricted by severe drought in all species. Malondialdehyde (MDA) and glycine betaine (GB) contents, as well as the ascorbate peroxidase (APX), guaiacol peroxidase (GPX) and catalase (CAT) activities were indicated an uprising behavior under drought stress. Principal component analysis (PCA) analysis revealed P. glabra as tolerant and P. communis as sensitive to drought stress. The expression rates of stress-responsive transcription factors (TFs); WRKY29 and DREB6 and their responding genes, including LEA29 and Dehydrin1, were analyzed in the two differentially drought-responding pear species i.e., P. glabra and P. communis. The expression of the studied TFs was induced when both species were exposed to higher drought levels. The species P. glabra exhibited better osmoregulation, antioxidant response, and higher up-regulation of WRKY29, DREB6, LEA29 and Dehydrin1. In conclusion, among the studied pear species, P. glabra could best tolerate drought stress by boosting protective mechanisms.

GABA and Proline Application Induce Drought Resistance in Oilseed Rape

This study investigates the effects of γ-aminobutyric acid (GABA) and proline, both individually and in combination, on the growth of oilseed rape under drought stress and following the resumption of irrigation. The goal was to determine whether the exogenous application of these compounds enhances the plants response to prolonged water deficit and, if so, to identify the biochemical processes involved in the plant tissue. The experiment was conducted under controlled laboratory conditions. After 21 days of plant cultivation, at the 3-4 leaf stage, seedlings were sprayed with aqueous solutions of GABA (0.1 mM) and proline (0.1 mM). The plants were then subjected to 8 days of severe drought stress, after which irrigation was resumed, and recovery was assessed over 4 days. The results showed that both amino acids alleviated the drought-induced stress as indicated by higher relative water content (RWC), increased levels of endogenous proline and photosynthetic pigments in leaves, and enhanced survival and growth recovery after drought. GABA-treated plants maintained membrane integrity and preserved plasma membrane (PM) ATPase activity during prolonged drought stress while reducing ethylene, H2O2, and MDA levels. Proline also influenced these biochemical responses, though to a lesser extent. The combination of GABA and proline facilitated better recovery of oilseed rape compared to the drought control group following rewatering. Notably, GABA treatment resulted in a significant increase in gene expression compared to the untreated control. Molecular analysis of drought-responsive genes revealed that the gene expression in plants treated with both proline and GABA was typically intermediate between those treated with proline alone and those treated with GABA alone. Based on these findings, we propose that GABA application could serve as an alternative to proline for improving oilseed rape's drought tolerance, potentially increasing both crop yield and quality.

The Trx-Prx redox pathway and PGR5/PGRL1-dependent cyclic electron transfer play key regulatory roles in poplar drought stress

Understanding drought resistance mechanisms is crucial for breeding poplar species suited to arid and semiarid regions. This study explored the drought responses of three newly developed 'Zhongxiong' series poplars using integrated transcriptomic and physiological analyses. Under drought stress, poplar leaves showed significant changes in differentially expressed genes linked to photosynthesis-related pathways, including photosynthesis-antenna proteins and carbon fixation, indicating impaired photosynthetic function and carbon assimilation. Additionally, drought stress triggered oxidative damage through increased reactive oxygen species production, leading to malondialdehyde accumulation. Weighted gene co-expression network analysis revealed that differentially expressed genes closely associated with physiological responses were enriched in cell redox homeostasis pathways, specifically the thioredoxin-peroxiredoxin pathway. Key genes in this pathway and in cyclic electron flow, such as PGR5-L1A, were downregulated, suggesting compromised reactive oxygen species scavenging and photoprotection under drought stress. Notably, ZX4 poplar exhibited higher drought tolerance, maintaining stronger activity in cyclic electron flow and the thioredoxin-peroxiredoxin pathway compared with ZX3 and ZX5. Genes like PGR5-L1A, 2-Cys Prx BAS1, PrxQ and TPX are promising candidates for enhancing drought resistance in poplars through genetic improvement, with potential applications for developing resilient forestry varieties.

