Salt stress of two rice varieties: root border cell response and multi-logistic quantification

How to capture the rice varieties salt stress sensitivity? Here, we measure responses of root border cells (1 day, +/- 60 mM NaCl) and apply multi-logistic quantification of growth variables (21 days, +/- 60 mM NaCl) to two rice varieties, salt-sensitive IR29 and tolerant Pokkali. Thus, logistic models determine the maximum response velocities (Vmax) and times of half-maximum (T0) for root border cell (RBC) and growth parameters. Thereof, seven variables show logistic models (0.58 < R <= 1) and monotonous responses in both Pokkali and IR29: root to shoot ratio by water content, primary root length, shoot water, adventitious root number, shoot dry and fresh weight, and root dry weight. Moreover, the regression to lognormal distribution (R = 0.99) of these seven Vmax fractionated by T0 represents the rice variety's comprehensive response. Its quotient IR29/Pokkali is peaking at 98-fold higher velocity of IR29, thus capturing the variety's sensitivity. Consequently, our finding of 66-fold higher Vmax of primary root length response of IR29 indicates an essential salt sensor in the root, including RBC. Finally, the effects of salt stress on RBC confirm multi-logistic quantification, showing 36% decrease of RBC mucilage layer in IR29, without change in Pokkali. Inversely, RBC number of Pokkali increases 43% without change in IR29. Briefly, this suggests both RBC and multi-logistic quantification for the screening for salt tolerance in two thousand rice varieties.