光叶眼子菜响应夏季高温的模拟研究

为探讨南四湖优势物种光叶眼子菜在夏季浅水区的衰亡原因, 用25℃、30℃、35℃和40℃的恒温水浴模拟夏季高温处理光叶眼子菜(Co. Potamogeton lucens L.)3h。生化结果显示, 在35℃及以上高温下, 光叶眼子菜的蛋白质含量、可溶性糖含量和叶绿素含量显著下降, 丙二醛含量显著上升, 说明35℃以上高温对光叶眼子菜产生了显著伤害。光叶眼子菜的光合系统对高温更为敏感, 在高温胁迫下标准化的叶绿素荧光动力学曲线上J相和K相显著隆起, 但并未发现明显的L-band。进一步解析叶片的叶绿素荧光动力学参数, 结果显示: 随着处理温度的升高, 反应中心的初始关闭速率(dVG/dt_o, dV/dt_o)变慢, 但到达P相的所需时间(T_fm)变短; 光系统Ⅱ (Photosystem Ⅱ, PSⅡ)的光化学效率(F_v/F_m)减小, 非光化学效率(K_n)、J相相对可变荧光强度(V_j)和热耗散(DI_o/RC、DI_o/CS_o、F_o/F_m)增大; 尽管高温下质体醌周转次数(N)、还原速率(S_m/T_fm)和I相相对可变荧光强度(V_i)变化不显著, 但质体醌库(S_m)明显减小; 单个反应中心光能的吸收(ABS/RC)和捕获效率(TR_o/RC)增加, 电子传递效率(ET_o/RC)却呈下降趋势; 单位激发态面积的光能捕获(TR_o/CS_o)和电子传递效率(ET_o/CS_o)均降低, 反应中心数目(RC/CS_o)显著减少。上述高温胁迫效应导致整个叶片的结构功能指数(SFI_abs)、性能指数(PI_abs)以及光合驱动力(DF)显著降低。高温对光叶眼子菜的伤害主要是导致其光系统II放氧复合体失活、反应中心数目减少和反应中心的光化学效率下降, 进而诱导活性氧的产生, 对细胞造成伤害。因此, 光叶眼子菜属于对高温敏感的水生植物。

A SIMULATION STUDY ON THE RESPONSES OF POTAMOGETON LUCENS TO HIGH TEMPERATURE IN SUMMER

To explore the cause of Potamogeton lucens’s decline, a dominant plant inhabiting the shallow water of Nansi Lake, the physiological and biochemical changes of P. lucens were examined under a group of constant temperatures at 25℃, 30℃, 35℃, and 40℃, respectively, for 3h. The results showed that the contents of protein, soluble sugar and chlorophyll decreased significantly, while the content of malondialdehyde (MDA) increased significantly at a high temperature above 35℃. The results indicated that high temperature above 35℃ had significant damage to P. lucens. The photosystem of P. lucens was more sensitive to heat stress. The characteristics of standardized chlorophyll fluorescence kinetics curves under heat stress were as follows. Peaks at J and K phases were observed, but no L-band was found on the normalized chlorophyll fluorescence kinetics curves. The chlorophyll fluorescence parameters were calculated from the OJIP curves of the heat-treated leaves. The results showed that the initial closing speed of the reaction center (dVG/dt_o, dV/dt_o) slowed down with the increase of temperature under heat stress, but it took a shorter time to reach the maximal fluorescence (T_fm). The maximum quantum yield of PSII (Photosystem II) photochemistry (F_v/F_m) decreased. However, the non-photochemical constants (K_n), relative variable fluorescence at the J-step (V_j), and dissipated energy flux (DI_o/RC, DI_o/CS_o, F_o/F_m) increased under heat stress. Although the turn-over number of Q_A (N), average redox state of Q_A (S_m/T_fm), and relative variable fluorescence at the I-step (V_i) barely changed, the plastoquinone pool (S_m) decreased significantly at high temperature. Absorption and trapped energy flux per RC (ABS/RC, TR_o/RC; reaction center, RC) increased, whereas the electron transport efficiency per RC (ET_o/RC) decreased when temperature increased. Heat stress also decreased the trapped energy flux, electron transport flux and density of RCs per CS (TR_o/CS_o, ET_o/CS_o, RC/CS_o; cross section, CS). These effects of heat stress on photosystem eventually led to a significant reduction in the structure and function index (SFI_abs), performance index (PI_abs), and drive force for photosynthesis (DF) of the P. lucens leaves. These results demonstrated that heat stress mainly caused inactivation of oxygen-evolving complex of PSII, reduction of the density of RCs, and decrease of photochemical efficiency of RC in P. lucens plants, and these led to the production of reactive oxygen species, and thus caused remarkable damage to cells. Therefore, P. lucens is a sensitive aquatic plant to high temperature in summer.