When a seed first germinates the first leaves are juvenile and are a different shape to their adult successors. This phenomenon is called heteroblasty. Genetic and environmental control of heteroblasty is important as the shape and position of a leaf dictates how good it is at producing carbohydrates. The 'Heteroblasty modelling: The timetable of ontogeny in Arabidopsis leaves' (HEMOTIONAL) project has investigated the genetic and environmental control of both leaf shape and size. The scientists did this by comparing models of development for the first leaf with that of leaf six in the model plant thale cress, Arabidopsis. Using an Arabidopsis model, the team gained data that supports the theory that growth slows over the whole leaf via a single global growth inhibitor that increases with time. The scientists also developed software to investigate the growth as well as cell division. The data do not show a direct relationship between rate of cell division and growth, but do suggest they are controlled by the same set of morphogens. HEMOTIONAL also investigated how genes involved in heteroblasty are able to modulate growth. A time-lapse microscopy platform was set up using fluorophores that mark cell outlines or indeed any gene of interest that turns on after heat shock induction. The construct is still being tested and validated. As Arabidopsis plants grown in agar are much smaller than their counterparts in soil, the team also looked at the effects of changing environmental conditions. Agar plants showed reduced heteroblasty. By transferring plants from agar to soil at different stages of development, the scientists showed that heteroblastic variations in leaf change are fixed early in leaf development. Leaf size, however, is affected by environmental changes. Results from HEMOTIONAL present an opportunity to address the global challenge of food security. Leaf development and growth are key areas in addressing the worldwide food shortage and may also be used to forecast the mitigating effects of plant growth on climate change.
Juvenile leaf, adult leaf, growth, shape, morphogen, Arabidopsis, food security, climate change