Abstract
In higher plants, fatty acids (FAs) with 18 carbons (18C) represent about 70% of total FAs, the most abundant species being 18:2 and 18:3. These two polyunsaturated FAs (PUFAs) represent about 55% of total FAs in Arabidopsis cell suspension cultures, whereas 18:1 represents about 10%. The level of PUFAs may vary, depending on ill-defined factors. Here, we compared various sets of plant cell cultures and noticed a correlation between the growth rate of a cell population and the level of unsaturation of 18C FAs. These observations suggest that the final level of PUFAs might depend in part on the rate of cell division, and that FAD2 and FAD3 desaturases, which are respectively responsible for the formation of 18:2 and 18:3 on phospholipids, have limiting activities in fast-growing cultures. In plant cell culture, phosphate (Pi) deprivation is known to impair cell division and to trigger lipid remodeling. We observed that Pi starvation had no effect on the expression of FAD genes, and that the level of PUFAs in this situation was also correlated with the growth rate. Thus, the level of PUFAs appears as a hallmark in determining cell maturity and aging.
Highlights
Process involving desaturation of the acyl groups followed by a rapid deacylation-reacylation cycle that exchanges fatty acids (FAs) from PC with FAs from the acyl-CoA pool[10]
These cells are growing either heterotrophically (Sycamore cells, Arabidopsis calli) or mixotrophically (Arabidopsis cells) and display only amyloplasts (Sycamore cells and Arabidopsis calli) or poorly developed thylakoid membranes with low amount of chlorophyll (Arabidopsis cells). This suggests that PUFAs in our plant models are mostly generated by the FAD2/FAD3 system in the ER, with a minor but significant contribution of the FAD6/ FAD7 couple in plastids. This composition is highly different in leaves where galactolipids represent more than 60% of glycerolipids[24], suggesting that FAD2 and FAD3 might not be the main providers of PUFAs in these tissues
These variations might be a source of information, and we looked for a possible correlation between the growth rate and the variability of the FA unsaturation level we often observed in these cultures
Summary
Process involving desaturation of the acyl groups followed by a rapid deacylation-reacylation cycle that exchanges FAs from PC with FAs from the acyl-CoA pool[10]. In addition to transcriptional controls[5,18], post-translational regulations of these desaturase activities might contribute to adjust the desaturation level in plants From this point of view, it was shown that FAD221 and FAD322 are less subjected to degradation at low temperatures, a process controlled by the proteasomal pathway that might play a role in this adaptative response. Beside these known environmental effects on the unsaturation level of FAs, other ill-defined factors may alter the level of PUFAs. Beside these known environmental effects on the unsaturation level of FAs, other ill-defined factors may alter the level of PUFAs This is apparent with cell suspension cultures where the extent of PUFAs may vary from one culture to another, making the comparison of results sometimes difficult. Using cell suspension cultures that mainly contain phospholipids, we observed a correlation between the growth rate and the level of unsaturation of 18C FAs, suggesting that FAD2 and FAD3 desaturases might have limiting activities in fast growing cultures and that the final level of unsaturation might depend on the rate of division of the plant cell population
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