Seed priming is a pre-sowing treatment which leads to a physiological state that enables seed to germinate more efficiently. The majority of seed treatments are based on seed imbibition allowing the seeds to go through the first reversible stage of germination but do not allow radical protrusion through the seed coat. Seeds keeping their desiccation tolerance are then dehydrated and can be stored until final sowing. During subsequent germination, primed seeds exhibit a faster and more synchronized germination and young seedlings are often more vigorous and resistant to abiotic stresses than seedlings obtained from unprimed seeds. Priming often involves soaking seed in predetermined amounts of water or limitation of the imbibition time. The imbibition rate could be somehow controlled by osmotic agents such as PEG and referred as osmopriming. Halopriming implies the use of specific salts while "hormopriming" relies on the use of plant growth regulators. Some physical treatments UV, cold or heat,.. also provide germination improvement thus suggesting that priming effects are not necessarily related to seed imbibition. " better understanding of the metabolic events taking place during the priming treatment and the subsequent germination should help to use this simple and cheap technology in a more efficient way.

Hydrogen peroxide was initially recognized as a toxic molecule that causes damage at different levels of cell organization and thus losses in cell viability. From the 1990s, the role of hydrogen peroxide as a signaling molecule in plants has also been discussed. The beneficial role of H2O2 as a central hub integrating signaling network in response to biotic and abiotic stress and during developmental processes is now well established. Seed germination is the most pivotal phase of the plant life cycle, affecting plant growth and productivity. The function of hydrogen peroxide in seed germination and seed aging has been illustrated in numerous studies; however, the exact role of this molecule remains unknown. This review evaluates evidence that shows that H2O2 functions as a signaling molecule in seed physiology in accordance with the known biology and biochemistry of H2O2. The importance of crosstalk between hydrogen peroxide and a number of signaling molecules, including plant phytohormones such as abscisic acid, gibberellins, and ethylene, and reactive molecules such as nitric oxide and hydrogen sulfide acting on cell communication and signaling during seed germination, is highlighted. The current study also focuses on the detrimental effects of H2O2 on seed biology, i.e., seed aging that leads to a loss of germination efficiency. The dual nature of hydrogen peroxide as a toxic molecule on one hand and as a signal molecule on the other is made possible through the precise spatial and temporal control of its production and degradation. Levels of hydrogen peroxide in germinating seeds and young seedlings can be modulated via pre-sowing seed priming/conditioning. This rather simple method is shown to be a valuable tool for improving seed quality and for enhancing seed stress tolerance during post-priming germination. In this review, we outline how seed priming/conditioning affects the integrative role of hydrogen peroxide in seed germination and aging.

Rape seeds primed with -1.2 MPa polyethylene glycol 6000 showed improved germination performance. To better understand the beneficial effect of osmopriming on seed germination, a global expression profiling method was used to compare, for the first time, transcriptomic and proteomic data for osmoprimed seeds at the crucial phases of priming procedure (soaking, drying), whole priming process and subsequent germination. Brassica napus was used here as a model to dissect the process of osmopriming into its essential components. A total number of 952 genes and 75 proteins were affected during the main phases of priming and post-priming germination. Transcription was not coordinately associated with translation resulting in a limited correspondence between mRNAs level and protein abundance. Soaking, drying and final germination of primed seeds triggered distinct specific pathways since only a minority of genes and proteins were involved in all phases of osmopriming while a vast majority was involved in only one single phase. A particular attention was paid to genes and proteins involved in the transcription, translation, reserve mobilization, water uptake, cell cycle and oxidative stress processes.

Osmopriming is a pre-sowing treatment that enhances germination performance and stress tolerance of germinating seeds. Brassica napus seeds showed osmopriming-improved germination and seedling growth under salinity stress. To understand the molecular and biochemical mechanisms of osmopriming-induced salinity tolerance, the accumulation of proline, gene expression and activity of enzymes involved in proline metabolism and the level of endogenous hydrogen peroxide were investigated in rape seeds during osmopriming and post-priming germination under control (H2O) and stress conditions (100 mM NaCl). The relationship between gene expression and enzymatic activity of pyrroline-5-carboxylate synthetase (P5CS), ornithine-δ-aminotransferase (OAT) and proline dehydrogenase (PDH) was determined. The improved germination performance of osmoprimed seeds was accompanied by a significant increase in proline content. The accumulation of proline during priming and post-priming germination was associated with strong up-regulation of the P5CSA gene, down-regulation of the PDH gene and accumulation of hydrogen peroxide. The up-regulated transcript level of P5CSA was consistent with the increase in P5CS activity. This study shows, for the first time, the role of priming-induced modulation of activities of particular genes and enzymes of proline turnover, and its relationship with higher content of hydrogen peroxide, in improving seed germination under salinity stress. Following initial stress-exposure, the primed seeds acquired stronger salinity stress tolerance during post-priming germination, a feature likely linked to a 'priming memory'.

Abiotic stresses are the major environmental factors that play a significant role in decreasing plant yield and production potential by influencing physiological, biochemical, and molecular processes. Abiotic stresses and global population growth have prompted scientists to use beneficial strategies to ensure food security. The use of organic compounds to improve tolerance to abiotic stresses has been considered for many years. For example, the application of potential external osmotic protective compounds such as proline is one of the approaches to counteract the adverse effects of abiotic stresses on plants. Proline level increases in plants in response to environmental stress. Proline accumulation is not just a signal of tension. Rather, according to research discussed in this article, this biomolecule improves plant resistance to abiotic stress by rising photosynthesis, enzymatic and non-enzymatic antioxidant activity, regulating osmolyte concentration, and sodium and potassium homeostasis. In this review, we discuss the biosynthesis, sensing, signaling, and transport of proline and its role in the development of various plant tissues, including seeds, floral components, and vegetative tissues. Further, the impacts of exogenous proline utilization under various non-living stresses such as drought, salinity, high and low temperatures, and heavy metals have been extensively studied. Numerous various studies have shown that exogenous proline can improve plant growth, yield, and stress tolerance under adverse environmental factors.