Photosynthesis, non‐photochemical pathways and activities of antioxidant enzymes in a resilient evergreen oak under different climatic conditions from a valley‐savanna in Southwest China

Physiologia Plantarum - Tập 135 Số 1 - Trang 62-72 - 2009
Junjie Zhu1, Jiao‐Lin Zhang, Hongcheng Liu, Kun‐Fang Cao
1Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Yunnan, China

Tóm tắt

Plants in the savanna‐valleys in Southwest China are annually exposed to different combinations of multiple stresses from the hot‐rainy, to chill‐dry, and to warm‐dry seasons. This study monitored seasonal changes in photosynthesis and photoprotection in an evergreen oak (Cyclobalanopsis helferiana) from one of these valleys for four years during which usual and abnormal drought occurred. In general, during the study period with decreasing xylem water potential (Ψx), photosynthetic gas exchange, quantum yield of photosystem II (PSII) photochemistry and activities of most of the measured antioxidant enzymes decreased, while activities of the xanthophyll cycle and associated non‐photochemical energy dissipation and glutathione peroxidase (GP) (EC 1.11.1.9) increased. In a fairly severe chill period, high concentration of reactive oxygen species induced high activities of most of the antioxidant enzymes and relatively stronger decrease in gas exchange. In the most severe dry period, even when predawn Ψx decreased down to −4 MPa, considerable Pn (maximum photosynthetic rate) (4 μmol m–2 s–1) was still maintained in midmorning. At this time, most of the antioxidant enzyme activities decreased to the lowest values, whereas the xanthophyll cycle and associated non‐photochemical energy dissipation and GP activities increased to their highest levels. High predawn antheraxanthin and zeaxanthin contents were observed in the severe and very severe drought periods. Superoxide dismutase maintained high and fairly constant activity (1500–1800 U mg−1 protein) and predawn maximum photochemistry efficiency of PSII was always above 0.8 throughout the whole study period. These results indicated that the photosynthetic apparatus of the oak leaves was highly capable of maintaining its function under the multiple stresses in different seasons in the present valley‐savanna.

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Physiologia Plantarum

Tập 135 Số 1

62-72

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