Effect of the interaction between light and touch stimuli on inducing curling seminal roots in rice seedlings.

Root development is sensitive to environmental stimuli. We have recently reported that the light signal could promote the helical growth of seminal roots and drive the wavy root morphology in rice (Oryza sativa L.) young seedlings. The light-stimulated wavy roots were mostly performed in indica-type rice varieties (e.g. Taichung Native 1; TCN1) but not in japonica rice (e.g. Tainung 67; TNG67). Here, we demonstrated that the light-driven circumutation trajectory of TCN1 seminal roots could be changed if the seedling roots were grown in the medium containing high concentration of Phytagel. The data showed the root morphology would be modulated from wavy to curling when the Phytagel concentration was increased to 2%. However, the touch-stimulated curling root phenotype could not be performed in dark. In addition, the touch-induced curling roots were not appeared in the TNG67 rice cultivar. Although touch stimuli could not induce wavy/curling root phenotype in dark, it could modify the light-promoted helical growth to conduct curling roots in TCN1 rice seedlings. Thus, it was suggested that there is a crosstalk mechanism between touching-induced root curling and light-stimulated root waving.