旱柳枝条叶绿体光化学特征的径向异质性

摘要

[目的]研究枝条叶绿体光化学特征的径向异质性和组织特异性,可为确定枝条中不同组织对枝条碳同化的贡献以及揭示叶绿体对枝条异质性光环境的适应机制提供依据.[方法]测定照光和黑暗条件下旱柳无性系当年生枝条的CO(2)释放速率,评价枝条光合的碳回收贡献.测定树皮绿色组织、木质部和髓心的光合色素含量、吸光系数、光化学效率、电子传递速率,分析不同组织中叶绿体光化学特征的差异.[结果]饱和光强下旱柳当年生枝条的总光合速率达到1.27μmolCO2·m-2s-1,可将77％呼吸消耗的碳回收固定.在旱柳当年生枝条中,树皮的总叶绿素含量显著高于木质部和髓心,分别是木质部和髓心的15.90和1.83倍.叶绿素b与叶绿素a的比例随径向深度的增加由树皮至髓心呈显著升高的趋势,树皮中的类胡萝卜素含量、类胡萝卜素与叶绿素的比例均显著高于木质部.旱柳当年生枝条不同组织的吸光系数沿径向方向显著降低,树皮绿色组织的最大光化学效率、实际光化学效率和相对电子传递速率显著高于木质部和髓心.[结论]枝条光合可将77％呼吸消耗的碳回收.不同组织的光合色素含量和光化学效率呈现随径向深度增加而显著降低的规律,树皮绿色组织是枝条光合的主要载体.树皮绿色组织具有较强的光保护能力,木质部和髓心通过光合色素比例的调整最大限度地捕捉组织中有限的光能.%[Objective]Stem photosynthesis plays an important role in growth, defense, reproduction and survival for woody plant, especially for deciduous trees. In this study, we investigate dradical heterogeneity and tissue specificity of chloroplast photochemical characteristics in branches, which can provide a basis for quantifying the contribution of different tissue to stem photosynthesis, and alsolay a foundation for revealing the adaptation mechanism of chloroplast to the heterogeneous light environment in twigs.[Methods]The CO2 release rates of current-year twigs of Salix matsudana clones were measured under light and dark conditions, and the contribution of stem photosynthesis to carbon recycle was evaluated. Besides, the photosynthetic pigment content, light absorption coefficient, photochemical efficiency and electron transport rate of bark, xylem and pith were determined, and the differences inphotochemical characteristics of chloroplasts between distinct tissues were analyzed. [Results]When exposed to the saturation light intensity, the stem photosynthesis rate of twig was 1.27 μmolCO2·m-2s-1, which was able to recover and fix 77％ of the carbon consumed by respiration. In the internal of twig, the total chlorophyll content of bark was highest, and was15.90 and 1.83 times higher than that of xylem and pith, respectively.The ratio of chlorophyll b to chlorophylla increased from bark to pith with the increase of radial depth. The carotenoid content and the ratio of carotenoid to chlorophyll in bark were significantly higher than those in xylem.The absorptivity coefficient of different tissues of the current-year-old branches significantly decreased along the radial direction.The maximum photochemical efficiency, effectively photochemical efficiency and relative electrontransport rate of PSII of bark were significantly higher than xylem and pith.[Conclusion]Stem photosynthesis in current-year-old twigs of Salix matsudana was able to recover and fix 77％ of the carbon consumed byrespiration. The photosynthetic pigment content and photochemical efficiency of chloroplasts decreased significantly with the increase of radial depth.Barkchlorenchyma was the major contributor to stem photosynthesis, and had a stronger capacity for quenching excess excitation energy. Xylem and pith chloroplasts maximized the limited light energy in the tissue by regulating the proportion of photosynthetic pigments.