Changes in leaf phosphate status have only small effects on the photochemical apparatus of sugar beet leaves

Abstract

The effects of orthophosphate (P i) on the structure and function of thylakoid membranes was investigated by monitoring changes in thylakoid polypeptides, pigment-proteins, cytochromes (Cyt), atrazine-binding sites, leaf fluorescence characteristics, photosynthesis quantum yield and electron transport (including Cyt f dark reduction) in leaves of sugar beet ( Beta vulgaris L. cv. F58-554H1) plants cultured hydroponically with different levels of P i supply. Low-P treatment (i.e. low external P i supply) decreased soluble leaf phosphorus (P) by 78% and total plant dry matter by 77%, and decreased light-saturated photosynthetic CO 2 fixation by 32%. The results show that low-P treatment had only minor effects on thylakoid membrane composition and function. There was some evidence that low-P increased the amounts of photosystem (PS) I and light harvesting chlorophyll-protein complexes and of the Cyt f and b 563 , relative to the amounts of PS II reaction center complex, the number of atrazine binding sites and Cyt b 559 . Low-P treatment had very little effect, if any, on photosynthetic quantum yield and small effects on chlorophyll fluorescence.