Green synthesized FeNPs ameliorate drought stress in Spinacia oleracea L. through improved photosynthetic capacity, redox balance, and antioxidant defense

The present study was designed to highlight the ameliorative role of iron nanoparticles (FeNPs) against drought stress in spinach (Spinacia oleracea L.) plants. A pot experiment was performed in two-way completely randomize design with three replicates. For drought stress three levels were used by maintaining field capacity of the soil. This included control (100% field capacity), moderate drought stress (D1; 50% field capacity) and severe drought stress (D2; 25% field capacity). FeNPs synthesized by green method using rice straw were applied along with precursor FeCl3, used as Fe source for the synthesis of FeNPs, through foliar spray (40 mg L- 1 for both). Growth parameters, efficiency of photosynthetic machinery, gas exchange attributes, total soluble proteins, and inorganic ions (Ca2+, K+ & Fe2+) were significantly reduced at both D1 and D2 stress levels, compared to control plants. Fe supplements in the form of FeCl3 and FeNPs improved these attributes in both control and drought conditions. Malondialdehyde, H2O2, relative membrane permeability (stress indicators) and the activities of antioxidants were increased in response to drought stress. Fe supplements further improved the antioxidant defense activities and efficiently lowered the effects of stress indicators. These effects of FeCl3 and FeNPs resulted in improved growth of S. oleracea plants in control and drought conditions. Results showed that FeNPs had more prominent effects on growth of S. oleracea plants compared to FeCl3. These findings suggest that FeNPs could be a helpful tool for lessening the harmful consequences of drought stress and this can be used for abiotic stress alleviation in other crops as well.

Changes in Secondary Metabolites Content and Antioxidant Enzymes Activity in Leaves of Two Prunus avium L. Genotypes During Various Phenological Phases

In addition to its fruit, the sweet cherry (Prunus avium L.) has other parts that can be used as a source of compounds with beneficial biological activity. The content of these metabolites is affected by different inner and outer factors, often as a response to plant defense against various stresses. Leaves of two P. avium. genotypes, Kordia and Regina, grafted on the same rootstock, were analyzed from trees grown in orchards in six different phenological phases for two years. The content of several groups of phenolic compounds, lipid peroxidation, antioxidant activity of the extracts, and enzyme activity were observed via colorimetric methods on a UV/Vis spectrophotometer. The obtained data showed that the content of metabolites and other parameters in these two genotypes are dependent on the term of harvest, as well as environmental conditions, mainly temperature, but sunshine duration and rainfall also had a certain effect on the compounds in the leaves of Kordia and Regina. Even though the differences between these genotypes were not always significant, it is important to consider the right time to harvest the leaves of the sweet cherry, as their content could vary as a result of the reaction to various other conditions and could reflect the resistance of the chosen genotype.

Insights into the response mechanisms of Tetradesmus obliquus to aged polylactic acid and tetracycline exposure via transcriptome analysis and physiological evaluations

Microplastics (MPs) and antibiotics, identified as emerging pollutants, are extensively prevalent in aquatic environments and display prolonged durability. Unlike conventional plastics, biodegradable plastics are more susceptible to decomposition in the environment, resulting in the generation of microplastics and posing potential risks to the aquatic ecosystems. In this study, we assessed growth inhibition, chlorophyll a content, malondialdehyde content (MDA), and antioxidant enzyme activities. These measurements were integrated with transcriptome analysis to explore the response mechanisms of virgin and aged polylactic acid (vPLA and aPLA) and tetracycline (TC) following 14-day exposure to Tetradesmus obliquus, either individually or in combination. The findings indicated that exposure to vPLA did not significantly impact the growth of T. obliquus. Conversely, aPLA demonstrated growth-promoting effects on T. obliquus, particularly in the latter incubation stages. Moreover, a 14-day exposure significantly increased the chlorophyll a content and the activities of superoxide dismutase (SOD), catalase glutathione (CAT) and glutathione S-transferase (GST) within the algal cells. Apart from 1 mg L-1, the TC concentrations of 2.5, 5.0, and 10 mg L-1 exhibited significant toxic effects on T. obliquus, including growth inhibition, decreased chlorophyll a content, elevated activities of SOD, CAT, and GST, and increased MDA levels. Exposure to a combination of 300 mg L-1 aPLA and 5.0 mg L-1 TC, compared to solely 5 mg L-1 TC, demonstrated a notable reduction in TC toxicity to T. obliquus in the presence of aPLA. This was indicated by elevated algal cell density and chlorophyll a content, as well as a decrease in MDA content. Transcriptome analysis indicated an enrichment of differentially expressed genes (DEGs) in pathways linked to porphyrin metabolism, photosynthesis, carbon fixation, and metabolism within the aPLA + TC combined exposure. The study aid in expanding our knowledge of the potential ecological risks posed by biodegradable plastics and accompanying pollutants in aquatic environments.

