Early Seedling Establishment Research Articles

EFFECTS OF MELATONIN ON PHYSIO-BIOCHEMICAL AND IONIC STRESS MARKERS IN MAIZE AT SEEDLING STAGE UNDER SALT STRESS

Oxidative stress due to salinity creates a challenging situation for seed germination and early seedling establishment in maize. Over than normal production of reactive oxygen species (ROS) leaves cataclysmic effects on the physiology of plants when subjected to saline environment. Melatonin is versatile stress mitigating organic molecule reported to have significant potential for scavenging ROS. The present study was conducted with the aim to study the effects of different concentrations of melatonin viz., control, 500, 1000 & 1500 µM on the physiological and bio-chemical stress markers in the six maize genotypes viz., MMRI-Yellow, NCEV-1530-9, YH-1898, Composite, SB-9617 and FH-949.The study was planned in sand culture (pot study) using CRD with factorial arrangement. The results of the present study demonstrated that melatonin priming in all the concentrations viz., 500,1000 and 1500µM significantly enhanced the germination percentage (by 14.0 , 25.0 and 27 %), chlorophyll a (23.3, 43.3 & 40.0 %), chlorophyll b contents (by 29.2, 50.0 & 50.0 %), total soluble sugar-TSS (by 20.0, 31.5 & 40.4 %), total soluble protein-TSP (by 10.0, 15.5 & 20.5%), chlorophyll stability index-CSI (by 15.0, 20.3 & 25.6%), membrane stability index-MSI (13.3, 25.7 & 26.6%), relative water contents-RWC (13.7, 23.3 & 24.0%), phenolic contents-TP (14.8, 24.3 & 26.8 %), proline contents-Pro (23.0, 35.2 & 37.7%), superoxide dismutase-SOD (by 25.5, 41.0 & 45.0 %), per-oxidase-POD (by 17.8, 25.1 & 24.7%), catalase-CAT (by 37.7, 51.5 & 54.3%) and reduced concentrations of H2O2 (by19.3, 26.5 & 30.1 %), malondialdehyde-MDA contents (by 15.1, 22.4 & 22.3%) and electrolyte leakage-EL (by 12.4, 18.0 & 16.5 %), compared to un-primed seed treatment. Interestingly the higher concentrations of melatonin were statistically produced the same effects. The genotype SB-9617outperformed, with respect to higher accumulation of photo-pigments, TSS, TSP and TP with improved of membrane stability, relative water contents and enhanced activities of the anti-oxidant enzymes (SOD, POD and CAT) showed reduced lipid per-oxidation and electrolyte. In PCA-bi-plot, PC1 and PC2 contributed maximally i.e. 90.9 and 3.7% to explain the total variations i.e 94.6 %. Additionally, SB-9617 with melatonin priming@ 1000µM proved the best to mitigate adverse effects of salt stress at germination and early seedling growth stage via cross taking with physiological and bio-chemical stress markers.

Effects of temperature regimes on seed germination and early growth of different soybean cultivars

High temperature is an important global issue that impedes agricultural production, especially of soybean (Glycine max [L.] Merr.) crop. Numerous studies were undertaken to estimate the effect of temperature on soybean seed germination under low temperatures. However, the effects of high-temperatures on seed germination and early seedling establishment of various soybean cultivars need to be explored further. Therefore, the current study was performed in growth chambers to evaluate genetic variations among different soybean cultivars for germination and early growth under varying temperatures. Five temperatures, i.e., 15, 20, 25, 30, and 35 ◦C, and four soybean cultivars (PI408105A, PI567731, PI567690, and PI416937) were used. The results showed that soybean cultivars revealed substantial variations in germination percentage (GP), germination rate index (GRI), germination energy (GE), seed vigor index (SVI), and seedling length under different temperatures mentioned above. The results indicated that higher temperature [35 °C] inhibited seed germination. Conversely, the intermediate temperatures [20, 25, and 30 ◦C] depicted good germination. Lower temperature declined the seed germination to some extent, and the germination percentage of PI408105A, PI567731, PI567690, and PI416937 were observed as 63.33%, 56.67%, 50%, and 40.11%, respectively. For all the soybean cultivars, the mean seed germination rate was maximum at 25 ◦C. However, the germination rate index continued to increase until 30 ◦C . The soybean cultivar PI408105A was the most promising under high temperature, exhibiting higher GP by 86.67%, highest SVI by 50.95%, and GRI by 50% at 30 ◦C. In contrast, PI416937 was among the cultivars sensitive to high temperature and showed a higher germination rate only at 20 ◦C. The seeds of PI408105A, PI567731, and PI567690 can germinate well under intermediate temperature conditions, making them a promising species for use in hot climatic zones. According to the current findings, it was concluded that soybean should be planted under mild temperatures for good crop stand and production. Moreover, it is recommended that cultivars such as PI408105A could be grown in warm conditions.

