Comparisons of Photosynthetic Activity and Lamellar Characteristics of Virescent and Normal Green Peanut Leaves

Abstract

Summary Several characteristics of the chloroplast lamellar system and the photosynthetic activity of virescent and wild type peanut leaves have been compared. The mutant leaves exhibited a 42 % reduction in chlorophyll, a higher chlorophyll a/b ratio, and an alteration in the proportions of the two major chlorophyll-protein complexes of the chloroplast. The mutant leaves showed a reduction in the number of photosystem I reaction center components (the P 700-chlorophyll a-protein) per unit leaf area, and consequently a stoichiometric reduction in the number of photosystem I electron transport assemblages (P 700, cytochromes f and b 6 ). In addition the mutant had a photosynthetic unit size which was 1.5 times larger than the wild type. These findings indicated that the chlorophyll deficient leaves had many fewer, but larger, photosynthetic units than the normal green leaves. As a consequence of these alterations it is suggested that the observed low photosynthetic rates on a leaf area basis (10 mg CO 2 /dm 2 -hr) as well as on a chlorophyll basis (8 mg CO 2 /mg Chl-hr) were likely due to a much reduced capacity of the mutant chloroplasts to produce sufficient quantities of ATP and NADPH to support high levels of carbon fixation. Furthermore, the alterations in chlorophyll-protein content and organization into photosynthetic units can explain the reduction in chlorophyll and higher chlorophyll a/b ratio of the virescent leaves.