Effects of various salts on growth, ion and glycine betaine contents and enzyme expression of glycine betaine synthesis in Amaranthus tricolor

To identify the factors that control the adaptation of Amaranthus tricolor to salt stress, the effects of different salt applications on the growth, the ion and glycine betaine (GB) contents and the related enzyme (betaine aldehyde dehydrogenase, BADH and choline monooxygenase, CMO) expression were examined. Salt stress was induced by the daily addition of 150 mM of one of five different salts, NaCl, KCl, CaCl2, Na2SO4 and NaHCO3 to a growth medium for 7 days. All plants supplied with NaHCO3 died during the experiment. The growth of roots and leaves was significantly reduced by salt applications, being markedly decreased by 34.4% for roots and 63.9% for leaves for CaCl2 treatment when compared to that in non-salt plants. The tissue concentrations of sodium were significantly increased by supplemental NaCl and Na2SO4, and the chlorine content was also increased by KCl, NaCl, and CaCl2. The accumulation of sodium and chlorine was higher in leaves than in roots. The effects of salinity on sodium and chlorine transports to the leaves appear to play a major role in the adaptation of Amaranthus to salt stress. The lowest growth rate, induced by CaCl, coincided with the greatest foliar values for calcium ion. In salt-stressed plants, the chlorophyll content and the ratio of variable to maximum chlorophyll fluorescence (Fv / Fm) tended to decrease. GB content in leaves was higher for plants supplied with NaCl, KCl and Na2SO4 than for those with CaCl2 and controls, and it was associated with the appearance of CMO in the leaves. BADH protein was expressed in all treatments and the levels of BADH protein did not always vary among different salt treatments. The present results suggest that the increase in GB content in leaves plays a role in adaptation to salt stress and that CMO protein is important to GB synthesis under salt stress in A. tricolor, although the effect of the addition of different salts on CMO synthesis remains to be elucidated.