Effect of cadmium and temperature on the lipoxygenase activity in barley root tip.

An analysis of different cell fractions isolated from barley roots revealed that lipoxygenase (LOX) activity occurred both extra- and intracellulary. Cadmium (Cd)-induced LOX activity was observed in the fraction containing cell walls, plasma membrane and the cytoplasm. High temperature-induced root growth inhibition and elevated LOX activity did not induce lipid peroxidation. In contrast, Cd inhibited root growth and caused both enhanced lipid peroxidation and elevated LOX activity at each of the temperatures analyzed. Spatial distribution studies revealed that the patterns of apoplastic LOX activity were different from those of cytoplasmic activity. Cd-induced intracellular LOX activity increased equally along the barley root tip, while Cd-induced apoplastic LOX activity was associated mainly with the differentiation zone of the barley root tip. Our results suggest the involvement of Cd-induced LOX activity in the premature differentiation of the barley root tip during Cd stress. We hypothesize that the role of LOX in plant metabolic processes in the root may depend on the level of reactive oxygen species in the roots: at physiological concentrations of ROS, LOX may be involved in the processes of root growth, while at the elevated harmful concentrations of ROS induced by different stress conditions, it may be involved in root growth inhibition through ectopic differentiation.