Redox status of cytochrome oxidase in darkened leaf of C4 crop plants.

Light is essential for growth, development and various metabolic processes in plant. One-third of the whole intact leaf blades of pearlmillet and maize were covered (treated leaf) with a black opaque plastic sheet at the middle region for 15 days. The leaf samples were taken from three regions: basal, middle and distal; from treated and parallel untreated leaves (control). Oxygen uptake was measured from all the three regions by taking randomized leaf discs. Oxygen uptake was nearly the same in all the regions of treated and parallel untreated leaf in pearlmillet and maize. Carbon monoxide used at 0.5 mM concentration with pearlmillet inhibited oxygen uptake slightly (22%) in covered leaf blade, whereas the inhibition with maize leaf at 1.12 mM CO was significantly higher (45%). However, CO did not inhibit oxygen uptake in untreated leaf from pearlmillet and maize. In contrast. cyanide brought about 33%, inhibition in oxygen uptake at 0.25 mM with pearlmillet and 60%, with maize at 0.4 mM, irrespective of the fact whether a portion of the leaf blade was covered or not with an opaque sheet. The results indicate that removing light from a portion of the leaf blade alters the redox state of the whole leaf in terms of an increase in the level of the ferrocytochrome a3 component of cytochrome c oxidase (cytochrome aa3).