The control of leaf water loss by coconut plants cultured in vitro dependson the type of membrane used for ventilation

The physiological responses to vessel ventilation of coconut plants culture d in vitro varied with the type of membrane used for ventilation. Plants cu ltured in vessels ventilated with one of three types of membranes, polyprop ylene (PP), polyvinyl chloride (PVC) or Whatman filter paper (W) were compa red with plants cultured in conventional sealed (S) vessels. Vessel gas exc hange, water loss and medium osmolality were greater in vessels ventilated with W compared with vessels ventilated with PP, PVC or S. Plants cultured in W vessels exhibited lower rates of leaf water loss, narrower stomatal ap ertures and higher leaf abscisic acid (ABA) concentrations than plants cult ured in PP, PVC or S vessels. Plants in PP and PVC vessels showed an interm ediate behaviour in all these parameters while plants cultured in S vessels exhibited comparatively high rates of leaf water loss, wide stomatal apert ures and low leaf ABA concentrations. The results from the plants cultured in W vessels suggest that dehydration of the vessel medium increased medium osmolality, inducing greater leaf ABA accumulation, which resulted in impr oved stomatal control and reduced leaf water loss in coconut plants culture d in vitro in the vessels. The use of PP and PVC membranes resulted only in intermediate control of leaf water loss and stomatal functionality compare d with S vessels. This occurred despite PP and PVC vessels having similar r ates of medium water loss and medium osmolalities compared with S vessels. Because PP and PVC had higher rates of ethylene diffusion, it would appear as if the slight improvement of leaf physiology between plants in PP and PV C vessels and S vessels may be related to differences in ethylene or other gas diffusion rather than differences in medium water loss. In any case, th e capacity of plants cultured in vitro to control leaf water loss was relat ed to their leaf ABA concentration. The results of the present work confirm that the use of ventilated systems in the in vitro preacclimatization phas e before transplanting results in plants with improved control of water los s that may prove beneficial for survival and performance in the field but c are must be taken when selecting the type of ventilation membrane.