Deconstructing the root system of grasses through an exploration of development, anatomy and function.

Well‐adapted root systems allow plants to grow under resource‐limiting environmental conditions and are important determinants of yield in agricultural systems. Important staple crops such as rice and maize belong to the family of grasses, which develop a complex root system that consists of an embryonic root system that emerges from the seed, and a postembryonic nodal root system that emerges from basal regions of the shoot after germination. While early seedling establishment is dependent on the embryonic root system, the nodal root system, and its associated branches, gains in importance as the plant matures and will ultimately constitute the bulk of below‐ground growth. In this review, we aim to give an overview of the different root types that develop in cereal grass root systems, explore the different physiological roles they play by defining their anatomical features, and outline the genetic networks that control their development. Through this deconstructed view of grass root system function, we provide a parts‐list of elements that function together in an integrated root system to promote survival and crop productivity.

Physiological Aspects of Germination and Early Seedling Establishment of Pleurotus sajor-caju Glyceraldehyde-3-Phosphate Dehydrogenase Expressing Transgenic Rice in Saline Environment.

GPD encodes glyceraldehyde-3-phosphate dehydrogenase enzyme involved in sugar mobilization, particularly glycolysis and gluconeogenesis. The objective of this study was to determine physiological aspects of germination and early seedling establishment of PsGPD (Pleurotus sajor-caju glyceraldehyde-3-phosphate dehydrogenase) expressing transgenic rice (T5) against different salt concentrations. The T5 line that carried 2 copies of T-DNA and had the highest level of PsGPD expression was used in the investigation. Final germination percentage, amylase activity, reducing sugar accumulation, and chlorophyll biosynthesis were comparatively higher in PsGPD expressing transgenic rice against elevating saline conditions. A slow-paced conversion of porphyrin's precursors was seen through the matrix model and further elaborated by a graphical model. A sustained level of porphyrin was observed in PsGPD expressing transgenic rice. These data were concurrent with the relative gene expression and thermal imaging (thermography) of PsGPD expressing transgenic rice against salt stress. Morphological attributes also favored the salt tolerance exhibited by PsGPD-transformed rice.

VARIETAL PERFORMANCE OF SPRING RICE SEEDLINGS AGAINST COLD STRESS IN WESTERN TERAI OF NEPAL

Rice is an important commodity in Nepalese agriculture occupying 1.46-million-hectare area, where 92% area falls under main (Barkhe) season and 7% under spring (Chaite) season. Among various constraints for spring rice seedling raising, cold stress during early seedling establishment is the major one. To address the problem, an on-station trial entitled “varietal performance of spring rice seedlings against cold stress in Western Terai of Nepal” was conducted from February to March, 2021 at Horticulture research farm of Paklihawa Campus, Rupandehi. Research was carried out in Completely Randomized Design with two growing environment (inside and outside polyhouse) as main factor and seven varieties as sub-factor, each replicated three times. Spring rice varieties includes five released varieties (Hardinath-1, Hardinath-3, Hardinath Hybrid-1, Hardinath Hybrid-3, Chaite-5) and two promising varieties (IR-1008 and PR 126). Data related to growth of seedling were collected at one week interval up to 5 weeks. Significant difference was observed within two environmental conditions on days to germination parameters, shoot length, root length, seedling dry weight and leaf area. The values for all the parameters were found maximum in seedlings inside the polyhouse as compared to that of outside polyhouse and in the variety Hardinath – 1. For early transplanting of spring rice, it was found better to choose Hardinath- 1 variety and raise seedlings under polyhouse nursery to escape cold stress.

Poor acclimation to experimental field drought in subalpine forest tree seedlings.

