A Humidity-induced Convective Throughflow Ventilation System Benefits Annona squamosa L. Explants and Coconut Calloid

A simple apparatus is described for generating pressurized throughflowventilation in plant tissue culture vessels. No pumps or gas-cylindersare required and the flow is driven by humidity-induced diffusionacross microporous membranes. In the experiments described,pressurized flows of sterile humidified air were supplied atrates of up to 1 ml min^-1and these had beneficial effects onleaf survival and production inAnnona cuttings and on calloidform in coconut. Ethylene (ethene) was removed more quicklyfrom the pressure-flow ventilated culture vessels (t ₅₀, 0.4–0.7h) than from those aerated by diffusion through conventionalpolypropylene membranes (t ₅₀, 1.6–2.4 h). InAnnona cuttings leaf production was greatly increased andethylene-induced leaf fall considerably delayed when culturedwith the forced as opposed to diffusion-based ventilation ofthe vessels. With throughflow ventilation, coconut calloid was more convolutedthan under wholly diffusive aeration and had a smooth distinctepidermal surface and clearly defined sub-epidermal meristematicnodules. It resembled freshly initiated calloid from which regenerationof plantlets via somatic embryogenesis can be obtained. Underwholly diffusive aeration, calloid developed a rough, relativelyundifferentiated surface, more haustorial (i.e. cotyledonary)in appearance, and characteristic of cultures where regenerationpotential has been lost. It is suggested that other benefits of the pressurized throughflowventilation may be the removal of volatiles such as ethanoland acetaldehyde, the removal of excess carbon dioxide at nightand its improved supply during the day, and sustained oxygenconcentrations at levels close to atmospheric both night andday. Abscission; callus; ethylene; explants; tissue-culture; growth; ventilation