Morphological Adaptability of Rice is Modelled

31/08/06 If a climate is too hot or too dry, or the opposite, plants are exposed to stress, but they are capable of adapting. Researchers can thus assess their resistance to stress, which may also lead plants to change their morphology and even their architecture, at any stage of their development. This plasticity is of crucial importance for crop productivity in variable, heterogeneous environments; it is thus a target for varietal breeding operations. However, to date, it has not been studied in detail. The modelling tool developed by the Oryzon project, which has just been completed, can now be used for this purpose in the case of rice.

It offers the possibility of simulating how new organs develop in rice plants, depending on assimilated nurtient availability within the plant. That availability is reflected in the levels of certain sugars. Sugar concentration is governed by enzyme activity, and acts as a signal, and thus as a regulator, in the zones that give rise to new organs. Plants thus adjust their morphology (root system and leaf size and number). It is these parameters that govern access to nutrient stocks, environmental stress resistance and competition with weeds.

To achieve this result, numerous observations were carried out, in controlled environments, on a range of rice varieties and mutants subjected to various constraints: phosphorus deficiency, shade periods, drought, etc. The morphogenesis of the rice plants and their organs, sugar content and key enzyme activity were measured. One major plasticity mechanism was demonstrated: in response to a phosphorus deficiency, root growth is stimulated–no doubt to improve access to the available phosphorus–through repeated inhibition of aerial system growth. This reduces carbon demand from the aerial organs, surplus assimilated nutritients are set aside and root growth is accelerated. Conversely, in the event of low sunshine levels, root system growth is inhibited in favour of leaf and stem elongation–no doubt in the search for light–while organogenesis is slowed down.

Modelling these adaptation processes could also serve to develop powerful molecular markers for use in varietal creation, avoiding the need for genetically modified organisms.