Photosynthesis product allocation and yield in sweet potato with spraying exogenous hormones under drought stress

Sweet potato yield and quality characteristics affected by different late-season irrigation levels

BACKGROUND

Seasonal late-season water deficits negatively affect the yield and quality of sweet potatoes in northern China. However, the amount of late-season irrigation to achieve high yield and consistent quality storage root remains undetermined. We assessed the yield and some qualitative traits of sweet potatoes such as size, shape, skin/flesh colour and nutritional content, as influenced by five irrigation levels (T0 : unirrigated control; T1 : 33% ETc ; T2 : 75% ETc ; T3 : 100% ETc ; and T4 : 125% ETc ).

RESULTS

Late-season irrigation significantly increased yield and marketable yield. Yields for T2 and T3 were significantly higher than other treatments, whereas T2 had the highest Grade A rating in a 2-year test. The vertical length of storage roots gradually increased with an increase in irrigation level, whereas the maximum width remained unchanged. The proportion of long elliptic and elliptic storage roots also increased, whereas the proportion of ovate, obovate and round storage roots gradually decreased. The skin and flesh colours became more vivid as the level of irrigation increased, with the skin colour becoming redder and the flesh colour becoming more orange-yellow. The levels of carotenoids, vitamin C and soluble sugar were significantly higher in irrigated crops, with the highest vitamin C and soluble sugar levels in T2 and the highest carotenoid levels in T3 treatment.

CONCLUSION

Taken together, these results demonstrate the potential of moderate irrigation in the late-season to improve both yield production and quality potential. The results are of great importance for improving the market value of sweet potatoes and increasing grower profits. © 2024 Society of Chemical Industry.

Exogenous abscisic acid (ABA) improves the filling process of maize grains at different ear positions by promoting starch accumulation and regulating hormone levels under high planting density

BACKGROUND

Higher planting densities typically cause a decline in grain weight, limiting the potential for high maize yield. Additionally, variations in grain filling occur at different positions within the maize ear. Abscisic acid (ABA) is important for grain filling and regulates grain weight. However, the effects of exogenous ABA on the filling process of maize grains at different ear positions under high planting density are poorly understood. In this study, two summer maize hybrids (DengHai605 (DH605) and ZhengDan958 (ZD958)) commonly grown in China were used to examine the effects of ABA application during the flowering stage on grain filling properties, starch accumulation, starch biosynthesis associated enzyme activities, and hormone levels of maize grain (including inferior grain (IG) and superior grain (SG)) under high planting density.

RESULTS

Our results showed that exogenous ABA significantly increased maize yield, primarily owing to a higher grain weight resulting from an accelerated grain filling rate relative to the control. There was no significant difference in yield between DH605 and ZD958 in the control and ABA treatments. Moreover, applying ABA promoted starch accumulation by raising the activities of sucrose synthase, ADP-glucose pyrophosphorylase, granule-bound starch synthases, soluble starch synthase, and starch branching enzyme in grains. It also increased the levels of zeatin riboside, indole-3-acetic acid, and ABA and decreased the level of gibberellin in grains, resulting in more efficient grain filling. Notably, IG exhibited a less efficient filling process compared to SG, probably due to lower starch biosynthesis associated enzyme activities and an imbalance in hormone contents. Nevertheless, IG displayed greater sensitivity to exogenous ABA than SG, suggesting that appropriate cultural measures to improve IG filling may be a viable strategy to further increase maize yield.

CONCLUSIONS

According to our results, spraying exogenous ABA could effectively improve grain filling properties, accelerate starch accumulation by increasing relevant enzyme activities, and regulate hormone levels in grains, resulting in higher grain weight and yield of maize under high planting density. Our findings offer more evidence for using exogenous hormones to improve maize yield under high planting density.

