Effect of plant growth rtgulators on photosynthesis in cotton (Gossypium hirsutum L.) under waterlogging

Thirty five to forty days old (vegetative stage) cotton plants were subjected to 2 and 8 days of waterlogging. One day prior to waterlogging, the plants were sprayed with 5×10⁻⁵ M of various plant growth regulators (PGRs) and gas exchange studies were conducted immediately after termination of waterlogging periods. These observations were repeated during revival periods. Various PGRs under field capacity (FC) enhanced net photosynthesis (pn), water use efficiency (WUE), quantum yield (QY) and mesophyll conductance (MC) while decreased stomatal conductance (SC) and transpiration (E) at vegetative stage. With increasing duration of waterlogging SC, Pn, E and QY decreased while WUE and MC increased. During waterlogging different gas exchange parameters were modified with PGRs in variable ways particularly by IAA, GA₃ and BAP. With increasing revival period from waterloging SC, Pn and E improved while MC decreased. After 10 days of revival from waterlogging SC increased with GA₃ and BAP. BAP increased WUE after revival from 8 days of waterlogging.