| Seedlings of Suaeda salsa and Zea mays growing in Hoagland nutrient solutions were treated with different concentrations of NaCl and Na2COs. Then the changes in dry weight, root vitality and osmotic potential; the contents of ions, MDA, amino acid, organic acid, proline, soluble sugar; the activities of V-H+-ATPase, V-H+-PPase, SOD were determined.The purpose of the experiment was to see what differences there are on various growth and physiology parameters under NaCl and Na2CO3 stress. Furthermore, the reasons of different stress effects of NaCl and Na2CO3 on plant were investigated too. The main results of the experiment are as follows:1 The comparison of the stress effects of NaCl and Na2CO3 on Suaedasalsa L.The growth of Suaeda salsa could be promoted by certain concentrations of NaCl but inhibited markedly by Na2CO3 The change in root vitality was not significant under NaCl stress but significant under Na2CO3 stress. All of these mean that Suaeda salsa can resist NaCl stress effectively but can' t resist Na2CO3 stress effectively.One of the common stress factors of NaCl and Na2CO3 is Na+ toxicity. Under NaCl stress, the hydrolytic activity of V-H+-ATPase and V-H+-PPase in the leaves of Suaeda salsa both increased markedly, which improved the ability of Na+ compartmentation and that corresponded to its high ability of resistance to NaCl stress. Under Na2CO3 stress, although the hydrolytic activity of V-H+- ATPase in the leaves of Suaeda salsa increased (The extent of increase was less than that of NaCl stress ), the hydrolytic activity of V-H+-PPase did not change much. This limited the improvement of the ability of Na+ compartmentation in the leaves of Suaeda salsa, resulting in the Na+ content in cytoplasm was higher than that of NaCl stress. The serious Na+ toxicity was one of the reasons which concerned with the low ability of Na2COs resistance in Suaeda salsa.Under NaiCOs stress, the extent of Na+ content increase and K+ content decrease in the leaves of Suaeda salsa were both greater than that of NaCl stress. Because of this the homeostasis of Na+ and K+ was disturbed seriously which is also one of the reasons which concerned with the low ability of Na2CO3 resistance in Suaeda salsa. In addition, Ca and Fe are the essential elements to the living of plant. Under Na2CO3 stress, the extent of Ca2+ and Fe2+ decrease were also greater than that of NaCl stress.This is also concerned with the living inhibition of Suaeda salsa.Another common stress factor of NaCl and Na2CO3 is osmotic stress. Compared with NaCl treatment, under Na2CO3 stress, the organic osmotica played a more important role in osmotic regulation of Suaeda salsa which maybe resulted from the adaptive reaction to high pH value. But more energy will be used if the plant depends mainly onthe organic osmotica to regulate its osmotic potential. This is another reason which made Suaeda salsa can't resist Na2CO3 stress effectively.The sole stress factor of alkaline salt is its high pH value. One of the adaptive means of plants to high pH value is to accumlate acidic buffer (e.g., organic acid, citric acid, proline) to regulate its high pH value. But the content of organic acid decreased under stress which maybe concerned with the low ability of Suaeda salsa to resist stress. Under Na2CO3 stress, the content of proline increased, so proline must be a kind of buffer in Suaeda salsa.Under NaCl stress, the activity of SOD in leaves of Suaeda salsa increased. So the ability of scavenging reactive oxygen species (ROS) was enhanced and the injury caused by ROS was alleviated. On the contrary, under Na2CO3 stress, the activity of SOD decreased which made the ROS can not be scavenged timely. Overabundant ROS aggravated the injury to Suaeda salsa and decreased its resistance ability to Na2CO3 stress.On the whole, the ability of resistance to Na2CO3 stress in Suaeda salsa was less than that of NaCl stress.The reason for this is concerned with many aspects. For example, the improvement extent of the ability of Na+ compartmentati...
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