In situ pod growth rate reveals contrasting diurnal sensitivity to water deficit in Phaseolus vulgaris.

The development of reproductive tissues determines plant fecundity and yield. Loading of resources into the developing reproductive tissue is thought to be under the co-limiting effects of source and sink strength. The dynamics of this co-limitation are unknown, largely due to an inability to measure the flux of resources into a developing sink. Here we use nuclear magnetic resonance (NMR) sensors to measure sink strength by quantifying rates of pod dry matter accumulation (pod loading) in Phaseolus vulgaris at 13-min intervals across the diel period. Rates of pod loading showed contrasting variation across light and dark periods during the onset of water deficit. In addition, rates of pod loading appeared decoupled from net photosynthetic rates when adjusted to the plant scale. Combined, these observations illustrate that the rate of pod development varies under water limitation and that continuous, non-invasive methodologies to measure sink strength provide insight into the governing processes that determine the development of reproductive tissues.

Trehalose 6-phosphate promotes seed filling by activating auxin biosynthesis.

Plants undergo several developmental transitions during their life cycle. One of these, the differentiation of the young embryo from a meristem-like structure into a highly specialized storage organ, is believed to be controlled by local connections between sugars and hormonal response systems. However, we know little about the regulatory networks underpinning the sugar-hormone interactions in developing seeds. By modulating the trehalose 6-phosphate (T6P) content in growing embryos of garden pea (Pisum sativum), we investigate here the role of this signaling sugar during the seed-filling process. Seeds deficient in T6P are compromised in size and starch production, resembling the wrinkled seeds studied by Gregor Mendel. We show also that T6P exerts these effects by stimulating the biosynthesis of the pivotal plant hormone, auxin. We found that T6P promotes the expression of the auxin biosynthesis gene TRYPTOPHAN AMINOTRANSFERASE RELATED2 (TAR2), and the resulting effect on auxin concentrations is required to mediate the T6P-induced activation of storage processes. Our results suggest that auxin acts downstream of T6P to facilitate seed filling, thereby providing a salient example of how a metabolic signal governs the hormonal control of an integral phase transition in a crop plant.

Has yield plasticity already been exploited by soybean breeding programmes in Argentina?

This study focuses on the impact of genetic improvement of seed yield plasticity in soybean (Glycine max L.) in high-yielding environments (between 4000 kg ha-1 and 7000 kg ha-1) of Central Argentina. The association between seed yield and its plasticity was analysed with (i) a historical collection of 148 genotypes released to the market between 1980 and 2013 and (ii) 165 currently available commercial genotypes. The impact on seed yield of soybean breeding programmes in Argentina reveals higher genetic progress of the lowest (1.7% year-1) rather than the highest yielding genotypes (0.9% year-1). At the same time, seed yield plasticity has been exploited indirectly. Increased seed yield plasticity over time contributed to a reduction in genotypic seed yield variability (P<0.0001). Seed yield plasticity was related to seed yield in high-yielding environments (>5500 kg ha-1). Plastic genotypes showed a positive correlation with the length of the seed-filling period (r=0.5), suggesting that a longer seed-filling period could be required to maximize seed yield plasticity under high-yielding environments. To increase productivity, clarifying the value of plasticity will aid genotype selection for target environments, as well as the development of high-yielding cultivars specifically adapted to high-yielding conditions.

Oil quality in sea-level quinoa as determined by cultivar-specific responses to temperature and radiation conditions.

BACKGROUND: There is renewed interest in quinoa as a potential source of vegetable oils; however, there is no information about how environmental conditions affect its fatty acid composition, a critical indicator of its oil quality. The fatty acid concentrations of four cultivars adapted to temperate environments were compared at three sowing dates to evaluate the effect of environmental conditions during the seed-filling period on the variation in oil quality. RESULTS: The interaction between cultivar and sowing date was the main source of variation explaining the changes in the lipid content and fatty acid concentrations in quinoa. Most of the variation in the concentration of unsaturated fatty acids was attributed to the temperature and solar radiation during the seed-filling period; cultivar-specific responses to photo-thermal conditions were observed among the sea-level quinoa cultivars evaluated. CONCLUSION: The lipid content and concentration of fatty acids in quinoa are affected by sowing date. This effect is exerted through changes in temperature and solar radiation conditions. This managing practice can therefore be used to achieve quinoa oil with different qualities. © 2019 Society of Chemical Industry.