Exogenously applied nicotinic acid alleviates drought stress by enhancing morpho-physiological traits and antioxidant defense mechanisms in wheat

Across the globe, the frequent occurrence of drought spells has significantly undermined the sustainability of modern high-input farming systems, particularly those focused on staple crops like wheat. To ameliorate the deleterious impacts of drought through a biologically viable and eco-friendly approach, a study was designed to explore the effect of nicotinic acid on different metabolic, and biochemical processes, growth and yield of wheat under optimal moisture and drought stress (DS). The current study was comprised of different levels of nicotinic acid applied as foliar spray (0 g L-1, 0.7368, 1.477, 2.2159 g L-1) and fertigation (0.4924, 0.9848, and 1.4773 g L-1) under normal conditions and imposed drought by withholding water at anthesis stage. The response variables were morphological traits such as roots and shoots characteristics, yield attributes, grain and biological yields along with biosynthesis of antioxidants. The results revealed that nicotinic acid dose of 2.2159 g L-1 out-performed rest of treatments under both normal and DS. The same treatment resulted in the maximum root growth (length, fresh and dry weights, surface area, diameter) and shoot traits (length, fresh and dry weights) growth. Additionally, foliar applied nicotinic acid (2.2159 g L-1) also produced as the highest spike length, grains spike-1, spikelet's spike-1 and weight of 1000 grains. Moreover, these better yield attributes led to significantly higher grain yield and biological productivity of wheat. Likewise in terms of physiological growth of wheat under DS, the same treatment remained superior by recording the highest SPAD value, relative water content, water potential of leaves, leaf area, stomatal conductance (292 mmolm-2S-1), internal carbon dioxide concentration, photosynthesis and transpiration rate. Interestingly, exogenously applied nicotinic acid remained effective in triggering the antioxidant system of wheat by recording significantly higher catalase, peroxidase, superoxide dismutase and ascorbate peroxidase.

Response of seed yield and biochemical traits of Eruca sativa Mill. to drought stress in a collection study

Drought tolerance is a complex trait in plants that involves different biochemical mechanisms. During two years of study (2019-2020), the responses of 64 arugula genotypes to drought stress were evaluated in a randomized complete block design with three replications under field conditions. Several metabolic traits were evaluated, i.e. relative water content, photosynthetic pigments (chlorophyll and carotenoids), proline, malondialdehyde, enzymatic antioxidants (catalase, ascorbate peroxidase, and peroxidase), total phenolic and flavonoid contents and seed yield. On average, the drought stress significantly increased the proline content (24%), catalase (42%), peroxidase (60%) and malondialdehyde activities (116%) over the two years of study. As a result of the drought stress, the seed yield (18%), relative water content (19.5%) and amount of photosynthetic pigments (chlorophyll and carotenoids) dropped significantly. However, the total phenolic and flavonoid contents showed no significant changes. Under drought stress, the highest seed yields were seen in the G50, G57, G54, G55 and G60 genotypes, while the lowest value was observed in the G16 genotype (94 g plant-1). According to the findings, when compared to the drought-sensitive genotypes, the drought-tolerant arugula genotypes were marked with higher levels of proline accumulation and antioxidant enzyme activity. Correlation analysis indicated the positive effects of peroxidase, catalase and proline on seed yield under drought conditions. These traits can be considered for the selection of drought-tolerant genotypes in breeding programs.