Silencing ZmPP2C-A10 with a foxtail mosaic virus (FoMV) derived vector benefits maize growth and development following water limitation

Global climate change is causing more frequent and severe droughts, which can have negative impacts on plant growth and crop productivity. Under drought conditions, plants produce the hormone ABA (abscisic acid), which regulates adaptive responses, such as stomatal closure and root elongation. Plant viruses have been used in the lab to convey new traits to plants and could also be used to increase production of ABA or to enhance downstream plant drought resistance responses. In this study, foxtail mosaic virus (FoMV) was used to silence ZmPP2C-A10, a negative regulator of ABA signalling, in maize (Zea mays L.). Both silenced and control plants were exposed to an 8-day drought treatment, followed by a 30-day period of rewatering, after which indicators of drought resistance were measured. After drought treatment, we observed a nearly twofold increase in expression of a stress-mitigation gene, ZmRAB17, reduced chlorophyll fluorescence changes (indicator of stress), and increased plant biomass and development in the ZmPP2C-A10-silenced maize compared to controls. These results demonstrate that the FoMV system can be used to silence endogenous expression of ZmPP2C-A10 and increase maize tolerance to drought. This could offer a useful tool to improve crop traits and reduce yield loss during the growing season.

Photosynthesis Product Allocation and Yield in Sweet Potato in Response to Different Late-Season Irrigation Levels

Soil water deficit is an important factor affecting the source-sink balance of sweet potato during its late-season growth, but water regulation during this period has not been well studied. Therefore, the aim of this study was to determine the appropriate irrigation level in late-season sweet potato, and the effect of irrigation level on accumulation and allocation of photosynthetic products. In this study, two yield-based field trials (2021-2022) were conducted in which five late-season irrigation levels set according to the crop evapotranspiration rate were tested (T₀: non-irrigation, T₁: 33% ET_c, T₂: 75% ET_c, T₃: 100% ET_c, T₄: 125% ET_c). The effects of the different irrigation levels on photosynthetic physiological indexes, ¹³C transfer allocation, water use efficiency (WUE), water productivity (WP), and the yield and economic benefit of sweet potato were studied. The results showed that late-season irrigation significantly increased the total chlorophyll content and net photosynthetic rate of functional leaves, in addition to promoting the accumulation of above-ground-source organic biomass (p < 0.05). The rate of ¹³C allocation, maximum accumulation rate (V_max), and average accumulation rate (V_mean) of dry matter in storage root were significantly higher under T₂ irrigation than under the other treatments (p < 0.05). This suggests that both non-irrigation (T₀) and over-irrigation (T₄) were not conducive to the transfer and allocation of photosynthetic products to storage roots in late-season sweet potato. However, moderate irrigation (T₂) effectively promoted the source-sink balance, enhanced the source photosynthetic rate and stimulated the sink activity, such that more photosynthate was allocated to the storage sink. The results also showed that T₂ irrigation treatments significantly increased yield, WUE and WP compared to T₀ and T₄ (p < 0.05), suggesting that moderate irrigation (T₂) can significantly promote the potential of storage root production and field productivity. There was a close relationship between economic benefit and marketable sweet potato yield, and both were highest under T₂ (p < 0.05), increasing by 36.1% and 59.9% compared with T₀ over the two-year study period. In conclusion, irrigation of late-season sweet potato with 75% evapotranspiration (T₂) can improve both the yield and production potential. Together, these results support the use of late-season water management in the production of sweet potato.

Long-Term Soil Drought Limits Starch Accumulation by Altering Sucrose Transport and Starch Synthesis in Sweet Potato Tuberous Root

