Effect of benzylaminopurine on rehydration of bean plants after water stress

The possibility of improving the recovery of plant photosynthesis after water stress by cytokinin-induced stimulation of stomatal opening or delay of leaf senescence was tested. The 6-benzylaminopurine (BAP) in concentrations 1 and 10 muM was applied to the substrate (sand + nutrient solution) or sprayed on primary leaves of 14-d-old Phaseolus vulgaris L. plants sufficiently supplied with water or water-stressed for 4 d. The later ones having relative water content decreased to 69 % were fully rehydrated during the following three days. Parameters of photosynthesis and water relations were measured in primary leaves of 7-, 10-, 14-, and 17-d-old plants. Application of 1 CIM BAP slightly delayed leaf senescence: in 17-d-old control plants, net photosynthetic rate (PN) and chlorophyll (Chl) content, and when sprayed on leaves also some of Chi a fluorescence kinetic parameters of BAP-treated leaves were slightly higher than those of untreated leaves. Both types of application of 1 muM BAP slightly improved recovery of plants during rehydration after water stress in terms of increased gad, gab and PN, i.e., parameters which were markedly decreased by mild water stress. However, contents of Chi a, Chi b and carotenoids and parameters of Chi a fluorescence kinetic were not markedly affected by mild water stress and after rehydration were not stimulated by 1 muM BAP. 10 muM BAP had mostly negative effects on the parameters measured.