André Dias de Azevedo Neto

Physiological and biochemical responses of peanut genotypes to water deficit

Abstract The effects of drought on water relations, gas exchanges, solutes accumulation, and catalase (CAT), ascorbato peroxidase (APX), and guaiacol peroxidase (GPX) activities were studied in five Arachis genotypes, grown under control or withholding water conditions. Drought stress reduced plant growth of all genotypes; the genotypes A. duranensis 7988 and A. stenosperma SV2411 being characterized as the most drought-sensitive and A. ipaensis as the most drought-tolerant. Data of transpiration and stomatal conductance confirmed the findings that A. ipaensis was more tolerant to drought conditions. Water deficit increased organic solutes content and reduced leaf water potential in all genotypes. The data suggest that solutes accumulation in roots may, at least in part, explain the greater tolerance of A. ipaensis to drought stress. CAT activity showed a significant increase in stressed leaves of sensitive genotypes. APX and GPX activities either increased or were not affected by drought in leaves of all genotypes.

Pretreatment with H2O2 in maize seeds: effects on germination and seedling acclimation to salt stress

The aim of this study was to evaluate the effects of H2O2 on germination and acclimation of maize plants subject to salt stress. Three experiments using BRS3003 seeds, a triple hybrid of maize, were carried out in a growth room and in greenhouse. In the first experiment, H2O2 accelerated the germination percentage of seeds at 100 mM, but not at 500 mM. In the second experiment, the pretreatment of seeds was observed to induce a pronounced increase in ascorbate peroxidase (APX) and catalase (CAT) enzyme activity after 30 h of soaking in H2O2. It was also observed that guaiacol peroxidase (GPX) activity was smaller in the seeds soaked in H2O2 for 12, 24, 30, 36 and 42 h, in relation to those soaked in distilled water. The superoxide dismutase (SOD) activity was not affected by the pretreatment of seeds, except for the 24 h treatment. Only one CAT isoform was detected. In the third experiment, seeds were pretreated with 36 h soaking in 100 mM H2O2 solution or in distilled water and later cultivated in Hoaglands nutrient solution or nutrient solution with 80 mM NaCl. The results showed the pretreatment of seeds with H2O2 induced acclimation of the plants to salinity. It decreased the deleterious effects of salt stress on the growth of maize. In addition, the differences in antioxidative enzyme activities may explain the increased tolerance to salt stress of plants originated from H2O2 pretreated seeds.

Changes in soluble amino-N, soluble proteins and free amino acids in leaves and roots of salt-stressed maize genotypes

Abstract The effects of salt stress on the contents of organic solutes and on the pattern of free amino acids were studied in leaves and roots of two maize genotypes, BR5033 (salt-tolerant) and BR5011 (salt-sensitive). In leaves and roots of salt-stressed plants, soluble amino-N increased with time when compared to the controls. Salt stress increased the soluble protein content only in leaves of BR5011. Salinity increased the content of the majority of the free amino acids in leaves and roots of genotypes studied. Results suggest the hypothesis of disturbances in translocation of N-containing compounds from shoot to root in the salt-sensitive genotype. Results also suggest that the accumulation of organic solutes, mainly in roots of BR5033, may have an important role in the tolerance of this genotype to salt stress.

Crescimento de plantas jovens de Nim-Indiano (Azadirachta indica a. juss. - Meliaceae) sob diferentes regimes hídricos

This work was performed aiming to evaluate the growth of neem seedlings (Azadirachta indica A. Juss.) under water deficit. The experimental design was entirely randomized, with seven treatments (100, 80, 60, 40 and 20% of field capacity, without water and re-watering). The height, number of leaves and stem diameter were analyzed weekly. At the end of the experiment, dry matter of the leaves, shoots, roots, root to shoot ratio and biomass allocation in leaf, stem and roots were determined. Leaf area, leaf area ratio and specific leaf area were also calculated. Water stress reduced the height, number of leaves and shoot diameter in the plants of the several treatments. Water stress reduced leaf, stem and root dry matter. Only the biomass allocation to leaves was reduced. Leaf area was also reduced; however, there were not significant differences for leaf area ratio and specific leaf area. The recovery of the re-watering plants was evident by emitting new leaves. The results suggest that neem seedlings must be cultivated, in the initial phase of development, under 80% of field capacity, with maximum production.

Fluorescência da clorofila como uma ferramenta possível para seleção de tolerância à salinidade em girassol

The effect of salt stress of known intensity and duration on chlorophyll fluorescence in sunflower plants was studied aiming to identify salt-tolerant and salt-sensitive genotypes. The experimental design was a completely randomized in a factorial arrangement among 10 genotypes and two salt levels, with four replications. Seeds were sown in sand, and after germination were transplanted to plastic pots with nutrient solution or nutrient solution containing 100 mM of NaCl and placed in a greenhouse. After 27 days, ground fluorescence (F0), maximum quantum yield of PS2 Fv/Fm, the Fv/F0 ratio and effective quantum yield of photosystem 2 - PS2 (Y) were evaluated. The photochemical (qP) and non-photochemical (qN, qCN e NPQ) coefficients were also calculated. Salt stress increased F0 and reduced Fv/Fm, Fv/F0, and Y, suggesting salt-induced structural damage in the thylakoid membranes. These effects were more pronounced in genotype AG-960 and lowest in AG-975. The highest increases in qN, qCN and NPQ were also found in genotype AG-960 in contrast with that observed in AG-975. Thus the AG-975 and AG-960 genotypes were characterized as the most salt-tolerant and salt-sensitive, respectively. The other genotypes showed intermediate tolerance to salt stress. Our results suggest that chlorophyll fluorescence could be used as a tool for the screening of sunflower genotypes for salinity tolerance.

