LEAF PHOTOSYNTHESIS AND CHLOROPHYLL FLUORESCENCE IN A CHLOROPHYLL-DEFICIENT SOYBEAN MUTANT

A comparative study of chlorophyll (Chi) fluorescence characteristics was made between a soybean [Glycine max (L.) Merr.] Chl-deficient mutant (light green leaf, LG, Y(11)y(11)()), and a nearly isogenic Chi normal biotype (dark green leaf, DG, Y11Y11) of cultivar Clark. LG had a lower light-saturated net photosynthetic rate (P-N), compared with DG at early stages of growth (before pod filling), but the difference in P-N between LG and DG became smaller at later stages of growth. The lower P-N of LG may result from lower Chi content (Chi a and b), lower carboxylation efficiency, and lower photochemical efficiency of photosystem 2. Both LG and DG grown at low iradiance [about 200-300 mu mol(photon) m(-2) s(-1)] in a growth cabinet had similar photochemical efficiencies. However, the efficiency was lower in LG than in DG grown in field sunlight in mid summer, especially during the afternoon on clear days, indicating that LG is more sensitive to photoinhibition.