角毛藻光合作用对连续强光照射的动态响应

Dynamic Responses of Photosynthesis in Chaetoceros sp. to Continuous High Irradiation

利用调制荧光技术研究了角毛藻(Chaetocerossp.)光合作用对连续强光照射的动态响应。用1000μmolm-2s-1的强光处理12h内,角毛藻的快速光曲线和荧光参数呈动态变化。处理30min内,最大光合速率P(m即最大相对电子传递速率)和光系统Ⅱ的最大量子产量Fv/Fm均逐渐下降至最低值,表明角毛藻受到了光抑制;初始斜率α的降低和非光化学淬灭NPQ的升高,表明角毛藻可以通过降低捕光色素对光能的吸收和增加热耗散来保护光合器官免受过度损伤。此后,α开始增加,但始终不能恢复到初始值,说明角毛藻逐渐适应了强光照状态,捕光能力逐渐增加;Pm逐渐恢复并超过初始值,最终(8h后)达初始值的2倍,表明经过光系统Ⅱ的电子传递明显加快;而Fv/Fm只能恢复到初始值的一半左右,说明强光下光系统Ⅱ的光能转换效率明显降低;NPQ达最大值(1h)后逐渐下降至低于初始值,表明热耗散在光保护中不再起主要作用。随处理时间的延长,出现光化光关闭后的短期荧光上升现象,且上升速度逐渐加快,说明围绕光系统Ⅰ的环式电子传递速度逐渐加快,可能在光保护中发挥重要作用。

The dynamic responses of photosynthesis of Chaetoceros sp. to continuous high irradiance （1 000 μmol m^-2·s^-1） for 12 h were demonstrated by measuring chlorophyll fluorescence. Both maximal photosynthetic rate （Pm, i.e. maximal relative electron transport rate） and maximal quantum yield ofphotosystem Ⅱ （Fv/Fm） decreased during 30 min of high light exposure, which showed obvious photoinhibition. Meanwhile, the initial slope α decreased while non-photochemical quenching （NPQ） increased, which means Chaetoceros sp. can reduce light absorption and dissipate more heat in order to protect their photosynthetic apparatus from damage. Chaetoceros sp. acclimated high light gradually and their photosynthetic activity recovered slowly during 1 000 μmol m^-2·s^-1 exposure from 30 min to 8 h. α increased （although cannot reach the value before high light exposure）, Pm recovered to initial value at 4 h and even reached 2 times of the initial value at 8 h. Fv/Fm could only recover to half of the initial value during the acclimation. NPQ reached the maximum at 1 h, and then decreased. This result indicates that heat dissipation does not play major role in photoprotection after 1 h high light exposure. After exposure to high irradiance, there appeared transient post-illumination increase in chlorophyll fluorescence. The increase in chlorophyll fluorescence enhanced with increased duration of high irradiance, which reflects enhancement of cyclic electron transport around photosystem Ⅰ. Thus, after NPQ decreased, cyclic electron transport around photosystem Ⅰ may play important role in photoprotection.