Studies on peanut green mosaic virus infected peanut ( Arachis hypogaea L.) leaves. I. Photosynthesis and photochemical reactions

Abstract

Changes in chlorophyll levels, in photosynthetic rates, and in photochemical reactions were studied in peanut plants infected with peanut green mosaic virus at three different stages of systemic infection: (1) early infection; (2) the stage of maximum symptom expression and (3) after the recovery phase of systemic disease development. Chlorophyll content per unit leaf area was reduced at all three stages of infection with the greatest reduction coinciding with the phase of maximum symptom expression. Net photosynthesis was also reduced over a range of light intensities, with the maximum reduction occurring at the highest light intensities. Infection inhibited photosystem II activity to a significantly greater extent, particularly at infection stage 2, than it did photosystem I activity. Non-cyclic photophorylation was also inhibited to a much greater extent than cyclic photophosphorylation. Chlorophyll a fluorescence measurements showed a reduced plastoquinone pool size. Evidence is presented to show that the reduced electron transport caused by infection is partly due to the reduction in chlorophyll levels, particularly chlorophyll a but also to direct inhibition of photosystem II, mainly at the plastoquinone level.