THE LACK OF CONTROL OF WATER-LOSS IN MICROPROPAGATED PLANTS IS NOT RELATED TO POOR CUTICLE DEVELOPMENT

To assess if cuticular transpiration could contribute significantly to the high rates of water loss often observed in micropropagated plants after transfer to the nursery, it was tested whether adaxial cuticular water permeance (P) of leaves grown in vitro was higher than that of leaves grown ex vitro. For four species of micropropagated plants with hypostomatous leaves (Delphinium elatum hybrid, Doronicum hybrid, Hosta sieboldiana var. elegans, Rodgersia pinnata), P was determined with two independent techniques which gave similar results. Minimum adaxial overall conductance was measured with the same methods for a Heuchera hybrid which had amphistomatous leaves. Leaves of all species except Heuchera lost 36-65% of their original weight within 25 min after excision. Detached leaves whose abaxial surfaces had been coated lost only 25-38% of their original weight within 5-9 h. Permeances (P) were between 1 x 10(-5) m s(-1) and 1 x 10(-4) m s(-1), which was within the range of typical values found with leaves grown ex vitro. From these results and a critical assessment of the literature it is concluded that there is no evidence that P of micropropagated plants was high enough to contribute significantly to the desiccation problem at the transfer stage.