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Oxygen‐independent temperature regulation of the microsomal oleate desaturase (FAD2) activity in developing sunflower (Helianthus annuus) seeds
Author(s) -
MartínezRivas José M.,
SánchezGarcía Alicia,
Sicardo M. Dolores,
GarcíaDíaz M. Teresa,
Mancha Manuel
Publication year - 2003
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1034/j.1399-3054.2003.00039.x
Subject(s) - helianthus annuus , achene , sunflower , helianthus , linoleic acid , enzyme assay , horticulture , food science , fatty acid desaturase , enzyme , chemistry , biology , biochemistry , fatty acid , polyunsaturated fatty acid
The temperature and oxygen regulation of the microsomal oleate desaturase (FAD2, EC 1.3.1.35) activity has been studied in developing sunflower ( Helianthus annuus L.) seeds. In plants cultivated in growth chambers, the linoleic acid content in the seed lipids increased along the 25/15°C (day/night) cycle, except during the first hours of the warm period, where it decreased significantly. In contrast, FAD2 activity decreased notably at the beginning of the warm period, showing a small and continuous increase during the rest of the cycle. The temperature effect on the linoleic acid content and the FAD2 activity was also investigated using peeled seeds and detached achenes subjected to temperature changes. In peeled seeds, a change of temperature from 10 to 30°C brought about a significant decrease of FAD2 activity. On the contrary, when the temperature shifted from 30 to 10°C, FAD2 activity only increased slightly. Unlike peeled seeds, detached achenes showed a fast and dramatic increase or decrease in the level of FAD2 activity in response to a temperature change from 30 to 10°C, or from 10 to 30°C, respectively. The in vivo and in vitro thermal properties of the FAD2 enzyme were also studied. Optimal temperature and heat‐resistance profile showed similar patterns in both conditions. All these data support the hypothesis that temperature regulates FAD2 activity by two different and independent mechanisms: a direct effect, and an indirect effect affecting oxygen availability. Furthermore, these results suggest that the low thermal stability of the enzyme is the main factor responsible for the direct temperature effect on FAD2 activity.