ناصر عسکری

The aerial parts of plants are covered by the cuticle, a skin containing among others waxes. The cuticle inhibits the outflow of compounds, in particular water, from the plant to the environment, and without a cuticle, plants dehydrate rapidly. In the cuticle, waxes are the chief actors in the blocking. In tissue culture, the humidity in the headspace is very high (close to 100 %) so evaporation is limited and the cuticle is less needed. The cuticle also inhibits the entry of compounds from the environment into plants. In tissue culture, the inflow of medium components occurs predominantly via wounds, primarily those made when explants are cut. The removal of the barrier is expected to enhance the uptake of medium components. This paper addresses the question as to whether the removal of the epidermal inflow barrier enhances growth in tissue culture of lily. Waxes were removed from scale explants by a short rinse (5 s) with chloroform. During this rinse, the stomata had to be closed since otherwise the tissue was severely damaged by the inflow of chloroform into the cavities below the stomata. The closure was achieved by an abscisic acid (ABA) pre-treatment. Removal of wax resulted in increased growth (50 %) relative to nonchloroform-treated explants. This procedure is, however, not suitable for practical application because the benefit was undone by an inhibitory effect of the ABA pre-treatment. The ABA pre-treatment also increased the percentage of contaminated cultures, probably because during surface-sterilization the disinfectant did not reach the contaminants inhabiting the cavities below the stomata when the stomata had been closed.