Mucilage production and differential tolerance to aluminum toxicity in maize (Zea mays L.)

摘要

Some of the functions proposed for mucilage are to protect the root tip from desication, increase root contact with the soil, and serve as a protective barrier against toxic agents including metals. Substances present in the mucilage that bind aluminium (Al), representing a physical and chemical barrier to the internal movement of this element, have also been proposed as a possible exclusion mechanism for Al tolerance. The objectives of this research were to study the effect of Al on root tip mucilage and citric acid exudation. Two inbred maize lines contrasting in their tolerance to Al, Cateto 237 (tolerant) and L53 (sensitive), and four sensitive and four tolerant recombinant inbred lines (RILs) originated from the cross of these inbred lines, were exposed to 39 μM Al for 0, 4, 12, 24 and 48 h in nutrient solution. The root tips were photographed to document mucilage exudation using sterioscopic and optical microscopes. Analysis of the images indicated that the tolerant inbred line Cateto 237 produced mucilage in all the Al exposure periods, with a visible increase in mucilage exudation after 4 and 12 h. The sensitive inbred line, L53, produced a little amount of mucilage without Al exposure, and mucilage production was reduced after 4 h. The sensitive and tolerant RILs produced mucilage amounts similar to the sensitive and tolerant parents, respectively. These preliminary results support the hypothesis that mucilage can act as an exclusion mechanism by forming a high concentration barrier of organic acids or other susbstances exudated by the root tip which can chelate toxic Al.