Source-sink regulation of cotyledonary reserve mobilization during cashew (Anacardium occidentale) seedling establishment under NaCl salinity

Wild soybean salt tolerance metabolic model: Assessment of storage protein mobilization in cotyledons and C/N balance in the hypocotyl/root axis

Salt stress has become one of the main factors limiting crop yield in recent years. The post-germinative growth is most sensitive to salt stress in soybean. In this study, cultivated and wild soybeans were used for an integrated metabonomics and transcriptomics analysis to determine whether wild soybean can resist salt stress by maintaining the mobilization of stored substances in cotyledons and the balance of carbon and nitrogen in the hypocotyl/root axis (HRA). Compared with wild soybean, the growth of cultivated soybean was significantly inhibited during the post-germinative growth period under salt stress. Integrating analysis found that the breakdown products of proteins, such as glutamate, glutamic acid, aspartic acid, and asparagine, increased significantly in wild soybean cotyledons. Asparagine synthase and fumarate hydratase genes and genes encoding HSP20 family proteins were specifically upregulated. In wild soybean HRA, levels of glutamic acid, aspartic acid, asparagine, citric acid, and succinic acid increased significantly, and the glutamate decarboxylase gene and the gene encoding carbonic anhydrase in nitrogen metabolism were significantly upregulated. The metabolic model indicated that wild soybean enhanced the decomposition of stored proteins and the transport of amino acids to the HRA in cotyledons and the GABA shunt to maintain carbon and nitrogen balance in the HRA to resist salt stress. This study provided a theoretical basis for cultivating salt-tolerant soybean varieties and opened opportunities for the development of sustainable agricultural practices.

Efficacy of biological agents and fillers seed coating in improving drought stress in anise

Many plants, including anise, have tiny, non-uniform seeds with low and light nutrient reserves. The seeds also show a weak establishment, especially under stressful conditions where their accurate planting in the soil and optimal yield are tough. This study sought to improve anise seeds' physical and physiological characteristics under drought stress. To this end, two factorial experiments under laboratory and greenhouse conditions were performed in a completely randomized design with 4 and 3 replications, respectively. Five levels of seed inoculation (inoculation with T36 and T43 of Trichoderma harzianum, and CHA0 and B52 of Pseudomonas fluorescent, and non-inoculation which means that control seeds were not treated with microbial inoculant), three levels of coating (K10P20, K10P10V5, and non-coating), and three levels of drought stress (0, -3, and -6 bars) were considered as the factorial experiment [vermiculite (V), kaolin (K), and perlite (P) numbers refer to the amount of material used in grams]. The laboratory experiment revealed that the combined treatments of bio-agents with coating increased the physical and germination characteristics of anise seeds compared to the control treatment. The greenhouse experiment showed that drought stress reduced the initial growth indices. Still, the combination treatments of biological agents and coating (fillers) could alleviate the destructive effects of drought stress to some extent and improve these indices. The best treatment was provided by T36 and K10P20 in both experiments, which significantly increased morphological indices.

Gas exchange and growth of soursop under salt stress and H2O2 application methods

Abstract The production of soursop seedlings in the Northeast region of Brazil has faced limitations due to the high concentrations of salts in the water, so it is necessary to use techniques that enable its cultivation, and the application of hydrogen peroxide to minimize the deleterious effects of salt stress stands out. In this context, the objective was to evaluate forms of application of hydrogen peroxide as an attenuator of salt stress on the gas exchange and growth of soursop seedlings cv. Morada Nova. The experiment was conducted under greenhouse conditions, in an Regolithic Neosol of sandy loam texture, from the municipality of Lagoa Seca - PB. A completely randomized design was used in a 5 × 4 factorial arrangement, whose treatments resulted from the combination of five levels of electrical conductivity of irrigation water - ECw (0.6 – control, 1.2, 1.8, 2.4 and 3.0 dS m-1) and four forms of hydrogen peroxide application (M1 - without H2O2 application, M2 - application by seed soaking, M3 - application by foliar spraying, and M4 - application by seed soaking + foliar spraying), with four replicates and two plants per experimental unit, totaling 160 plants. The concentration of H2O2 used in the different forms of application was 20 µM. Irrigation water salinity from 0.6 dS m-1 reduced the gas exchange and growth of soursop. The method of H2O2 application by foliar spraying minimized the effects of salt stress on gas exchange. The method of H2O2 application by seed soaking reduced the effect of salt stress on the growth of soursop at 85 days after sowing.

