Na+ Retention in the Root is a Key Adaptive Mechanism to Low and High Salinity in the Glycophyte, Talinum paniculatum (Jacq.) Gaertn. (Portulacaceae)

Talinum paniculatum is an important leafy vegetable and medicinal plant, used in many parts of South America, Africa and Asia. Its adaptation to abiotic stress has received little attention and therefore worthy of interest, especially as environmental conditions are rendering arable lands increasingly unfavourable for agriculture. Therefore, this study was undertaken to examine the influence of salt stress on the vegetative growth of the plant by subjecting seedlings to 0, 25, 50, 100, 200 and 300 mm NaCl stress for 10 days. The dry weight, ion concentrations, relative water content, oxidative damage, proline, osmotic potential and some antioxidants were determined. The plants were found to retain Na+ mainly in the root, with less affected leaf K+ concentration, and consequently very low shoot Na+/K+ ratios (<0.2) under all the stress treatments. The proline content significantly increased under the 100–300 mm treatments (18- to 244-fold), with a corresponding significant reduction in osmotic potential and hence high osmotic adjustment. The antioxidant enzyme activities and non-enzyme antioxidants showed significant increase only under the highest salinity. Taken together, these results suggest that shoot Na+ exclusion is characteristic of this plant and is mainly responsible for its adaptation to low salinity.