In this study, the influences of long-term soil drought with three levels [soil-relative water content (SRWC) (75 ± 5)%, as the control; SRWC (55 ± 5)%, mild drought; SRWC (45 ± 5)%, severe drought] were investigated on sucrose-starch metabolism in sweet potato tuberous roots (TRs) by pot experiment. Compared to the control, drought stress increased soluble sugar and sucrose content by 4-60% and 9-75%, respectively, but reduced starch accumulation by 30-66% through decreasing the starch accumulate rate in TRs. In the drought-treated TRs, the inhibition of sucrose decomposition was attributed to the reduced activities of acid invertase (AI) and alkaline invertase (AKI) and the IbA-INV3 expression, rather than sucrose synthase (SuSy), consequently leading to the increased sucrose content in TRs. In addition, starch synthesis was inhibited mainly by reducing ADP-glucose pyrophosphorylase (AGPase), granular starch synthase (GBSS) and starch branching enzyme (SBE) activities in TRs under drought stress, and AGPase was the rate-limiting enzyme. Furthermore, soil drought remarkably up-regulated the IbSWEET11, IbSWEET605, and IbSUT4 expressions in Jishu 26 TRs, while it down-regulated or had no significant differences in Xushu 32 and Ningzishu 1 TRs. These results suggested that the sucrose-loading capability in Jishu 26 TRs were stronger than that in Xushu 32 and Ningzishu 1 TRs. Moreover, IbA-INV3, IbAGPS1, IbAGPS2, IbGBSSI and IbSBEII play important roles in different drought-tolerant cultivars under drought stress.

Carbon allocation in cassava is affected by water deficit and potassium application - A 13 C-CO2 pulse labelling assessment

RATIONALE

Cassava production faces challenges in a changing climate. Pulse labelling cassava with ¹³ C-CO₂ has the potential to elucidate carbon allocation mechanisms of cassava under drought stress and with potassium application. Understanding these mechanisms could guide efforts to mitigate effects of drought in cassava cropping systems.

METHODS

Forty-eight cassava plants received a nutrient solution high or low in potassium. Water deficit was imposed on half of the plants at bulk root initiation stage, after which they were labelled for 8 h with ¹³ C-CO₂ in a 15 m³ growth chamber. Plants were harvested 8 h, 9 days and 24 days after labelling, and separated into leaves, stems and roots. δ¹³ C values of the different parts were measured using an isotope ratio mass spectrometer, from which ¹³ C excess was calculated.

RESULTS

Water deficit decreased transpiration (P < 0.001) and increased carbon respiration (P < 0.05). Potassium application increased assimilate distribution to the roots (P < 0.05) at 9 days after labelling, more strongly for plants under water deficit. The opposite was found at 24 days (P < 0.05) with the legacy of water deficit additionally increasing assimilate distribution to roots (P < 0.05). Youngest, fully expanded leaves contained up to 47% of initial ¹³ C excess at 24 days after labelling.

CONCLUSIONS

Pulse labelling proved to be successful in shedding light on carbon allocation in relation to water and potassium availability. This technique, once adapted to field conditions, could further be used to improve fertilizer recommendations or change agronomic practices to cope with plant stress.

Genome-Wide Identification of DUF668 Gene Family and Expression Analysis under Drought and Salt Stresses in Sweet Potato [Ipomoea batatas (L.) Lam]

The domain of unknown function 668 (DUF668) is a gene family that plays a vital role in responses to adversity coercion stresses in plant. However, the function of the DUF668 gene family is not fully understood in sweet potato. In this study, bioinformatics methods were used to analyze the number, physicochemical properties, evolution, structure, and promoter cis-acting elements of the IbDUF668 family genes, and RNA-seq and qRT-PCR were performed to detect gene expression and their regulation under hormonal and abiotic stress. A total of 14 IbDUF668 proteins were identified in sweet potato, distributed on nine chromosomes. By phylogenetic analysis, IbDUF668 proteins can be divided into two subfamilies. Transcriptome expression profiling revealed that many genes from DUF668 in sweet potato showed specificity and differential expression under cold, heat, drought, salt and hormones (ABA, GA3 and IAA). Four genes (IbDUF668-6, 7, 11 and 13) of sweet potato were significantly upregulated by qRT-PCR under ABA, drought and NaCl stress. Results suggest that the DUF668 gene family is involved in drought and salt tolerance in sweet potato, and it will further provide the basic information of DUF668 gene mechanisms in plants.

