Leaf anatomy of in vitro tobacco and cauliflower plantlets as affected by different types of ventilation

Tobacco and cauliflower plantlets were grown in vitro under forced ventilation (fast flow; 10 cm(3) min(-1) and slow flow, 5 cm(3) min(-1)), diffusive ventilation and in airtight vessels. Culture vessel headspace atmosphere (CO2 and ethylene concentrations, relative humidity), leaf-stomatal structure, density and function, internal leaf anatomy, epicuticular waxes of leaves have been studied and compared with those grown in vivo (growth room conditions). No ethylene accumulation was noticed in the headspace of the culture vessel under forced ventilation (slow or fast); however, ethylene accumulation was noticed in airtight vessels. During the photoperiod, CO2 depletion occurred in the headspace of the airtight vessels, the CO2 concentration increased with increasing the efficiency of ventilation. Relative humidity was nearly 100% in the airtight vessel at the end of the experiment; the value was 92% in the fast forced ventilation. The stomatal density in both the species was significantly higher in plantlets subjected to the airtight vessel and diffusive treatments, and densities decreased with increasing efficiency of ventilation. In general stomatal sizes appeared to be inversely related to efficiencies of ventilation; comparatively large in the leaves grown in airtight and diffusive treatments. Relatively larger areas were occupied by stomata in both the airtight condition and diffusive ventilation in both the species and was significantly lower in in vivo grown plantlets and in forced ventilation treatment. Permanently widely-open stomata which do not respond normally by closing in the dark or under conditions of low relative humidity, and which are in abnormally exposed positions on the leaf were noticed in the airtight and the diffusive ventilation; stomata were functional in the forced ventilation and in vivo treatments. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.