Rates of electron transfer and of non-cyclic photophosphorylation for chloroplasts isolated from maize populations selected for differences in juvenile productivity and in leaf widths.

In vitro studies with chloroplasts isolated from maize populations differing in juvenile productivity by the sixth leaf stage of growth demonstrated differences in rates of ferricyanide reduction and of non-cyclic photophosphorylation. Similar results were obtained for two independent sets of replicate selections for high and for low productivity. Chloroplasts from low productive selections had about 115 percent of the reduction rate and 129 percent of the phosphorylation rate found for the high productive selections. Differences in ferricyanide reduction held for a fourfold range of experimentally induced rates. The contrasting rates of electron flow did not result from differential extraction environments following cell disruption nor from the failure to protect chloroplasts during extraction. Light-dependent phosphate uptake gave evidence, though inconclusive, of being so modified. No evidence was found for reciprocal effects between low-high and high-low hybrids. No difference in activities was found between chloroplasts isolated from two populations selected for narrow and for wide leaf widths. These two selections differed markedly in leaf areas. While in vitro measures of chloroplast efficiency reflected differences which were under genetic control, the results did not follow those expected from photosynthetic studies. The differences in rates appeared to reflect modification of processes other than those in the photosynthetic pathway.