超高产杂交稻‘华安3号’冠层不同衰老程度叶片的光合功能

PHOTOSYNTHETIC FUNCTIONS OF DIFFERENT SENESCING LEAVES IN THE CANOPY OF SUPERHIGH-YIELD RICE `HUA-AN 3'

较系统地研究了抽穗期超高产杂交稻‘华安 3号’(‘X0 75’ב紫恢 10 0’)冠层顶部 5片叶片的光合功能。结果表明 ,‘华安 3号’剑叶的光系统Ⅱ (PSⅡ )光化学最大效率 (Fv/Fm)、开放的PSⅡ反应中心捕获激发能效率(Fv′/Fm′)、PSⅡ电子传递量子效率 (ΦPSⅡ)、光化学猝灭系数 (qP)、表观电子传递效率 (ETR)、光合色素尤其是叶绿素 (Chl)和类胡萝卜素 (Car)中的新黄素、黄体素和 β_胡萝卜素 (β_Car)的含量等均优于其下的各叶 ,而PSⅡ的激发压力 (1_qP)低于其它叶片。经对叶片低温 (77K)荧光发射光谱的Gaussian解析 ,与其它各叶片相比 ,剑叶PSⅡ核心天线复合物CP4 7和光系统Ⅰ (PSⅠ )的含量较高 ,而非活性的PSⅡ捕光色素蛋白复合体 (LHCⅡ )聚集态含量较少。研究证明 :1)水稻在决定籽粒产量的生育后期 ,其干物质的积累主要是由冠层最上面的 3片叶的光合作用所提供 ;2 )在叶片衰老过程中 ,光合反应中心的衰老早于天线系统 ;3)杂交稻的光保护途径之一 ,可能在于光抑制条件下通过增加PSⅠ含量及其对光能的吸收并刺激环式电子传递高速运转 ,从而对光合器起保护作用 ;4 )水稻叶片在衰老过程中 ,可能通过部分Chlb还原为Chla ,以降低LHCⅡ的含量 ,从而减少对光能的捕获 。

In order to improve rice yields to feed a growing population, China has carried out a `Super High-Yield Rice Project' since 1996. Tremendous progress was made during the `Ninth Five-Year Plan' and several new varieties of rice hybrids were released. `Hua-an 3' (`X07S'×`Zihui100') is a new high yield variety that has yields of more than 10 500 kg·hm -2; this compares with yields of 7 500-8 500 kg·hm -2 in the traditional hybrid rice `Shanyou 63' (`Zhenshan 97A'×`Minghui 63'). The photosynthetic functions and pigments of the upper most 5 senescing leaves of the canopy of `Hua-an 3' were studied by techniques of fluorescence induction kinetics, low temperature (77K) fluorescence emission spectrum and HPLC. The results showed that the maximal quantum yield of PSⅡ photochemistry (F v/F m), efficiency of excitation energy captured by open PSⅡ reaction centers (F v′/F m′), quantum yield of PSⅡ electron transport (Φ PSⅡ), photochemical quenching coefficient (qP), and the content of photosynthetic pigments, especially chlorophyll (Chl), neoxanthin (N), lutein (L) and β-carotene (β-Car), of the flag leaf were higher than those of other leaves but its excitation pressure (1-qP) was lower. It was shown that the content of the core antenna complex CP47 in photosystemⅡ (PSⅡ) and photosystem Ⅰ (PS Ⅰ) of the flag leaf also was higher than in other leaves, but the content of its non-active aggregate of light harvesting complex in PSⅡ (LHCⅡ) derived from the Gaussian analysis of low-temperature (77K) fluorescence emission spectra was lower than that of the other leaves. Our research results are as follows: 1) at later growth and development stages of rice, the dry matter of grain was mainly provided by most photosynthesis occurred in the uppermost 3 leaves in the canopy; 2) in the course of leaf senescence, the senescence of photosynthetic reaction centers was quicker than that of the antenna system; 3) one of the photoprotective pathways in hybrid rice may be through an increase in the content of PS Ⅰ, absorption of more light energy, and stimulating a high speed electron transport cycle in order to protect the photosynthetic apparatus under photoinhibitory conditions; 4) in the course of leaf senescence of rice, partial chlorophyll b was probably reduced to chlorophyll a, to decrease the content of LHCⅡ, thus reducing the amount of energy absorbed by LHCⅡ and decreasing the amount of photoinhibitory damage.