Abstract
The fab1 mutant of Arabidopsis thaliana, which contains increased levels of saturated fatty acids, was indistinguishable from the wild type when it was grown at 22 or 12 degrees C. During the first 7 to 10 d after transfer to 2 degrees C, the growth and photosynthetic characteristics of the fab1 plants remained indistinguishable from the wild type, with values for the potential quantum efficiency of photosystem II decreasing from 0.8 to 0.7 in plants of both lines. Whereas wild-type plants maintained quantum efficiency of photosystem II at approximately 0.7 for at least 35 d at 2 degrees C, this parameter declined rapidly in the mutant after 7 d and reached a value of less than 0.1 after 28 d at 2 degrees C. This decline in photosynthetic capacity was accompanied by reductions in chlorophyll content and the amount of chloroplast glycerolipids per gram of leaf. Electron microscopic examination of leaf samples revealed a rapid and extensive disruption of the thylakoid and chloroplast structure in the mutant, which is interpreted here as a form of selective autophagy. Despite the almost complete loss of photosynthetic function and the destruction of photosynthetic machinery, fab1 plants retained a substantial capacity for recovery following transfer to 22 degrees C. These results provide a further demonstration of the importance of chloroplast membrane unsaturation to the proper growth and development of plants at low temperature.