Low temperature treatments induce an increase in the relative content of both linolenic and delta3-trans-hexadecenoic acids in thylakoid membrane phosphatidylglycerol of squash cotyledons
1997
Xu, Y. | Siegenthaler, P.A.
The effect of low temperatures on the fatty acid composition of phosphatidylglycerol (PG) in thylakoid membranes, in particular on the ratios of nmol% 16:1(3t) (mg fresh weight)-1 of cotyledons and nmol 16:1(3t) (mg chlorophyll)-1 were measured during squash seedling growth. Plants were germinated and grown for one day at 30 degrees C, then were either kept at 30 degrees C (control plants) or transferred to low temperatures (18, 14 or 10 degrees C). When plants were transferred from 30 degrees C to low temperatures, the increase in fresh weight was gradually limited. The lower the temperature, the smaller was the fresh weight. In contrast, the relative content of 16:1(3t) and 18:3, as well as the ratios of nmol 16:1(3t) (mg chlorophyll)-1 and mol% 16:1(3t) (mg cotyledon fresh weight)-1 increased indicating that the increase of fresh weight and chlorophyll was more sensitive to low temperature than PG desaturation in thylakoid membranes. Furthermore, low temperatures induced an increase in 16:1(3t) and 18:3 (the final products of PG synthesis) at the expense of 16:0 and 18:1 (the initial products of PG synthesis). However, within a range of temperature from 10 to 18 degrees C, the extent of these changes (nmol% of 18:3 or 16:1(3t) per day) was gradually limited by lower temperatures. We therefore propose that low temperatures inhibit both fatty acid synthesis and desaturation activities. However, at low temperatures the fatty acid synthesis is likely to be more strongly inhibited than the desaturation activities, thus explaining the observed increase in the relative content of PG-18:3 and PG-16:1(3t). Results are discussed in terms of the mechanism which could be involved in the metabolism of PG in squash cotyledons.
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