LAUSR

Intralaminar galls of Meunieriella result from ground-tissue proliferation in leaves of Avicennia schaueriana, a halophytic plant typical of mangroves. We tested if the preferential sites of gall induction were the midribs and secondary veins at the basal leaf third, where the galls were expected to be largest; and if the vascular system in galls and adjacent regions was altered to favor water supply in galls, increasing their growth. Gall induction sites and gall sizes were quantified according to thirds and regions. Anatomical and histometrical analyses in vascular and ground tissues of galls and adjacent regions were compared to equivalent regions of non-galled leaves. The galls grow largest at basal sites on the leaves, on the midrib and secondary veins. More galls occurred on the apical third of the leaf, and on the leaf blade and secondary vein regions. Changes in shape and vascular system area, number and diameter of vessel elements were detected in both the galls and adjacent regions. Fewer and smaller-caliber vessel elements were observed in the regions proximal to the galls and inside them. Gall size is not related with preferential induction sites, which could be explained by factors as thermal balance. Alterations in vascular system indicates the reduction of hydraulic conductivity in the xylem in the proximal region and inside galls, leading to water leakage to gall parenchyma cells. This compensatory mechanism explains the expansion and proliferation of water-storage and spongy parenchyma cells in the galls, explaining the higher growth in more-vascularized regions.