Chloroplastic activity in response to gibberellic acid treatment of dwarf and normal cultivars of pea (Pisum sativum L.)

Abstract

Levels of ferricyanide reduction, cyclic and non-cyclic photophosphorylation were measured in chloroplasts of two cultivars of pea and a comparison of their P/2e+ ratios were made. No differences were observed in cyclic photophosphorylation or ferricyanide reduction but non-cyclic photophosphorylation was lower in chloroplasts from the dwarf than the normal cultivar. Thus the P/2e+ ratio of the dwarf was lower than the normal. Dwarf seedlings treated with gibberellic acid (GA3) had similar rates of cyclic photophosphorylation as the untreated dwarf but non-cyclic photophosphorylation was lower as was ferricyanide reduction. This resulted in P/2e+ ratios that were higher in chloroplasts from the GA3 treated dwarf seedlings than the untreated, and were the same as the untreated normal. Addition of GA3 directly to the chloroplasts did not alter the activity in any way. Hence gibberellins do not directly affect changes in chloroplastic activity but may conceivably be involved in a feed-back control system.