Pod-wall proteomics provide novel insights into soybean seed-filling process under chemical-induced terminal drought stress.

BACKGROUND: Drought is very detrimental when it occurs during the reproductive phase of soybeans, leading to considerable yield loss due to the disproportionate allocation of photo-assimilates to competing sinks. As pod walls are known to play a crucial role in regulating carbon partitioning during seed filling under stress conditions, the present study aims to analyze the stage-specific carbon allocation pattern during potassium iodide (KI)-simulated terminal drought, and to provide an insight into the pod-wall proteome responses during drought onset. RESULTS: A comparative proteomics approach was adopted to visualize the differential protein expression in soybean pod-wall at stage R5 (seed initiation). Sugar status was analyzed using high-performance liquid chromatography (HPLC) and biochemical methods. Potassium iodide-simulated terminal drought during reproductive stages 4, 5 and 6 (R4, R5, and R6) caused a significant decline in starch, total carbohydrate, and reducing sugar in the leaves; however, the pod-wall and seeds showed a reduction only in the total carbohydrate content, whereas starch and reducing sugar levels remained unchanged. A pod-wall proteome at stage R5 showed immediate induction of proteins belonging to stress signaling / regulation, protein folding / stabilization, redox-homeostasis, cellular energy, and carbon utilization and down-regulation of negative regulators of drought stress and protein degradation-related proteins. CONCLUSIONS: A KI spray effectively simulated terminal drought stress and caused around 50% yield loss when compared to controls. Our results indicate that, at the very onset of desiccation stress, the pod wall (stage R5) activates strong protective responses to maintain the carbon allocation to the surviving seeds. © 2018 Society of Chemical Industry.

Mechanisms of Maturation and Germination in Crop Seeds Exposed to Environmental Stresses with a Focus on Nutrients, Water Status, and Reactive Oxygen Species.

Environmental stresses can reduce crop yield and quality considerably. Plants protect cell metabolism in response to abiotic stresses at all stages of their life cycle, including seed production. As the production of vigorous seeds is important to both yield and crop growth, we analyzed causes of yield loss and reduced grain quality in staple crops exposed to environmental stresses such as drought and temperature extremes, with a focus on the remobilization of nutrients and water status during seed filling. Because water is one of the factors that limit seed development, seeds must have mechanisms that allow them to withstand water loss during seed maturation. In addition, analysis of the effects of reactive oxygen species (ROS) on transcription regulation and signaling should help to elucidate the regulation of seed dormancy and germination. In this review, we focus on nutrient remobilization, water mobility, plant hormones (gibberellins, abscisic acid, and ethylene), and ROS in sink and source organs and describe how rice, wheat, barley, soybean, and cowpea plants control seed maturation and germination under environmental stresses.

Response of chickpea (Cicer arietinum L.) to terminal drought: leaf stomatal conductance, pod abscisic acid concentration, and seed set.

Flower and pod production and seed set of chickpea (Cicer arietinum L.) are sensitive to drought stress. A 2-fold range in seed yield was found among a large number of chickpea genotypes grown at three dryland field sites in south-western Australia. Leaf water potential, photosynthetic characteristics, and reproductive development of two chickpea genotypes with contrasting yields in the field were compared when subjected to terminal drought in 106kg containers of soil in a glasshouse. The terminal drought imposed from early podding reduced biomass, reproductive growth, harvest index, and seed yield of both genotypes. Terminal drought at least doubled the percentage of flower abortion, pod abscission, and number of empty pods. Pollen viability and germination decreased when the fraction of transpirable soil water (FTSW) decreased below 0.18 (82% of the plant-available soil water had been transpired); however, at least one pollen tube in each flower reached the ovary. The young pods which developed from flowers produced when the FTSW was 0.50 had viable embryos, but contained higher abscisic acid (ABA) concentrations than those of the well-watered plants; all pods ultimately aborted in the drought treatment. Cessation of seed set at the same soil water content at which stomata began to close and ABA increased strongly suggested a role for ABA signalling in the failure to set seed either directly through abscission of developing pods or seeds or indirectly through the reduction of photosynthesis and assimilate supply to the seeds.

