In order to understand some physiological mechanism of chilling and cold sensitivity in plants we investigate the effects of chilling and cold stress on chlorophyll and proline content, lipid peroxidation and variable chlorophyll fluorescence (Fv/Fm) of Arabidopsis (thaliana L.) The four weeks-old plants (WT, and four chilling sensitive mutants [chs2-2], [chs2-1], [chs1-2] and [chs1-1]) were subjected to two different low temperature treatments (control (23^̊ C), chilling (13^̊ C) and cold (4^̊ C)), for one week. Fv/Fm and chlorophyll content changed significantly in all mutants except in WT by chilling stress (13^̊ C), compared with control and 4^̊ C treatments. Two out of four mutants, chs1-1 and chs1-2, had lowest chlorophyll content and Fv/Fm value among the tested genotypes. The proline content increased in all mutant genotypes, as well as in WT by chilling stress and 4^̊ C, compared with control. MDA content of shoots changed dramatically in all mutant genotypes except in WT by chilling stress, compared with control and 4^̊  C treatments. Our findings showed that two mutants, chs1-1 and chs1-2, have had highest chilling sensitivity among the tested genotypes and had the highest proline and MDA contents. It is possible that some damages in photosynthetic systems and/or in proline metabolism via mutation cause these plants more sensitive to chilling and cold stress

Keywords: chilling sensitive, chlorophyll content, Fv Fm, proline, MDA, Arabidopsis thaliana

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