Tolerance mechanisms to aluminum in popcorn inbred lines involving aluminum compartmentalization and ascorbate-glutathione redox pathway.

MAIN CONCLUSION: Inbred line 11-133 of popcorn showed the lowest apoplast Al and total Al concentrations and Al-lumogallion complex, associated with a more efficient antioxidant system, mainly due to glutathione metabolism. Popcorn (Zea mays L. var. everta) is largely intended for human consumption. About 40% of the world's arable soils are acidic. In soils acidic, aluminum (Al) ionizes producing the trivalent cation, which is highly toxic to plants. Hence, this work aimed to: (1) evaluate the Al toxicity sites and its effect on the structure of the root tips, (2) quantify Al concentrations in the apoplast and symplast of the roots, and (3) to elucidate the modulation on the activity of antioxidant enzymes and metabolites of the ascorbate-glutathione cycle in two popcorn inbred lines (ILs) 11-133 and 11-60, classified as tolerant and sensitive to this metal, respectively. Aluminum toxicity did not affect the shoot growth; however, there was a yellowing of the oldest leaf blade only in 11-60. The better performance of 11-133 is related to lower apoplastic and total Al concentrations and Al accumulation in the root associated with a lower fluorescence of Al-lumogallion complex at the root tip, indicating the presence of mechanisms of chelation with this metal. Consequently, this IL showed less change in root morphoanatomy and lower reactive oxygen species and malondialdehyde content, which are associated with a more efficient enzymatic and non-enzymatic system, mainly due to the higher content of the glutathione metabolite and the higher activities of superoxide dismutase, monodehydroascorbate reductase, dehydroascorbate reductase, γ-glutamylcysteine synthetase, and glutathione peroxidase enzymes. Thus, these findings illustrated above indicate how internal mechanisms of detoxification respond to Al in popcorn, which can be used as tolerance biomarkers.

Aluminum promotes changes in rice root structure and ascorbate and glutathione metabolism.

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.

Application of 2,4-D hormetic dose associated with the supply of nitrogen and nickel on cotton plants.

Growth traits, yield, N content, photosynthetic pigments, ammonia and amino acids were measured to verify the effect of the interaction between N, Ni, and 2,4-D applied in the cotton crop. The objective was to study the hormonal effect of 2,4-D associated with the application of N and Ni in coverage to improve yield. The N (0, 40, 80, and 120 kg ha-1) and Ni(0, 300, 450, and 600 g ha-1) were applied to the soil in the square phenological growth stage. The commercial 2,4-D DMA® BR (0 and 1.8 g a.e ha-1) was applied to the leaves at the same growth stage. The supply of N in cover fertilization up to 120 kg ha-1 was beneficial for cotton, providing greater yield and content of photosynthetic pigments. The application of 2,4-D in a hormetic dose, as a synthetic auxin during the beginning of flowering, proved to be a promising technique to improve cotton yield. This end-of-cycle response is related to the requirement for auxins during the cotton fruiting process.

Response of soybean to soil waterlogging associated with iron excess in the reproductive stage.

Soil waterlogging is a common problem in some agricultural areas, including regions under soybean (Glycine max) cultivation. In waterlogged soils, soil O2 depletion occurs due to aerobic microorganisms and plants, affecting the metabolic and physiological processes of plants after suffering anoxia in their root tissue. Another harmful factor in this situation is the exponential increase in the availability of iron (Fe) in the soil, which may result in absorption of excess Fe. The present study sought to evaluate the response mechanisms in soybean leaves 'Agroeste 3680' by physiological and biochemical analyses associating them with the development of pods in non-waterlogged and waterlogged soil, combined with one moderate and two toxic levels of Fe. Gas exchange was strongly affected by soil waterlogging. Excess Fe without soil waterlogging reduced photosynthetic pigments, and potentiated this reduction when associated with soil waterlogging. Starch and ureide accumulation in the first newly expanded trifoliate leaves proved to be response mechanisms induced by soil waterlogging and excess Fe, since plants cultivated under soil non-waterlogged soil at 25 mg dm-3 Fe showed lower contents when compared to stressed plants. Thus, starch and ureide accumulation could be considered efficient biomarkers of phytotoxicity caused by soil waterlogging and excess Fe in soybean plants. The reproductive development was abruptly interrupted by the imposition of stresses, leading to a loss of pod dry biomass, which was largely due to the substantial decrease in the net photosynthetic rate, as expressed by area (A), the blockage of carbohydrate transport to sink tissues and an increase of malondialdehyde (MDA). The negative effect on reproductive development was more pronounced under waterlogged soil.