Once flowering has started, depending on the plant, events can occur in one of two ways. In the first case, the apical meristem itself produces a flower, thus using up all its stem cell reserve. Should this occur, only a single flower will be produced, as is the case for a tulip for example. If the plant has to produce several flowers, the apical meristem undergoes certain changes enabling it to both produce a flower and maintain a stem cell reserve in order to be able to produce other flowers. "This is what is known as an inflorescence meristem" states Claire Périlleux. "This is a general mechanism which is found in all plants forming  inflorescences such as wheat, vines, tomatoes, etc." The location and way in which stem cells are maintained determine the shape of the inflorescence.

The tomato plant's somewhat unusual growth

The tomato plant not only forms inflorescences but also presents somewhat unusual and complex flowering. "When the apical meristem produces its first inflorescence, another meristem at the axil of a leaf (an ‘axillary meristem’) takes on its role for plant growth. This type of growth is known as sympodial growth", says Claire Périlleux. In this way, the axillary meristem goes on to form a stem segment consisting of two or three leaves. It will then in turn produce an inflorescence while another axillary meristem continues plant growth, producing three leaves, etc. "This is why on tomato plants we see seven to ten leaves before the first inflorescence and then two or three leaves, followed by an inflorescence, another two or three leaves and then another inflorescence, and so on. This is also why people are advised to pinch their tomato plants so they stop producing inflorescences and so that the first fruits can grow" continues the scientist.

In order to achieve even greater productivity, some horticultural companies would like to obtain cultivars which only produce two leaves between each inflorescence. In an article published in 2008 in the journal Plant Physiology (1), Claire Périlleux and her colleagues described the expression of a gene which is of great interest to these horticultural companies. The Self Pruning gene (SP) in tomatoes prevents lateral meristems from flowering too quickly. It is thus ‘because’ of this gene that the plant produces three leaves before the next inflorescence.

(1) Thouet, J., Quinet, M., Ormenese, S., Kinet, J.-M. and Périlleux, C., 2008. Revisiting the involvement of SELF PRUNING in the sympodial growth of tomato. Plant Physiology, 148, 61-64.