Combinative effects of Azospirillum brasilense inoculation and chemical priming on germination behavior and seedling growth in aged grass seeds

Alcaligenes faecalis Juj3 alleviates Plasmodiophora brassicae stress to cabbage via promoting growth and inducing resistance

Clubroot is a devastating disease threatening global cruciferous vegetable production caused by Plasmodiophora brassicae (Pb). We have evaluated the positive effects of the Alcaligenes faecalis Juj3 on cabbage growth promotion and Pb stress alleviation through pot and field experiments. The Juj3 strain was isolated from a healthy cabbage rhizosphere with growth-promoting characteristics and was identified as A. faecalis based on morphological traits and phylogeny. Seed germination assays revealed that Juj3 inoculation enhances cabbage bud shoot and root growth. In pot experiments, inoculation with Juj3 fermentation powder at cabbage sowing dates significantly improved the seedling biomass. Combining seed treatments with root irrigation after transplanting considerably reduced the clubroot disease index and resulted in appreciable biocontrol efficacy (83.7%). Gene expression analyses of cabbage after Juj3 inoculation showed that PR2 and EIN3 expression were significantly up-regulated. Physiologically, Juj3 inoculation enhanced cabbage chlorophyll content and root activity in a normal environment. Irrespective of whether plants were under normal environment or Pb stresses, Juj3 improved photosynthesis. Field trial analyses revealed that Juj3 exhibits satisfactory biocontrol efficacy in cabbage (51.4%) and Chinese cabbage (37.7%). Moreover, Juj3 could also enhance cabbage and Chinese cabbage biomass to improve the yield quality. These findings pave the way for future use of A. faecalis as biocontrol agents for clubroot and reveal the great potential of the rhizobacterium for plant growth-promoting applications in agriculture and horticulture.

Seed 'primeomics': plants memorize their germination under stress

Seed priming is a pre-germination treatment administered through various chemical, physical and biological agents, which induce mild stress during the early phases of germination. Priming facilitates synchronized seed germination, better seedling establishment, improved plant growth and enhanced yield, especially in stressful environments. In parallel, the phenomenon of 'stress memory' in which exposure to a sub-lethal stress leads to better responses to future or recurring lethal stresses has gained widespread attention in recent years. The versatility and realistic yield gains associated with seed priming and its connection with stress memory make a critical examination useful for the design of robust approaches for maximizing future yield gains. Herein, a literature review identified selenium, salicylic acid, poly-ethylene glycol, CaCl₂ and thiourea as the seed priming agents (SPRs) for which the most studies have been carried out. The average priming duration for SPRs generally ranged from 2 to 48 h, i.e. during phase I/II of germination. The major signalling events for regulating early seed germination, including the DOG1 (delay of germination 1)-abscisic acid (ABA)-heme regulatory module, ABA-gibberellic acid antagonism and nucleus-organelle communication are detailed. We propose that both seed priming and stress memory invoke a 'bet-hedging' strategy in plants, wherein their growth under optimal conditions is compromised in exchange for better growth under stressful conditions. The molecular basis of stress memory is explained at the level of chromatin reorganization, alternative transcript splicing, metabolite accumulation and autophagy. This provides a useful framework to study similar mechanisms operating during seed priming. In addition, we highlight the potential for merging findings on seed priming with those of stress memory, with the dual benefit of advancing fundamental research and boosting crop productivity. Finally, a roadmap for future work, entailing identification of SPR-responsive varieties and the development of dual/multiple-benefit SPRs, is proposed for enhancing SPR-mediated agricultural productivity worldwide.

Comparative Time-Course Physiological Responses and Proteomic Analysis of Melatonin Priming on Promoting Germination in Aged Oat (Avena sativa L.) Seeds

Melatonin priming is an effective strategy to improve the germination of aged oat (Avena sativa L.) seeds, but the mechanism involved in its time-course responses has remained largely unknown. In the present study, the phenotypic differences, ultrastructural changes, physiological characteristics, and proteomic profiles were examined in aged and melatonin-primed seed (with 10 μM melatonin treatment for 12, 24, and 36 h). Thus, 36 h priming (T36) had a better remediation effect on aged seeds, reflecting in the improved germinability and seedlings, relatively intact cell ultrastructures, and enhanced antioxidant capacity. Proteomic analysis revealed 201 differentially abundant proteins between aged and T36 seeds, of which 96 were up-accumulated. In melatonin-primed seeds, the restoration of membrane integrity by improved antioxidant capacity, which was affected by the stimulation of jasmonic acid synthesis via up-accumulation of 12-oxo-phytodienoic acid reductase, might be a candidate mechanism. Moreover, the relatively intact ultrastructures enabled amino acid metabolism and phenylpropanoid biosynthesis, which were closely associated with energy generation through intermediates of pyruvate, phosphoenolpyruvate, fumarate, and α-ketoglutarate, thus providing energy, active amino acids, and secondary metabolites necessary for germination improvement of aged seeds. These findings clarify the time-course related pathways associated with melatonin priming on promoting the germination of aged oat seeds.

Comparative Physiological and Proteomic Analysis Reveals Different Involvement of Proteins during Artificial Aging of Siberian Wildrye Seeds

Seed aging has an important effect on the germplasm preservation and industrialized production of Siberian wildrye (Elymus sibiricus) in the Qinghai-Tibet Plateau. However, so far its underlying molecular mechanisms still largely remain unknown. To shed light on this topic, one-year stored seeds of E. sibiricus were exposed to artificial aging treatments (AAT), followed by seed vigor characteristics and physiological status monitoring. Then global proteomics analysis was undertaken by the tandem mass tags (TMT) technique, and the proteins were quantified with liquid chromatography-tandem mass spectrometry on three aging time points (0 h, 36 h and 72 h). Finally, we verified the expression of related proteins by parallel reaction monitoring (PRM). Our results demonstrated that the seed vigor decreased remarkably in response to artificial aging, but the relative ion-leakage and malondialdehyde content, superoxide anion and hydrogen peroxide showed the opposite situation. Proteomic results showed that a total of 4169 proteins were identified and quantified. Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that a series of key pathways including carbohydrate metabolism, lipid metabolism, and antioxidant activity were severely damaged by aging treatments. Numerous key proteins such as glyceraldehyde triphosphate glyceraldehyde dehydrogenase, succinate dehydrogenase, lipoxygenase, peroxidase, glutathione-s-transferase and late embryogenesis abundant proteins were significantly down-regulated. However, the up-regulation of the heat shock protein family has made a positive contribution to oxidative stress resistance in seeds. This study provides a useful catalog of the E. sibiricus proteomes with insights into the future genetic improvement of seed storability.