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The present study aimed to evaluate root cortical aerenchyma formation in response to Cd‐driven hydrogen peroxide (H2O2) production and the role of nitric oxide (NO) in the alleviation of Cd oxidative stress in maize roots and its effects on aerenchyma development. Maize plants were subjected to continuous flooding for 30 days, and the following treatments were applied weekly: Cd(NO3)2 at 0, 10, and 50 μM and Na2[Fe(CN)5NO]·2H2O (an NO donor) at 0.5, 0.1, and 0.2 μM. The root biometrics; oxidative stress indicators H2O2 and malondialdehyde (MDA); and activities of catalase (CAT), superoxide dismutase (SOD), and ascorbate peroxidase (APX) were analyzed. The root dry and fresh masses decreased at higher concentrations of NO and Cd. H2O2 also decreased at higher NO concentrations; however, MDA increased only at higher Cd levels. SOD activity decreased at higher concentrations of NO, but CAT activity increased. Aerenchyma development decreased in response to NO. Consequently, NO acts as an antagonist to Cd, decreasing the concentration of H2O2 by reducing SOD activity and increasing CAT activity. Although H2O2 is directly linked to aerenchyma formation, increased H2O2 concentrations are necessary for root cortical aerenchyma development.

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Typha domingensis Pers. (Typhaceae) is found growing naturally at high and low population densities in wetlands and shows remarkable invasive potential worldwide. The objective of this study was to verify the occurrence of changes in the environmental characteristics as well as in the biometry, anatomy, photosynthesis, and nutrient uptake of T. domingensis from natural populations growing at different densities. Plants were sampled from two populations exhibiting high and low densities and were further submitted to biometric, anatomical and physiological analyses. The experimental design was completely randomized with two treatments and 15 replicates. Data were submitted to ANOVA and the Scott-Knott test (P ≤ 0.05). At a high population density, T. domingensis showed close plant spacing, a high number of plants and a large leaf area. In addition, high-density conditions promoted self-shading of the middle and lower parts of the shoots and led to increased whole plant photosynthesis. Soil nutrients were reduced under high-density conditions. In addition, plants from high-density population developed adaptations in their vascular tissues and aerenchyma. Therefore, the high-density population condition of T. domingensis causes and increased vegetative growth of these populations, as well as its invasive potential, may be related to mild self-shading, which promotes a large leaf area and high rate of photosynthesis.

The objective of this study was to test the tolerance of two species of Schinus and two species of Handroanthus cultivated in iron mining tailings from the rupture of the dam in Mariana, Brazil. Samples of mining tailings were collected 1 km away from the dam location and then dried, stored in plastic bags and further analysed for elemental composition. The seeds, later seedlings, were cultivated in the mining waste and in sand in two experiments separately and the experimental design was in a 2 × 3 factorial scheme (two substrates and three combinations of species), with six replications (n = 36). After 60 d of the establishment of the experiments, the germination data, biometric and anatomical measurements of the leaves were evaluated, in addition to the elemental characterization of the tailings. Mining tailings showed macro and micronutrients in addition to potentially toxic elements (As, Al, Cr, Pb and Ni). Seeds germinated and seedlings survived in the mining tailings. Mining tailings reduced the seedling emergence in Handroanthus, whereas it increased the emergence in S. molle and had no significant effect in S. terebinthifolia. Mining tailings reduced the number and length of roots in Schinus but increased these traits in Handroanthus species. Moreover, mining tailings reduced the fresh mass in Handroanthus but had no effect in the Schinus species. Mining tailings reduced the palisade and spongy parenchyma Handroanthus but only the spongy parenchyma was reduced in Schinus species. Therefore, mining tailings provided conditions for seed germination and seedling growth and Schinus species showed higher tolerance.