Drought and global hunger: biotechnological interventions in sustainability and management

Drought may be efficiently managed using the following strategies: prevention, mitigation, readiness, recovery, and transformation. Biotechnological interventions may become highly important in reducing plants' drought stress in order to address key plant challenges such as population growth and climate change. Drought is a multidimensional construct with several triggering mechanisms or contributing factors working at various spatiotemporal scales, making it one of the known natural catastrophes. Drought is among the causes of hunger and malnutrition, decreasing agricultural output, and poor nutrition. Many deaths caused in children are due to hunger situations, and one in four children face stunted growth. All this hunger and malnutrition may be responsible for the reduction in agricultural productivity caused due to the drought situations affecting food security. Global Hunger Index has been accelerating due to under-nutrition and under-5 deaths. Drought has been covering more than 20% of the world's agricultural areas, leading to significantly less food production than what is required for consumption. Drought reduces soil fertility and adversely affects soil biological activity reducing the inherent capacity of the soil to support vegetation. Recent droughts have had a much greater effect on people's lives, even beyond causing poverty and hunger. Drought may have substantial financial consequences across the globe it may cause a severe impact on the world economy. It is a natural feature of the environment that will appear and disappear as it has in history. Due to increasing temperatures and growing vulnerabilities, it will undoubtedly occur more often and seriously in the coming years. To ensure sustainable socio-economic and social development, it is critical to reducing the effects of potential droughts worldwide using different biotechnological interventions. It's part of a long-term growth plan, and forecasting is essential for early warnings and global hunger management.

Physiological Responses to Drought, Salinity, and Heat Stress in Plants: A Review

On the world stage, the increase in temperatures due to global warming is already a reality that has become one of the main challenges faced by the scientific community. Since agriculture is highly dependent on climatic conditions, it may suffer a great impact in the short term if no measures are taken to adapt and mitigate the agricultural system. Plant responses to abiotic stresses have been the subject of research by numerous groups worldwide. Initially, these studies were concentrated on model plants, and, later, they expanded their studies in several economically important crops such as rice, corn, soybeans, coffee, and others. However, agronomic evaluations for the launching of cultivars and the classical genetic improvement process focus, above all, on productivity, historically leaving factors such as tolerance to abiotic stresses in the background. Considering the importance of the impact that abiotic stresses can have on agriculture in the short term, new strategies are currently being sought and adopted in breeding programs to understand the physiological, biochemical, and molecular responses to environmental disturbances in plants of agronomic interest, thus ensuring the world food security. Moreover, integration of these approaches is bringing new insights on breeding. We will discuss how water deficit, high temperatures, and salinity exert effects on plants.

Improving crop drought resistance with plant growth regulators and rhizobacteria: Mechanisms, applications, and perspectives

Drought is one of the main abiotic stresses that cause crop yield loss. Improving crop yield under drought stress is a major goal of crop breeding, as it is critical to food security. The mechanism of plant drought resistance has been well studied, and diverse drought resistance genes have been identified in recent years, but transferring this knowledge from the laboratory to field production remains a significant challenge. Recently, some new strategies have become research frontiers owing to their advantages of low cost, convenience, strong field operability, and/or environmental friendliness. Exogenous plant growth regulator (PGR) treatment and microbe-based plant biotechnology have been used to effectively improve crop drought tolerance and preserve yield under drought stress. However, our understanding of the mechanisms by which PGRs regulate plant drought resistance and of plant-microbiome interactions under drought is still incomplete. In this review, we summarize these two strategies reported in recent studies, focusing on the mechanisms by which these exogenous treatments regulate crop drought resistance. Finally, future challenges and directions in crop drought resistance breeding are discussed.

Beneficial effects of abscisic acid and melatonin in overcoming drought stress in cotton (Gossypium hirsutum L.)

