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 subse‐ quent 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. A 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.

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Seed Priming: New Comprehensive Approaches for an Old Empirical Technique

Increased endogenous chitosan (CTS) could be associated with improved drought resistance in white clover (Trifolium repens). Plants were pretreated with or without 1 mg/mL CTS and then were subjected to optimal or water-limited condition in controlled growth chambers for 6 days. Phenotypic and physiological results indicated that exogenous CTS significantly improved drought resistance of white clover. Metabolome results showed that exogenous CTS induced a significant increase in endogenous CTS content during dehydration accompanied by the maintenance of greater accumulation of sugars, sugar alcohols, amino acids, organic acids, and other metabolites (ascorbate, glutathione, flavonoids, putrescine, and spermidine). These compounds are associated with osmotic adjustment, antioxidant defense, stress signaling, and energy metabolism under stress condition. Similarly, transcriptome revealed that many genes in relation to amino acid and carbohydrate metabolism, energy production and conversion, and ascorbate–gl...

Metabolic Pathways Regulated by Chitosan Contributing to Drought Resistance in White Clover

Molecular processes induced in primed seeds-increasing the potential to stabilize crop yields under drought conditions.

Plants under natural conditions often face multiple environmental constraints in terms of submergence, temperature extremes, salinity, and drought stress. Plant growth and productivity is negatively influenced by these abiotic stresses. Presently, a variety of approaches are being used to overcome abiotic stresses in plants. Recently, seed soaking with various priming agents has emerged as a promising strategy to induce tolerance in plants against abiotic stresses. In seed priming, seeds are treated with synthetic or natural compounds prior to germination so as to initiate specific physiological state in plants. Seed priming could also be defined as physiological state which enables plants to more quickly respond to abiotic stresses. Plants raised from seeds treated with various priming agents tend to show greater abiotic stress tolerance over unprimed seeds. Induction of abiotic stress tolerance through priming is an intricate process that involves various metabolic events. Primed seeds show early and uniform germination and seedling emergence. Seed priming enables plants to survive adverse environmental conditions and gives appropriate yield. In this book chapter, we have discussed a wide range of chemical which are extensively being used for seed priming.

Recent Advances in Abiotic Stress Tolerance of Plants Through Chemical Priming: An Overview

Abiotic stress is one of the major factors limiting plant growth and yield globally. Though substantial progress has been made in breeding and genetic manipulation of plants to enhance abiotic stress tolerance, the task remains as a challenge even today. Investigations on the priming activity of various chemicals in plants for enhancing abiotic stress tolerance have been undertaken over the past few years. Priming with γ-amino butyric acid (GABA) and β-amino butyric acid (BABA) gains greater attention, because priming with these non-protein amino acids equips the plants to resist abiotic stresses effectively without suffering costly energy investments in operating defence mechanisms. It is well documented that the protective effect of non-protein amino acids like BABA and GABA on plants is due to a potentiation of natural defence mechanisms against abiotic stresses but at the same time not activating the complete defence arsenal before the stress exposure. The exact mode of action of priming with GABA/BABA in plants is still a puzzle, though their importance as signaling molecules during stress is undoubtful. The better understanding of molecular, physiological, and ecological aspects of GABA/BABA priming might lead to the emergence of this technique as a successful strategy for enhancing the abiotic stress(es) tolerance potential of plants in the field, without compromising much on productivity.

GABA/BABA priming: a means for enhancing abiotic stress tolerance potential of plants with less energy investments on defence cache

Seed priming is a method to improve germination and seedling establishment under stress conditions. The effect of seed priming in chemical solutions such as urea and KNO3, on protein and proline content, germination, and seedling growth responses of four maize (Zea mays L.) hybrids under drought and salt stress conditions was studied in a controlled environment in 2010. Treatments included stress type and intensity at five levels: moderate drought (MD), severe drought (SD), moderate salt (MS), severe salt (SS), and control (C1, without stress), three seed priming types including water (C2, as control), KNO3, and urea (as chemical priming), and four maize hybrids including Maxima, SC704, Zola, and 307. The results showed that the highest germination percentage (Ger %), germination rate (GR), seedling length (SL), radical length (RL), and seedling to radical length ratio (S/R) were achieved in no stress treatments and most proline content in SD treatment. Urea priming led to more Ger%, GR, and SL compared to other primers and treatment under KNO3 priming resulted in higher RL compared to other primers. Chemical priming had no effect on S/R and proline content. Also, in terms of most traits, no difference was found among the four hybrids. Results showed that salt stress could affect GR and RL more than the drought stress. Drought stress affected germination percentage and S/R more than the salt stress. Both stresses decreased all measured parameters, except protein and proline content which were increased remarkably, and more under drought compared to salt stress. Based on proline content, hybrid 304 appeared to be more resistant to stress than other hybrids. Generally, KNO3 and urea alleviated effects of both stresses and led to increased germination and seedling growth as well as the root length. Therefore, priming could be recommended for enhancing maize growth responses under stressful conditions.

Hadi Pirasteh Anosheh

Papers

Chemical priming with urea and KNO3 enhances maize hybrids (Zea mays L.) seed viability under abiotic stress