EFFECTS OF SALICYLIC-ACID ON GROWTH AND PHOTOSYNTHESIS IN BARLEY PLANTS

Hordeum vulgare L./cv. Alfa/was grown for 7 days over a range of salic ylic acid (SA) concentrations (100 mu M - 1 mM), and the effects on gr owth and photosynthetic performance were examined. Leaf and root growt h, and chlorophyll and protein contents were reduced by SA. Gas exchan ge measurements and analysis of carboxylating enzyme activities were u sed to study the reactions of photosynthesis to SA. Long-term treatmen t of barley seedlings with SA led to a noticeable decrease in both the initial slope of the curves representing net photosynthetic rate vers us intercellular CO2 concentration and the maximal rate of photosynthe sis. The calculated values of the intercellular CO2 concentration, CO2 -compensation point and the maximal carboxylating efficiency of ribulo se-1,5-bisphosphate carboxylase (RuBP carboxylase, EC 4.1.1.39) suppor t the suggestion that biochemical factors are involved in the response of photosynthesis to SA. RuBP carboxylase activity decreased with inc reasing SA concentrations, while the activity of phosphoenolpyruvate c arboxylase (PEP carboxylase, EC 4.1.1.31) increased. When 7-day-old ba rley seedlings were supplied with SA through the transpiration scream for 2 h no changes in photosynthetic reactions were observed. Six and 24 h after treatment of barley seedlings with SA the rare of photosynt hesis declined in a concentration-dependent manner. Possible reasons f or the responses of photosynthesis to SA are discussed.