Larisse de Freitas-Silva

In acidic soil, aluminum (Al) ionizes into trivalent cation and becomes highly toxic to plants. Thus, the objectives of this work were (i) to evaluate the Al concentration and identify sites of Al toxicity and its effect on the structure on rice root tips and (ii) to elucidate the adjustments involved in the activities/contents of enzymes/compounds in the roots against Al. For this, two genotypes with contrasting Al tolerance were used. Our results showed that the root length of the tolerant genotype was not affected after Al exposure. We also observed that both the genotypes used strategies to avoid Al uptake, such as the overlap of P and Al in the tolerant genotype and the presence of border cells in the sensitive genotype, which proved inefficient. In the tolerant genotype, other external Al detoxification mechanisms may have contributed to the lower Al concentration in roots and lower fluorescence of the Al–lumogallion complex. Additionally, both genotypes present the activation of key enzymes to decrease oxidative stress, such as CAT, POX, APX, and DHAR, and a more reducing redox environment, mainly due to the increase in the AA/DHA ratio. However, higher total ascorbate, AA, total glutathione, and GSH contents associated with higher SOD, GPX, and GR activities contributed to the reduction of oxidative stress in the tolerant genotype after Al exposure. Furthermore, there was a strong association between the sensitive genotype to Al concentration, O₂^•– content, and MDA amount; therefore, these traits can be used as sensitivity indicators in Al studies.

Potassium (K⁺) is an essential macro-element for plant growth and development given its implication in major processes such as photosynthesis, osmoregulation, protein synthesis, and enzyme function. Using 30-day-old Cakile maritima plants as halophyte model grown under K⁺ deprivation for 15 days, it was analyzed at the biochemical level to determine the metabolism of reactive oxygen species (ROS), key photorespiratory enzymes, and the main NADPH-generating systems. K⁺ starvation-induced oxidative stress was noticed by high malondialdehyde (MDA) content associated with an increase of superoxide radical (O₂^•−) in leaves from K⁺-deficient plants. K⁺ shortage led to an overall increase in the activity of hydroxypyruvate reductase (HPR) and glycolate oxidase (GOX), as well as of antioxidant enzymes catalase (CAT), those of the ascorbate-glutathione cycle, peroxidase (POX), and superoxide dismutase (SOD), and the main enzymes involved in the NADPH generation in both leaves and roots. Especially remarkable was the induction of up to seven CuZn-SOD isozymes in leaves due to K⁺ deficiency. As a whole, data show that the K⁺ starvation has associated oxidative stress that boosts a biochemical response leading to a general increase of the antioxidant and NADPH-generating systems that allow the survival of the halophyte Cakile maritima.

When glyphosate is applied, some of the herbicide can reach adjacent vegetation and impact the natural plant community structure and diversity over the long term. This study evaluated the response of leaves of Zeyheria tuberculosa (Vell.) Bureau ex Verl. (Bignoniaceae) to the herbicide glyphosate. Plants were exposed to aerial applications of the herbicide at concentrations of 0, 360, 720, 1080, or 1440 g acid equivalent (a.e.)·ha⁻¹. The concentrations of shikimic acid in leaves of the herbicide-treated plants were always higher than the controls. Visual symptoms became apparent four days after the application of 720 g·ha⁻¹. Glyphosate induced an increase in malondialdehyde in Z. tuberculosa leaves. The lowest levels of chlorophyll a were found for the three last applied doses, and protein content decreased with the glyphosate treatment. Necrosis was observed on the epidermis and in the mesophyll. Glandular trichomes were also plasmolyzed. On the midrib there was plasmolysis of non-lignified cells. Micromorphologically, there were cell plasmolysis and rupture of glandular trichomes. Thus, glyphosate is phytotoxic to Z. tuberculosa by causing biochemical, anatomical, and morphological changes. The morphoanatomical injuries found on Z. tuberculosa were severe, suggesting that the presence of glyphosate can irreversibly affect this species and compromise its survival.

O objetivo deste trabalho foi avaliar o efeito do silício (Si) no processo infeccioso de Phakopsora pachyrhizi em folíolos de soja cultivada em solução nutritiva com ou sem Si. Observações realizadas sob microscópio de luz e microscópio eletrônico de varredura indicaram que, nos folíolos das plantas supridas com Si, as urédias foram menores e em menor número. Houve redução de 27, 23 e 60% no número de lesões, urédias fechadas e urédias abertas, respectivamente, nos folíolos das plantas com Si. Plantas de soja supridas com Si apresentam redução nos sintomas da ferrugem-asiática-da-soja.