Ammopiptanthus mongolicus (Maxim.) Cheng f. is one of the evergreen shrubs in the desert region of China. In midday its leaves bear photon flux density over 1500 μmol·m-2·s-1 at natural habitat. They show the obvious phenomenon of photoinhibition. For the study of the effects of drought stress on the major protective mechanism against strong light in A. mongolicus leaves, the diurnal variations of photosynthetic rate and chlorophyll fluorescence parameters were investigated under natural conditions with portable photosynthetic measurement system (CIRAS 1) and portable fluorometer (MFMS 2). The experimental results showed that, under normal and drought stress conditions，the net photosynthetic rate (Pn), the primary maximum photochemical efficiency of PSⅡ (Fv/Fm) and the quantum efficiency of noncyclic electron transport of PSⅡ (ΦPSⅡ) decreased obviously at noon (Figs.2,3A,4B). In comparison with plants under normal condition, under drought stress minimal chlorophyll fluorescence (Fo) decreased at first and then increased (Fig.3A), non photochemical quenching （NPQ） quickly increased and sustained at a higher level (Fig.4B). This indicated that the major photoprotective mechanism of A. mongolicus leaves was the xanthophyll cycle dependent thermal energy dissipation under normal condition, while under drought stress, the major photoprotective mechanism was both the xanthophyll cycle dependent thermal energy dissipation and the reversible inactivation of PSⅡ reaction center.
干旱胁迫对沙冬青叶片防御光破坏机制的影响
赵长明 王根轩*
（兰州大学干旱农业生态国家重点实验室，兰州730000）
摘要： 沙冬青(Ammopiptanthus mongolicus (Maxim.) Cheng f.)是生长在沙漠及干旱荒漠地区的常绿灌木.在夏季,其叶片经常遭受中午强光(超过1 500 μmol.m-2.s-1) 胁迫,出现明显的光抑制现象.我们利用便携式光合测定系统(CIRAS-1)和脉冲调制荧光仪(MFMS-2)测定了自然形成的干旱胁迫条件下沙冬青光合和荧光参数的日变化,主要探讨了干旱胁迫对沙冬青叶片防御强光破坏机制的影响.结果表明,正常水分和干旱胁迫下,沙冬青叶片的净光合速率(Pn)、 PSⅡ最大光化学效率(Fv/Fm)和PSⅡ非环式电子传递效率(ΦPS )在中午都明显降低;相对正常水分条件而言,干旱胁迫下初始荧光(Fo)先下降后上升,荧光的非光化学淬灭(NPQ)上升较快并在一定水平上维持不变.由此推断晴天中午沙冬青叶片在正常水分条件下主要采取依赖叶黄素循环的热耗散机制;而在干旱胁迫条件下主要采取了依赖叶黄素循环的热耗散和PSⅡ反应中心可逆失活两种保护机制.
关键词： 沙冬青；光抑制；防御光破坏机制；叶绿素荧光参数；PSII反应中心
通讯作者。E-mail:<wamggx @ lzu.edu.cn>.
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