Shedding new light on leaf formation

“A core aspect of this challenge is to improve our understanding of the growth and form of plants.”

Almost all plants share a striking property: their organs are arranged in a very regular geometric fashion. These regular arrangements are called phyllotaxis, a Greek term which reflects how this question has fascinated many scholars since ancient history. And yet, it remains a puzzle to modern day scientists.

Research in the last few decades has shown how a plant hormone, called auxin, is transported in a complex way throughout the plant, generating microscopic patterns which eventually lead to phyllotaxis.

In this study, researchers have shown that auxin alone does not explain phyllotaxis. By looking more closely at these patterns some inversions were observed, whereby groups of 2 or 3 leaves have their vertical positions mingled.

In other words, organs look like they are at the correct position, but do not appear in the right order. These accidents, though rare, are frequent enough to be observed in some common plants found in the garden. To fully understand these accidents, techniques from combinatorics — or the mathematics of counting finite objects — and statistics were required. Based on these techniques, it was possible to evaluate the frequency of these accidents, both in sound plants and in plants which have a defect in the functioning of another plant hormone, called cytokinin.

Using tools from molecular biology and microscopy, it was possible to confirm that in addition to the spatial position of leaves, controlled by auxin, cytokinin is responsible for their correct sequential arrangement, thus improving our understanding of plant growth and form.

Co-author Dr Anthony Bishopp added: “The arrangement of leaves on a plant affects the amount of light the leaves capture and the amount the plant can photosynthesise — the process by which they convert light to energy.

Improvements in photosynthesis is one of the key areas that plant researchers are targeting to try and create new generations of crops with improved yields to feed the world’s growing population.”

The research, Cytokinin Signalling Inhibitory Fields Provide Robustness to Phyllotaxis, is the outcome of the PhD project of Fabrice Besnard and was led by Teva Vernoux, research director at theEcole Normale Supérieure of Lyon and involved colleagues at theInstitut de Biologie Computationelle in Montpellier and the Laboratoire de Physiologie Cellulaire et Vegetale in Grenoble, France and the University of Helsinki.

Dr Farcot, now in the University’s School of Mathematical Sciences, co-authored the work while in his previous position at the Institut de Biologie Computationelle, while Dr Anthony Bishopp, now based in Nottingham’s School of Biosciences, was working in his previous position at the University of Helsinki.

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