Light-dependent Elongation of Anaerobically Maintained Green Pea Stem Segments and Its Implications.

Anaerobic conditions reversibly inhibit the elongation of isolated green pea (Pisum sativum L. var Alaska) stem segments. Illumination of segments maintained under anoxia causes a resumption of growth. Polarographic studies show pea stem segments are photosynthetically competent as determined by O(2) evolution. Although O(2) production is totally inhibited by dichlorophenyldimethylurea (DCMU) and dinitrophenol (DNP) inhibits O(2)-dependent growth, neither DCMU nor DNP completely abolishes light-dependent growth, although both reduce the effect markedly. Phenazine methosulfate promotes the growth of anaerobically maintained, illuminated, DCMU-treated segments. The data indicate that the principal effect of light in inducing growth under anaerobic conditions is the photosynthetic provision of O(2) for respiration. There is also some evidence that, at least in the absence of O(2), a small amount of elongation is due to some other light-driven process, perhaps cyclic photophosphorylation.