Cadmium-induced reactive oxygen species generation, changes in morphogenic responses and activity of some enzymes in barley root tip are regulated by auxin

Morphogenic responses, ROS generation and changes in enzymes activity induced by the short-term exposure of barley roots to Cd were very similar to those of triiodobenzoic acid (TIBA) treatment. Both Cd and TIBA markedly increased the amount of IAA in root apex. In addition, the treatment of roots with TIBA before Cd treatment had an additive effect on morphogenic responses, changes in enzymes activity and ROS generation. In turn, the application of auxin efflux/influx inhibitor 1-naphthoxyacetic acid (1-NOA) before Cd treatment significantly reduced the Cd-induced ROS generation, root growth inhibition and enzymes activity in spite of the elevated level of IAA in the root apex. The auxin signalling inhibitor p-chlorophenoxyisobutyric acid (PCIB) nearly fully eliminated some of these Cd-induced responses. These results indicated that the short-term Cd treatment-induced ROS generation, morphogenic responses and activity of some enzymes can be attributed to the disturbance of IAA homeostasis in root apex. While auxin efflux inhibitor TIBA evoked similar response to Cd, auxin efflux/influx inhibitor 1-NOA attenuated and auxin signalling inhibitor PCIB blocked these Cd-induced responses suggesting that apart from the elevated level of IAA in root apex its enter and accumulation inside of until closely undetermined cells or tissues is a prerequisite for the induction of characteristic root responses to short-term Cd exposure.