Adaptative changes of leaf surface of tropical orchid Cattleya gaskelliana (N.E.Br.) B.S. Williams after transferring from in vitro to ex vitro conditions

The leaf surface micromorphology of Cattleya gaskellianajuvenile plants, propagated in vitrofrom seeds, as well as of adult plants, cultivated in glasshouse, was analyzed by scanning electron microscopy (SEM). The leaves of both juvenile and adult plants are hypostomatic, their stomata are of tetracytic type. It was found that development of single stomata on the adaxial leaf surface of juvenile plants was induced byin vitro conditions. During the acclimation of in vitro propagated plants to glasshouse conditions the following changes of leaf surface micromorphology have been observed: 1) configuration of epidermal cells changed; 2) dimensions of typical epidermal cells reduced; 3) stomata density and their dimensions increased. The results suggest that structural changes, probably, can be regarded as an adaptation to avoid excessive rate leaf transpiration during a period of C. gaskelliana juvenile plants acclimation to glasshouse conditions. In the case when micromorphological leaf characteristics (stomata density per mm2, stomatal index, epidermal cells number per mm 2 ) of in vitro propagated plants of C. gaskelliana were comparable to those of adult plants, survival rate was more than 95%.