Plants make smart decisions in complex environments

This review proposes that plants make smart decision and encourages scientists to formulate and test hypotheses about plant's decisions as an option to investigate complex phenomena that are hardly explained through the predominant mechanistic approach. Three physiological processes (seed germination and seedling emergence, abortion of reproductive structures, and regulation of photosynthesis) are discussed to illustrate the plant's ability to make decisions from three different perspectives. It is proposed that plant scientists could access a rich pool of information by formulating and testing hypothesis on plant's decisions, even when it is not possible elucidating the full mechanism underpinning the decision. Decisions with a strategic component are discussed for seed germination and seedling emergence, in which the plant depends on limited information for making early decisions that will influence its survival and potential growth. Decisions consistent with an analysis of benefit/cost are illustrated with observations from abortion of reproductive structures. Decisions that search the optimization of complex processes are exemplified with the regulation of photosynthesis. For each type of decision, some draft experiments are suggested as exercise on how this framework could be applied. It is proposed that scientists could make experiments with plant's decisions adapting methods that were developed for other disciplines.

Asymmetry of Plant Cell Divisions under Salt Stress

Salt stress causes several damaging effects in plant cells. These commonly observed effects are the results of oxidative, osmotic, and toxic stresses. To ensure normal growth and development of tissues, the cellular compartments of multicellular plants have a unique system that provides the specified parameters of growth and differentiation. The cell shape and the direction of division support the steady development of the organism, the habit, and the typical shape of the organs and the whole plant. When dividing, daughter cells evenly or unevenly distribute the components of cytoplasm. Factors such as impaired osmotic regulation, exposure to toxic compounds, and imbalance in the antioxidant system cause disorders associated with the moving of organelles, distribution transformations of the endoplasmic reticulum, and the vacuolar compartment. In some cases, one can observe a different degree of plasmolysis manifestation, local changes in the density of cytoplasm. Together, these processes can cause disturbances in the direction of cell division, the formation of a phragmoplast, the formation of nuclei of daughter cells, and a violation of their fine structural organization. These processes are often accompanied by significant damage to the cytoskeleton, the formation of nonspecific structures formed by proteins of the cytoskeleton. The consequences of these processes can lead to the death of some cells or to a significant change in their morphology and properties, deformation of newly formed tissues and organs, and changes in the plant phenotype. Thus, as a result of significant violations of the cytoskeleton, causing critical destabilization of the symmetric distribution of the cell content, disturbances in the distribution of chromosomes, especially in polyploid cells, may occur, resulting in the appearance of micronuclei. Hence, the asymmetry of a certain component of the plant cell is a marker of susceptibility to abiotic damage.

Salt stress differentially regulates mobilisation of carbon and nitrogen reserves during seedling establishment of Pityrocarpa moniliformis

Seedling establishment is a critical step in environment colonisation by higher plants that frequently occurs under adverse conditions. Thus, we carried out an integrated analysis of seedling growth, water status, ion accumulation, reserve mobilisation, metabolite partitioning and hydrolase activity during seedling establishment of the native Caatinga species Piptadenia moniliformis (Benth.) Luckow & R.W. Jobson under salinity. Two-day-old seedlings were cultivated in vitro for 4 days in water agar (control) or supplemented with 50 or 100 mm NaCl. Biochemical determinations were performed according to standard spectrophotometric protocols. We found that 100 mm NaCl stimulated starch degradation, amylase activity and soluble sugar accumulation, but limited storage protein hydrolysis in the cotyledons of P. moniliformis seedlings. Although Na⁺ accumulation in the seedling affected K⁺ partitioning between different organs, it was not possible to associate the salt-induced changes in reserve mobilisation with Na⁺ toxicity, or water status, in the cotyledons. Remarkably, we found that starch content increased in the roots of P. moniliformis seedlings under 100 mm NaCl, probably in response to the toxic effects of Na⁺ . The mobilisation of carbon and nitrogen reserves is independently regulated in P. moniliformis seedlings under salt stress. The salt-induced delay in seedling establishment and the resulting changes in the source-sink relationship may lead to storage protein retention in the cotyledons. Possibly, the intensification of starch mobilisation in the cotyledons supported starch accumulation in the root as a potential mechanism to mitigate Na⁺ toxicity.

