CYTOLOGICAL COMPARISON OF LEAVES AND STEMS OF PRUNUS-AVIUM L. SHOOTS CULTURED ON A SOLID MEDIUM WITH AGAR OR GELRITE

An axillary proliferating clone of Prunus avium L. was subcultured eve ry four weeks on solid MS medium with agar as the gelling agent, Vitri fication (hyperhydricity) of shoots was induced in one four week cycle with the same medium except that agar was replaced by gel-rite, Durin g culture on the vitrifying medium, the water content of the shoots pr ogressively increased with a parallel decrease in chlorophyll content, Cytological differences between the leaves and stems of the vitrified and normal shoots were detected by light and electron (both transmiss ion and scanning) microscopy, Leaves of vitrified shoots were characte rized by lower number of chloroplasts in the palisade parenchyma and b y a defective cuticle, The stems of vitrified shoots had a less develo ped and lignified xylem tissue, lacked sclerenchymatic areas and showe d hypertrophy of the cortical parenchyma, More intense vacuolar activi ty with evaginations of the chloroplast envelope into the vacuole was noted in cells of vitrified leaves.