Thigmotropic responses of Oryza sativa L. to external rubbing stimulation

Our aim was to study the morphological and physiological responses of rice to rubbing stimulation. Rice was subjected to rubbing 30 times/day (R30), 60 times/day (R60), 90 times/day (R90) and 0 times/day (control) for 35 days. The height, elongation rates and second internode length were significantly decreased by the three treatments, whereas stem width increased significantly. The tiller number and chlorophyll contents of the top third and top fifth of leaves increased significantly after R30 and R60. In R90, the aboveground biomass was significantly decreased and dead leaf biomass was increased. In R30 and R60, the transpiration rates were 16% and 13% higher than in the control, whereas photosynthetic rates increased 25% and 23%, respectively. Root biomass was significantly increased in R30, and root/aboveground was enhanced in R90. Stomatal conductance and root triphenyltetrazolium chloride-deoxidizing ability was significantly increased by the three treatments. The SOD activities in all treatments and the control were similar after stimulation. POD and CAT activities increased significantly in R30 and R60, and malondialdehyde increased by 42% in R90. Membrane permeability in R30 and R60 decreased 26% and 15%, respectively. The calcium content and soluble protein content increased in R30, whereas the magnesium content decreased. The nitrogen content increased significantly in R30 and R60. The silicon content in the whole plant and the size of stomata increased significantly in the three treatments. Thus, rubbing stimulation had complex effects on rice growth.