Photosynthetic efficiency of plants of Brassica juncea, treated with chlorosubstituted auxins

The leaves of 29-d-old plants of Brassica juncea Czern & Coss cv. Varuna were sprayed with 10(-6) or 10(-8) M aqueous solutions of indole-3-yl-acetic acid (IAA) or its substituted derivatives 4-CI-IAA, 7-Cl-IAA, and 4,7-Cl-2-IAA. All the auxins improved the vegetative growth and seed yield at harvest compared with those sprayed with de-ionised water (control). 4-Cl-IAA was most prominent in its effect, generating 21.6, 39.7, 61.0, 35.0, 65.5, and 56.2 % higher values for dry mass, leaf chlorophyll content, carbonic anhydrase (E.C. 4.2.1.1) and nitrate reductase (E.C. 1.6.6.1) activities, net photosynthetic rate, and carboxylation efficiency, respectively, in 60-d-old plants. It also enhanced the seed yield by 31.1 % over the control. The order of response of the plants to various auxins was 4-Cl IAA greater than or equal to 7-Cl IAA > 4,7-Cl-2 IAA = IAA > control.