Pot experiments were performed to study the effects of abscisic acid (ABA) and melatonin (MT) on cotton drought tolerance and to explore their combined effects. ABA or MT spraying promoted water status and antioxidant capacity of drought-stressed leaves, which was conducive to scavenge ROS, finally increasing lint yield. However, the mitigation mechanisms of ABA and MT on drought were not identical, which were mainly manifested as: (1) ABA increased the relative water content (RWC) of drought-stressed leaves via, reducing water loss, but MT increased it via, promoting water uptake efficiency; (2) for enzymatic antioxidant system, ABA and MT might modulate different kinds of superoxide dismutase to catalyze the reduction of O₂ ^- under drought; and (3) for ascorbic acid (AsA)-glutathione (GSH) cycle, MT increased the glutathione reductase activity in drought-stressed leaves, but ABA did not. ABA + MT spraying led to higher leaf RWC and total antioxidant capacity than single hormone under drought, leading to a lower H₂ O₂ level. For the enzymatic antioxidant system, single hormone treatment affected Cu/ZnSOD or MnSOD expression, but ABA + MT upregulated both genes in drought-stressed leaves. Hormones combined application also had higher CAT expression than single hormone. For AsA-GSH cycle, ABA + MT had higher dehydroascorbic acid reductase activity than single hormone, resulting in higher AsA content. Moreover, hormones combined application caused higher ascorbate peroxidase activity than single hormone, suggesting that their combination synergistically improved the ability of AsA to eliminate ROS. All these confirmed that ABA plus MT had synergistic effects on improving crop drought resistance.

Exogenous 6-Benzyladenine Improves Waterlogging Tolerance in Maize Seedlings by Mitigating Oxidative Stress and Upregulating the Ascorbate-Glutathione Cycle

The synthetic cytokinin 6-benzyladenine (6-BA) regulates plant growth and prevents the negative consequences of various forms of abiotic stress, including waterlogging in crop plants. The present study aimed to investigate the effects of exogenous 6-BA on the growth, oxidative stress, and ascorbate-glutathione (AsA-GSH) cycle system in the inbred SY-MY13 (waterlogging-resistant) and SY-XT1 (waterlogging-sensitive) seedlings of waxy corn in conditions of waterlogging stress. The results demonstrated that waterlogging stress causes chlorosis and necrosis in waxy corn leaves, inhibiting growth and leading to the accumulation of reactive oxygen species (ROS), which induces oxidative stress and, in turn, reduces membrane lipid peroxidation and the disruption of membrane homeostasis. This is specifically manifested in the increased concentrations of superoxide anion radicals ( O 2 - ), hydrogen peroxide (H₂O₂), and malondialdehyde (MDA), in addition to increased relative electrical conductivity (REC%) values. The SY-MY13 strain exhibited growth superior to that of SY-XT1 when waterlogged due to its excellent waterlogging resistance. Thus, exogenous 6-BA was found to be effective in enhancing the growth of plants stressed by waterlogging in terms of the weight of the shoots and roots, shoot height, and leaf area. In addition to this, exogenous 6-BA also reduced the accumulation of O 2 - , H₂O₂, and MDA, increased ascorbate peroxidase (APX), glutathione reductase (GR), dehydroascorbate reductase (DHAR), and monodehydroascorbate reductase (MDHAR) activity, and enhanced ascorbic acid (AsA), and reduced glutathione (GSH) concentration through the regulation of the efficiency of the AsA-GSH cycle system in maize plants. Hence, the application of exogenous 6-BA can alleviate waterlogging-induced damage and improve waterlogging tolerance in waxy corn via the activation of the AsA-GSH cycle system and the elimination of ROS.

