SPATIAL AND TEMPORAL ASPECTS OF GROWTH IN THE PRIMARY ROOT OF COTTON SEEDLINGS - EFFECTS OF NACL AND CACL2

Seedlings of cotton (Gossypium hirsutum L. cv. Acala SJ-2) were grown in modified Hoagland nutrient solution with various combinations of NaCl and CaCl2. Marking experiments and numerical analysis were conducted to characterize the spatial and temporal patterns of cotton root growth at varied Na/Ca ratios. At 1 mol m-3 Ca, 150 mol m-3 NaCl reduced overall root elongation rate to 60% of the control, while increasing Ca to 10 mol m-3 at the same NaCl concentration restored the elongation rate to 80% of the control. Analysis of the spatial distribution of elongation revealed that the presence of 150 mol m-3 NaCl in the medium shortened the growth zone by about 2 mm from the approximate 10 mm in the control and also reduced the relative elemental elongation rate (i.e. the longitudinal strain rate, defined as the derivatives of displacement velocity of a cellular particle with respect to position on root axis). Supply of 10 mol m - 3 Ca at the high salt condition restored partially the relative elemental elongation rate, but not the length of the growth zone. Compared to the control, the growth trajectories showed that at 1 mol m-3 CaCl 2 it took more time for a cellular particle to move through the growth zone at 150 mol m-3 NaCl, while at 10 mol m-3 CaCl it took less time and there was no difference between the NaCl treatments.