A HUMIDITY-INDUCED CONVECTIVE THROUGHFLOW VENTILATION SYSTEM BENEFITSANNONA-SQUAMOSA L EXPLANTS AND COCONUT CALLOID

A simple apparatus is described for generating pressurized throughflow ventilation in plant tissue culture vessels. No pumps or gas-cylinder s are required and the flow is driven by humidity-induced diffusion ac ross microporous membranes. In the experiments described, pressurized flows of sterile humidified air were supplied at rates of up to 1 mi m in(-1) and these had beneficial effects on leaf survival and productio n in Annona cuttings and on calloid form in coconut. Ethylene (ethene) was removed more quickly from the pressure-flow ventilated culture ve ssels (t(50), 0.4-0.7 h) than from those aerated by diffusion through conventional polypropylene membranes (t(50), 1.6-2.4 h). In Annona cut tings leaf production was greatly increased and ethylene-induced leaf fall considerably delayed when cultured with the forced as opposed to diffusion-based Ventilation of the vessels. With throughflow ventilati on, coconut calloid was more convoluted than under wholly diffusive ae ration and had a smooth distinct epidermal surface and clearly defined sub-epidermal meristematic nodules. It resembled freshly initiated ca lloid from which regeneration of plantlets via somatic embryogenesis c an be obtained. Under wholly diffusive aeration, calloid developed a r ough, relatively undifferentiated surface, more haustorial (i.e. cotyl edonary) in appearance, and characteristic of cultures where regenerat ion potential has been lost. It is suggested that other benefits of th e pressurized throughflow ventilation may be the removal of volatiles such as ethanol and acetaldehyde, the removal of excess carbon dioxide at night and its improved supply during the day, and sustained oxygen concentrations at levels close to atmospheric both night and day. (C) 1997 Annals of Botany Company