We have studied the photosynthetic adaptability of amaranth under salt stress, the synthesis and expression of betaine, the osmotic regulator, the dynamics of changes in photosynthetic rate and betaine content after salt treatment, and the effects of different kinds of salt on the growth, ion absorption and betaine content of amaranth. We found that when amaranth cultivated in the artificial culture room was treated with 300mmol · L NaC1, its growth, photosynthetic rate and transpiration rate were inhibited, The content of betaine in leaves increased up to 40 times. Considering the close relationship between plant reaction after salt treatment and environmental conditions such as temperature, illumination and humidity, the effects of different concentrations of NaC1 on the growth, photosynthetic rate, betaine content and ion absorption of amaranth seedlings were studied under greenhouse conditions.

After treating amaranth seedlings with different concentrations of NaC1 from the lower part of the nutrient bowl for 5 days, the growth of the seedlings was inhibited to varying degrees, of which 500mmol · L was the most significant, and the expansion of new leaf area slowed down with the increase of NaC1 concentration. However, even under 500rmnol · L NaC1, it was observed that the leaf area expanded and the growth was slow. After 5 days of treatment, the net photosynthetic rate, transpiration rate and stomatal conductance decreased with NaC1 treatment, and the inhibition degree increased with the increase of NaC1 concentration.

The reason why halophytes can tolerate the high concentration of ions in cells is that these ions are mainly accumulated in the liquid cells, and the osmotic pressure of the cytoplasm is mainly regulated by neutral organic solutes that are harmless to metabolic reactions. The concentration of betaine in the cytoplasm was 16 mmol · L~, but only 0.24 mmol · L~in the cytoplasm. Amaranth is a mesophyte with strong salt tolerance. It has similar properties with halophytes, that is, under salt stress, it can accumulate high concentrations of Na, Cl - and neutral organic solute betaine in its leaves.

Betaine as a neutral osmotic regulator has attracted extensive attention in the study of plant resistance. The content of betaine increased by 50% - 200%. The content of betaine increased obviously under the salt concentration with weak growth inhibition; When the inhibition of growth exceeds 50%, the content of betaine will not increase.