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How tomato fruits develop under stressful conditions

Under stressful conditions, such as a lack of water or light, a plant reacts through a general equilibration that impacts not only its architecture and metabolism but also its reproductive strategy.  It thus determines the resources that should be allocated to the development of its fruits.  To study the impact of a water or light deficiency on nutrient fluxes and fruit growth, INRA researchers have developed a mathematical model, applied to the tomato, that takes account of the different stages of fruit development.

Tomatoes. © INRA, ADRIAN Michel
Updated on 06/30/2014
Published on 06/16/2014

Map of water potentials in a plant.  The lighter colours indicate a weaker water potential that is less favourable to fruit growth. © INRA, Gilles Vercambre
Map of water potentials in a plant. The lighter colours indicate a weaker water potential that is less favourable to fruit growth © INRA, Gilles Vercambre
Understanding the mechanisms that underlie fruit development is a crucial issue in agronomy.  From the early stages of growth, when the fruit cells undergo an intense period of division and expansion, to harvest, the effects of resource availability on the mass and composition of fruits are a determinant factor.

Research scientists in the Plants and Cropping Systems in Horticulture Unit in Avignon have developed a detailed modelling system that integrates different physiological, metabolic and physical mechanisms. Within this model, the tomato fruit is seen as an aggregation of cell populations of different ages.  The intensity of cell proliferation is dependent on the age of the fruit, while the growth of cells depends on both their age and the availability of water and sugars, according to the fruit's position on the plant.  At the plant scale, the model calculates sugar production by photosynthesis and simulates its storage and transport within the plant and towards the fruits.  Water losses by transpiration, and water fluxes within the plant, are calculated in order to evaluate the water status of different tissues, quantified using the water potential (see image above: water status is better in the purple zones and less satisfactory in white and yellow zones).

This new model is able to predict and analyse in silico the effects of stress at both the cellular level and at the scales ranging from the fruit to the cluster and plant.  Thus, although a water deficit will markedly reduce the mass of tomatoes, the model has revealed that a limitation on carbon intake through shade can lead to a temporary increase in mass and water content, due to the response dynamics at the levels of both the fruits and leaves.

The predictions of this model have highlighted the importance of the symplasmic flux of sugars towards fruit cells.  The symplasm is the intracellular continuum formed by plant cells by means of small channels called plasmodesma.  Thus, even before the first days of life of a fruit, the availability of sugars in this space favours the early growth of cells.  This early growth plays a very important role, because it determines the growth potential of cells during subsequent stages.

For this reason, the age of cells and the transport mechanisms between the plant and fruits can identify the time at which the impact of a stress on fruit development will be the most marked.  According to the model, this so-called "sensitive" phase occurs at around 20 days after flowering, during the period of major fruit expansion which sees an intense production of new cells whose growth is markedly affected by any water or carbon deficiency.

The scientists have thus modelled the effects of water or light restriction on the size of the tomato as being dependent on the age of the fruit and its cells.  One significant prediction of this model is the important role played by the symplasmic flux of sugars during the early stages of fruit development.

Contact(s)
Scientific contact(s):

Press Relations:
INRA News Office (33 (0)1 42 75 91 86)
Associated Division(s):
Environment and Agronomy
Associated Centre(s):
Provence-Alpes-Côte d'Azur

Reference

Baldazzi V, Pinet A, Vercambre G, Bénard C, Biais B, Génard M. 2013. In-silico analysis of water and carbon relations under stress conditions. A multi-scale perspective centered on fruit. Frontiers in Plant Science, 09 December 2013. doi:10.3389/fpls.2013.00495