摘要
Angiosperms need light to synthesize chlorophyll, but lotus (Nelumbo nucifera Gaertn.) embryo was suspected to have the ability to form chlorophyll in the dark because lotus embryo can turn into green under the coverage of four layers of integuments (cotyledon, seed coat, pericarp, lotus pod) which were thought impossible for light to pass through. The authors excluded this possibility based on two experimental results: First, enclosing the young lotus pod with aluminium foil, the growth of louts embryo continued, but the chlorophyll formation was seriously inhibited. A lot of protochlorophyllide, chlorophyll precursor, were accumulated, most of which were combined with LPOR (light dependent protochlorophyllide oxidoreductase). Second, DPOR (dark or light-independent protochlorophyllide oxidoreductase) was the enzyme necessary for chlorophyll synthesis in the dark. The genes encoding DPOR were conservative in many species, but no homologues could be found in lotus genome. Taken together, authers' results clearly demonstrated that lotus embryo synthesizes chlorophyll only through the light-dependent pathway.
被子植物的叶绿素合成需要光照 ,但是莲 (NelumbonuciferaGaertn .)胚芽却一直被猜测具有在黑暗中合成叶绿素的能力 ,因为莲胚芽变绿是在四重覆盖物 (子叶、种皮、果皮和莲蓬 )包被下几乎不大可能透光的环境中发生的。本实验从正反两个方面否定了这种可能性 :首先对处于发育早期的莲蓬进行遮光处理 ,结果发现莲胚芽虽然可以继续发育 ,但是它的叶绿素合成却受到严重抑制 ,积累了大量合成叶绿素的前体 ,并且这些前体主要与依赖光的原叶绿素酸酯氧还酶 (LPOR)结合在一起 ;其次不依赖光的原叶绿素酸酯氧还酶 (DPOR)的编码基因在物种间高度保守 ,但是用PCR的方法在莲基因组中却扩增不到同源序列 ,表明莲胚芽不大可能具有在黑暗中合成叶绿素所必需的酶。两方面实验结果表明 ,莲胚芽的叶绿素合成只能通过依赖光的途径进行。
基金
SupportedbytheStateKeyBasicResearchandDevelopmentPlan (G19980 10 10 0 )ofChinaandtheInnovativeFoundationofLaboratoryofPhotosynth