The ability of tree species to acclimate and tolerate projected increases in drought frequency and intensity has fundamental implications for future forest dynamics with climate change. Inquiries to date on the drought tolerance capacities of tree species, however, have focused almost exclusively on mature trees with scant in situ work on seedlings, despite the central role that regeneration dynamics play in forest responses to changing conditions. We subjected naturally established seedlings of co-dominant subalpine conifer species (Abies lasiocarpa and Picea engelmannii) in the southern Rocky Mountains to 2 years of in situ summer precipitation exclusion, simulating summer drought conditions similar to a failure of the North American monsoon. We compared the morphological and physiological responses of seedlings growing in drought vs. ambient conditions to assess the relative changes in drought tolerance traits as a function of seedling size. Drought treatments had a marked impact on soil moisture: volumetric water content averaged ≈5–8 % in drought treatments and ≈8–12 % in ambient controls. We detected no significant shifts in morphology (e.g. root biomass, leaf:stem area ratio) in response to drought for either species, but net photosynthesis in drought treatments was 78 % lower for spruce and 37 % lower for fir. Greater stomatal control associated with increasing stem diameter conferred greater water use efficiencies in larger seedlings in both species but was not significantly different between drought and ambient conditions, suggesting an overall lack of responsivity to water stress and a prioritization of carbon gain over investment in drought mitigation traits. These results indicate a canonization of traits that, while useful for early seedling establishment, may portend substantial vulnerability of subalpine seedling populations to prolonged or recurrent droughts, especially for spruce.

Plant iron nutrition: the long road from soil to seeds.

Iron (Fe) is an essential plant micronutrient since many cellular processes including photosynthesis, respiration, and the scavenging of reactive oxygen species depend on adequate Fe levels; however, non-complexed Fe ions can be dangerous for cells, as they can act as pro-oxidants. Hence, plants possess a complex homeostatic control system for safely taking up Fe from the soil and transporting it to its various cellular destinations, and for its subcellular compartmentalization. At the end of the plant's life cycle, maturing seeds are loaded with the required amount of Fe needed for germination and early seedling establishment. In this review, we discuss recent findings on how the microbiota in the rhizosphere influence and interact with the strategies adopted by plants to take up iron from the soil. We also focus on the process of seed-loading with Fe, and for crop species we also consider its associated metabolism in wild relatives. These two aspects of plant Fe nutrition may provide promising avenues for a better comprehension of the long pathway of Fe from soil to seeds.

Salicylic acid improves seed germination through modulating antioxidant enzymes under salt stress in chickpea (Cicer arietinum)

An experiment was conducted to investigate the role of Antioxidant Enzymes (AOE) in Salicylic Acid (SA) induced salt-stress tolerance during chickpea (Cicer arietinum L.) seed germination at ICAR- Indian Institute of Seed Science, Mau during 2018. Results showed the differential germination performance of salt-sensitive (PG 186) and salt-tolerant (CSG 8962) chickpea cultivars under three levels (0, 75, 150 mM NaCl) of salt stresses. Salt stress adversely affected the seed germination and traits of early seedling establishment in PG 186 cultivar than in CSG 8962. Sand matrix priming (SMP) of seeds using SA @ 150 ppm improved the germination (up to 2 times) and other seed quality parameters in sensitive cultivar under higher (150 mM NaCl) salt-stress level. Further investigating the role of SA on modulating AOE, a negative influence of SA on major AOE (POX, CAT and GR) was observed in cotyledons of PG 186 genotype under high salt stress. However, the level of APX was observed to be constitutively higher in tolerant CSG 8962 chickpea genotype. The summary of results suggested that, SA alleviates oxidative stress through reducing major AOE in cotyledon to improve chickpea seed germination.

Biocrusts do not differentially influence emergence and early establishment of native and non‐native grasses

