Abstract:

The thylakoid membrane inside the chloroplast is the position where the light reaction of photosynthesis takes place, therefore, its structure and function are nearly correlative with photosynthesis of the plant leaves. Glysinebetaine (GB) is a quaternary ammonium compound. Several authors have studied the function of GB as an osmoprotectant in the adaptation to water, salt and cold stress. The objectives of this study were to determine the effects of salt stress on the structure and function of thylakoid membrane and the protection of GB on it under salt stress condition. Two wheat (Triticum aestivum L.) lines HF9703 (drought-tolerant) and SN215953 (drought-sensitive) were used in these examinations. 100 mmol/L NaCl was used to induce salt stress condition. 1.5 mmol/L GB was used to study the function of GB on protecting thylakoid membrane from the damage of salt stress. The seedlings of two wheat lines were pretreated with Hoagland solution containing 1.5 mmol/L GB for 72 h, and then cultured with Hoagland solution containing 100 mmol/L NaCl for 48 h. The seedling leaves were used to study the effects of GB on the fatty acid composition and function of thylakoid membrane under salt stress. The results indicated that the level of linolenic acid (18∶3) in phosphatidylglycerol (PG) and phosphatidylcholin (PC) of SN215953 were decreased significantly by salt stress (Table 2), while it was only the level of linolenic acid (18∶3) in PC of HF9703 was decreased markedly by salt stress (Table 1). The decrease GB could be alleviated well by GB (Table 1, Table 2). Ca²⁺-ATPase activity of thylakoid membrane (Fig.3), Hill-reaction activity (Fig.4), chlorophyll content (Fig.2) and photosynthesis (Fig.5) were decreased markedly under salt stress, and that did more markedly in SN215953 than in HF9703. These effects of salt stress on thylakoid membrane were also ameliorated by GB. The salt tolerance of different wheat lines was accordant with their drought tolerance character, but there was some difference between them also. Discussions were made on the possible mechanism of the effects of salt stress on fatty acid composition and function of thylakoid membrane, as well as the presumable mechanism of the effects of GB on alleviating the change of fatty acid composition and improving the function of thylakoid membrane. However, the affirmable mechanism about it needs to be studied further.

Key words: Wheat, Glycinebetaine, Salt stress, Fatty acid of thylakoid membrane, Ca²⁺-ATPase activity, Hill -reaction