Comparison of nutrient uptake and antioxidative response among four Labiatae herb species under salt stress condition

Herbs of the Labiatae have relatively low salt tolerance. They are widely grown in drylands, but salt stress there is a typical problem and may reduce yields. To examine their salt tolerance mechanisms, we grew basil, sage, thyme, and oregano in nutrient solution containing 50mM NaCl and determined the biomass; contents of Na, K, and Mg in leaf blades, stems, and roots; contents of total chlorophyll, malondialdehyde (MDA), hydrogen peroxide in leaf blades; and activities of antioxidative enzymes in leaf blades. The salt tolerance decreased in the order of basil approximate to sage>thyme>oregano. The good salt tolerance of basil was explained by a significant increase in the activity of catalase, in addition to the low Na/K ratio of leaf blades due to the retention of Na in stems and roots and of K in leaf blades. The good salt tolerance of sage was explained by the low Na/K ratio in leaf blades and the prevention of lipid peroxidation by high antioxidative enzyme activities, despite its poorer management of nutrient uptake. In thyme, although catalase activity increased significantly to alleviate salt-induced oxidative stress caused by Na influx into all parts, low K and Mg allowed shoot weight in particular to decrease. In oregano, antioxidative responses appeared as significant increases in ascorbate peroxidase and glutathione reductase activity, and K was accumulated in leaf blades, but serious salt-induced oxidative stress caused by high Na influx into all parts reduced the growth of all parts. These results show that despite similar responses among species, salt tolerance is not necessarily the same. In this experiment, we revealed the salt tolerance mechanism of each of four Labiatae herbs by revealing their strengths and weaknesses in nutrient uptake and antioxidative responses.