关键词: 枝条皮层组织, 叶绿体, 光化学特性, 亚细胞器结构特化

Abstract: [Objective] Corticular photosynthesis is the process of CO₂ re-fixation which derived from respiration and transpiration streaming, it could increase carbon income and guarantee plant survival when leaf photosynthesis is inhibited. Photosynthesis is determined by the structure and function of chloroplast. The study of photochemical characteristics and structure specializations of cortex chloroplast was to reveal the physiological and molecular mechanism of operation and regulation of corticular photosynthesis.[Method] New twigs of Salix matsudana were taken as the experimental material, the chloroplast distribution in cross section and its photochemical efficiency were illustrated. On the basis of that, the differences of photochemical characteristic and structure between twig and leaf were analyzed.[Result] The results showed that chloroplast distribution from pith to epidermis in twig, and the max photochemical efficiency of PSⅡ of cortex was the highest, significantly higher than vascular tissue and pith. The ratio of chlorophyll a to chlorophyll b and carotenoid to total chlorophyll of cortex chloroplast were significantly higher than leaf chloroplast. The proportion of excited energy allocation of PSⅡ of cortex chloroplast was 1.4 times of leaf chloroplast. The ratio of long to short axis of cortex was larger. The sub-organelle structure was complete in cortex chloroplast, and the ratio of grana lamella to total lamellas and starch grain area to whole chloroplast was significantly higher than leaf chloroplast.[Conclusion] Cortex chloroplasts are the main contributor to twig photosynthesis. In order to capture the limited light in the tissues of twigs and to reduce photo-oxidative stress, the ratio of antenna pigment, light exposed area and the ratio of light protective pigment were increased. For promoting excited energy allocation to PSⅡ reaction center, the proportion of thylakoid stack area was increased. And cortex chloroplast guaranteed the demand for nonstructural carbohydrates through starch accumulation. Collectively, dependent on the adjustment of photosynthetic pigments composition and the specialization of sub-organelle structures, cortex chloroplast adapted to the physicochemical environment and made maximum use of the limited light energy inside the twigs.

Key words: twig cortex tissue, chloroplast, photochemical characteristic, sub-organelle structural specialization