Light-dependent Induction of Polyunsaturated Fatty Acid Biosynthesis in Greening Cucumber Cotyledons

Abstract

Greening cucumber ( Cucumis sativus L.) cotyledons exhibited dramatic increases in the ability to desaturate exogenously added 11-t4CIoleic acid and II_14Cllinoleic acid within 2 to 3 hours of illumination. These increases were effectively inhibited by 10 micrograms per milliliter cycloheximide. Oleate desaturation remained at a high level in constant light for 5 to 6 days after induction and then declined by about 50%; when returned to the dark, the tissue showed a sharp decrease in conversion of 114CIoleate to 114Cllinoleate. Linoleate desaturation reached a maximum about 15 hours after induction and declined immediately thereafter while the tissue still was in the light; after induction had peaked return of the tissue to the dark showed a dramatic fall of linoleate desaturation. The changes in desaturation were correlated with the conversion of the principal fatty acid in the etiolated cotyledons, linoleate, to a-linolenate, and with the assembly of the chlorophyll-containing photosynthetic membranes. The incorporation of 11-4Clacetate into lipids showed no significant light stimulation. The role of light in the regulation of certain aspects of plant metabolism during development is discussed.

Temperature regulation of oleate desaturase in sunflower (Helianthus annuus L.) seeds

“…In the first two organisms the effect has been shown using inhibitors of protein synthesis before the shift to low temperature and in Pimelodus by comparing the Vmax and Km of the microsomal A6-desaturase obtained from fish maintained at low or high temperature. Cycloheximide inhibits protein synthesis in eukaryotic cells and has been shown to inhibit the light-mediated induction of oleate-desaturase synthesis in greening cucumber (Murphy and Stumpf 1979). In seeds, the longterm effect produced by accumulation of specific fatty acids in the lipid molecules can be induced by changing the growth temperature over a 24-h period in developing soybean and linseed (Slack and Roughan 1978).…”

Regulation of 5-Aminolevulinic Acid Synthesis in Developing Chloroplasts

“…On the other hand, the ALA synthesizing capacity of barley plastid stroma changed very slowly when greening seedlings were transferred from light to dark (18). This difference between cucumber cotyledons and grass leaves in the rapidity of the light responses was noticed also by Stumpf and coworkers (13,22) working on fatty acid desaturation in cucumber and maize. In cucumber, Murphy and Stumpf (22) observed fast light responses which were inhibited by cycloheximide, whereas in maize the same process was largely light independent (13).…”

“…This difference between cucumber cotyledons and grass leaves in the rapidity of the light responses was noticed also by Stumpf and coworkers (13,22) working on fatty acid desaturation in cucumber and maize. In cucumber, Murphy and Stumpf (22) observed fast light responses which were inhibited by cycloheximide, whereas in maize the same process was largely light independent (13). Therefore, the possibility must be considered that this difference in the light regulation of ALA synthesis between cucumber and barley reflects a broader difference in the way in which chloroplast development is controlled by light in different angiosperm tissues.…”

Purification and characterization of a plant peroxisomal Δ2,Δ3‐enoyl‐CoA isomerase acting on 3‐cis‐enoyl‐CoA and 3‐trans‐enoyl‐CoA

“…9A). Within the storage lipid of cucumber cotyledons, linoleic acid is the dominant fatty acid moiety [31]. The isomerase activity acting on long-chain 3-trans-enoyl-CoA species is required, as during the metabolism of linoleic acid the catalysis of 2,4-dienoylCoA reductase leads to 3-trans-decenoyl-CoA [4].…”