Silicon on the Root Morphology of Upland Rice Plants Grown Under Aluminum Toxicity.

The aluminum (Al) is one of the most limiting plant growth in tropical soils. The first toxic effect caused by Al is the inhibition of root growth, therefore to obtain high yield is necessary mitigate this toxicity. The silicon (Si) may be use to alleviate the Al toxicity, however, the interaction between Si and Al is not well understood, specially the role of Si on the root morphology. The aimed of this study was to evaluate the capacity of the Si mediate the alleviation of Al toxicity on the root anatomy of upland rice plants. The experiment was conducted in nutrient solutions and was laid out in randomized complete block design, with a 2 x 5 factorial and five replications. The treatments were composed of two upland rice cultivars (ANa7007 - Al tolerant and Maravilha - Al susceptible) and four forms of Si and Al supply (Control = without Si and Al; +Si = with Si and without Al; +Al = without Si and with Al; and +Si+Al = with Si and with Al). Root samples were collected of each treatment and processed according to conventional protocols in light microscopy. In the roots exposed to Al on their treatments, the exodermis cells showed protoplast shrinkage and decreased volume, that result in cellular destruction. In the Al tolerant cultivar, the structural changes were similar between +Si+Al and +Al treatments. However, in the Al susceptible cultivar, the +Si+Al treatment was able to maintain the external cortical cells with similar characteristics of control treatment. It may be attributed to the Si-mediated alleviation of damage caused by Al on the roots of this cultivar. The root diameter, cortex thickness, vessel wall thickness and number of vessel elements were not statistically different between the treatments. This counteracts the hypothesis that the Al increase the root thickness at least when evaluated anatomically.