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Agricultural scientists say they have uncovered the last big secret of vitamin C in plants, and it will create the chance to breed healthier fruits.
The breakthrough in understanding just how plants manufacture vitamin C will enable state science company Hortresearch to identify DNA markers for individual plants naturally producing high levels of the vitamin.
These plants are likely to be used in selective breeding programmes to produce fruit with more vitamin C in a form easily retained by the body, unlike large doses taken in vitamin pills.
Cultivars of apples or bananas provide less than half the recommended US daily intake of 90mg/day of vitamin C for an adult male, and even an orange doesn't quite measure up - but the new research will lead to more potent fruit.
Hortresearch's science general manager, Dr Bruce Campbell, said the team had isolated the last undiscovered enzyme and proved it controlled vitamin C in plants.
The enzyme was the last step in a chain of research begun overseas nearly 80 years ago by scientist seeking to understand how plants produce vitamin C.
NZ scientists studied kiwifruit, a plant naturally high in vitamin C, with typical green kiwifruit - bred from Actinidia deliciosa - containing about 100mg in each 100g of fruit.
The scientists worked on an inedible wild kiwifruit variety called Actinidia eriantha - with a white, hairy skin which is easy to peel - because it contains a massive 800mg of vitamin C per 100g.
Genetically engineered forms of the small and non-vigorous vines have also been used by HortResearch in containment to investigate how specific genes in the many different kiwifruit species affect biological processes in the plants.
In these studies, transgenic plants were flowered and fruited in the greenhouse to check how inserted genetic material was expressed in the plant and inherited.
A paper outlining HortResearch's enzyme discovery was recently published in the US-based Proceedings of the National Academy of Science, and it will be presented by one of the researchers, Sean Bulley, at this week's Queenstown conference on molecular biology.
People needed vitamin C from eating fruit and vegetables to help rebuild body tissues and fight infection and disease.
But people who turned to high doses of man-made vitamin C in capsules and pills could find it flushed from their system by their kidneys.
"While the vitamin C in a pill is quickly absorbed by our bodies, often a lot of it is just as quickly excreted," said Dr Bulley.
- NZPA
