较系统地研究了抽穗期超高产杂交稻‘华安3号’（`X075’×`紫恢100’）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CP47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Chl b还原为Chl a，以降低LHCⅡ的含量，从而减少对光能的捕获，达到降低光抑制的伤害。
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‘בMinghui 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 (Fv/Fm), efficiency of excitation energy captured by open PSⅡ reaction centers (Fv′/Fm′), quantum yield of PSⅡ electron transport (ΦPSⅡ), 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.