The ubiquitin-binding protein MdRAD23D1 mediates drought response by regulating degradation of the proline-rich protein MdPRP6 in apple (Malus domestica)

RAD23 (RADIATION SENSITIVE23) proteins are a group of UBL-UBA (ubiquitin-like-ubiquitin-associated) proteins that shuttle ubiquitylated proteins to the 26S proteasome for breakdown. Drought stress is a major environmental constraint that limits plant growth and production, but whether RAD23 proteins are involved in this process is unclear. Here, we demonstrated that a shuttle protein, MdRAD23D1, mediated drought response in apple plants (Malus domestica). MdRAD23D1 levels increased under drought stress, and its suppression resulted in decreased stress tolerance in apple plants. Through in vitro and in vivo assays, we demonstrated that MdRAD23D1 interacted with a proline-rich protein MdPRP6, resulting in the degradation of MdPRP6 by the 26S proteasome. And MdRAD23D1 accelerated the degradation of MdPRP6 under drought stress. Suppression of MdPRP6 resulted in enhanced drought tolerance in apple plants, mainly because the free proline accumulation is changed. And the free proline is also involved in MdRAD23D1-mediated drought response. Taken together, these findings demonstrated that MdRAD23D1 and MdPRP6 oppositely regulated drought response. MdRAD23D1 levels increased under drought, accelerating the degradation of MdPRP6. MdPRP6 negatively regulated drought response, probably by regulating proline accumulation. Thus, "MdRAD23D1-MdPRP6" conferred drought stress tolerance in apple plants.

Zinc oxide nanoparticles mediated biostimulant impact on cadmium detoxification and in silico analysis of zinc oxide-cadmium networks in Zea mays L. regulome

Cadmium (Cd) toxicity can significantly limit plant growth and development. To eliminate the toxic effects of Cd stress, we intended to evaluate the biochemical mediated physiological responses in maize treated with biostimulant and zinc oxide nanoparticles (ZnPs). In silico analysis exhibited that the maize treated with Cd stress (200 μM) had an adverse impact on CAT1, CAT2, CAT3 and gor1 proteins, which are influential in managing the machinery of redox homeostasis. While maize inoculated with bacteria-based biostimulant and ZnPs (10 ppm) showed prominently improved biomass, chlorophyll a, b and carotenoid content. We found a significant increase in the total sugar, protein, proline content and antioxidants under the effect of Cd stress. However, these parameters are further enhanced by applying biostimulants and ZnPs. Declined lipid peroxidation and membrane solubilization index under the effect of biostimulant and ZnPs was observed. Furthermore, these treatments improved maize's zinc, copper, sodium, magnesium, iron, potassium and calcium content. Based on these results, an antagonistic relationship between Zn and Cd uptake that triggered efficient Cd detoxification in maize shoot was found. Scanning electron micrography showed distorted leaf structure of the Cd stressed plants while the biostimulant and ZnPs reduced the structural cell damage of maize leaves. In silico study showed that ZnO positively regulates all protein interactors, including GRMZM2G317386_P01 (Metallo endo proteinase 1-MMP), GRMZM2G110220_P01 (Metallo endo proteinase 5-MMP), GRMZM2G103055_P01 (Alpha-amylase) and GRMZM2G006069_P01 (Zn-dependent exo peptidase superfamily) proteins which are involved in energy generating processes, channels formation, matrix re-localization and stress response. This suggests that ZnO offers an ideal role with protein interactors in maize. Our findings depict that these treatments, i.e., biostimulant and ZnPs alone, are efficient enough to exhibit Cd remediation potential in maize; however, their combination showed synergistic effects.

