THE CONSEQUENCES OF CHLOROPHYLL DEFICIENCY FOR PHOTOSYNTHETIC LIGHT USE EFFICIENCY IN A SINGLE NUCLEAR GENE MUTATION OF COWPEA

The light harvesting and photosynthetic characteristics of a chlorophy ll-deficient mutant of cowpea (Vigna unguilata), resulting from a sing le nuclear gene mutation, are examined. The 40% reduction in total chl orophyll content per leaf area in the mutant is associated with a 55% reduction in pigment-proteins of the light harvesting complex associat ed with Photosystem II (LHC II), and to a lesser extent (35%) in the l ight harvesting complex associated with Photosystem I(LHC I). No signi ficant differences were found in the Photosystem I(PS I) and Photosyst em II (PS II) contents per leaf area of the mutant compared to the wil dtype parent. The decreases in the PS I and PS II antennae sizes in th e mutant were not accompanied by any major changes in quantum efficien cies of PS I and PS II in leaves at non-saturating light levels for CO 2 assimilation. Although the chlorophyll deficiency resulted in an 11% decrease in light absorption by mutant leaves, their maximum quantum yield and light saturated rate of CO2 assimilation were similar to tho se of wildtype leaves. Consequently, the large and different decreases in the antennae of PS II and PS I in the mutant are not associated wi th any loss of light use efficiency in photosynthesis.