第四节 传粉与受精
一、传粉 (pollination) The transfer of pollen from microsporangia to the stigma in angiosperms or to directly to the ovule in gymnosperms. 由花粉囊散出花粉借助于一定的媒介力 量被送到同花或另一花的柱头, 这一过程 称为传粉
( 一 ) 传粉的方式 自花传粉 异花传粉 两性花, 雌雄蕊同时成熟 ; 柱头对接受自身的花粉无生理上的障碍 单性花 ; 若是两性花, 雌雄蕊不同时成熟, 或自交有 生理障碍
( 二 ) 传粉媒介 1. 风媒花 2. 虫媒花 3. 鸟媒花 4. 其他传粉媒介
穗状或柔荑花序 花粉量大,体积轻,表面光滑,少纹饰 雌蕊柱头长, 常有羽毛 先叶开花 1. 风 媒 花
1. 风媒( anemophily ): about 10% of angiosperms , Gramineae 、 Populus 杨属、 Salix 柳属、 Betula 桦 木 well-exposed stamens ; abundant smooth and small pollen grains ; stigmas specialized ; flowering before leaves developed
Lolium 毒麦属
Zea mays
Corylus 榛属植物 Gramineae 禾本科
2. 虫 媒 花 多数有花蜜,有气 味 花大,具鲜艳的颜 色,醒目 花粉粒较大,表面 有粘液和纹饰,易 粘着
Female Male Structure of a flower
Beetle-pollinated flowers Flowers large or singly; or small and aggregated in an inflorescence; special strong odors; white or dull in color; ovules inferior Beetles developed sense of smell; with strong chewing jaws; can’t fly so far away
Beetles eating floral appendages
Asclera ruficornis and Hepatica americana
Cetoniine scarabid beetle with membranous mouthparts used for drawing up nectar.
Eastern Skunk Cabbage Flies
Western skunk Cabbage Flying rove Beetles
Devil’s tongue Good smelling? rotting fish mixed with bunt sugar
Bee-, wasp-, and fly- pollinated flowers Bees at least 80 million years old; well developed nectar and pollen collecting and carrying apparatus; special visual system; highly constant in their visits to flowers
Bee flowers showy,brightly colored petals; distinct patterns; never pure red; nectar at special position; “landing platform” for visitors
foxglove Honey guides Landing platform Bee pollination
In natural light as viewed by humans 驴蹄草 Caltha palustris
In ultraviolet light Light portions reflect yellow and ultraviolet (“bee’s purple”) Dark portions absorb ultraviolet (pure yellow viewed by a bee)
Taraxacum
A honeybee foraging in a rosemary flower 迷迭香
Bumblebee visiting a flower and its underground nest California poppy
Beelike flower of orchid
Flowers of orchids
Carrion fly visiting a flower of Asclepiadaceae (milkweed family)
Some small-flowered orchids are pollinated by mosquitoes
Flowers pollinated by moths and butterflies Some butterflies are able to perceive red as a distinct color; some flowers are red and orange; nectars are often located at the base of a long and slender corolla or spur 鳞翅目(蝴蝶、蛾)具长嘴(吸器), 善飞行 → 具长矩或花冠筒包含花蜜的花。
Butterfly pollination Mouthparts: 1 to 2 cm long
Mouthparts: several millimeters long in some of the smallest moths Moth pollination
hawkmoth
Yucca moth and yucca flower
Bird-pollinated flowers Copious and thin nectar but usually have little odor; colorful with red and yellow ones; flowers large or form parts of large inflorescences e.g. columbine, fuchsia, passion flower, eucalyptus, hibiscus, poinsettia, and many members of the cactus, banana, and orchid families 3. 鸟 媒 花
A male Anna’s hummingbird at a flower of the scarlet monkeyflower (Mimulus cardinalis) (沟酸浆)
Columbine ( Aquilegia canadensis )
Common poinsettia Euphorbia pulcherrima
Common poinsettia 一品红
蜂鸟与西番莲属植物 宽尾蜂鸟 好望角糖鸟与普罗梯亚木
太阳鸟( sunbird )取食 鹤望兰( bird-of-paradise flower )的花蜜
Bat-pollinated flowers Copious nectar; dully colored; often open at night; strong fermenting or fruitlike odors e.g. bananas, mangoes, kapok, sisal
A bat is eating honeydew of cactus
花蝠与黎豆植物 短鼻果蝠
hydrophily 水媒 About 18 among 380 genera ( 79 families ) of aquatic plants Ephydrophily 水表传粉 Vallisneria 、 some sea grass Hyphydrophily 水下传粉 Potamogetonaceae 眼子菜科 4. 其他传粉媒介.
Amphibolis
Vallisneria spiralis (苦草)
Bat-pollinated flowers Copious nectar; dully colored; often open at night; strong fermenting or fruitlike odors e.g. bananas, mangoes, kapok, sisal
A bat is eating honeydew of cactus
花蝠与黎豆植物 短鼻果蝠
花粉在柱头上的萌发 相互识别 湿润型柱头 : 表面的分泌物能 粘住花粉, 并为花粉提供营养 干燥型柱头 : 花粉通过表面的 蛋白质薄膜和角质层的裂隙 获得水份 花粉吸水膨胀, 伸出花粉管 有多个萌发孔的花粉粒, 最终 只有一个花粉管到达胚囊 二 受精作用
花粉管在雌蕊组织中的生长 花粉管在雌蕊组织中的生长
花粉管到达胚珠进入胚囊 珠孔受精 : 多数植物 合点受精 : 如核桃 中部受精 : 少数植物 花粉管向化性生长,而且雌蕊分泌的向化 性物质是热稳定性的,与钙离子浓度有关; 助细胞退化,花粉管进入
双受精 双受精:是被子植物花粉粒中的一对精子分别与卵 细胞和中央细胞结合的过程。 是被子植物所特有的 现象 花粉管 从丝状 器处进 入助细 胞 花粉管顶端孔裂, 精子、营养核和少 量细胞质释放 精子细胞从卵细胞和 中央细胞无细胞壁处 进入,完成双受精
双受精过程及其生物学意义 一个精子与卵结合形成受精卵并成为二倍体的合子,合 子将来发育成为产生新个体的胚 另一个精子与中央细胞极核结合,成为三倍体的受精极 核并进一步发育成为胚乳 这种双受精是被子植物特有的现象,也是植物有性生殖 中最进化的形式 首先, 2 个单倍体的雌、雄配子融合在一起,成为二倍 体的合子,恢复了植物原有的染色体数目,保持了物种 的相对稳定性。其次,双受精在传递亲本遗传性,加强 后代的生活力和适应性方面具有较大的意义。因为精、 卵融合把父、母本具有差异的遗传物质重新组合,形成 具有双受精的极核发展成的胚乳是三倍体的,同样兼有 父、母本的遗传特性,生理上更活跃,并作为营养物质 被胚吸收,使子代的生活力更强,适应性更广
无融合生殖与多胚现象 无融合生殖 减数胚囊中的无融合生殖 o 孤雌生殖:卵不经受精而发育成单倍体植株 o 无配生殖:助细胞和反足细胞直接发育成植株 o 雄核发育:精子核进入卵后,卵核消失,雄核发育为个体 未减数配囊中的无融合生殖 o 大孢子母细胞不经减数分裂,产生二倍体孢子,形成二倍 体配囊 o 珠心细胞发育形成二倍体配囊 多胚现象:种子中出现一个以上的胚 来源:出现无融合生殖; 合子分裂