Changes in the cellular components of sugar beet under salt stress

The acclimation of a plant to a constantly changing environment involves the accumulation of certain organic compounds of low molecular mass, known collectively as compatible solutes, in the cytoplasm. Evidence from numerous investigations of plants strongly suggests that glycine betaine (GB), an amphoteric quaternary amine, plays an important role as a compatible solute under various types of environmental stress, such as high levels of salts and low temperature. In this work, sugar beet (Beta vulgaris) was grown at NaCl concentrations of up to 300 mmol/l soil, and the effects of salt on the growth, contents of water, chlorophyll, soluble protein, soluble saccharide and GB in leaf were measured. The addition of NaCl up to 300 mmol/l soil significantly affected the growth, and the contents of water and chlorophyll decreased, whereas the soluble protein and saccharide concentrations in the leaf changed little. On the other hand, the GB concentration increased 6-fold with increasing the salinity of the medium, suggesting that GB is a main osmoprotectant in this plant. The induction of GB was monitored by cultivating the plant seed under salt stress. It was found that the GB originally contained in the seed was lost during the early stage of cultivation, and new GB was synthesized in the stage of germination in a dose-dependent fashion with respect to the salt concentration.