Photosynthesis Growth and the Role of Chloride

摘要

Previous studies with isolated chloroplasts have indicated that Cl⁻ is an essential cofactor for photosynthesis. Considerable support for the postulated Cl⁻ requirement in photosynthesis came from the observation that Cl⁻ is essential for growth. Data are presented which show that a 60% reduction in growth which occurred in Cl⁻ -deficient sugar beet (Beta vulgaris L.) was not due to an effect of Cl⁻ on the rate of photosynthesis in vivo (net CO2 uptake per unit area of attached leaves). The principal effect of Cl⁻ deficiency was to lower cell multiplication rates in leaves, thus slowing down their growth and ultimately decreasing their area. The absence of an effect of Cl⁻ on photosynthesis in vivo was unlikely to have been due to Cl⁻ retention by the chloroplasts because their Cl⁻ concentration (measured after nonaqueous isolation) decreased progressively with decrease in leaf Cl⁻.An effect of Cl⁻ with isolated chloroplasts in vitro, however, was confirmed. Addition of Cl⁻ to the reaction medium after washing chloroplasts in EDTA increased the rate of ferricyanide photoreduction 10-fold. This effect of Cl⁻ did not appear to be related to the Cl⁻ concentration of the chloroplasts since chloroplast Cl⁻ was not decreased further by washing in EDTA. It is concluded that Cl⁻ has not yet unequivocally been shown to be an essential cofactor for photosynthesis and that the response to Cl⁻in vitro probably does not have a physiological basis.