Leaf-transcriptome profiles of phoebe bournei provide insights into temporal drought stress responses

Phoebe bournei (Hemsl.) Yang is used as a commercial wood in China and is enlisted as a near-threatened species. Prolonged droughts pose a serious threat to young seedlings (1-2 years old). A transcriptome sequencing approach, together with the measurement of growth parameters and biochemical analyses were used to understand P. bournei's drought responses on 15d, 30d, and 45d of drought stress treatment. The stem and root dry weights decreased significantly with drought stress duration. Activities of antioxidative enzymes i.e., peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) increased significantly with the increase in drought stress duration. A total of 13,274, 15,648, and 9,949 genes were differentially expressed in CKvs15d, CKvs30d, and CKvs45d, respectively. The differential expression analyses showed that photosystem I and II underwent structural changes, chlorophyll biosynthesis, and photosynthesis were reduced. The genes annotated as POD, SOD, and CAT were upregulated in drought-treated leaves as compared to control. Additionally, plant-hormone signal transduction, MAPK signaling-plant, phenylpropanoid biosynthesis, flavonoid biosynthesis, and starch and sucrose metabolism pathways showed large-scale expression changes in major genes. We also found that members of 25 transcription factor families were differentially expressed. Our study presents and discusses these transcriptome signatures. Overall, our findings represent key data for breeding towards drought stress tolerance in P. bournei.

Photosynthetic Variability of Oblačinska Sour Cherry Ecotypes under Drought

The selection of drought-tolerant sour cherry genotypes is essential for developing sustainable fruit production in today’s climate-change conditions. The phenotypic heterogenic population of sour cherry Oblačinska, with high and regular yield suitable for mechanical harvesting and industrial processing, is a traditional and predominant cultivar in northern Croatia (Pannonian region) and Serbia commercial orchards. In this context, 2-year old virus-free sour cherry plants of 4 isolated Oblačinska sour cherry ecotypes (OS, 18, D6, and BOR) produced by micropropagation were exposed to severe drought in a greenhouse under semi-controlled conditions to evaluate its photosynthetic intra-varietal variability. Relative water content (RWC), chlorophyll fluorescence (ChlF), and photosynthetic pigments were evaluated during the ten days of the experiment. As a visible symptom of stress, the withering of plants was followed by a diminution of RWC and photosynthetic pigments in the drought exposed leaves of sour cherry ecotypes compared to the control treatment. ChlF elucidated variability in the photosynthetic efficiency within studied sour cherry ecotypes, highlighting PI_ABS, PI_total, and ψE₀ as the most sensitive and thus the most informative JIP parameters for drought screening. Among the investigated ecotypes, BOR proved to be the most sensitive. The Oblačinska sour cherry ecotype OS showed the highest tolerance to drought conditions and, therefore, can be used as a source of tolerance in sour cherry breeding programs.

Foliar Functional Traits of Resource Island-Forming Nurse Tree Species from a Semi-Arid Ecosystem of La Guajira, Colombia

Semi-arid environments characterized by low rainfall are subject to soil desertification processes. These environments have heterogeneous landscapes with patches of vegetation known as resource islands that are generated by nurse species that delay the desertification process because they increase the availability of water and nutrients in the soil. The study aimed to characterize some foliar physiological, biochemical, and anatomical traits of three nurse tree species that form resource islands in the semi-arid environment of La Guajira, Colombia, i.e., Haematoxylum brasiletto, Pithecellobium dulce, and Pereskia guamacho. The results showed that H. brasiletto and P. dulce have sclerophyllous strategies, are thin (0.2 and 0.23 mm, respectively), and have a high leaf dry matter content (364.8 and 437.47 mg/g). Moreover, both species have a high photochemical performance, reaching Fv/Fm values of 0.84 and 0.82 and PI_ABS values of 5.84 and 4.42, respectively. These results agree with the OJIP curves and JIP parameters. Both species had a compact leaf with a similar dorsiventral mesophyll. On the other hand, P. guamacho has a typical succulent, equifacial leaf with a 97.78% relative water content and 0.81 mm thickness. This species had the lowest Fv/Fm (0.73) and PI_ABS (1.16) values and OJIP curve but had the highest energy dissipation value (DIo/RC).

