PHYSIOLOGY OF DESICCATION-SENSITIVE (RECALCITRANT) SEEDS AND THE IMPLICATIONS FOR CRYOPRESERVATION

Desiccation-tolerant (orthodox) seeds can survive in the dry state for considerable periods and so can be stored successfully at low water content and subzero temperatures. Orthodox seeds possess a variety of protective processes and mechanisms that confer desiccation tolerance, important among them being metabolic shutdown and intracellular dedifferentiation. In contrast, desiccation-sensitive (recalcitrant) seeds cannot tolerate water loss and so cannot be stored using conventional seed bank conditions. Particularly with respect to storage, recalcitrant seeds do not undergo intracellular dedifferentiation nor any significant metabolic shutdown. Embryos of recalcitrant seeds remain metabolically active, with little or no reduction in extent of the extensive intracellular membranes. At the water content at which they are shed, with the ongoing metabolism in recalcitrant seeds, developmental phenomena grade imperceptibly into those associated with germination. Thus, recalcitrant seeds can be stored intact ...