XVI International Botanical Congess

Leaves of the alpine plants Soldanella alpina (L.) And Ranunculus glacialis (L.) Were highly resistant to photoinactivation of PSII and catalase. The turnover of the D1 protein in light was slow. In S. alpina a high capacity of antioxidative protection correlated with a high paraquat tolerance. Treatments with dithiothreitol (DTT) indicated that non-photochemical quenching of excitation energy related to zeaxanthin formation was essential for photo-protection. In contrast, in R. glacialis capacities of antioxidative protection were low, sensitivity to paraquat high and DTT had only minor effects. In R. glacialis photoinhibition of PSII was enhanced, also at low temperature, when photorespiration was blocked by phosphinothricin, an inhibitor of glutamine-synthetase. We conclude that in leaves of S. alpina protection against light and cold stress appeared to depend mainly on antioxidative mechanisms and energy dissipation. In R. glacialis photoinhibitory damage was mainly prevented by efficient electron sinks related to photorespiration and carbon metabolism. Potential electron sinks in alpine plants are further investigated by13C-NMR spectroscopy.