Water relations and osmotic adjustment in Apium graveolens during long-term NaCl stress and subsequent relief

To investigate the relationship between salt tolerance and plant mineral status in celery (Apium graveolens L.) growth and the concentration of N, P, K, Ca, Na and Cl in different tissues were determined in plants grown in hydroculture with nutrient solutions containing 5 (control), 50, 100 and 300 mM NaCl for 4 weeks. At salinity levels of 50 and 100 mM NaCl there was a moderate, albeit significantly, reduction of growth, while a drastic decrease in both fresh and dry weight was found at 300 mM NaCl. Regardless of the salinity level, growth resumed promptly and completely once the stress was ceased. NaCl stress reduced the accumulation of nitrate-N in all plant tissues, but there were no relevant effects on the concentration of reduced N and P. The concentration of K in roots and leaf petioles was unaffected by NaCl treatment, but it gradually declined with increasing salinity in leaf blades; this reduction was less pronounced in the young leaves as compared to the mature ones. Increasing NaCl concentration decreased the concentration of Ca in all tissues, but it prevented the occurrence of black-heart, a typical Ca-related physiological disorder which affected severely the controls. Salt-stressed plants absorbed large amount of Na and Cl, which were accumulated in the mature leaves, particularly in the oldest leaves. These findings suggests that the relatively high salt tolerance of celery relies on the ability to maintain an adequate nutritional status and to protect shoot meristem from salt toxicity