The root system architecture in low phytic acis1-1 maize mutant : phenotypic and morphological characterization

Phytic acid (PA) represents the major storage form of phosphate (P) in the seeds. It is accumulated as phytate salts with different cations, reducing their bioavailability. Only ruminants can degrade PA due to the presence of phytases in the digestive tract, while monogastric animals assimilate only 10% of phytate in feed and 90% is excreted, contributing to P pollution and water eutrophication. In underdeveloped countries, the lack of important cations such as iron and zinc in the diet represents a serious problem for human health. On the other hand, in rich countries the problem is not nutritional, but related to feed: farmers must supply mineral phosphorus to the feed of monogastric animals, thus implying an economic problem. Hence, many low phytic acid (lpa) mutants have been isolated in all major crops. Among different lpa mutants in maize, lpa1-1 is characterized by a 66% reduction in PA, followed by a proportional increase in inorganic P. Unfortunately, PA decrease is often followed by different negative pleiotropic effects on the seed and on plant performance. One of these agronomic defects observed on lpa1-1 in field conditions is a greater susceptibility to drought stress, which could be caused by an alteration in the Root System Architecture (RSA). With the aim to assess the effect of drought stress on the mutant, we have compared the RSA of lpa1-1 to a wild phenotype in a two-replicates pot experiment. In this work we present the results obtained, which clearly show that a variety of morphological changes occurred in the aerial part of the mutant plant rather than in the root system. The pleiotropic effect of drought stress in the mutant seems to be caused by a different photosynthetic efficiency and not by a shallower root system. Studying and overcoming the pleiotropic effects affecting lpa mutants would determine numerous potential benefits for the nutritional quality of food and feed and for the environmental P sustainability in agriculture.