AbstractBiological soil crusts (biocrusts) cover the soil surface of global drylands and interact with vascular plants. Biocrusts may influence the availability and nature of safe sites for plant recruitment and the susceptibility of an area to invasion by non‐native species. Therefore, to investigate the potential role of biocrusts in invasive species management, we sought to determine whether native and non‐native grass recruitments in two North American deserts were differentially affected by biocrusts. We conducted a series of coordinated experiments in field, semi‐controlled, and controlled environment settings in the Colorado Plateau and Sonoran Desert using contrasting biocrust and grass functional types. Experiments in field environments focused on early establishment of grass seedlings whereas controlled environment experiments focused on seedling emergence. Within each experiment, we compared responses (frequency, magnitude, and timing of emergence/establishment) both across species (biocrust types pooled) and across species and levels of biocrust development. Native grasses varied by experiment and included Aristida purpurea, A. purpurea var. longiseta, Bouteloua gracilis, and Vulpia octoflora. Emergence of non‐native Bromus tectorum was similar to that of native grasses on the Colorado Plateau. Differences in emergence of native vs. non‐native grasses in the Sonoran Desert were species‐ and response‐specific. Emergence of the non‐native Bromus rubens was comparable to that of native grasses whereas emergence frequency and magnitude of the non‐native Pennisetum ciliare was lower compared with two of four native species. Within a grass species, emergence was higher and faster on bare soil compared with biocrusts in the Sonoran Desert semi‐controlled and greenhouse environment experiments. However, the pattern was not consistent across other experiments. When comparing across Colorado Plateau and Sonoran Desert biocrusts in greenhouse experiments, we found that emergence of native grasses was higher on Colorado Plateau biocrusts. Based on the lack of consistent results across our experiments, grass recruitment on biocrusts appears to be driven more by species‐specific traits than species provenance. Our greenhouse experiments suggest that biocrust topographic relief is an important safe site trait influencing plant recruitment.

The evolutionarily conserved kinase SnRK1 orchestrates resource mobilization during Arabidopsis seedling establishment.

The onset of plant life is characterized by a major phase transition. During early heterotrophic seedling establishment, seed storage reserves fuel metabolic demands, allowing the plant to switch to autotrophic metabolism. Although metabolic pathways leading to storage compound mobilization are well-described, the regulatory circuits remain largely unresolved. Using an inducible knockdown approach of the evolutionarily conserved energy master regulator Snf1-RELATED-PROTEIN-KINASE1 (SnRK1), phenotypic studies reveal its crucial function in Arabidopsis thaliana seedling establishment. Importantly, glucose feeding largely restores growth defects of the kinase mutant, supporting its major impact in resource mobilization. Detailed metabolite studies reveal sucrose as a primary resource early in seedling establishment, in a SnRK1-independent manner. Later, SnRK1 orchestrates catabolism of triacylglycerols and amino acids. Concurrent transcriptomic studies highlight SnRK1 functions in controlling metabolic hubs fuelling gluconeogenesis, as exemplified by cytosolic PYRUVATE ORTHOPHOSPHATE DIKINASE (cyPPDK). Here, SnRK1 establishes its function via phosphorylation of the transcription factor BASIC LEUCINE ZIPPER63 (bZIP63), which directly targets and activates the cyPPDK promoter. Taken together, our results disclose developmental and catabolic functions of SnRK1 in seed storage mobilization and describe a prototypic gene regulatory mechanism. As seedling establishment is important for plant vigor and crop yield, our findings are of agronomical importance.

Unraveling relationships of prompt germination among four species of Inga Mill detected by morpho-anatomical and histochemical traits

Seeds are structured with specific morphological attributes that influence their ability to establish new sporophytes in their environments. In this sense, studies of the morphological traits of seeds contribute to the understanding of processes related to the germination, storage and management of plant species. The aim of this study was to characterize the seeds of four species of Inga in terms of biometrics, morphoanatomy and histochemistry. Furthermore, the relationships between these trait variations among Inga species and their impact on seed germination were investigated. The seeds presented high moisture levels, above 40%. I. edulis had 20% viviparity, in contrast to I. cinnamomea, which had 0.1% viviparity. The seeds of I. pezizifera presented more than 50% polyembryony, which influenced seedling vigor. The tegument did not affect the germination percentage. On the other hand, the presence of the tegument influenced the mean germination time for I. cinnamomea, whose seeds with tegument germinated, on average, after 16 days, while the seeds of the other species germinated in 2 to 3 days. Morphologically, the seeds were anatropous, elliptical and exalbuminous. The embryonic axis was well developed and hairy. The tegument was membranous or leathery and caused no physical barrier to germination. However, differences were observed among species in terms of the thickness of the tegument and of the tegument cell walls. In cotyledons and on the embryonic axis, there was a wide distribution of neutral polysaccharides, starches and proteins. Lipids were scarce. Therefore, when taken together, the results concerning Inga seed characteristics contributed to elucidating the factors related to their accelerated and high rates of germination, which reflect their potential for early seedling establishment.

