生长在温带沙漠地区的植物在夏季时常遭受正午短时间的高温胁迫, 频繁和骤然的热胁迫在很大程度上限制了荒漠植物的光合作用。以塔克拉玛干沙漠南缘防风固沙的优势植物疏叶骆驼刺(Alhagi sparsifolia)为材料, 分别用叶绿素荧光诱导动力学和CO₂响应方法分析热胁迫后光系统II (PSII)和RuBP羧化酶的热稳定性。结果表明: (1)在叶片温度超过43 ℃后PSII最大光化学量子产量、有活性反应中心数目、活力指数均出现明显的降低; 中高温度下PSII的电子供体侧比电子受体侧组分更容易受到热胁迫的伤害; 在58 ℃出现明显的K点(300 μs), 说明放氧复合体放氧结构受到破坏而失去活性。(2)随着叶片温度的上升, Rubisco活性先升高后降低, 在34 ℃时具有最高的活性水平。(3)叶片受到高温胁迫时, 细胞内氨态氮和活性氧分子等大量积累。(4)疏叶骆驼刺叶片处于短时间的高温环境时, 光合作用的光反应和暗反应阶段均表现出功能的不稳定性, 其中PSII和Rubisco是主要的热敏感位点。

Aims Our general objective was to determine the effects of short time heat stress on photosystem II (PSII) activity and Rubisco activity in Alhagi sparsifolia. Specifically, we wanted to determine that temperature range within which the plant can photosynthesize, the critical temperature that damaged leaves and characters of reactive oxidative accumulation under high temperature.
Methods Samples of A. sparsifolia were collected on a sunny morning with low winds in early August 2010. We selected healthy growing shoots randomly, washed them lightly to remove leaf dust, cut and quickly inserted them into damp soil and covered them with a plastic cover. Samples were immediately put into black plastic bags, which contained damp filter papers. The bags were placed into a heat-resistant case for transport to the laboratory and then immersed in water baths for 15 min at temperatures of 30, 38, 43, 48, 53, 58 and 63 ℃. Twenty intact and mature leaves were used to measure leaf fluorescence and CO₂ response curves at each temperature.
Important findings At leaf temperatures up to 43 ℃, the maximum photochemical efficiency of PSII, number of active reaction centers and leaf vitality index all decreased markedly. At moderately high temperatures, the electron donors of PSII were more heat-vulnerable than the electron acceptors of PSII, and the appearance of fluorescence K point (300 μs) in the fluorescence curve at 58 ℃ indicated that the structure of oxygen-evolving complexes was damaged, resulting in loss of oxygen-evolving function. At higher leaf temperatures, the activity of Rubisco first increased and then decreased, with a maximum at 34 ℃. Under high temperature stress, considerable oxidative radicals, e.g., ammoniacal nitrogen, H₂O₂ and O₂^-· were produced and continually accumulated in cells. We conclude that heat stress has strong impacts on both light reaction and dark reaction phases of photosynthesis, especially their two heat sensitive components comprised of PSII and Rubisco.