Photosynthetic energy storage efficiency, oxygen evolution and chloroplast movement

Abstract

When there is a saturating supply of dissolved carbon available, photosynthetic energy storage efficiency (ES) varies linearly with light fluence rate (I) for both Vallisneria americana and Pisum sativum leaves. The frequently reported hyperbolic relationship between ES and I occurs only when low levels of dissolved carbon are present in the medium. The linear relationship has its origin in intracellular events and implies that two heat-producing processes limit the value of ES. The rate of one process varies as I and the other varies as I². The rates of both processes were changed after a 2 hour exposure to 400 μmol photons m⁻² s⁻¹ of red light, speeding up the process that depends linearly on I and slowing the other. Illumination for 1 hour with 100 μmol photons m⁻² s⁻¹ of blue (but not red) light moves many chloroplasts from the periclinal to the anticlinal cell walls [Inoue and Shibata (1973) Planta 114: 341–358]. Blue light exposure of V. americana leaf sections (a) reduced the rate of oxygen evolution under light-limiting conditions by about 22%; (b) increased the value of ES by an amount dependent on the light fluence rate; and (c) decreased the slope of (ES v I). The slope change indicated that light absorption had fallen by 26% after blue light exposure. The rate of oxygen evolution (V) was measured under light-limiting conditions with leaf sections in which the chloroplasts had been immobilised after blue or red light exposure. With both red and blue-exposed leaf sections, V fell by about 50% after exposure to 1 hour of 1250 μmol photons m⁻² s⁻¹ of white light. Thus accumulation of chloroplasts on anticlinal walls did not protect the leaf from photoinactivation by a high light fluence rate.