Auxin and defoliation effects on photosynthesis and ethylene evolution in mustard

The aim of the work was to examine the effect of defoliation (50% lower or 50% upper leaves) and subsequent auxin treatment, at pre-flowering stage (40 days after sowing) on growth, net photosynthetic rate (P_N), photosynthetic water use efficiency (WUE), auxin, indole acetic acid (IAA) oxidase and ethylene evolution. Defoliation of upper leaves showed higher decrease in P_N and WUE compared to no defoliation and defoliation of lower leaves. Maximum auxin content and ethylene evolution was noted when upper leaves were removed, but IAA oxidase showed reverse trend. Finally, plant biomass was reduced with defoliation of upper leaves showing that the leaves in the region are more photosynthetically efficient than lower leaves. Application of auxins (IAA, IBA and NAA) helped in partial restoration of the decrease in the characteristics. The adaptive morphological changes of the plant are brought about by signals produced in the form of ethylene and auxin.