Becoming a Flower

Development of inner floral organs is exposed in mutants with impaired sepal development. ZEISS UltraPlus SEM image by Ryan McQuinn

How plants initially trigger their cells to develop into flowers has long confounded researchers.

However, a new class of signalling molecules called apocarotenoids may hold the answer. Plant biologists have recently demonstrated that apocarotenoid signals (ACS) give the plants essential cues for root, leaf, and flower development, as well as protecting them from adverse environmental conditions. Exactly how they do this is being investigated by Dr Ryan McQuinn and Prof. Barry Pogson at the ARC Centre of Excellence for Plant Energy Biology at the Australian National University (ANU) in collaboration with Prof. Patricia Leon at the National Autonomous University of Mexico (UNAM).

There is an experimental plant system where one of these molecules, called ACS1, accumulates to well above normal levels. This disrupts normal plant growth. The pattern of gene activity in these plants suggests that ACS1 promotes flower development. To research this possibility, Dr McQuinn analysed the plant architecture and leaf structure by using cryo scanning electron microscopy at the Centre for Advanced Microscopy, and compared them to normal plants.

In the normal plant, leaves develop in a spiral like pattern, with an abundance of spiky hairs. The experimental plants lack the spiral leaf arrangement and hairs. Instead, the surface is much bumpier with cells more closely resembling the part of a flower where pollen attaches for pollination. This functionality was confirmed when pollen came in contact with the lumpy cells of the experimental plant, “inflating” like it would at normal pollination.

ACS1 appears to be the first chemical signal discovered that triggers flower formation. Elucidating this previously enigmatic step opens up the possibility of developing new ways of controlling the flowering process with significant implications for agriculture and future food security.