Wheat seed weight and quality differ temporally in sensitivity to warm or cool conditions during seed development and maturation.

Background and aims: Short periods of extreme temperature may affect wheat (Triticum aestivum) seed weight, but also quality. Temporal sensitivity to extreme temperature during seed development and maturation was investigated. Methods: Plants of 'Tybalt' grown at ambient temperature were moved to growth cabinets at 29/20°C or 34/20°C (2010), or 15/10°C or 34/20°C (2011), for successive 7-d periods from 7 DAA (days after anthesis) onwards, and also 7-65 DAA in 2011. Seed samples were harvested serially and moisture content, weight, ability to germinate, subsequent longevity in air-dry storage and bread-making quality were determined. Key Results: High temperature (34/20°C) reduced final seed weight, with greatest temporal sensitivity at 7-14 or 14-21 DAA. Several aspects of bread-making quality were also most sensitive to high temperature then, but whereas protein quality decreased protein and sulphur concentrations improved. Early exposure to high temperature provided earlier development of ability to germinate and tolerate desiccation, but had little effect on maximum germination capacity. All treatments at 15/10°C resulted in ability to germinate declining between 58 and 65 DAA. Early exposure to high temperature hastened improvement in seed storage longevity, but the subsequent decline in late maturation preceded that in the control. Long (7-65 DAA) exposure to 15/10°C disrupted the development of seed longevity, with no improvement after seed filling ended. Longevity improved during maturation drying in other treatments. Early (7-14 DAA) exposure to high temperature reduced and low temperature increased subsequent longevity at harvest maturity, whereas late (35 or 42-49 DAA) exposure to high temperature increased and low temperature reduced it. Conclusions: Temporal sensitivity to extreme temperature was detected. It varied considerably amongst the contrasting seed variables investigated. Subsequent seed longevity at harvest maturity responded negatively to temperature early in development, but positively later in development and throughout maturation.

Soybean fruit development and set at the node level under combined photoperiod and radiation conditions.

In soybean, long days during post-flowering increase seed number. This positive photoperiodic effect on seed number has been previously associated with increments in the amount of radiation accumulated during the crop cycle because long days extend the duration of the crop cycle. However, evidence of intra-nodal processes independent of the availability of assimilates suggests that photoperiodic effects at the node level might also contribute to pod set. This work aims to identify the main mechanisms responsible for the increase in pod number per node in response to long days; including the dynamics of flowering, pod development, growth and set at the node level. Long days increased pods per node on the main stems, by increasing pods on lateral racemes (usually dominated positions) at some main stem nodes. Long days lengthened the flowering period and thereby increased the number of opened flowers on lateral racemes. The flowering period was prolonged under long days because effective seed filling was delayed on primary racemes (dominant positions). Long days also delayed the development of flowers into pods with filling seeds, delaying the initiation of pod elongation without modifying pod elongation rate. The embryo development matched the external pod length irrespective of the pod's chronological age. These results suggest that long days during post-flowering enhance pod number per node through a relief of the competition between pods of different hierarchy within the node. The photoperiodic effect on the development of dominant pods, delaying their elongation and therefore postponing their active growth, extends flowering and allows pod set at positions that are usually dominated.

Regulation of galactomannan biosynthesis in coffee seeds.

