POTASSIUM TRANSPORT AND PARTITIONING ALLEVIATES TOXIC EFFECTS OF SODIUM ON YOUNG PHYSIC NUT PLANTS

A number of studies have pointed out how potassium can alleviate the effects of sodium toxicity on plants. However, the mechanisms of interaction between these two ions at the whole plant level are poorly understood so far. This study assessed some physiological mechanisms involved with the K-Na interaction in Jatropha curcas seedlings exposed to salinity. The experiment was carried out in a completely randomized, 2 x 2 factorial design (two Na and K levels in nutrient solution, with five replications). The plants were exposed to the following treatments: K0Na0 (absence of both Na and K), K0Na1 (0 mmol L-1 K and 50 mmol L-1 Na), K1Na0 (10 mmol L-1 K and 0 mmol L-1 Na) and K1Na1 (10 mmol L-1 Kand 50 mmol L-1 Na). After the test period, the results showed a strong antagonistic interaction in terms of K and Na transport rates in roots, stems and leaves. Without [K](ext) in the nutrient solution, the Na transport rate in physic nut leaves was high, contributing to an excessive accumulation of this ion in the shoot and inducing toxicity symptoms in leaves. Conversely, the presence of adequate K levels alleviated the excessive accumulation of sodium in various plant parts, causing a decrease in the xylem Na flux rate. These data suggest that [K](ext) can mitigate the adverse effects of sodium excess and reduce sodium contents in Jatropha curcas tissues.