Why forest fails to recover after repeated wildfires in Amazonian floodplains? Experimental evidence on tree recruitment limitation

Abstract Amazonian floodplain forests are particularly vulnerable to wildfires that spread during extreme droughts, causing large‐scale forest dieback. After a second wildfire, these forests persist trapped with low tree cover and empty seed banks, yet the mechanisms that could explain this arrested succession remain unknown. Here we use a 4‐year field experiment to test whether tree recruitment failures in burnt floodplain forests are caused by environmental filtering, limiting early seedling emergence and establishment. We sowed seeds and planted seedlings of six floodplain trees with contrasting life strategies, and tested the roles of environmental filters by comparing tree seedling performances under different habitats (i.e. unburned forest, forest edge with burnt site, forest burnt once and forest burnt twice), and by manipulating soil root mats and herbaceous cover. Our results show that seedling emergence was around 15% across all habitats. In general, seedlings performed best in burnt forests. Seedling growth was highest in forests burnt once, possibly because of high nutrient availability after fire. In forests burnt twice, tree seedlings grew relatively less, as nutrients become limiting due to flood erosion; yet, seedlings survived longer, possibly because of lower competition with sparse, naturally recruiting trees. We found similar patterns for seedlings that emerged in the field from sowed seeds. Synthesis. Our experimental evidence suggests that environmental filtering related to soil nutrient limitations may slow down forest recovery after repeated wildfires. Yet, our findings showing that floodplain trees are able to germinate from seeds and establish successfully in twice burnt forests suggest that seed limitation may be the reason why forest recovery fails persistently. A corollary to the problem is that repeatedly burnt forests seem to be trapped by a self‐reinforcing feedback, in which low tree cover reduces seed dispersal and consequently seed availability, keeping tree cover low. Overall, our findings indicate that active restoration initiatives based on seeding native tree species may help accelerating the recovery of degraded floodplain forests after repeated wildfires.

GIBBERELLIC ACID PRIMING ENHANCES MAIZE SEED GERMINATION UNDER LOW WATER POTENTIAL

<p class="abstrakinggris"><span lang="EN-US">Germination is a portentous yield determining factor that is a challenge in the low water potential environment due to disrupted imbibition. Hormonal seed priming can markedly increase the germination on maize even in such a stressful environment. Therefore, research was aimed to analyze the application of gibberellic acid (GA<sub>3</sub>) priming to maize seeds to minimize the deleterious effects of reduced water potential. GA<sub>3</sub> priming was done at 0, 50, 100, 150, and 200 ppm for 12 hours and subjected to drought levels of 0, 0.15, 0.50, 1.05, and 1.75 MPa by using NaCl solution. Different germination parameters, i.e., germination percentage, mean germination time, germination index, relative water content, seedling vigor index, root length, and shoot length, were determined on the final day of the experiment. The results showed that all germination parameters were adversely influenced by low water potential. Every level of GA<sub>3</sub> priming has hastened all parameters. GA<sub>3</sub> priming at 100 ppm decreased the mean germination time by 35 hours under 1.75 MPa compared to non-primed seeds. GA<sub>3</sub> priming increased the shoot length of maize seedlings with a shoot length of 2.9 cm in non-primed seedlings compared to 6.4 cm in 200 ppm GA<sub>3</sub> priming under 1.05 MPa. GA<sub>3</sub> priming is the best method for the early establishment of maize seedlings in low water potential conditions. As a result, it may be utilized as a low-cost and straightforward approach for establishing maize crops under saline and drought conditions.</span></p>

Seed Priming With Protein Hydrolysates Improves Arabidopsis Growth and Stress Tolerance to Abiotic Stresses.

The use of plant biostimulants contributes to more sustainable and environmentally friendly farming techniques and offers a sustainable alternative to mitigate the adverse effects of stress. Protein hydrolysate-based biostimulants have been described to promote plant growth and reduce the negative effect of abiotic stresses in different crops. However, limited information is available about their mechanism of action, how plants perceive their application, and which metabolic pathways are activating. Here we used a multi-trait high-throughput screening approach based on simple RGB imaging and combined with untargeted metabolomics to screen and unravel the mode of action/mechanism of protein hydrolysates in Arabidopsis plants grown in optimal and in salt-stress conditions (0, 75, or 150 mM NaCl). Eleven protein hydrolysates from different protein sources were used as priming agents in Arabidopsis seeds in three different concentrations (0.001, 0.01, or 0.1 μl ml–1). Growth and development-related traits as early seedling establishment, growth response under stress and photosynthetic performance of the plants were dynamically scored throughout and at the end of the growth period. To effectively classify the functional properties of the 11 products a Plant Biostimulant Characterization (PBC) index was used, which helped to characterize the activity of a protein hydrolysate based on its ability to promote plant growth and mitigate stress, and to categorize the products as plant growth promoters, growth inhibitors and/or stress alleviator. Out of 11 products, two were identified as highly effective growth regulators and stress alleviators because they showed a PBC index always above 0.51. Using the untargeted metabolomics approach, we showed that plants primed with these best performing biostimulants had reduced contents of stress-related molecules (such as flavonoids and terpenoids, and some degradation/conjugation compounds of phytohormones such as cytokinins, auxins, gibberellins, etc.), which alleviated the salt stress response-related growth inhibition.