The seed of Coffea arabica accumulates large amounts of cell wall storage polysaccharides (CWSPs) of the mannan family in the cell walls of the endosperm. The variability induced by the growing environment and extensive pairwise correlation analysis with stringent significance thresholds was used to investigate transcript-transcript and transcript-metabolite relationships among 26 sugar-related genes, and the amount of CWSPs and seven soluble low molecular weight carbohydrates in the developing coffee endosperm. A dense module of nine quantitatively co-expressed genes was detected at the mid-developmental stage when CWSPs accumulate. This module included the five genes of the core galactomannan synthetic machinery, namely genes coding for the enzymes needed to assemble the mannan backbone (mannan synthase, ManS), and genes that introduce the galactosyl side chains (galactosyltransferase, GMGT), modulate the post-depositional degree of galactose substitution (α-galactosidase), and produce the nucleotide sugar building blocks GDP-mannose and UDP-galactose (mannose-1P guanyltransferase and UDP-glucose 4'-epimerase, respectively). The amount of CWSPs stored in the endosperm at the onset of their accumulation was primarily and quantitatively modulated at the transcriptional level (i.e. positively correlated with the expression level of these key galactomannan biosynthetic genes). This analysis also suggests a role for sorbitol and raffinose family oligosaccharides as transient auxiliary sources of building blocks for galactomannan synthesis. Finally, a microarray-based analysis of the developing seed transcriptome revealed that all genes of the core galactomannan synthesis machinery grouped in a single cluster of 209 co-expressed genes. Analysis of the gene composition of this cluster revealed remarkable functional coherence and identified transcription factors that putatively control galactomannan biosynthesis in coffee.

Critical period for yield determination across grain crops.

Studies across different crops demonstrated that grain or seed number per unit area (GN m-2) is the dominant yield component. Although grains or seeds derive from floret or flower production and survival, the timing of the critical period for GN m-2 determination is known to vary noticeably, from mainly pre-flowering to strongly post-flowering, across major grain crops. Here, we demonstrate that discrepancy between crops in the timing of their critical period is related to the flowering phase duration and the proportion of the whole cycle allocated to pre-flowering development. Changing the perspective, positioning the critical period at the end of the phase when grain abortion occurs instead of flowering, results in the critical period virtually coinciding among contrasting grain crops.

Plasmodesmata and their role in assimilate translocation.

During multicellularization, plants evolved unique cell-cell connections, the plasmodesmata (PD). PD of angiosperms are complex cellular domains, embedded in the cell wall and consisting of multiple membranes and a large number of proteins. From the beginning, it had been assumed that PD provide passage for a wide range of molecules, from ions to metabolites and hormones, to RNAs and even proteins. In the context of assimilate allocation, it has been hypothesized that sucrose produced in mesophyll cells is transported via PD from cell to cell down a concentration gradient towards the phloem. Entry into the sieve element companion cell complex (SECCC) is then mediated on three potential routes, depending on the species and conditions, - either via diffusion across PD, after conversion to raffinose via PD using a polymer trap mechanism, or via a set of transporters which secrete sucrose from one cell and secondary active uptake into the SECCC. Multiple loading mechanisms can likely coexist. We here review the current knowledge regarding photoassimilate transport across PD between cells as a prerequisite for translocation from leaves to recipient organs, in particular roots and developing seeds. We summarize the state-of-the-art in protein composition, structure, transport mechanism and regulation of PD to apprehend their functions in carbohydrate allocation. Since many aspects of PD biology remain elusive, we highlight areas that require new approaches and technologies to advance our understanding of these enigmatic and important cell-cell connections.

Leaf photosynthesis and senescence in heated and droughted field-grown soybean with contrasting seed protein concentration.

