Effect of external Ca²⁺ in the Na⁺ and K⁺ content in cashew exposed to salinity

Abstract

To evaluate the effect of external Ca²⁺ on Na⁺ and K⁺ absorption and transport in dwarf cashew seedlings exposed to high levels of NaCl, seeds of the cashew clone, CCP 06, were germinated and grown in vermiculite inside a greenhouse. Seedlings with about 8 leaves were transferred to controlled temperature conditions at 25 ± 2°C, RH 80%, 12 h photoperiod and 240 ?mol m^-2 s^-1, where they were divided into two trials. In the first one, the roots were detached from the shoot and immersed into NaCl solutions (0; 100; 200; 300; 400 mM) + CaCl₂ (0.0; 0.3; 5.0 mM). In the second trial, intact seedlings were immersed in NaCl solutions (0; 200 mM) + CaCl₂ (0; 3 mM). The seedlings remained in the solutions above for 48 hours period. The NaCl increased the Na⁺ absorption and accumulation in different organs of the seedlings and reduced the K⁺ content in the roots and stems. The presence of external Ca²⁺ in the environment with NaCl increased even more the Na⁺ absorption and accumulation in different organs of the seedlings and it also retained the K⁺ content in the organs at the level of the control treatments. The effect of Ca²⁺ in increasing the Na⁺ absorption and transport remains unknown.  However, this effect on cashew plants seedlings exposed to high doses of NaCl is very evident.