Influence of Magnesium Supply on the Root Development of Arabidopsis thaliana

The root system exhibits a high degree of architectural plasticity in response to nutrient availability in the soil. For instance, the scarcity of certain major mineral elements (nitrogen, phosphorus, sulfur) triggers the proliferation of lateral roots. On the opposite, the depletion of magnesium (Mg) noticeably represses lateral root branching in Arabidopsis thaliana seedlings grown in vitro, which makes it a remarkable case of study. First, microscopic analyses were performed to determine if the absence of lateral root proliferation was associated with any distinct program of cell divisions. A slowdown in the growth of pre-emerged lateral roots was observed upon low Mg supply. Second, two experimental settings (split-root or strip band systems) were designed to study systemic and local responses to Mg availability. Seemingly, there was not any sensing mechanism to refrain lateral root growth in unfavorable nutrient zone. The extra source of the element acquired by the plant in Mg-rich zone, stimulated lateral root outgrowth in Mg-deprived zone. Third, the roles played by hormones in shaping root architecture in response to Mg depletion were examined. We previously identified higher expression of genes encoding enzymes in the ethylene biosynthetic pathway (New Phytol 187:132-144) and double gas production in Mg-deficient plants (Ann Bot 111:347-360). New lines of evidence support a role of abscisic acid in the control exerted on lateral root elongation by low Mg availability. Further in depth characterization of those identified hormonal pathways will bring new insight into signaling networks involved in the root morphological response to low Mg in plants.