PopW enhances drought stress tolerance of alfalfa via activating antioxidative enzymes, endogenous hormones, drought related genes and inhibiting senescence genes

Alfalfa (Medicago sativa L.) has the advantages of high yield and nutritional value as a perennial forage. However, one of the drawbacks of alfalfa is its susceptibility to drought conditions, which is a global problem in agriculture. The purpose of this study was to reveal the effects of exogenous PopW, a harpin protein from Ralstonia solanacearum, treatment on growth parameters, physiological and biochemical mechanism of alfalfa under drought-stress conditions. Growth parameters, relative water content, free proline, leaf area, total chlorophyll, antioxidative enzymes, endogenous hormones including ABA, CTK, GA, JA, SA and IAA were determined in response to exogenous PopW treatment under drought stress in alfalfa cultivar (Victoria). Moreover, relative gene expressions of drought-related and leaf senescence genes were determined. Under drought stress, alfalfa plants had lower shoot dry weight, shoot length, relative water content, leaf area, and total chlorophyll content, compared to control (non-stressed). However, Exogenous PopW treatment significantly increased growth values, relative water content, free proline, leaf area, total chlorophyll content, catalase, glutathione reductase and superoxide dismutase under drought conditions, compared to control and drought stress alone. Moreover, exogenous PopW treatment significantly increased ABA, GA, JA, SA, IAA contents, up-regulated auxin- and drought-responsive genes, down-regulated leaf senescence genes. Exogenous PopW treatment enhanced drought stress tolerance of alfalfa due to changes of endogenous hormone contents and expression levels of drought stress and leaf senescence genes. The results of the study show that PopW treatment could be used to increase the forage yield of alfalfa on areas having drought problem.

Phylogenetic Analysis of the SQUAMOSA Promoter-Binding Protein-Like Genes in Four Ipomoea Species and Expression Profiling of the IbSPLs During Storage Root Development in Sweet Potato (Ipomoea batatas)

As a major plant-specific transcription factor family, SPL genes play a crucial role in plant growth, development, and stress tolerance. The SPL transcription factor family has been widely studied in various plant species; however, systematic studies on SPL genes in the genus Ipomoea are lacking. Here, we identified a total of 29, 27, 26, and 23 SPLs in Ipomoea batatas, Ipomoea trifida, Ipomoea triloba, and Ipomoea nil, respectively. Based on the phylogenetic analysis of SPL proteins from model plants, the Ipomoea SPLs were classified into eight clades, which included conserved gene structures, domain organizations and motif compositions. Moreover, segmental duplication, which is derived from the Ipomoea lineage-specific whole-genome triplication event, was speculated to have a predominant role in Ipomoea SPL expansion. Particularly, tandem duplication was primarily responsible for the expansion of SPL subclades IV-b and IV-c. Furthermore, 25 interspecific orthologous groups were identified in Ipomoea, rice, Arabidopsis, and tomato. These findings support the expansion of SPLs in Ipomoea genus, with most of the SPLs being evolutionarily conserved. Of the 105 Ipomoea SPLs, 69 were predicted to be the targets of miR156, with seven IbSPLs being further verified as targets using degradome-seq data. Using transcriptomic data from aboveground and underground sweet potato tissues, IbSPLs showed diverse expression patterns, including seven highly expressed IbSPLs in the underground tissues. Furthermore, the expression of 11 IbSPLs was validated using qRT-PCR, and two (IbSPL17/IbSPL28) showed significantly increased expression during root development. Additionally, the qRT-PCR analysis revealed that six IbSPLs were strongly induced in the roots under phytohormone treatments, particularly zeatin and abscisic acid. Finally, the transcriptomic data of storage roots from 88 sweet potato accessions were used for weighted gene co-expression network analysis, which revealed four IbSPLs (IbSPL16/IbSPL17/IbSPL21/IbSPL28) clusters with genes involved in "regulation of root morphogenesis," "cell division," "cytoskeleton organization," and "plant-type cell wall organization or biogenesis," indicating their potential role in storage root development. This study not only provides novel insights into the evolutionary and functional divergence of the SPLs in the genus Ipomoea but also lays a foundation for further elucidation of the potential functional roles of IbSPLs on storage root development.