Differential abundance proteins associated with rapid growth of etiolated coleoptiles in maize

AbstractSince Charles Darwin discovered growth movements of the shoot tip (coleoptile) toward light, the grass coleoptiles have long been used as a model system to study plant growth. Rapid growth of the coleoptile is vital for successful seed germination and early seedling establishment. However, the proteome changes underlying the rapid growth of the coleoptiles are not yet clear in the model plant maize (Zea mays). In the present study, we investigated proteome changes in vivo occurring in the rapidly growing coleoptiles of maize with two‐dimensional gel electrophoresis combined with mass spectrometry. A quantitative comparison of the proteomes at 1.5, 3, and 5 days after germination showed significant changes in protein profiles with coleoptile growth. As a result, 31 differential abundance proteins (DAPs) representing 44 protein spots were identified, of which 21 DAPs with increased abundances were implied in growth‐related processes, including translational initiation, transcription regulation, protein and other compound synthesis, H+‐transmembrane transport and cytoskeleton organization. The selected DAPs were confirmed by reverse transcription quantitative PCR and immunoblot analysis. We suggested that the rapid growth of the coleoptile is largely due to its ability to quickly enhance relevant cellular processes, especially the increased synthesis of the growth‐related DAPs. The content of indole‐3‐acetic acid, salicylic acid, and jasmonic acid decreased significantly, and the content of gibberellins first decreased and then increased during the elongation of coleoptile. This study provides new insight into the significance of proteome changes in coleoptile growth.

Safeners improve early‐stage chilling‐stress tolerance in sorghum

AbstractSorghum [Sorghum bicolor (L.) Moench] is highly sensitive to chilling temperatures (<15°C soil temperatures) during germination and early seedling establishment. Hence, the main objectives of this research were to (a) validate the potential level of chilling tolerance in selected sorghum genotypes, (b) determine effective concentrations of selected safeners for improving chilling tolerance and (c) determine if safener combinations further enhance chilling tolerance compared to individual safener treatments. Four experiments were conducted with five sorghum genotypes, four safeners (oxabetrinil, fluxofenim, naphthalic anhydride and benoxacor), nine safener concentrations (0–25 μM) and two temperatures. The chilling‐tolerant genotypes recorded higher germination percentage (98% vs. 63%) and root (3.0 vs. 0.8 cm) and shoot lengths (0.7 vs. 0.1 cm) compared to sensitive genotypes under continuous 15℃. Each of the four safeners applied at the highest concentrations tested (20 and 25 μM) significantly enhanced seed germination and seedling growth at 15℃. The combination of four safeners was more effective in reducing chilling stress‐induced injury compared to individual, two‐ or three‐way combinations. Enhanced chilling tolerance may be extended to other cereal crops after optimizing the genetic background and effects of agro‐climatic conditions on safener chemistry, concentration, and proper combination of seed‐applied safeners.

English

Nitrate is one of the key sources of nitrogen in natural and agricultural soils. The distribution and concentration of nitrate determine root system architecture in plants. Soybean (Glycine max L) is one of the key leguminous crops, while farmers rarely apply nitrogen in soybean crops except for a starter nitrogen dose at the time of sowing. However, the effects of severe deficiency nitrate on early seedling establishment of soybean before nodulation are not yet studied. Therefore, this study evaluated the effects of high dose of nitrate (54.3 mM) and its deprivationon (0 mM) on the root system architecture of soybean during seedling establishment. Results showed that the root traits including primary root length, fresh biomass, total length, surface area, tips, forks, and its crossings were significantly higher under no nitrate condition than nigh nitrate condition except for root volume, its dry biomass and diameter. Shoot growth attributes such as shoot length, shoot fresh biomass, shoot dry biomass, single leaf area, soil-plant analysis development value, and photosynthesis was significantly decreased while leaf dry mass per area was increased significantly under no nitrate condition. Furthermore, high nitrate supply significantly enhanced the content of nitrate in root tissue, but there was no significant difference between low and optimal nitrate supply. In summary, this study indicated that soybean root system architecture adopts a foraging strategy under nitrogen deprived environment. © 2021 Friends Science Publishers

Arabidopsis FAR-RED ELONGATED HYPOCOTYL3 negatively regulates carbon starvation responses.

