Studies on stomatal function, epicuticular wax and stem-root transition region of polyethylene glycol-treated and nontreated in vitro grape plantlets

Scanning electron microscopy, light microscopy, and gravimetric analysis was used to evaluate stomatal function; epicuticular wax, and the stem-root transition region of grape (Vitis sp. 'Valiant') plantlets grown in vitro, polyethylene glycol-treated in. vitro, and greenhouse-grown plants. Scanning electron microscopic studies of leaf surfaces of in vitro-grown plants showed widely open stomata as compared to leaf stomata of polyethylene glycol-treated in. vitro-cultured and greenhouse-grown plants. Ultrastructurally, leaf epicuticular wax of in vitro plants was less dense than in their polyethylene-treated and greenhouse counterparts. Quantitatively, in vitro-grown plants had reduced epicuticular wax as compared to polyethylene glycol-treated and greenhouse-grown plants. Light microscopic studies showed no obvious differences in the vascular connections in the stem-root transition region of in vitro-cultured, polyethylene glycol-treated in vitro-cultured, and greenhouse-grown plants. It is therefore likely that the rapid wilting and desiccation observed after transplanting in vitro grape plantlets is due to their defective stomatal function and reduced epicuticular wax and map not be due to poor water transport associated with vascular connection.