While ascorbic acid (vitamin C) is a familiar molecule
because of its dietary significance, most aspects of its
metabolism and some aspects of its function in plants are
very poorly understood. For example, its biosynthetic
pathway has not been firmly established even though it
reaches millimolar concentrations in most tissues. Humans
and some other animals (including other primates and
guinea pigs) depend on ascorbate in their diet because of
loss of a functional form of the last enzyme (l-gulono-1,4-
lactone oxidase) of the biosynthesis pathway. Ascorbate is
best known for its function as an antioxidant and for its role
in collagen synthesis. Collagen deficiency results in the
symptoms of scurvy.
The purpose of this review is to outline recent advances
and new approaches to the investigation of ascorbate
biosynthesis and function. Its role in photosynthesis and
photoprotection, in defence against ozone and other
oxidative stresses and speculations about its role in cell
expansion and cell division will be emphasized. Improved
understanding of ascorbate in plants will lead to the
possibility of increasing ascorbate concentration in plants
by genetic manipulation. This will have benefits for human
nutrition and possibly for tolerance of plants to photooxidative
stresses