Over The Horizon

How Plants Grow

Internationally significant research into one of the big unsolved questions of plant science -- how plants grow -- is taking place in New Zealand, with planned participation from scientists in the UK, Australia and Italy. The keen interest follows a recent workshop in Lower Hutt which attracted eight overseas scientists.

The technique of observing growth in a living plant, developed by HortResearch scientists Dr Peter Minchin and Dr Michael Thorpe, is not available anywhere else in the world. They measure radioactive carbon-11 (¹¹C) movement within plants to learn more about how the growth of different plant parts is co-ordinated and how plants respond to different challenges and stresses.

"We are working with ¹¹C to try and explain how plants function or malfunction, and why there is an increase in yield in some plants," Minchin said. "Understanding plant growth will give us the knowledge for manipulating where the growth occurs so it can influence yield and size, sweetness or acidity."

Yield is a critical factor in food production. Understanding why some plants produce more than others is one aim of the programme, for example why apple trees produce more in New Zealand than they do in the northern hemisphere. Understanding plant growth and plant adaptation to different environments is important to provide information for bigger and better crops and better tasting produce. More yield, more output, less land use.

The amount of international interest in the workshop amazed Minchin and Thorpe, though they admit they were able to "capture" the scientists on their way to a "very specialised" conference on assimilate transport and partitioning that the two helped to organise in Australia.

Both physicists by training, Minchin and Thorpe started this work 23 years ago and have developed special analysis procedures central to this work. They now have some answers and can explain how a change in growth pattern happens, but don't yet know if it is the only reason.

Because of the rapid decay of the ¹¹C (it has a "half-life" of 20 minutes) it must be used at the site where it is produced in a particle accelerator at the Institute of Geological and Nuclear Sciences (GNS). Though the two scientists are based at Ruakura in Hamilton, they make five or six trips a year to Lower Hutt to use the radioactive material with living plants.

Another aspect of the research is the Biological Accelerator Mass Spectrometry technique for detecting another form of carbon, carbon-14, in plants at extremely low levels. This has been developed by GNS from a carbon-dating technique, and can measure ¹⁴C from tiny samples as small as a single plant cell.