Effects of Two Exogenous Phytolectins on Outer Envelope Membrane of Chloroplasts from Young Leaves of Fraxinus mandshurica under Freezing Stress

Fraxinus mandshurica is one important tree specie for plantation in the northeastern forest region of China. Its seedlings often suffer from late frosts. It is practically significant to increase the tolerance to freezing of its seedling and to lengthen their growth period. The chloroplasts were isolated from young leaves, then soybean lectin and peanut lectin was bound to the outer envelope membrane. Afterwards the chloroplasts were frozen at -10 ℃ for 3 h.The effects of the two lectins on fluidity of the outer envelope membrane were different. The hydrophobicity of soybean lectin was less than that of peanut lectin. Soybean lectin reduced while peanut lectin increased the fluidity of fatty acyl chains and glycerol backbone, which was related with their hydrophobicity. This suggested that peanut lectin had cryoprotective effects on the outer envelope membrane of chloroplasts.