茄子(Solanum melongena L．)叶上表皮紫色花色素苷对光合机构的保护效应

Protective action on photosynthetic apparatus by purple anthocyanin in the epidermal cells of eggplant (Solanum melongena L.) leaves

以茄子同一叶片上紫斑区域和绿斑区域为材料，采用发光二极管LED发出的混合光谱（白光）和单色光谱（红、蓝、绿光）照射后，通过光合仪（CIRAS-2）和叶绿素荧光仪（PEA和Dual—PAM-100）测定了茄子叶上表皮紫色花色素苷（purpleanthocyanin，PA）对光合机构的影响。结果表明，分布于茄子叶片上表皮的PA，主要截获约53．2％-73．6％的500～600am（黄绿光）可见光。紫斑区域的叶绿素a含量较低以及PA截获27％的400～480nm（蓝光）和10％的630～700nm（红光），可能是其最大净光合速率Pnmax降低的原因。随着白光照射强度（0～3000μmol·m^-2s^-1）的增大，茄子叶片的PSⅡ最大光化学效率Fv／Fm、单位面积的光合机构含有的反应中心数目RC／CS0和天线色素能量吸收驱动力DFABS下降，而初始荧光F0、J相的相对可变荧光K和单位反应中心耗散的能量DIo／RC增加，但紫斑区域的上述参数变幅明显较小，表现为光抑制程度减轻。用2000μmol·m^-2·s^-1的不同光质照射30min后，茄子叶片Fv／Fm降低，但只有绿光和白光下紫斑区域的Fv／Fm显著的高于绿斑区域；同时白光照射后，茄子叶片的P700氧化还原动力学曲线降幅明显的大于PSⅡ动力学曲线，但紫斑区域的这两个光系统动力学曲线的下降幅度明显减小。这反映出茄子叶上表皮PA有效的保护了PsⅡ和PSⅠ反应中心，减轻了电子传递链的还原程度和热耗散机构的运转压力，较好地维持了PSⅡ与PSⅠ之间的功能协调性。这种通过PA截获500～600nm（黄绿光）可见光对光合机构的保护效应属于生物物理水平的防御系统。

The paper focuses on the question if purple anthocyanin （PA） shields the photosynthetic apparatus of eggplant （Solanum melongena L. ） leaves against excess light. Light response curves of photosynthetic activity of green-speckled parts （GSP） or purple-speckled parts （PSP） of the same leaf were measured with a CIRAS-2 instrument. Chlorophyll fluorescence transients were measured by two chlorophyll fluorometers （PEA and Dual-PAM-100） after illuminating with mixed spectrum （white light） or homo-chrome （red, blue or green） light produced by light-emitting diodes （LEDs） on GSP or PSP. The PA, which is localized in the epidermal cells of the leaves, mainly screens out green and yellow light （between 500 and 600 nm） removing 53.2% to 73.6% of the light in this range. The maximum net photosynthetic rate （Pomax） of the PSP was smaller than that of the GSP, which may be caused not only by the smaller chlorophyll-a-content but also by the screening of 27% of the blue light between 400 and 480 nm and 10% of red light between 630 and 700 nm by PA. Increasing the intensity of the white light from 0 to 3000 μmol photons· m^-2· s^-1 photosynthetically active radiation （PAR） , the maximum quantum yield of primary photochemistry of photosystem （PS） Ⅱ （Fv/Fm）, the density of reaction centers （RCs） per excited cross section （RC/CSo ） and the driving force on absorption basis of antenna chlorophyll in PSⅡ （ DFABs） declined gradually, whereas the minimum fluorescence （ Fo ）, the relative variable fluorescence at the J-step （ VJ ） and the dissipated energy flux per RC （DI0/RC） increased gradually in GSP and PSP. However, the change in the size of the parameters mentioned above was smaller in PSP than in GSP, implying that the susceptibility to photoinhibition was lower in PSP. After the GSP or PSP of eggplant were irradiated for 30 min with white, red, blue or green light of 2000 μmol photons μm^-2· s^-1, the Fv/Fm declined , but the Fv/Fm of PSP was significantly higher than that of GSP only in the case of an irradiation with white or green light. In addition, the decrease in the amplitude of the P700 （photosystem Ⅰ） redox transients was bigger than that of PSII chlorophyll a fluorescence transient curves after irradiation with white light of GSP and PSP. However, the effect was smaller in PSP. We suggest that the RCs of PSI and PSII were effectively shielded by PA in the epidermal cells of the leaves. It prevents an excess reduction of electron transport chain and alleviates the need for a strong energy dissipation. It maintained the coordination between PS Ⅰ and PS Ⅱ. So, it is concluded that the protective effect of PA with respect to the photosynthetic apparatus is due to a screening of light in the visible spectrum between 500 and 600 nm. In other words PA is part of the biophysical defense system of the leaf.