Storage lipid formation in seeds

Abstract

The mechanisms and regulation of storage lipid formation in seeds are reviewed. Seed storage lipids are ultimately derived from simple carbon compounds, such as sucrose, which are imported into seeds from source tissues, such as leaves or pods. The partitioning of this important carbon towards storage lipid, carbohydrate or protein is regulated by a complex interaction between genetically-determined endogenous factors and external environmental influences. Storage lipids are synthesized from fatty acids, derived from acetyl-CoA, and glycerol 3-phosphate. Fatty acid biosynthesis and probably acetyl-CoA formation, occurs within the plastids to produce oleoyl-CoA. Further elaboration of oleoyl-CoA to produce polyunsaturates, hydroxylates or very long chain acyl-CoAs occurs on the endoplasmic reticulum, as does the esterification of acyl-CoAs to glycerol-3-phosphate to produce the final triacylglycerol storage oil. The temporal and hormonal regulation of storage lipid accumulation in seeds is discussed.

1-Acylglycerophosphocholine O-acyltransferase in maturing safflower seeds

“…Triacylglycerol is synthesized from sn-glycerol 3-phosphate (GP) and acyl-CoA by a series of sequential acylations accompanying dephosphorylation on the ER membrane (Murphy et al 1993). During the rapid TAG synthesis in seed development, interconversion occurs between the diacylglycerol (DAG) intermediate of the GP pathway and membrane PC (Slack et al 1985;Stobart and Stymne 1985a).…”

“…The linoleoyl moiety formed is released in the form of CoA derivative and utilized for the sequential acylations of GP to form TAG. In addition, PC is the substrate for the desaturation of linoleate to ~-and 7-1inolenate, for the hydroxylation of oleate to ricinoleate, and for the epoxidation of linoleate to vernolate (Bafor et al 1991(Bafor et al , 1993Murphy et al 1993). The incorporation of acyl moieties to be modified into 1-acyl-GPC and the release of some acyl moieties modified from PC depend on the activity of acyl-CoA: 1-acyl-GPC O-acyltransferase or lysolecithin acyltransferase.…”

The activity of acetyl-CoA carboxylase is not correlated with the rate of lipid synthesis during development of oilseed rape (Brassica napus L.) embryos

“…The principal fatty acids present in the seed storage oil also vary considerably between species (Murphy et al 1993). The pathway of de-novo fatty-acid biosynthesis has been studied extensively and is essentially the same in all plant tissues (Harwood 1988;Murphy et al 1993). However, the regulation of this pathway and of the Kennedy pathway of triacylglycerol synthesis is not so thoroughly understood.…”

The use of conventional and molecular genetics to produce new diversity in seed oil composition for the use of plant breeders-progress, problems and future prospects

“…In most plant species, the seeds contain all the enzymes required for the conversion of sucrose into all three classes of storage product . It is the rate of sucrose uptake by the various competing biosynthetic pathways, which eventually gives rise to a seed containing a particular storage product composition (Murphy et al ., 1993) .…”

“…The formation of storage oil from sucrose alone involves dozens of enzymes, any one of which may be a potential candidate for genetic manipulation (Murphy, 1993a ;Murphy et al ., 1993) . As a first step to investigating this process, several groups have selected the first and last enzymes of this pathway, in order to ascertain their contribution to oil yield in a developing seed.…”