Subcuticular secretion by cactus seeds improves germination by means of rapid uptake and distribution of water

We report a formerly unknown mechanism in seeds which improves germination under relatively dry conditions. During seed development of several South American cacti, epidermal cells produce proteinaceous material that appears to pass through ectodesmata in the outer cell wall and which accumulates under the cuticle. Once moistened, this secretory layer readily absorbs water and distributes it over the seed surface. It thus improves water uptake and ensures germination with the minimum amount of available water, which may be advantageous in (semi-)arid regions. In experiments with seeds of Echinopsis thionantha (Speg.) Werd. and Gymnocalycium gibbosum (Haw.) Pfeiff. under water stress, intact seeds took up significantly more water and germinated better than seeds from which the hydrophilous layer had been artificially removed. (C) 1997 Annals of Botany Company.