Occurrence of Patulin and Polyphenol Profile of Croatian Traditional and Conventional Apple Cultivars during Storage

Apples and apple-based products are among the most consumed fruits around the world. However, they are susceptible to infection with the fungi Penicilium expansum. In addition to the reduction of apple quality, secondary metabolism of this fungus produces a mycotoxin patulin that has a negative effect on human health. Currently, there is no available research in the literature on the resistance of Croatian traditional apple cultivars to contamination with P. expansum, and consequently, on the patulin content in apples and apple juice produced from those apples. Although the mechanism of apple resistance to fungal diseases has not yet been sufficiently investigated, some studies have shown that polyphenolic compounds have some impact on fungi growth. In order to contribute with new knowledge, this research deals with monitoring the growth of P. expansum on apples, patulin detection by LC/MS-MS, determination of polyphenol profile by validated HPLC method, and determining the effect of polyphenolic compounds on fungi growth and patulin production during apple storage. The results of this study have shown that Croatian traditional apple cultivars harvested from family farm Horvatić contain higher concentration of polyphenolic compounds and higher antioxidant activity. At the same time, they showed more resistance to infection by P. expansum than conventional ones. The higher content of dihydrochalcones and flavanols encouraged the biosynthesis of patulin in examined cultivars. However, the higher content of non-flavonoids such as 2-6 dimethoxybenzoic acid, 4-hydroxycinnamic acid and chlorogenic acid leads to decrease in content of patulin. In conclusion, it seems that content of polyphenols and patulin production are correlated.

Ameliorative effects of plant growth promoting bacteria, zinc oxide nanoparticles and oxalic acid on Luffa acutangula grown on arsenic enriched soil

Arsenic (As) contamination and bioaccumulation are a serious threat to agricultural plants. To address this issue, we checked the efficacy of As tolerant plant growth promoting bacteria (PGPB), zinc oxide nanoparticles (ZnO NPs) and oxalic acid (OA) in Luffa acutangula grown on As rich soil. The selected most As tolerant PGPB i.e Providencia vermicola exhibited plant growth promoting features i.e solubilzation of phosphate, potassium and siderophores production. Innovatively, we observed the synergistic effects of P. vermicola, ZnO NPs (10 ppm) and OA (100 ppm) in L. acutangula grown on As enriched soil (150 ppm). Our treatments both as alone and in combination alleviated As toxicity exhibited by better plant growth and metabolism. Results revealed significantly enhanced photosynthetic pigments, proline, relative water content, total sugars, proteins and indole acetic acid along with As amelioration in L. acutangula. Furthermore, upregulated plant resistance was manifested with marked reduction in the lipid peroxidation and electrolyte leakage and pronounced antagonism of As and zinc content in leaves under toxic conditions. These treatments also improved level of nutrients, abscisic acid and antioxidants to mitigate As toxicity. This marked improvement in plants' defense mechanism of treated plants under As stress is confirmed by less damaged leaves cell structures observed through the scanning electron micrographs. We also found substantial decrease in the As bioaccumulation in the L. acutangula shoots and roots by 40 and 58% respectively under the co-application of P. vermicola, ZnO NPs and OA in comparison with control. Moreover, the better activity of soil phosphatase and invertase was assessed under the effect of our application. These results cast a new light on the application of P. vermicola, ZnO NPs and OA in both separate and combined form as a feasible and ecofriendly tool to alleviate As stress in L. acutangula.

The Photosynthetic Efficiency and Carbohydrates Responses of Six Edamame (Glycine max. L. Merrill) Cultivars under Drought Stress

