桦木科植物花柱适应风媒传粉的特征

植物体为适应自己的传粉系统, 表现出高度的适应特征。风媒花植物为适应风传播花粉, 要形成特殊的结构, 以扩大接受花粉粒的面积。利用扫描电镜观察了桦木科(Betulaceae)6属18种植物花柱的形态及花粉粒在花柱上的萌发过程, 探讨了桦木科植物花柱适应风媒传粉的特征。结果表明, 桦木科植物的二心皮(铁木、云南鹅耳枥稀为三心皮)雌蕊具柱状花柱, 柱头不发达, 花柱表皮细胞长条状, 纵向排列紧密。传粉时, 花柱表皮细胞能执行柱头的功能, 接受花粉粒, 为花粉粒萌发提供场所和萌发条件。桦木科植物花柱有2种类型: 一种是花柱表皮细胞能形成乳突, 花粉管经乳突细胞进入花柱; 另一种是花柱表皮细胞不形成乳突, 花粉管经过花柱表皮细胞或胞间隙进入花柱。无论花柱表皮细胞是否形成乳突, 乳突的形态、大小以及花粉管和乳突的结合方式等在族间、属间、属内种间存在差异。与基部被子植物相比, 桦木科植物的花柱呈现适应风媒传粉的进化特征。桦木科植物花柱表皮细胞形成的乳突与基部被子植物柱头乳突功能相同, 是桦木科植物风媒传粉的适应策略。

Wind Pollination Characteristics of Styles in Betulaceae

For pollination, plants show a high degree of adaptation. To expand the area to accept pollen, wind-pollinated flowering plants form a special structure to adapt to wind-spread pollen. We investigated the morphology of styles and pollen tube growth on styles (including stigmas) for 18 species of 6 genera in Betulaceae by scanning electron microscopy. Betulaceae have two-carpel (or rarely tri-carpel in Ostrya japonica and Carpinus monbeigiana) gynoecia, usually with cylindrical styles and not well-developed stigmas. Styles have elongate epidermal cells, arranged longitudinally and tightly; styles function as stigma to receive mature pollen grains and provide a suitable germination environment. Betulaceae have two types of styles: in one, epidermal cells have bubble or tubular papillae, and the pollen tube enters the style through papilla; in the other, epidermal cells have no papillae, and the pollen tube enters the style between the epidermal cells. Whether style epidermal cells can form papillae or not, the morphology or size of papillae and the binding mode of pollen and papilla differs by tribe, gender and genus. The style epidermal cells in Betulaceae could perform the function of a stigma, receiving pollen and providing locations and conditions for pollen germination. The papillae formed by style epidermal cells in Betulaceae have the same function as in basal angiosperms, an adaptation strategy for plants with wind pollination.