Effects of salicylic acid on growth and photosynthesis in barley plants

Abstract

Summary Hordeum vulgare L./cv. Alfa /was grown for 7 days over a range of salicylic acid (SA) concentrations (100 μM – 1 mM), and the effects on growth and photosynthetic performance were examined. Leaf and root growth, and chlorophyll and protein contents were reduced by SA. Gas exchange measurements and analysis of carboxylating enzyme activities were used to study the reactions of photosynthesis to SA. Longterm treatment of barley seedlings with SA led to a noticeable decrease in both the initial slope of the curves representing net photosynthetic rate versus intercellular CO 2 concentration and the maximal rate of photosynthesis. The calculated values of the intercellular CO 2 concentration, CO 2 -compensation point and the maximal carboxylating efficiency of ribulose-l,5-bisphosphate carboxylase (RuBP carboxylase, EC 4.1.1.39) support the suggestion that biochemical factors are involved in the response of photosynthesis to SA. RuBP carboxylase activity decreased with increasing SA concentrations, while the activity of phosphoenolpyruvate carboxylase (PEP carboxylase, EC 4.1.1.31) increased. When 7-day-old barley seedlings were supplied with SA through the transpiration stream for 2 h no changes in photosynthetic reactions were observed. Six and 24 h after treatment of barley seedlings with SA the rate of photosynthesis declined in a concentration-dependent manner. Possible reasons for the responses of photosynthesis to SA are discussed.