Electron Transport between Photosystem 1 and Photosystem 2 and Establishment of a Trans-Thylakoid Energy Gradient during Chloroplast Biogenesis in the Wheat Leaf

Abstract

Monocotyledons such as wheat have a basal intercalary meristem and as a result exhibit a progressive series of cell development along the leaf and provide a convenient experimental system with which to examine chloroplast development (Boffey et.al. 1979). When wheat leaves are grown under a diurnal light regime chlorophyll accumulates extremely rapidly in the newly formed cells (Boffey et. al. 1980) and primary photochemical activities associated with the two photosystems rapidly appears (Webber et.al. unpublished). Although photochemically active reaction centres, primary chlorophyll antennae of both PS1 an PS2 and excitation energy transfer between the chlorophyll antennae complexes of PS1 and PS2 are evident at early stages of development, it is not known whether electron transfer occurs from water to a terminal electron acceptor via PS2 to PS1 with a concomitant proton pumping and establishment of a proton motive force across the thylakoids. Clearly the ability of the thylakoid to facilitate electron transport from water to NADP with associated proton pumping and an ability to maintain the proton electro-chemical gradient across the thylakoid are essential prerequisites, and possibly limiting factors, for ATP synthesis.

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