Holm oak proteomic response to water limitation at seedling establishment stage reveals specific changes in different plant parts as well as interaction between roots and cotyledons

Quercus ilex is a dominant tree species in the Mediterranean region with double economic and ecological importance and increasing use in reforestation. Seedling establishment is extremely vulnerable to environmental stresses, particularly drought. A time course study on physiological and proteomic response of holm oak to water limitation stress and recovery during early heterotrophic growth is reported. Applied stress led to diminution in plant water content and root growth, oxidative stress in roots and some alterations in the anti-oxidative protection. Plant parts differed substantially in soluble sugar and free phenolic content, and in their changes during stress and recovery. Proteomic response in holm oak roots and cotyledons was estimated using combined 1-DE/2-DE approach and protein identification by MALDI TOF-TOF PMF and MS/MS. A total of 127 differentially abundant protein species (DAPs) were identified. DAPs related to starch metabolism, lipid to sugar conversion, reserve proteins and their mobilization were typical for cotyledons. DAPs in roots were involved in sugar utilization, secondary metabolism and defense, including pathogenesis related proteins from PR-5 and PR-10 families. Results emphasize specific proteome signatures of separate plant parts as well as importance of sink-source interaction between root and cotyledon in the time course of stress and in recovery.

Ultrastructural and biochemical changes induced by salt stress in Jatropha curcas seeds during germination and seedling development

Jatropha curcas L. is a multipurpose species of the Euphorbiaceae family that is widespread in arid and semiarid regions. This study investigated the ultrastructural and biochemical changes induced by salt stress during J. curcas seed germination and seedling development. Salt stress negatively affected seed germination and increased Na+ and Cl- contents in endosperms and embryo-axis. Lipids represented the most abundant reserves (64% of the quiescent seed dry mass), and their levels were strongly decreased at 8 days after imbibition (DAI) under salinity stress. Proteins were the second most important reserve (21.3%), and their levels were also reduced under salt stress conditions. Starch showed a transient increase at 5 DAI under control conditions, which was correlated with intense lipid mobilisation during this period. Non-reducing sugars and free amino acids were increased in control seeds compared with quiescent seeds, whereas under the salt-stress conditions, minimal changes were observed. In addition, cytochemical and ultrastructural analyses confirmed greater alterations in the cellular reserves of seeds that had been germinated under NaCl stress conditions. Salt stress promoted delays in protein and lipid mobilisation and induced ultrastructural changes in salt-stressed endosperm cells, consistent with delayed protein and oil body degradation.

Salt-induced delay in cotyledonary globulin mobilization is abolished by induction of proteases and leaf growth sink strength at late seedling establishment in cashew

