Science - February 12, 2015

'Traffic lights' reveal plant hormone

Rob Ramaker

Wageningen biologists have presented a new method that uses coloured light to reveal the distribution of the plant hormone auxin. The resulting images literally shed new light on how plants develop.

Dolf Weijers, a professor holding a personal chair, and PhD candidate Che-Yang Liao of the Biochemistry group published their technique, which they call R2D2, on 3 February in Nature Methods. Weijers wants to use the technique in his research to help figure out how auxin shapes plants. The hormone has several functions and it is not clear why it has different effects in different parts of the plant. In addition to basic scientific knowledge R2D2 can also provide practical information, says Weijers. For instance, auxin controls asexual reproduction in crops. A better understanding of this process would enable more efficient reproduction. Weijers: ‘I am expecting a lot from this.’

Third colour
R2D2 lets plants — in this case thale cress — create two light-emitting proteins. One emits green light but is broken down if the cell contains auxin. The red protein, on the other hand, is stable and remains present. So the cell colour varies from yellowish green to red. The yellowish-green cells hardly contain any hormone, while cells turn orange or even red as the amount of auxin increases. In the images the researchers have made so far, R2D2 produces pictures that seem almost like the diagrams in a biology textbook. All that is missing is a legend describing the exact concentration. Unfortunately the method doesn’t work like that.

The colours can be compared with one another but they cannot be converted into precise hormone concentrations. Weijers wants to extend R2D2 by adding a third colour. ‘That would give us an auxin rainbow,’ says Weijers. In addition to showing the amount of hormone, the new system would also show how powerful the hormone is. Weijers thinks we could learn a lot about how the hormone works by studying these differences. ‘With three colours we can see the actual amount of hormone in each cell and the reaction it is causing.’