The Synthesis of vitamins in plant photosynthetic tissue.

Many of the compounds that are involved in plastidic isoprenoid synthesis have important human nutrition impacts. There are two major classes of lipid soluble photosynthetic antioxidants.

1. Carotenoids - over 700 known compounds, usually involved in colour and pigmentation, these include b-Carotene and other precursors of Vitamin A (Retinaldehyde).
2. Tocochromanol - 4 tocopherols and 4 tocotrienols - vitamin E

The identification of many of the core genes that are involved in the pathways responsible for the synthesis of vitamins in the plastids have been discovered by an integrated approach that that has involved a combination of genetic, genomic and molecular approaches.

Knowledge of plastid genes helps to improve human health.

The identification of these genes has enabled metabolic engineering to take place; this has led to changes in the vitamin A and Vitamin E levels in many plants. This can have an enhanced effect upon human health. An example of this is Golden Rice, which contains an enhanced level of Carotenoids (vitamin A); this has helped many people get a sufficient quantity of Vitamin A in their diet, with out making any major changes in their diet (I will leave the arguments about the rights and wrongs of genetically modified foods to people with more passion and knowledge on the subject.

Synthesis of carotenoids and tocochromanol in the plastids

Both Carotenoids (vitamn A) and Tocochromanol synthesis occurs in the plastidic isoprenoid biosynthetic pathway. There are two distinct pathways that are involved in Isopetenylpyrophosphate production.

1. MEP - Methylerythritol 4-phosphate Pathway
2. Cytosolic Mevalonic acid pathway

The production of Isopetenylpyrophosphate in turn leads to the production of geranylgeranyl diphosphate, which is an intermediate in many plastidic isoprenoids such as tocochromanols and carotenoids.

The next section on plant vitamin synthesis takes a look at the biosynthesis of carotenoids