Light is one of the most important environmental factors that affects various cellular processes in plant growth and development; it is also crucial for the metabolism of carbohydrates as it provides the energy source for photosynthesis. Under extended darkness conditions, carbon starvation responses are triggered by depletion of stored energy. Although light rapidly inhibits starvation responses, the molecular mechanisms by which light signalling affects this process remain largely unknown. In this study, we showed that the Arabidopsis thaliana light signalling protein FAR-RED ELONGATED HYPOCOTYL3 (FHY3) and its homolog FAR-RED IMPAIRED RESPONSE1 (FAR1) are essential for plant survival after extended darkness treatment at both seedling and adult stages. Transmission electron microscopy analyses revealed that disruption of both FHY3 and FAR1 resulted in destruction of chloroplast envelopes and thylakoid membranes under extended darkness conditions. Furthermore, treatment with sucrose, but not glucose, completely rescued carbon starvation-induced cell death in the rosette leaves and arrested early seedling establishment in the fhy3 far1 plants. We thus concluded that the light signalling proteins FHY3 and FAR1 negatively regulate carbon starvation responses in Arabidopsis.

Cotton Seed Priming with Brassinosteroid Promotes Germination and Seedling Growth

Cotton (Gossypium hirsutum) is the largest fibre crop globally and an important oilseed crop. Rising temperatures and declining water supplies, which are also impacting soil salinity, threaten cotton plant productivity. Germination, emergence and young seedling stages in cotton are highly sensitive to salinity and heat stresses. Brassinosteroids (BRs) are plant steroid hormones that are essential for proper plant growth and development and also promote tolerance to a range of environmental stresses. Cotton seeds were primed with BR (24-epibrassinolide) alone or in combination with other hormones (abscisic acid, auxin and gibberellic acid) and tested for germination and early seedling growth. BR promoted germination under no stress as well as under salinity and heat stress conditions, while other hormones were ineffective under stress conditions. BR also promoted cotyledon opening and the development of lateral roots in germinated seedlings. The ability of BR to positively impact seedling growth across different stress conditions suggests that priming cotton seeds with BR may help in early and successful establishment of seedlings, which may benefit the plant through its lifecycle.

The Arabidopsis thaliana E3 Ubiquitin Ligase BRIZ Functions in Abscisic Acid Response.

The ubiquitin system is essential for multiple hormone signaling pathways in plants. Here, we show that the Arabidopsis thaliana E3 ligase BRIZ, a heteromeric ligase that consists minimally of BRIZ1 and BRIZ2 proteins, functions in abscisic acid (ABA) signaling or response. briz1 and briz2 homozygous mutants either fail to germinate or emerge later than wild-type seedlings, with little cotyledon expansion or root elongation and no visible greening. Viability staining indicates that briz1 and briz2 embryos are alive but growth-arrested. Germination of briz mutants is improved by addition of the carotenoid biosynthetic inhibitor fluridone or gibberellic acid (GA3), and briz mutants have improved development in backgrounds deficient in ABA synthesis (gin1-3/aba2) or signaling (abi5-7). Endogenous ABA is not higher in briz2 seeds compared to wild-type seeds, and exogenous ABA does not affect BRIZ mRNAs in imbibed seeds. These results indicate that briz embryos are hypersensitive to ABA and that under normal growth conditions, BRIZ acts to suppress ABA signaling or response. ABA signaling and sugar signaling are linked, and we found that briz1 and briz2 mutants excised from seed coats are hypersensitive to sucrose. Although briz single mutants do not grow to maturity, we were able to generate mature briz2-3 abi5-7 double mutant plants that produced seeds. These seeds are more sensitive to exogenous sugar and are larger than seeds from sibling abi5-7 BRIZ2/briz2-3 plants, suggesting that BRIZ has a parental effect on seed development. From these data, we propose a model in which the BRIZ E3 ligase suppresses ABA responses during seed maturation and germination and early seedling establishment.