Vegetable-type soybean, also known as edamame, was recently introduced to South Africa. However, there is lack of information on its responses to drought. The aim of this study was to investigate the photosynthetic efficiency and carbohydrates responses of six edamame cultivars under drought stress. Photosynthetic efficiency parameters, including chlorophyll fluorescence and stomatal conductance, were determined using non-invasive methods, while pigments were quantified spectrophotometrically. Non-structural carbohydrates were quantified using Megazyme kits. Structural carbohydrates were determined using Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Drought stress significantly increased the Fv/Fm and PIabs of AGS429 and UVE17 at pod filling stage. Chlorophyll-a, which was most sensitive to drought, was significantly reduced in AGS429 and UVE17, but chlorophyll-b was relatively stable in all cultivars, except UVE17, which showed a significant decline at flowering stage. AGS354 and AGS429 also showed reduced chlorophyll-b at pod filling. UVE17 showed a significant reduction in carotenoid content and a substantial reduction in stomatal conductance during pod filling. Drought stress during pod filling resulted in a significant increase in the contents of trehalose, sucrose and starch, but glucose was decreased. Chlorophyll-a positively correlated with starch. The FTIR and XRD results suggest that the cell wall of UVE14, followed by UVE8 and AGS429, was the most intact during drought stress. It was concluded that carotenoids, stomatal conductance, starch and hemicellulose could be used as physiological/biochemical indicators of drought tolerance in edamame. This information expands our knowledge of the drought defense responses in edamame, and it is essential for the physiological and biochemical screening of drought tolerance.

Physiological Response to Short-Term Heat Stress in the Leaves of Traditional and Modern Plum (Prunus domestica L.) Cultivars

The aim of this study was to evaluate physiological responses to short-term heat stress in the leaves of traditional (Bistrica) and modern (Toptaste) plum cultivars. In this study, detached plum leaves were incubated at 25 °C (control) and 40 °C (stress). After 1 h of exposure to heat (40 °C), chlorophyll a fluorescence transients were measured, and several biochemical parameters were analyzed. Elevated temperature caused heat stress in both plum cultivars, seen as a decrease in water content (WT), but in the leaves of the cultivar Bistrica, an accumulation of proline and phenols, as well as an accumulation of photosynthetic pigments, suggest the activation of a significant response to unfavorable conditions. Conversely, in the leaves of Toptaste, a significant accumulation of malondialdehyde (MDA) and an activation of guaiacol peroxidase (GPOD), all together with a decreased soluble proteins content, indicate an inadequate response to maintaining homeostasis in the leaf metabolism. The impact of an elevated temperature on photosynthesis was significant in both plum cultivars as reflected in the decrease in performance indexes (PIABS and PItotal) and the maximum quantum yield of PSII (Fv/Fm), with significantly pronounced changes found in Toptaste. Unlike the traditional plum cultivar, Bistrica, in the modern cultivar, Toptaste, short-term heat stress increased the minimal fluorescence (F0) and absorption (ABS/RC), as well as Chl b in total chlorophylls. Additionally, the inactivation of RCs (RC/ABS) suggests that excitation energy was not trapped efficiently in the electron chain transport, which resulted in stronger dissipation (DI0/RC) and the formation of ROSs. Considering all presented results, it can be presumed that the traditional cultivar Bistrica has better tolerance to heat stress than the modern cultivar Toptaste. The cultivar, Bistrica, can be used as a basis in further plum breeding programs, as a source of tolerance for high temperature stress.

Diurnal Change of the Photosynthetic Light-Response Curve of Buckbean (Menyanthes trifoliata), an Emergent Aquatic Plant

Understanding plant physiological responses to high temperature is an important concern pertaining to climate change. However, compared with terrestrial plants, information about aquatic plants remains limited. Since the degree of midday depression of photosynthesis under high temperature depends on soil water conditions, it is expected that emergent aquatic plants, for which soil water conditions are always saturated, will show different patterns compared with terrestrial plants. We investigated the diurnal course of the photosynthetic light-response curve and incident light intensity for a freshwater emergent plant, buckbean (Menyanthes trifoliata L.; Menyanthaceae) in a cool temperate region. The effect of midday depression was observed only on a very hot day, but not on a moderately hot day, in summer. The diurnal course of photosynthetic light-response curves on this hot day showed that latent morning reduction of photosynthetic capacity started at dawn, preceding the apparent depression around the midday, in agreement with results reported in terrestrial plants. We concluded that (1) midday depression of emergent plants occurs when the stress intensity exceeds the species' tolerance, and (2) measurements of not only photosynthetic rate under field conditions but also diurnal course of photosynthetic light-response curve are necessary to quantify the effect of midday depression.