The competence to acquire cellular desiccation tolerance is independent of seed morphological development.

Acquisition of desiccation tolerance and the related changes at the cellular level in wheat (Triticum aestivum cv. Priokskaya) kernels during normal development and premature drying on the ear were studied using a spin probe technique and low temperature scanning electron microscopy. During normal development, the ability of embryos to germinate after rapid drying and rehydration was acquired after completion of morphological development, which is a few days before mass maturity. The acquisition of desiccation tolerance, as assessed by germination, was associated with an upsurge in cytoplasmic viscosity, the onset of accumulation of protein and oil bodies, and the retention of membrane integrity upon dehydration/rehydration. These features were also used to assess cellular desiccation tolerance in the cases when germination could not occur. Slow premature drying was used to decouple the acquisition of cellular desiccation tolerance from morphogenesis. Upon premature drying of kernels on the ears of plants cut at 5 d after anthesis, desiccation-tolerant dwarf embryos were formed that were able to germinate. When plants were cut at earlier stages poorly developed embryos were formed that were unable to germinate, but cellular desiccation tolerance was nevertheless acquired. In such prematurely dried kernels, peripheral meristematic endosperm cells had already passed through similar physiological and ultrastructural changes associated with the acquisition of cellular desiccation tolerance. It is concluded that despite the apparent strong integration in seed development, desiccation tolerance can be acquired by the meristematic cells in the developing embryo and cambial layer of endosperm, independently of morphological development.