Seedling establishment in saline conditions is crucial for plant survival and productivity. This study was performed to elucidate the biochemical and physiological mechanisms involved with the recovery and establishment of cashew seedlings subjected to salinity. The changes in the Na+ levels and K/Na ratios, associated with relative water content, indicated that osmotic effects were more important than salt toxicity in the inhibition of seedling growth and cotyledonary protein mobilization. Salinity (50mM NaCl) induced a strong delay in protein breakdown and amino acid accumulation in cotyledons, and this effect was closely related to azocaseinolytic and protease activities. In parallel, proline and free amino acids accumulated in the leaves whereas the protein content decreased. Assays with specific inhibitors indicated that the most important proteases in cotyledons were of serine, cysteine and aspartic types. Proteomic analysis revealed that most of the cashew reserve proteins are 11S globulin-type and that these proteins were similarly degraded under salinity. In the late establishment phase, the salt-treated seedlings displayed an unexpected recovery in terms of leaf growth and N mobilization from cotyledon to leaves. This recovery coordinately involved a great leaf expansion, decreased amino acid content and increased protein synthesis in leaves. This response occurred in parallel with a prominent induction in the cotyledon proteolytic activity. Altogether, these data suggest that a source-sink mechanism involving leaf growth and protein synthesis may have acted as an important sink for reserve mobilization contributing to the seedling establishment under salinity. The amino acids that accumulated in the leaves may have exerted negative feedback to act as a signal for the induction of protease activity in the cotyledon. Overall, these mechanisms employed by cashew seedlings may be part of an adaptive process for the efficient rescue of cotyledonary proteins, as the cashew species originates from an environment with N-poor soil and high salinity.

Transcriptional regulations of the genes of starch metabolism and physiological changes in response to salt stress rice (Oryza sativa L.) seedlings

The aim of this investigation was to compare the transcriptional expression of starch metabolism, involving genes and physiological characters, in seedlings of two contrasting salt-tolerant rice genotypes, in response to salt-stress. The soluble sugar content in rice seedlings of both salt-tolerant and salt-sensitive genotypes was enriched, relating to starch degradation, in plants subjected to 200 mM NaCl. In the salt-tolerant cultivar Pokkali, a major source of carbon may be that derived from the photosynthetic system and starch degradation. In starch degradation, only Pho and PWD genes in Pokkali were upregulated in plants subjected to salt stress. In contrast, the photosynthetic abilities of IR29 salt-susceptible cultivar dropped significantly, relating to growth reduction. The major source of carbohydrate in salt-stressed seedlings of the IR29 cultivar may be gained from starch metabolism, regulated by ADP-glucose pyrophosphorylase (AGP), starch synthase (SS), starch branching enzyme (SBE), starch debranching enzyme (ISA), glucan-water dikinase (GWD), dispropotionating enzyme (DPE), phospho glucan-water dikinase (PWD) and starch phosphorylase (Pho). Also, the major route of soluble sugar in salt-stressed Pokkali seedlings was derived from photosynthesis and starch metabolism. This was identified as novel information in the present study.

Low-temperature effect on enzyme activities involved in sucrose-starch partitioning in salt-stressed and salt-acclimated cotyledons of quinoa (Chenopodium quinoa Willd.) seedlings

The effect of low temperature on growth, sucrose-starch partitioning and related enzymes in salt-stressed and salt-acclimated cotyledons of quinoa (Chenopodium quinoa Willd.) was studied. The growth of cotyledons and growing axes in seedlings grown at 25/20 degrees C (light/dark) and shifted to 5/5 degrees C was lower than in those only growing at 25/20 degrees C (unstressed). However, there were no significant differences between low-temperature control and salt-treated seedlings. The higher activities of sucrose phosphate synthase (SPS, EC 2.4.1.14) and soluble acid invertase (acid INV, EC 3.2.1.25) were observed in salt-stressed cotyledons; however, the highest acid INV activity was observed in unstressed cotyledons. ADP-glucose pyrophosphorylase (ADP-GPPase, EC 2.7.7.27) was higher in unstressed cotyledons than in stressed ones. However, between 0 and 4days the highest value was observed in salt-stressed cotyledons. The lowest value of ADP-GPPase was observed in salt-acclimated cotyledons. Low temperature also affected sucrose synthase (SuSy, EC 2.4.1.13) activity in salt-treated cotyledons. Sucrose and glucose were higher in salt-stressed cotyledons, but fructose was essentially higher in low-temperature control. Starch was higher in low-temperature control; however, the highest content was observed at 0day in salt-acclimated cotyledons. Results demonstrated that low temperature induces different responses on sucrose-starch partitioning in salt-stressed and salt-acclimated cotyledons. Data also suggest that in salt-treated cotyledons source-sink relations (SSR) are changed in order to supply soluble sugars and proline for the osmotic adjustment. Relationships between starch formation and SuSy activity are also discussed.