Soybean plants under heat and drought generate a multiplicity of responses in photosynthesis and senescence, impairing growth, yield, and seed quality. The goal of this study was to analyze and quantify independent and combined effects of heat and drought during seed filling on photosynthesis and senescence, and its subsequent effects on the filling duration in soybean genotypes contrasting on seed protein. Two field experiments were conducted using high and low seed protein genotypes. During seed filling plants were exposed to four treatments: control (ambient temperature and soil water content near field capacity), heat stress (HS, episodes above 32 °C 6 h d-1) during 15-d, drought stress (DS, soil water content ≤ 25% of field capacity) during the entire seed filling, and HS × DS. We found non-genotypic variation in leaf photosynthesis in both experiments. Irrigated HS, did no alter photosynthesis and senescence. Drought, regardless of heat, reduced photosynthesis, carbohydrate production and affected membranes integrity, leading to premature leaf senescence and shortening the filling duration. The magnitude of responses was similar between drought alone and stresses combined, indicating a dominant role of drought over heat. The seed filling duration was not shorter in high protein compared to low protein genotype, nor was senescence pattern altered across treatments. These results indicated that the higher seed protein content exhibited by some genotypes are not necessarily associated with an earlier onset of senescence and shortening of the filling period as suggested by previous studies analyzing genotypes differing in protein concentration.

Soybean Yield Formation Physiology - A Foundation for Precision Breeding Based Improvement.

The continued improvement of crop yield is a fundamental driver in agriculture and is the goal of both plant breeders and researchers. Plant breeders have been remarkably successful in improving crop yield, as demonstrated by the continued release of varieties with improved yield potential. This has largely been accomplished through performance-based selection, without specific knowledge of the molecular mechanisms underpinning these improvements. Insight into molecular mechanisms has been provided by plant molecular, genetic, and biochemical research through elucidation of the function of genes and pathways that underlie many of the physiological processes that contribute to yield potential. Despite this knowledge, the impact of most genes and pathways on yield components have not been tested in key crops or in a field environment for yield assessment. This gap is difficult to bridge, but field-based physiological knowledge offers a starting point for leveraging molecular targets to successfully apply precision breeding technologies such as genome editing. A better understanding of both the molecular mechanisms underlying crop yield physiology and yield limiting processes under field conditions is essential for elucidating which combinations of favorable alleles are required for yield improvement. Consequently, one goal in plant biology should be to more fully integrate crop physiology, breeding, genetics, and molecular knowledge to identify impactful precision breeding targets for relevant yield traits. The foundation for this is an understanding of yield formation physiology. Here, using soybean as an example, we provide a top-down review of yield physiology, starting with the fact that yield is derived from a population of plants growing together in a community. We review yield and yield-related components to provide a basic overview of yield physiology, synthesizing these concepts to highlight how such knowledge can be leveraged for soybean improvement. Using genome editing as an example, we discuss why multiple disciplines must be brought together to fully realize the promise of precision breeding-based crop improvement.

Autophagy Controls Sulphur Metabolism in the Rosette Leaves of Arabidopsis and Facilitates S Remobilization to the Seeds.

Sulphur deficiency in crops became an agricultural concern several decades ago, due to the decrease of S deposition and the atmospheric sulphur dioxide emissions released by industrial plants. Autophagy, which is a conserved mechanism for nutrient recycling in eukaryotes, is involved in nitrogen, iron, zinc and manganese remobilizations from the rosette to the seeds in Arabidopsis thaliana. Here, we have compared the role of autophagy in sulphur and nitrogen management at the whole plant level, performing concurrent labelling with 34S and 15N isotopes on atg5 mutants and control lines. We show that both 34S and 15N remobilizations from the rosette to the seeds are impaired in the atg5 mutants irrespective of salicylic acid accumulation and of sulphur nutrition. The comparison in each genotype of the partitions of 15N and 34S in the seeds (as % of the whole plant) indicates that the remobilization of 34S to the seeds was twice more efficient than that of 15N in both autophagy mutants and control lines under high S conditions, and also in control lines under low S conditions. This was different in the autophagy mutants grown under low S conditions. Under low S, the partition of 34S to their seeds was indeed not twice as high but similar to that of 15N. Such discrepancy shows that when sulphate availability is scarce, autophagy mutants display stronger defects for 34S remobilization relative to 15N remobilization than under high S conditions. It suggests, moreover, that autophagy mainly affects the transport of N-poor S-containing molecules and possibly sulphate.

ACCELERATED CELL DEATH 6 Acts on Natural Leaf Senescence and Nitrogen Fluxes in Arabidopsis.

