Modified Leaf Anatomy of Cauliflower Plantlets Regenerated from Meristem Culture

Abstract

Investigations concerned with the regeneration of Brassica oleracea var botrytis (cauliflower) from meristem culture have shown that, whilst in culture, plantlets differ from conventionally-produced seedlings in a number of morphological and physiological features (Grout and Aston, 1 911a , b ; Grout and Crisp, 1 977). Plantlets removed from shaken liquid cultures have little epicuticular wax and poor vascular connection between root and shoot, making them particularly vulnerable to severe wilting. Plantlets regenerated on solid medium have increased levels of epicuticular wax, although still significantly less than seedlings of comparable age or size, and are better able to restrict water loss. The rate of photosynthesis in both types of regenerated plantlets is so low as to make no positive contribution to the net carbon balance at the time of transplanting. Plantlets make the transition to normal whole plant morphology and physiology during growth after transplanting, surviving the transfer to the glasshouse if the appropriate hardening procedures are used (Grout and Crisp, 1977). Plantlet leaves are produced in culture under conditions of relatively high humidity, especially with liquid medium, and with nutrient conditions that are designed to sustain heterotrophic, not autotrophic, growth. This investigation was begun to see if leaves were modified internally as a consequence of development in such a culture environment. Comparisons were made between leaves produced in culture, leaves produced by the regenerated plantlets after transplanting, and those of glasshouse-grown seedlings. Meristem cultures were established as previously described (Crisp and Walkey, 1974; Grout and Crisp, 1977), using Brassica oleracea var botrytis cv. Armado Tardo. These cultures were examined 7 weeks after isolation. Regenerated plantlets were taken from culture and hardened (Grout and Crisp, 1977) before becoming established under standard horticultural glasshouse conditions. These plants were examined 3 weeks after transplanting from culture. Seedlings were grown under normal horticultural conditions in the glasshouse and also in culture vessels in the culture room. Seeds in these latter conditions were germinated and grown in conical flasks, in small aluminium thimbles containing peat compost, with 30 ml of water to simulate the physical effects of the culture medium (Grout and Aston, 1977a). Seeds were also grown in these small thimbles embedded in