Influence of drought, high temperature, and carbamide cytokinin 4-PU-30 onphotosynthetic activity of plants. 2. Chloroplast ultrastructure of primary bean leaves

Ultrastructural changes in chloroplasts of primary leaves of 15-d-old bean plants (Phaseolus vulgaris L, cv. Cheren Starozagorski) in response to a si ngle stress (increasing water deficit, WD) as well as to combined stress (W D piers high temperature, WD+HT) were investigated under the possible prote ctive or reparatory effects of the carbamide cytokinin 4-PU-30 [N-(2-chloro -4-pyridyl)-N-phenylurea] applied before or after the stress. Essential str uctural changes in chloroplast ultrastructure occurred mainly in plants tha t had experienced WD+HT: the thylakoids were swollen, the envelope was dest royed, and the spatial orientation of inner membrane system was not typical . Changed starch accumulation was also observed. 4-PU-30 protected chloropl ast ultrastructure under WD+HT.