Bursting buds are dicing with death

Scientists from the John Innes Centre (JIC), Norwich (1) have today reported that highly toxic compounds, called free radicals, are essential to plant growth. The researchers had found that the controlled production of free radicals is an essential first step in switching on the expansion of cells that underlies the growth of plant shoots, roots, leaves and buds. A phenomenon that is especially evident in the spring. The research is reported in the international scientific journal Nature.

“This is a completely novel discovery” said Dr Liam Dolan (leader of the research project at JIC). “For the first time we have strong evidence that all cell growth is controlled by the production of these highly reactive and therefore very toxic free radicals. At this time of year plants are juggling with a life and death balance as cells in sprouting seedlings and opening buds make high levels of these molecules in order to drive the expansion of new leaves, roots and shoots”.

The research team have identified a gene (RHD2) that makes a protein, which produces free radicals(2). They have demonstrated that controlled production of free radicals by RHD2 stimulates calcium channels in the membranes of cells resulting in calcium being taken up by the cells. The accumulation of calcium in turn activates cell expansion. The scientists measured cell growth in roots and root hairs of Arabidopsis thaliana(3). In plants where the RHD2 gene was inactivated by a mutation the roots and root hairs were stunted. The multidisciplinary team used sophisticated microscopy to reveal the effect of RHD2 on free radical production and calcium movement into cells.

Free radicals have a two-edged role in biology.
They are produced by many living systems as a by-product of normal metabolism. In humans they are known to cause cancer by damaging DNA (the genetic material) but they also have an important role in the immune system where they are used to kill viruses and bacteria invading the body. This report describes a similar two-edged role in plants for these powerful toxins that play an essential role in plant growth.

“RHD2 is one of a large family of genes involved in free radical production. Variation in the activities of different genes in the family could cause differences in plant height and leaf size, in fact anything affected by cell expansion”, concludes Dr Dolan. “It may be possible to screen plants for differences in the RHD2 gene family and match this to differences in their appearance. This would give us new information about how the shape and size of plants is controlled and how breeders might alter these characteristics in precise ways”.