BIOMASS AND PHOTOSYNTHESIS RESPONSES OF ROUGH LEMON (Citrus jambhiri Lush.) TO GROWTH REGULATORS

Abstract

Four-month-old plants of rough lemon (Citrus jambhiri Lush.) were sprayed, once a week, for 7 consecutive weeks with 100-μM concentrations of abscisic acid (ABA), benzyladenine (BA), gibberellic acid (GA3), naphthaleneacetic acid (NAA), and paclobutrazol (PP333). Leaf photosynthetic rates, photosynthetic carboxylating enzymes, and biomass partitioning were determined for individual treatments. Growth of rough lemon was influenced more with sprays of PP333 and GA3 than with ABA, BA, and NAA. PP333 sprays resulted in about 25, 30, and 33% reductions in both plant height and total plant weight, leaf biomass, and leaf area, respectively. The GA3 treatment, which caused 43 and 38% reductions in leaf biomass and leaf area, respectively, induced increased stem height and thickness, resulting in 48% more stem dry weight. There were no apparent differences in leaf photosynthetic rates and activities of ribulose bisphosphate carboxylase between control plants and plants treated with the growth regulators. The activities of phosphoenolpyruvate carboxylase, however, were depressed from 45 to 60% for the BA, GA3, NAA, and PP333 treatments. This suggests that organic acid metabolism in rough lemon leaves would be affected during repeated sprays of growth regulators.Key words: Plant growth, chemical retardants, carbon assimilation, RuBP carboxylase, PEP carboxylase