Utrecht University, The Netherlands

A plant scientist finds beauty in floral arrangements.

On the face of it, flower arranging is a fiddly affair, and its underlying rules are not immediately obvious to the beholder. But a plant's flowers are always arranged in one of three basic architectures, or 'inflorescences'. These take the form of panicles, loosely but highly branched clusters in which each flower has its own stalk (as in the foxglove); racemes, in which flowers are arranged individually along an unbranched, growing stem (the snapdragon); or cymes, typified by a cluster of branches at the end of a stem that each terminate with flower (the forget-me-not). Simple rules must lie behind this, and simple rules are the foodstuff of mathematical models.

That is the logic behind the work of Przemyslaw Prusinkiewicz at the University of Calgary in Alberta, Canada, and his colleagues. Last year, they published a model in which they imagined that meristems grow into shoots or flowers according to the value of a factor that they named 'veg' (P. Prusinkiewicz et al. Science 316, 1452–1456; 2007). When veg is high, a shoot springs forth; when it is low, a blossom flourishes. Thus, if over time veg decreases at the same rate in all of a plant's growing tips, the model grows a panicle. Other simple rules give rise to a raceme or cyme.

Prusinkiewicz et al. found that, in Arabidopsis, a gene called LEAFY influences the value of veg. But how does this concept apply to plants with different architectures? Recently, Erik Souer of Vrije University in Amsterdam and his collaborators showed that modification of LEAFY activity is crucial for floral architecture in petunia, a cyme, just as the model predicts (E. Souer et al. Plant Cell 20, 2033–2048; 2008). They identify a protein that activates LEAFY only in developing flower buds and that is essential for their architecture. I find the tidy simplicity of these findings more beautiful than any bouquet.

Posted by Anna Petherick at 12:20 PM | Permalink | Comments (0) | TrackBacks (0)

The Natural History Museum, London, UK

A palaeobotanist finds answers to the origin of roots in the genes of a living moss.

Roots have been called the hidden half of plant diversity. Confined mainly to the subterranean, their unseen influence extends well beyond the plant that they sustain to form an integral component of soil ecosystems and a significant link in the carbon cycle.

In my research, I use fossils to piece together how the fundamental organs and basic lifecycles of plants evolved, and roots are one of the key systems. The fossil record shows that roots were an early innovation in the colonization of the land, and that they evolved remarkably rapidly, developing a diversity of forms comparable to those of the aerial shoots, stems and leaves. Comparative morphology is good for documenting how roots evolved, but are there any underlying molecular developmental similarities among the rooting structures of early plants?

An elegant piece of recent research shows that a similar transcription factor encoded by the gene ROOT HAIR DEFECTIVE 6 regulates root-hair development in the flowering plant Arabidopsis thaliana and rhizoid development in the moss Physcomitrella patens (B. Menand et al. Science 316, 1477–1480; 2007). Because flowering plants and mosses diverged more than 400 million years ago, this surprising result implies that the cells with a key role in nutrient acquisition and anchorage in most land plants share a molecular developmental pathway that is very ancient indeed.

More surprising still is the notion that these genes are expressed in both haploid and diploid plants — that is, those whose cells have one or two sets of chromosomes, respectively. Many plants cycle between haploid and diploid forms during their lifecycles. Menand et al. propose that genes expressed in early haploid plants were turned on in many tissues during the evolution of plants with diploid phases. Pending further testing, this interesting model is plausible for components of the vascular system, cortex, epidermis, shoot and root.

Posted by at 06:00 PM | Permalink | Comments (0) | TrackBacks (0)