As the last step of leaf development, senescence is a molecular process involving cell death mechanism. Leaf senescence is trigged by both internal age-dependent factors and environmental stresses. It must be tightly regulated for the plant to adopt a proper response to environmental variation and to allow the plant to recycle nutrients stored in senescing organs. However, little is known about factors that regulate both nutrients fluxes and plant senescence. Taking advantage of variation for natural leaf senescence between Arabidopsis thaliana accessions, Col-0 and Ct-1, we did a fine mapping of a quantitative trait loci for leaf senescence and identified ACCELERATED CELL DEATH 6 (ACD6) as the causal gene. Using two near-isogeneic lines, differing solely around the ACD6 locus, we showed that ACD6 regulates rosette growth, leaf chlorophyll content, as well as leaf nitrogen and carbon percentages. To unravel the role of ACD6 in N remobilization, the two isogenic lines and acd6 mutant were grown and labeled with 15N at the vegetative stage in order to determine 15N partitioning between plant organs at harvest. Results showed that N remobilization efficiency was significantly lower in all the genotypes with lower ACD6 activity irrespective of plant growth and productivity. Measurement of N uptake at vegetative and reproductive stages revealed that ACD6 did not modify N uptake efficiency but enhanced nitrogen translocation from root to silique. In this study, we have evidenced a new role of ACD6 in regulating both sequential and monocarpic senescences and disrupting the balance between N remobilization and N uptake that is required for a good seed filling.

High Temperatures During the Seed-Filling Period Decrease Seed Nitrogen Amount in Pea (Pisum sativum L.): Evidence for a Sink Limitation.

Higher temperatures induced by the on-going climate change are a major cause of yield reduction in legumes. Pea (Pisum sativum L.) is an important annual legume crop grown in temperate regions for its high seed nitrogen (N) concentration. In addition to yield, seed N amount at harvest is a crucial characteristic because pea seeds are a source of protein in animal and human nutrition. However, there is little knowledge on the impacts of high temperatures on plant N partitioning determining seed N amount. Therefore, this study investigates the response of seed dry matter and N fluxes at the whole-plant level (plant N uptake, partitioning in vegetative organs, remobilization, and accumulation in seeds) to a range of air temperature (from 18.4 to 33.2°C) during the seed-filling-period. As pea is a legume crop, plants relying on two different N nutrition pathways were grown in glasshouse: N2-fixing plants or NO3 --assimilating plants. Labeled nitrate (15NO3 -) and intra-plant N budgets were used to quantify N fluxes. High temperatures decreased seed-filling duration (by 0.8 day per °C), seed dry-matter and N accumulation rates (respectively by 0.8 and 0.032 mg seed-1 day-1 per °C), and N remobilization from vegetative organs to seeds (by 0.053 mg seed-1 day-1 per °C). Plant N2-fixation decreased with temperatures, while plant NO3 - assimilation increased. However, the additional plant N uptake in NO3 --assimilating plants was never allocated to seeds and a significant quantity of N was still available at maturity in vegetative organs, whatever the plant N nutrition pathway. Thus, we concluded that seed N accumulation under high temperatures is sink limited related to a shorter seed-filling duration and a reduced seed dry-matter accumulation rate. Consequently, sustaining seed sink demand and preserving photosynthetic capacity of stressed plants during the seed-filling period should be promising strategies to promote N allocation to seeds from vegetative parts and thus to maintain crop N production under exacerbated abiotic constraints in field due to the on-going climate change.

A Reduced Phosphorus Application Rate Using a Mycorrhizal Plant as the Preceding Crop Maintains Soybean Seeds' Nutritional Quality.

