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

Abstract

SummaryThe physiological responses to vessel ventilation of coconut plants cultured in vitro varied with the type of membrane used for ventilation. Plants cultured in vessels ventilated with one of three types of membranes, polypropylene (PP), polyvinyl chloride (PVC) or Whatman filter paper (W) were compared with plants cultured in conventional sealed (S) vessels. Vessel gas exchange, 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 apertures and higher leaf abscisic acid (ABA) concentrations than plants cultured in PP, PVC or S vessels. Plants in PP and PVC vessels showed an intermediate behaviour in all these parameters while plants cultured in S vessels exhibited comparatively high rates of leaf water loss, wide stomatal apertures 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 improved stomatal control and reduced leaf water loss in coconut plants cultured in vitro in the vessels. The use of PP and PVC membranes resulted only in intermediate control of leaf water loss and stomatal functionality compared with S vessels. This occurred despite PP and PVC vessels having similar rates 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 PVC 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, the capacity of plants cultured in vitro to control leaf water loss was related to their leaf ABA concentration. The results of the present work confirm that the use of ventilated systems in the in vitro preacclimatization phase before transplanting results in plants with improved control of water loss that may prove beneficial for survival and performance in the field but care must be taken when selecting the type of ventilation membrane.