Effect of growth irradiance on plastocyanin levels in barley

Plastocyanin levels in barley (Hordeum vulgare cv Boone) were found to be dependent on growth irradiance. An immunochemical assay was developed and used to measure the plastocyanin content of isolated thylakoid membranes. Barley grown under 600 mole photons m^–2s^–1 contained two- to four-fold greater quantities of plastocyanin per unit chlorophyll compared with plants grown under 60 mole photons m^–2s^–1. The plastocyanin/Photosystem I ratio was found to be 2 to 3 under high irradiance compared with 0.5 to 1.5 under low irradiance. The reduced plastocyanin pool size in low light plants contributed to a two-fold reduction in photosynthetic electron transport activity. Plastocyanin levels increased upon transfer of low light plants to high irradiance conditions. In contrast, plastocyanin levels were not affected in plants transferred from high to low irradiance, suggesting that plastocyanin is not involved in the acclimation of photosynthesis to shade.Abbreviations: BSA bovine serum albumin - chl chlorophyll - cyt cytochrome - DCIP 2,6-dichlorophenolindophenol - PS I Photosystem I - PS II Photosystem II - P700 reaction center of Photosystem I - TBS 20 mM Tris-HCl pH 7.5, 500 mM NaCl - TTBS 20 mM Tris-HCl pH 7.5, 500 mM NaCl, 0.5% (w/v) polyoxyethylenesorbitan monolaurate (Tween-20)