We tested whether introducing an arbuscular mycorrhizal fungi (AMF)-host plant with a reduced P application rate could maintain soybean seeds' nutrient quality. The dynamic variation of 14 nutrients was analyzed in source and sink organs during the seed-filling stage. The AMF-host and non-AMF-host plants, sunflower and mustard, were grown as preceding crops (PCs). Soybeans, the succeeding crops, were planted with three different phosphorus levels, namely, 0, 50, and 150 kg P2O5 ha-1. The results showed that the AMF-host PC with a reduced P application rate maintained the seed's yield and nutrients quality. During the seed-filling stage, the AMF-host PC with a reduced P application rate increased the uptake of most nutrients compared to the non-AMF-host PC, and improved the remobilization efficiency of all nutrients except Mn, Fe, and Se, compared to the optimal P application rate. These results could help improve the utilization efficiency of P fertilizers and protect soybeans' nutritional value.

Seed filling in maize and hormones crosstalk regulated by exogenous application of uniconazole in semiarid regions.

In semiarid regions, deficit and unpredictable precipitation results in yield losses. Uniconazole is a plant growth regulator and its application is beneficial in water saving agriculture and improves maize production in semiarid regions. In order to determine the effects of uniconazole application on seed filling and hormonal changes of maize, a field study was conducted in the summer of 2015 and 2016. Seeds were soaked in uniconazole at concentration of 0 (SCK), 25 (S25), 50 (S50), and 75 (S75) mg kg-1, while in the second experiment, uniconazole was applied to the foliage at concentration of 0 (FCK), 25 (F25), 50 (F50), and 75 (F75) mg L-1 at the eight-leaf. Uniconazole application significantly improves the seed filling rates by regulating the endogenous hormones contents. Uniconazole seed soaking treatments improved significantly the seed filling rate of superior, middle, and inferior seeds compared with foliar application treatments. Uniconazole improved significantly the zeatin (Z) + zeatin riboside (ZR) and abscisic acid (ABA) contents while reducing the gibberellic acid (GA) content in the seeds during the process of seed filling. The Z + ZR and ABA contents were significantly positively correlated while the GA content was negatively correlated with maximum seed weight, maximum seed filling rates, and mean seed filling rates. Treatments S25 and F25 significantly improved the above dry matter accumulation plant-1, seed filling rates, ABA, Z + ZR contents, characters of ear, and grain yield while reduced the GA content. It is concluded from our results that the uniconazole application at concentration of 25 mg kg-1 as seed soaking or 25 mg L-1 foliar applied at the eight-leaf stage is beneficial to improve the seed filling rates and grain yield of maize in semiarid regions.

Drought or/and Heat-Stress Effects on Seed Filling in Food Crops: Impacts on Functional Biochemistry, Seed Yields, and Nutritional Quality.

Drought (water deficits) and heat (high temperatures) stress are the prime abiotic constraints, under the current and climate change scenario in future. Any further increase in the occurrence, and extremity of these stresses, either individually or in combination, would severely reduce the crop productivity and food security, globally. Although, they obstruct productivity at all crop growth stages, the extent of damage at reproductive phase of crop growth, mainly the seed filling phase, is critical and causes considerable yield losses. Drought and heat stress substantially affect the seed yields by reducing seed size and number, eventually affecting the commercial trait '100 seed weight' and seed quality. Seed filling is influenced by various metabolic processes occurring in the leaves, especially production and translocation of photoassimilates, importing precursors for biosynthesis of seed reserves, minerals and other functional constituents. These processes are highly sensitive to drought and heat, due to involvement of array of diverse enzymes and transporters, located in the leaves and seeds. We highlight here the findings in various food crops showing how their seed composition is drastically impacted at various cellular levels due to drought and heat stresses, applied separately, or in combination. The combined stresses are extremely detrimental for seed yield and its quality, and thus need more attention. Understanding the precise target sites regulating seed filling events in leaves and seeds, and how they are affected by abiotic stresses, is imperative to enhance the seed quality. It is vital to know the physiological, biochemical and genetic mechanisms, which govern the various seed filling events under stress environments, to devise strategies to improve stress tolerance. Converging modern advances in physiology, biochemistry and biotechnology, especially the "omics" technologies might provide a strong impetus to research on this aspect. Such application, along with effective agronomic management system would pave the way in developing crop genotypes/varieties with improved productivity under drought and/or heat stresses.