Cecidomyiidae galls commonly present a zonation of tissues with lignified cell layers externally limiting a reserve tissue and internally limiting a specialized nutritive tissue next to the larval chamber. The cytological aspects of this specialized tissue indicate high metabolic activity as well as carbohydrate accumulation. In Aspidosperma spruceanum-Cecidomyiidae gall system, ultrastructural and histochemical investigations corroborated this pattern and also revealed the storage of proteins in the nutritive cells. Reactive oxygen species (ROS), callose, and pectin accumulation were related to the feeding activity of the galling herbivore. Phosphorylase, glucose-6-phosphatase, acid phosphatases, invertases, and sucrose synthase activities were detected for the first time, in the Neotropical region, and discussed in relation to gall maintenance and the feeding activity of the Cecidomyiidae.

We correlated root growth inhibition with aluminium (Al(3+)) localization and toxicity symptoms in rice roots using seedlings of two genotypes (tolerant and sensitive) that were exposed to different AlCl(3) concentrations. Al(3+) localization was evaluated by hematoxylin in primary roots and by morin in cross-sections of the root tips. Neutral invertase enzyme activity and callose (1 -- 3, beta-D-glucan) accumulation were observed and compared with Al(3+) accumulation sites. Root growth was inhibited by Al(3+) in a concentration-specific manner and proportional to the increase of hematoxylin staining, being more pronounced in the sensitive genotype. Morin staining showed the presence of Al(3+) deep within the roots of the sensitive genotype, indicating that the metal was able to penetrate beyond the first few cell layers. In the tolerant genotype, Al(3+) penetration was restricted to the first two cell layers. Ruptures in exodermis and epidermis layers by lateral root protrusions in both genotypes allowed Al3+ to enter into the roots. More intense activity of invertase in roots of the tolerant genotype was also observed, which could be related to greater root growth of this cultivar when submitted to Al(3+) stress. Moreover, Al(3+)-induced callose accumulation was a late response occurring in the same areas where Al(3+) was present.

Aluminum toxicity on root systems was analyzed through comparing root growth and evaluating the protective function of mucilage in Urochloa decumbens and Urochloa brizantha. Seedlings were grown in a solution with different concentrations of AlCl 3 and with mucilage removed or present. The root elongation rate, total length, number of roots and presence of aluminum at the root apex were measured. Root development was inhibited by aluminum and the elongation rate was maintained without any difference between the two species. A significant reduction in root length was found in U. brizantha. Aluminum did not influence root branching in either species and accumulated mostly in the rhizosphere of U. brizantha, where the mucilage has less of a protective function. The greatest aluminum tolerance was found in U. decumbens, observed through maintenance of total root system growth from lower to higher aluminum toxicity.

The present study examined the action of nitric oxide (NO) on the germination process of rice seeds and early root growth under aluminum (Al) stress. Seeds and seedlings of two rice genotypes, with different levels of sensitivity to aluminum stress, were examined after treatment with Al and NO or only with Al. Further, the histochemical localization of Al and NO was performed on the root tissues. In both genotypes, NO was able to neutralize the inhibitory Al effects on germination. In the roots of seedlings, a reduction of Al toxicity as mediated by NO was indicated by an increased root elongation and a reduction of Al accumulation on the root surface in the Al hematoxylin complexation, irrespective of the genotype. The histolocalization of NO in roots using diaminofluorescein diacetate (DAF-2DA) and confocal microscopy revealed endogenous Al-induced levels of NO. It is concluded that NO can alleviate Al stress in the seedlings of the studied rice genotypes by improving germination and early root growth and is likely to play a role in a specific stress-signaling pathway.

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