Bio-priming of seeds: Plant stress management and its underlying cellular, biochemical and molecular mechanisms

Exposure of crops to stress is the most significant barrier to agricultural output and food security worldwide. Stress induces changes in plants' physiological functions, which leads to lower plant growth and agricultural yield. Plants undergo a variety of molecular, cellular, and physiological changes to combat various abiotic stresses. Plants suffer from increased osmotic pressure outside the root due to osmotic stresses like drought or salt stress that ultimately result in reduced water availability to plant roots. In addition to morphological modifications, physiological changes such as lower leaf osmotic potential, accumulation of osmoprotectants, increased antioxidant activities, and so on occur in response to such abiotic stresses. Seed priming is a novel yet simple technique that involves the use of beneficial and eco-friendly biological agents to improve the physiological functioning of seeds. This technique also plays a vital role in restoring agro-ecological balances through the improvement of soil fertility or by decreasing soil and water contamination. An understanding of the mechanisms involved in seed bio-priming with plant growth-promoting microbes is very crucial to efficiently utilise this technique towards agricultural sustainability. It is generally thought that the advancement of metabolic processes along with activation of repairing systems during the pre-germination stage are the central reasons behind growth promotion and acquired stress tolerance. The application of plant growth-promoting rhizobacteria in agriculture has been emerging to improve stress resilience. Bio-priming of seeds ensures early protein and DNA synthesis, and also helps in effective mitochondrial development. This review aims to summarise the current state of understanding of the mechanisms involved in this eco-friendly technique.