Ionic relations and proline accumulation in shoots of two Chinese Iris germplasms during NaCl stress and subsequent relief

Adaptation to salinity in plant includes not only their response to stress, but also their ability to recover from it. Seeds of Chinese Iris (Iris lactea var. chinensis) collected randomly from an arid area in inland province of Xinjiang (Xj, E93A degrees 30('), N42A degrees 48('), 740 m), and a semi-arid coastal area in Beijing Municipality (Bj, N40A degrees 34('), E116A degrees 10('), 540 m) were studied. The objectives were to determine differences between germplasms in ionic relations or accumulation of proline in the shoots and establish how I. lactea adapts to salt stress and subsequent relief. Hydroponically-grown seedlings of the two germplasms were supplied with nutrient solutions containing 0.1 (control), 140 and 280 mM NaCl for 12 days, and supplied subsequently with a non-saline control solution for 12 days to relieve NaCl stress. Germplasm Xj had larger shoot mass and shoot/root ratio than Bj during stress and recovery periods. Salinity, even subsequent recovery, more adversely affected the water content in Bj than Xj. Under identical provision of treatments, the Xj maintained relatively higher K+/Na+ ratio and selectivity for transportation of K+ over Na+ than Bj. Additionally, we observed a slight proline accumulation in shoots of Bj, but its content was insufficient for lowering the solute potential. Germplasm Xj exhibits better adaptation to salinity and subsequent recovery. This is mainly due to its higher selectivity for transporting K+ over Na+. Proline accumulation did not play a key role the osmotic adjustment of the two I. lactea germplasms studied.