Desiccation Tolerance in Orthodox and Recalcitrant Seeds

Abstract

Desiccation tolerance is defined as the ability of some organisms to cope with water loss of less than 0.1 g of water per gram of dry weight and rehydration without damage. In plants, desiccation means the loss of free water of the protoplast, which is found among low plants (many lichens, ferns, and mosses), seeds, pollen grains, and regenerative plants. The desiccation in seeds is different from the vegetative tissue, and in orthodox seeds, it is part of their developmental stages that this mechanism allows them to enter a state of dry stagnation and, subsequently, their storage and survival in different environmental conditions. In fact, the desiccation is considered as a bridge between seed maturation and germination, which is usually induced at the end of seed maturation before drying and disappears during germination. In general, the orthodox seed’s ability to tolerate desiccation occurs during the stockpiling phase and also depends on the rate of drying (the type of drying method) that affects seed survival after drying. The onset of desiccation tolerance as well as the achievement of maximum desiccation tolerance, depending on the plant species, the rate of seed moisture loss, and the stage of maturity at which the seed is harvested can be affected by harvest time and drying method. Desiccation tolerance with the help of various cellular and biochemical processes such as LEA proteins, accumulation of high amounts of non-reducing soluble sugars such as sucrose and RFO (raffinose, galactinol, stachyose, vermiculose, and PEGhal AU: Please check and confirm the spelling and usage of the term ‘PEGhal’.) reduce damage caused by desiccation and thus improve seed quality. It therefore seems likely that desiccation tolerance is not attributed to a single mechanism, but is a multifactorial trait, each of which is equally important and decisive. However, the participation of all these processes in inducing desiccation tolerance is necessary to achieve maximum desiccation tolerance, so this chapter will try to evaluate and explore the majority of mechanisms involved in desiccation tolerance.