Comparison of Ca effect on the salt tolerance of suspension cells and intact plants of tobacco (Nicotiana tabacum L., cv. Bright Yellow-2)

Salt tolerance and the effect of Ca application on the salt tolerance were compared between suspension culture cells and intact plants of tobacco (Nicotiana tabacum L., cv. Bright Yellow-2). The suspension culture cells and intact plants of tobacco were grown in a culture medium without NaCl and with 100mM NaCl containing 0.3 or 10 mM CaCl2. At 7 d after the treatment, the dry weight of the cells and intact plants grown in the medium containing 100mM NaCl with 0.3mM CaCl2 decreased and the decreasing rate of the weight was much higher in the intact plants. In the medium containing 100mM NaCl with 10mM CaCl2, the growth of the cells and intact plants was improved, and the improvement of the growth by Ca application was much more significant in the cultured cells. Sodium content in the intact plants markedly increased with the increase of the NaCl concentration, compared to that in the cells. Calcium application decreased the Na content both in the cells and intact plants and the decreasing rate was higher in the cells than in the intact plants. Thus, it was suggested that the growth inhibition and the increase of the Na content under 100mM NaCl conditions were more pronounced in intact plants, and that the alleviatory effect of Ca on the growth inhibition was much more conspicuous in the cells. Although the contents of total Ca and pectic acid-binding Ca in the cells and plant roots decreased with the increase of the NaCl concentration, they increased by Ca application. The activity of plasmalemma ATPase of the cells and plant roots decreased in the medium containing 10mM NaCl with 0.3 mM CaC12, but increased by Ca application, regardless of the NaCl concentration. In summary, Ca application to the culture medium containing 100mM NaCl alleviated the growth inhibition, and the difference in the growth inhibition induced by 100mM NaCl between the suspension culture cells and intact plants was closely related to that in the Na content. It appears that the alleviatory effect of Ca on the growth inhibition might be caused mainly by the enhancement of the Na-excluding function. The high content of pectic acid-binding Ca on the cell wall also contributed moderately to the alleviatory effect of Ca through the decrease of apoplasmic Na translocation.