KINETICS OF MAIZE LEAF ELONGATION .2. RESPONSES OF A NA-EXCLUDING CULTIVAR AND A NA-INCLUDING CULTIVAR TO VARYING NA/CA SALINITIES

Salinity causes physiological and morphological changes in plants and calcium can mitigate many of these effects. In this study, the effects of salinity (75 mol m-3 NaCl) with or without supplemental Ca (10 mol m-3) on the kinetics of maize (Zea mays L.) leaf elongation were examined using Linear Variable Differential Transformers (LVDTs). Short-term growth responses of two cultivars (Dekalb hybrid XL75 and Pioneer hybrid 3906) differing in salt tolerance were compared. Salinity caused an immediate reduction in the leaf elongation rate (LER). Within 2 h, elongation rates had increased and reached new steady rates. Significant differences between salinity treatments with high and low Ca could be detected within the first 2 h after imposition of salinity for Dekalb hybrid XL75, but not for Pioneer hybrid 3906. After 24 h, distinct differences for both cultivars were detected. Dekalb hybrid XL75, a Na-includer, was more salt-sensitive and responsive to supplemental Ca (10 mol m-3) than Pioneer hybrid 3906, a Na-excluder. Turgor was not reduced 24 h after salinization because there was complete osmotic adjustment in the elongation zone of the leaves. Analysis of the growth parameters limiting LER indicated that the yield threshold (Y) was increased for salt-stressed plants. In addition, both the cell wall extensibility and hydraulic conductance were reduced 24 h after salinization. Supplemental Ca increased LER of salt-stressed plants by increasing hydraulic conductance. The differences in LER of the two cultivars under saline conditions was attributed to differences in the increase of Y caused by salinity.