Cohen C E, Rebeiz C A
Department of Horticulture, University of Illinois, Urbana, Illinois 61801.
Plant Physiol. 1978 May;61(5):824-9. doi: 10.1104/pp.61.5.824.
The contribution of short and long wavelength membrane-bound fluorescing protochlorophyll species to the over-all process of chlorophyll formation was assessed during photoperiodic growth. Protochlorophyll forms were monitored spectrofluorometrically at 77 K during the first six light and dark cycles in homogenates of cucumber (Cucumis sativus L.) cotyledons grown under a 14-hour light/10-hour dark photoperiodic regime, and in cotyledons developing in complete darkness. In the etiolated tissue, short wavelength protochlorophyll having a broad emission maximum between 630 and 640 nm appeared within 24 hours after sowing. Subsequently, the long wavelength species fluorescing at 657 nm appeared, and accumulated rapidly. This resulted in the preponderance of the long wavelength species which characterizes the protochlorophyll profile of etiolated tissues. The forms of protochlorophyll present in etiolated cucumber cotyledons resembled those in etiolated bean leaves in their absorption, fluorescence, and phototransformability. A different pattern of protochlorophyll accumulation was observed during the dark cycles of photoperiodic greening. The short wavelength species appeared within 24 hours after sowing. Subsequently, the long wavelength form accumulated and disappeared. The long wavelength to short wavelength protochlorophyll emission intensity ratio reached a maximum (~3:1) during the second dark cycle, then declined during subsequent dark cycles. Short wavelength species were continuously present in the light and dark. Primary corn and bean leaves exhibited a similar pattern of protochlorophyll accumulation. In cucumber cotyledons, both the short and long wavelengths species appeared to be directly phototransformable at all stages of photoperiodic development. It thus appears that whereas the long wavelength protochlorophyll species is the major chlorophyll precursor during primary photoconversion in older etiolated tissues, both long wavelength and short wavelength species seem to contribute to chlorophyll formation during greening under natural photoperiodic conditions.
在光周期生长过程中，评估了短波长和长波长膜结合荧光原叶绿素物种对叶绿素形成整体过程的贡献。在14小时光照/10小时黑暗光周期条件下生长的黄瓜（Cucumis sativus L.）子叶匀浆以及在完全黑暗中发育的子叶的前六个光暗周期中，于77 K下用荧光光谱法监测原叶绿素形式。在黄化组织中，播种后24小时内出现了发射峰在630至640 nm之间的宽峰的短波长原叶绿素。随后，出现了在657 nm处发荧光的长波长物种，并迅速积累。这导致了长波长物种占优势，这是黄化组织中原叶绿素谱的特征。黄化黄瓜子叶中存在的原叶绿素形式在吸收、荧光和光转化能力方面与黄化豆叶中的相似。在光周期绿化的黑暗周期中观察到了不同的原叶绿素积累模式。短波长物种在播种后24小时内出现。随后，长波长形式积累并消失。长波长与短波长原叶绿素发射强度比在第二个黑暗周期达到最大值（约3:1），然后在随后的黑暗周期中下降。短波长物种在光照和黑暗中持续存在。初生玉米和豆叶表现出相似的原叶绿素积累模式。在黄瓜子叶中，短波长和长波长物种在光周期发育的所有阶段似乎都可直接光转化。因此，似乎虽然长波长原叶绿素物种是较老黄化组织初级光转化过程中的主要叶绿素前体，但在自然光周期条件下绿化过程中，长波长和短波长物种似乎都对叶绿素形成有贡献。
