GAS-EXCHANGE AND IN-VIVO CHLOROPHYLL FLUORESCENCE IN POTATO AND TOBACCO PLANTLETS IN-VITRO AS AFFECTED BY VARIOUS CONCENTRATIONS OF 6-BENZYLAMINOPURINE

Application of 6-benzylaminopurine (BAP) into cultivation medium of po tato and tobacco plantlets caused changes in their growth, morphology and photosynthetic parameters in dependence on the plant species and t he concentration used. The stimulating effect of BAP added to the cult ivation medium was found only at very low BAP concentrations (up to 0. 01 g m(-3) in tobacco and 0.1 g m(-3) in potato plantlets). BAP induce d only a very slight tendency to increasing chlorophyll (Chl) a+b cont ent and the ratios Chl a/b, Chl/carotenoids and net photosynthetic rat e/dark respiration rate (P-N/R(D)) in both plant species. Also the inc rease of the photochemical efficiency of photosystem 2 as indicated by the ratio of variable to maximal fluorescence (F-v/F-m) and P-N was n ot statistically significant and was found only in potato plantlets. T he stomatal transpiration rate (E(s)) in tobacco plantlets increased w ith increasing BAP concentrations up to 0.1 g m(-3). However, this was a rather negative effect as it increased a danger of plantlet wilting . In both plant species the BAP concentration of 1.0 g m(-3) inhibited growth of plantlet roots; their shoots had altered morphology, their P-N, light respiration rate (R(L)), E(S), P-N/R(D) ratio, Chi contents and parameters of in vivo fluorescence (F-v/F-m, qp, Rfd) decreased a nd CO2 compensation concentration increased. This negative effect of B AP was more pronounced in tobacco than in potato plantlets. The above mentioned changes in photosynthetic parameters in plantlets treated wi th BAP corresponded to the changes in photosynthetic parameters in tra nsgenic plants of the same species with T-DNA carrying gene 4 and resu lting from increased level of endogenous cytokinins. However, the appl ication of BAP lead to a decrease in endogenous cytokinins level and t hus the effects described are probably due to the action of BAP itself .