不同色彩珙桐叶片和苞片解剖结构及色素含量比较研究

以生长于同一生境下的粉红珙桐(粉红色叶片、苞片)与普通珙桐(绿色叶片、白色苞片)为试材，对比两种色彩珙桐叶片/苞片解剖结构和色素含量的差异，以揭示珙桐色彩转变的规律。结果显示：(1)两种珙桐叶片均属于异面叶类型，栅栏组织由一层长柱形细胞整齐排列而成，海绵组织排列疏松，部分粉红叶片的上表皮细胞向外凸起，绿叶无此现象；粉红叶片的总厚度及其表皮角质层、栅栏组织和海绵组织厚度都高于绿叶，而表皮较薄。(2)两种珙桐苞片均无栅栏组织和海绵组织的分化，粉红苞片上表皮细胞明显隆起，上表皮角质层增厚，而下表皮变薄。(3)粉红叶片的类黄酮、花色苷含量分别是绿色叶片的1.52倍、3.67倍，两者的光合色素含量无显著差异，但粉红叶片的叶绿素a/b值比绿色叶低很多；粉红苞片花色苷含量显著高于白色苞片，而两者类黄酮含量差异不大。研究表明，花色苷是珙桐叶片和苞片色彩转红的直接因素，类黄酮有助于叶片呈红色；粉红珙桐叶片/苞片的解剖结构发生了一定变化，对光能的利用效率更高，对阴湿环境的适应性增强。

Anatomical Structure and Pigment Content of Davidia involucrata Leaves and Bracts with Different Colors

To explore the law of leaf color change of Davidia involucrata, we selected pink D. involucrata (pink bracts and leaves) and common D. involucrata (green leaves and white bracts) to compare the anatomical structure and pigment content. The results showed that: (1) two colors of D. involucrata leaves were bifacial leaf, containing a palisade tissue with onelayer neatly arranged long columnar cells and a loosely arranged sponge tissue. The upper epidermal cells of some pink leaves bulged outward, and the total thickness, cuticle, palisade tissue and sponge tissue of the pink were thicker than those of green ones, while the epidermis was thinner. (2) There was no differentiation between palisade tissue and sponge tissue in two D. involucrata bracts. The upper epidermal cells of the pink bracts bulged significantly with the thickening of the cuticle, while the lower epidermis became thinner. (3) The contents of flavonoid and anthocyanin in pink leaves were 1.52 times and 3.67 times that of green leaves. The difference of photosynthetic pigment content between two leaves was not obvious, but the chlorophyll a/b value of pink leaves was significantly lower. The anthocyanin content of pink bracts was significantly higher than that of white bracts, while the flavonoid content of the two was not much different. In conclusion, anthocyanin directly caused D. involucrata leaves and bracts to turn pink, and flavonoid helped the leaves appear pink. The anatomical structure of pink D. involucrata leaves and bracts had changed, which had the higher light energy utilization efficiency and were more suitable for the wet environment.