PARENT SESSION
Posters P3B Photosynthetic acclimation: Ecophysiology, diverse environments. Abstracts (479-522)

Plant responses to water stress as affected by abscisic acid and benzyladenine. Jana Pospíšilová^*,1, Daniel Haisel¹, Renáta Pechová¹, Helena Synková¹, Petra Batková², ¹ Institute of Experimental Botany, Prague, Czech Republic² Faculty of Science, Prague, Czech Republic

ABSTRACT- With the aim to contribute to elucidation of the role of phytohormones in response of plants to adverse environmental conditions, the seedlings of Phaseolus vulgaris, Beta vulgaris, and Zea mays were immediately before imposition of water stress irrigated with water (control), 10^-4 M abscisic acid (ABA), or 10^-5 M N⁶-benzyladenine (BA). In all three species, application of ABA decreased stomatal conductance (g_s), transpiration rate (E), and net photosynthetic rate (P_N) already 1 h after application. However, g_s, E, and P_N in plants pre-treated with ABA remained during water stress higher than in plants pre-treated with water even if the relative water content did not differ. Positive effects of ABA application were observed also 2 days after rehydration. In contrast, the effects of pre-treatment with BA on gas exchange parameters were species-specific. While in bean plants BA application ameliorated the negative effect of water stress on g_s, E, and P_N, only very slight effects were observed in maize, and in sugar beet BA even aggravated the effects of water stress. In all three species, pre-treatment with ABA or BA protected photosynthetic pigments: contents of chlorophylls and carotenoids during water stress and after rehydration were markedly decreased only in plants irrigated with water. Contents of pigments of xanthophyll cycle increased during water stress more in plants pre-treated with ABA or BA than in those irrigated with water, but the degree of their deepoxidation was highest in the later. Similarly, the efficiency of photosystem 2, determined as variable to maximal chlorophyll fluorescence ratio, was not markedly decreased in plants pre-treated with ABA or BA in contrast to those irrigated with water. Thus the application of BA and especially of ABA can ameliorate the negative effects of subsequent water stress. The financial support of the GA CR (grant No. 522/02/1099) is acknowledged.

KEY WORDS: photosynthesis, xanthophylls, chlorophyll, stomata