Integration of Root Border Cells in Salt Stress Response of Thai Jasmine Rice

Salt stress is a challenge at the diverse cellular and organismic levels. However, a historical point of view neglects the role of root border cells (RBCs), considering RBCs as a simple passive mechanical barrier sacrificed during root elongation. Here, we investigate the time kinetics of salt stress (60 mM NaCl, 21 days) in Oryza sativa L. cv. KDML105. Multiplicative analyses include standard growth variables of root and shoot, as well as root architecture, RBC number and mucilage layer thickness. We find a proportion (12%) of 4-day old seedlings responding already within 1 day to salt stress. Reduced root growth associates with RBC number and mucilage layer thickness. Moreover, analyses of time kinetics extract regressions with logistic (R & GE; 0.9965, P & LE; 0.0831) and Lorentzian models (R & GE; 0.9965, P & LE; 0.0193). The resulting times of half-maximum responses of 13 growth variables reveal an increasing order, ranking from root fresh weight and water (< 1 h) to adventitious root number (94 days). Notably, this order determines a logistic regression of response time (R = 0.9521, P < 0.0001). Finally, RBC developmental production depends on root length by lognormal 3-parameter distribution (R = 0.9302, P = 0.0024). We suggest RBCs for an essential active role in rice salt stress, i.e., mucilage secretion as fast non-osmotic salt stress response followed by RBC number. Both RBC parameters are promising for eco-physiological multiplicative models.

Automated summary

Salt stress negatively affects root growth, root border cell (RBC) number, and mucilage layer thickness in rice. Time kinetics analysis reveals that a small portion of seedlings already respond to salt stress within one day. These findings are important for understanding the mechanism of salt stress resistance in rice and for constructing models.