Effects of NaCl and CaCl₂ on Water Transport across Root Cells of Maize (Zea mays L.) Seedlings

Abstract

The effect of salinity and calcium levels on water flows and on hydraulic parameters of individual cortical cells of excised roots of young maize (Zea mays L. cv Halamish) plants have been measured using the cell pressure probe. Maize seedlings were grown in onethird strength Hoagland solution modified by additions of NaCI and/or extra calcium so that the seedlings received one of four treatments: control; +100 millimolar NaCI; +10 millimolar CaC12; +100 millimolar NaCI + 10 millimolar CaC12. From the hydrostatic and osmotic relaxations of turgor, the hydraulic conductivity (Lp) and the reflection coefficient (a.) of cortical cells of different root layers were determined. Mean Lp values in the different layers (first to third, fourth to sixth, seventh to ninth) of the four different treatments ranged from 11.8 to 14.5 (Control), 2.5 to 3.8 (+NaCI), 6.9 to 8.7 (+CaCI2), and 6.6 to 7.2. 10-7 meter per second per megapascal (+NaCI + CaC12). These results indicate that salinization of the growth media at regular calcium levels (0.5 millimolar) decreased Lp significantly (three to six times). The addition of extra calcium (10 millimolar) to the salinized media produced compensating effects. Mean cell as values of NaCI ranged from 1.08 to 1.16, 1.15 to 1.22, 0.94 to 1.00, and 1.32 to 1.46 in different root cell layers of the four different treatments, respectively. Some of these a, values were probably overestimated due to an underestimation of the elastic modulus of cells. os values of close to unity were in line with the fact that root cell membranes were practically not permeable to NaCI. However, the root cylinder exhibited some permeability to NaCI as was demonstrated by the root pressure probe measurements that resulted in as,r of less than unity. Compared with the controls, salinity and calcium increased the root cell diameter. Salinized seedlings grown at regular calcium levels resulted in shorter cell length compared with control (by a factor of 2). The results demonstrate that NaCI has adverse effects on water transport parameters of root cells. Extra calcium could, in part, compensate for these effects. The data suggest a considerable apoplasmic water flow in the root cortex. However, the cell-to-cell path also contributed to the overall water transport in maize roots and appeared to be responsible for the decrease in root hydraulic conductivity reported earlier (Azaizeh H, Steudle E [1991] Plant Physiol 97: 1136-1145. Accordingly, the effect of high salinity on the cell Lp was much larger than that on root Lpr.

Does calcium ameliorate the negative effect of NaCl on melon root water transport by regulating aquaporin activity?

“…The results clearly showed that there was a very great decrease in osmotic water permeability in NaClstressed protoplasts. That finding was observed for the first time in membranes of a higher plant by Azaizeh et al (1992), who reported in response to NaCl reductions of one order of magnitude in the hydraulic conductivity of maize cortical cells, compared with the control, being 10 −' and 10 −( m s −" MPa −" for the control and NaCl-treated cells, respectively. After conversion of our data from P f to L p , the values were in the range 0.2-1.1 10 −( m s −" MPa −" , in agreement with those found in the literature for different species (Steudle et al, 1987 ;Zhu & Steudle, 1991).…”

Salinity–mineral nutrient relations in horticultural crops

“…Water transport properties of maize primary roots are adversely affected by NaCl-induced morphological and anatomical changes (Evlagon et al, 1990;Neumann et al, 1994). Supplemental calcium tended to reverse or prevent these changes and mitigated reductions in root hydraulic conductivity (Evlagon et al, 1990(Evlagon et al, , 1992Azaizeh and Steudle, 1991;Azaizeh et al, 1992;Neumann et al, 1994).…”

Calcium induces salinity tolerance in pistachio rootstocks

“…The primitive effects of Ca 2+ on seed germination and seedling growth of P. vera, especially in the Ghazvini rootstock in salt treatments, would have resulted, at least partly, from reduced efflux of K + (and possibly other solutes) from the seedlings, and eventual maintenance of a low Ψ W of seedling water. Additionally, it is possible that Ca 2+ alleviated the reduction in cell wall extensibility caused by salts and/or water conductance of the plasma membrane [13,14] in P. vera cv. Ghazvini seedlings, thus favouring water uptake and extension growth.…”

“…Secondly, NaCl causes hardening of the cell wall [12] and a decrease in water conductance of the plasma membrane [13,14]. These effects of NaCl on cellular functions are alleviated by the addition of Ca 2+ to the external medium [9,11,13].…”