Aluminum Tolerance in Sunflower Plants Is Associated with Phosphorus Content in the Roots

Sunflower is considered one of the most promising crops for agro-industry development. This plant is adaptable to different soil and climate conditions but is very sensitive to aluminum (Al). Considering that the different plant species have developed different mechanisms to cope with Al, this work evaluated the effect of Al stress on plant growth and nitrogen (N), phosphorus (P), and potassium (K) contents in 25 sunflower genotypes. The results showed that Catissol, EXP 11-26, HLA 860 HO, and H 358 were the most Al-tolerant and IAC-Uruguai, AG 960, EXP 44-49, IAC-Iarama, BRS G27, EXP 887, and H 251 were the most Al-sensitive. We also observed that maintenance of P content in roots of stressed plants seems to play an important role in Al-stressed sunflower plants, suggesting that it could be used as a physiological marker during the screening for Al tolerance in this species.Sunflower is considered one of the most promising crops for agro-industry development. This plant is adaptable to different soil and climate conditions but is very sensitive to aluminum (Al). Considering that the different plant species have developed different mechanisms to cope with Al, this work evaluated the effect of Al stress on plant growth and nitrogen (N), phosphorus (P), and potassium (K) contents in 25 sunflower genotypes. The results showed that Catissol, EXP 11-26, HLA 860 HO, and H 358 were the most Al-tolerant and IAC-Uruguai, AG 960, EXP 44-49, IAC-Iarama, BRS G27, EXP 887, and H 251 were the most Al-sensitive. We also observed that maintenance of P content in roots of stressed plants seems to play an important role in Al-stressed sunflower plants, suggesting that it could be used as a physiological marker during the screening for Al tolerance in this species.

Growth and contents of organic and inorganic solutes in amaranth under salt stress

Amaranthus cruentus L. is a forage species, with grains that exhibit excellent nutritional characteristics, being the ‘BRS Alegria’ the first cultivar recommended for cultivation in Brazil. This study aimed at evaluating the effect of salt stress on the growth and concentrations of organic and inorganic solutes in Amaranthus cruentus L. (‘BRS Alegria’ cultivar). Height, stem diameter, number of leaves, leaf, stem and root dry mass, leaf area, relative water content and membrane integrity percentage, as well as soluble carbohydrate, free amino acid, soluble protein, free proline, Na + , Cl - and K + contents, were evaluated in different plant organs. Salinity significantly reduced the biomass yield and leaf area from the treatment with 25 mM of NaCl, indicating that the ‘BRS Alegria’ cultivar is sensitive to salt stress. Soluble carbohydrates in the leaves decreased by 59 %, while the other organic solutes showed no substantial increases. These results, coupled with the reduction in the relative water content and membrane integrity, suggest a low ability of this cultivar to adjust osmotically under salt stress. The K + /Na + ratio abruptly decreased in 25 mM of NaCl, suggesting an ionic imbalance, which may partially explain the salt-induced growth reduction.

Effect of salt stress on growth and contents of organic and inorganic compounds in noni ( Morinda citrifolia L.)

Salinity is one of the abiotic stresses that most affect agricultural production, especially in arid and semi-arid regions; however, among species there are large differences in salt tolerance. In this study, the effects of salinity on the growth and accumulation of organic and inorganic solutes were evaluated in ‘noni’ seedlings at 1, 10, 20, 30 and 40 days of salt stress in a 5 x 2 completely randomized experimental design. Seedlings of ‘noni’ were grown in the nutrient solution at two salinity levels (0 and 100 mM sodium chloride). Plant height, number of leaves, stem diameter and dry matter of leaves, stems and roots, the allocation of biomass and the contents of organic and inorganic solutes were determined in the different plant organs. Salinity reduced all growth variables, being less expressive in stem diameter. The biomass allocation in leaves was higher than in roots, regardless of treatment or time considered. The contents of organic and inorganic solutes varied according to the plant part and the time of exposure to salinity. In general, salinity increased the contents of sodium ion (Na + ), chloride ion (Cl - ) and reduced potassium ion (K + ), nitrogen (N) and phosphorus (P). Soluble carbohydrates and free amino acids were the main organic solutes contributing to osmotic potential of noni to salt stress. The salinity increased proline content in roots more than in leaves, but the proline content in the leaves was, on average 17 and 6 times higher than that of roots of plants under control and stressed conditions, respectively. Quantitatively, proline does not contribute substantially to the osmotic potential of noni, however its increase suggests that it plays a role in the salt stress acclimation or is an indicator of salt-induced metabolic disorders. Keywords: Amino acids, carbohydrates, toxic ions, proline, proteins

Crescimento de girassol em função da inoculação de sementes com bactérias endofíticas

The sunflower crop has a great importance worldwide, due to the oil of excellent quality extracted from its seeds and in natura grains that are consumed in various ways. However, drought is one of the main environmental factors that limit its yield. An experiment was carried out under controlled greenhouse conditions, in a completely randomized experimental design, in order to determine the effect of endophytic bacteria inoculation ( Bacillus sp. and Enterobacter cloacae ) on the growth and contents of nutrients and organic solutes, in sunflower leaves and roots under water deficit. Plant height, stem diameter, fresh and dry biomass of shoot and roots, as well as contents of N, P, K, soluble carbohydrates, free proline, free amino acids and soluble proteins, were determined at 35 days after the plant emergence. The water deficit reduced plant growth regardless inoculation. However, under optimum conditions of soil moisture, the combination of both endophytic bacteria increased the sunflower growth. The water deficit also increased the N and K contents in leaves, as well as the organic solutes content in shoots, especially in inoculated plants. These results suggest that the inoculation of endophytic bacteria may increase the capacity of drought stressed plants to perform the osmotic adjustment through a higher accumulation of organic solutes, when compared to plants not inoculated.