MEPIQUAT CHLORIDE (PIX)-INDUCED CHANGES IN PHOTOSYNTHESIS AND GROWTH OF COTTON

Mepiquat chloride (N, N-dimethylpiperidinium chloride), well known as PIX, is a potential systemic plant growth regulator The effects of PIX on plant height, stem elongation, leaf area, net photosynthetic rates , chlorophyll content, sucrose and starch levels, and RuBP carboxylase activity in cotton (Gossypium hirsutum L. cv. DES 119) plants were me asured. PIX was sprayed (0, 7.65, 15.3, 30.6 or 61.2 g active ingredie nt ha(-1)) on the plants at first square (25 days after emergence) and measurements were made at frequent intervals. Plant height was clearl y reduced by PIX. The total length of vegetative branches and fruiting branches was 40% and 50% less than the control. Total leaf area in PI X treated plants was 16% less than the control. Net photosynthetic rat es were 25% less in PIX-treated leaves. PIX treated leaves had more ch lorophyll content. The activity of RuBP carboxylase was decreased in P IX treated plants. Starch accumulation was noticed in PIX treated leav es while sucrose content was not changed. The data reported here sugge st that reduced growth responses induced by PIX results in partial los s of photosynthetic capacity in cotton at least up to 20 days after ap plication of the growth regulator.