[Effects of high- and low temperature stress on the leaf PSII functions and physiological characteristics of tree peony (Paeonia suffruticosa cv. 'Roufurong')].

Taking the detached leaves of tree peony (Paeonia suffruticosa cv. 'Roufurong') as test materials, this paper studied the effects of high temperature (40 degrees C) and low temperature (15 degrees C) stresses on the PS II functions and physiological characteristics of peony leaves under strong light intensity (1400 micromol x m(-2) x s(-1)), with 25 degrees C as the control. With the increasing time of high- and low temperature stress, the maximal photochemical efficiency (Fv/Fm), actual quantum yield of photosystem II (Phi(PS II)) , and efficiency of excitation capture of open PS II center (Fv'/Fm') all decreased continuously. After recovered in the dark for 4 hours, the Fv/Fm in treatments 15 degrees C and 25 degrees C quickly recovered, but that in treatment 40 degrees C only recovered to 75.5% of non-treatment, even if the leaves were treated in the dark for 15 hours. At 40 degrees C, the balance of excited energy between PS I and PS II under strong light intensity was perturbed seriously. Treatment 40 degrees C inhibited the superoxide dismutase (SOD) activity, enhanced the production of O2-, H2O2, and MDA, and reduced the contents of chlorophyll and soluble protein. This study revealed that strong light combined with high temperature impaired the photosynthetic apparatus of the tree peony irreversibly, whereas strong light plus low temperature had weaker impact.