Carbon assimilation, isotope discrimination, proline and lipid peroxidation contribution to barley (Hordeum vulgare) salinity tolerance

Barley (Hordeum vulgare L.) exhibits great adaptability to salt tolerance in marginal environments because of its great genetic diversity. Differences in main biochemical, physiological, and molecular processes, which could explain the different tolerance to soil salinity of 16 barley varieties, were examined during a two-year field experiment. The study was conducted in a saline soil with an electrical conductivity ranging from 7.3 to 11.5 dS/m. During the experiment, a number of different physiological and biochemical characteristics were evaluated when barley was at the two-to three-nodes growing stage (BBCH code 32–33). The results indicated that there were significant (p < 0.001) effects due to varieties for tolerance to salinity. Carbon isotopes discrimination was higher by 11.8% to 16.0% in salt tolerant varieties than that in the sensitive ones. Additionally, in the tolerant varieties, assimilation rates of CO2 and proline concentration were 200% and up to 67% higher than the sensitive varieties, respectively. However, in sensitive varieties, hydrogen peroxide and lipid peroxidation were enhanced, indicating an increased lipid peroxidation. The expression of the genes Hsdr4, HvA1, and HvTX1 did not differ among barley varieties tested. This study suggests that the increased carbon isotopes discrimination, increased proline concentration (play an osmolyte source role), and decreased lipid peroxidation are traits that are associated with barley tolerance to soil salinity. Moreover, our findings that proline improves salt tolerance by up-regulating stress-protective enzymes and reducing oxidation of lipid membranes will encourage our hypothesis that there are specific mechanisms that can be co-related with the salt sensitivity or the tolerance of barley. Therefore, further research is needed to ensure the tolerance mechanisms that exclude NaCl in salt tolerant barley varieties and diminish accumulation of lipid peroxides through adaptive plant responses. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

Anthocyanin accumulation in poinsettia leaves and its functional role in photo-oxidative stress

The role of anthocyanin accumulation in poinsettia leaves exposed to photo-oxidative stress was evaluated by comparing green (anthocyanin less) and reddish (anthocyanin well equipped) leaves, co-occurring in poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch). For the assessment we compared the photoprotective and antioxidant mechanisms in the two leaf types in response to photo-oxidative stress, generated in chloroplasts by the application of methyl viologen (MV). MV accepts electrons from photosystem I (PSI) with subsequent transfer to molecular oxygen to produce superoxide anions (O2 [rad] –) that are converted by the chloroplast superoxide dismutase (SOD) to hydrogen peroxide (H2O2) that is reduced by ascorbate peroxidase (APX) to water and oxygen. At 90ömin after MV application, the decrease in the activity of the H2O2-scavenging enzyme APX resulted in increased H2O2 levels in both leaf types, but to a significantly lower level in the reddish leaves, possibly due to the significantly higher anthocyanin and phenolic content that are considered as H2O2-scavengers. Reddish poinsettia leaves having higher antioxidant activity possessed more effective photoprotective and reactive oxygen species (ROS)-scavenging mechanisms, including higher enzymatic (SOD and APX), and non-enzymatic (anthocyanin and phenolic) content over the green ones. Anthocyanin well equipped poinsettia leaves were in advantage in response to photo-oxidative stress over the anthocyanin less ones that appeared not to be equally protected. This superiority in the avoidance of the photo-oxidative stress by the reddish leaves was also associated to a higher effective quantum yield of PSII photochemistry (ΦPSII), a lower excitation pressure (1- qp) and a lower H2O2 generation, compared to their green counterparts. © 2020 Elsevier B.V

Differences in Al tolerance between Plantago algarbiensis and P. almogravensis reflect their ability to respond to oxidative stress

We evaluated the impact of low pH and aluminum (Al) on the leaves and roots of Plantago almogravensis Franco and Plantago algarbiensis Samp., focusing on energy partitioning in photosystem II, H2O2 levels, lipid peroxidation, electrolyte leakage (EL), protein oxidation, total soluble protein content and antioxidant enzyme activities. In both species, Al triggered more changes in oxidative metabolism than low pH alone, particularly in the roots. We found that Al increased the levels of H2O2 in P. algarbiensis roots, but reduced the levels of H2O2 in P. almogravensis leaves and roots. Neither low pH nor Al affected the spatial heterogeneity of chlorophyll fluorescence, the maximum photochemical efficiency of PSII (F-v/F-m), the actual quantum efficiency of PSII (I center dot(PSII)) or the quantum yields of regulated (I center dot(NPQ)) and nonregulated (I center dot(NO)) energy dissipation, and there was no significant change in total soluble protein content and EL. In P. algarbiensis, Al increased the carbonyl content and the activities of superoxide dismutase (SOD) and catalase (CAT) in the roots, and also CAT, ascorbate peroxidase and guaiacol peroxidase activities in the leaves. In P. almogravensis, Al reduced the level of malondialdehyde in the roots as well as SOD activity in the leaves and roots. We found that P. almogravensis plantlets could manage the oxidative stress caused by low pH and Al, whereas the P. algarbiensis antioxidant system was unable to suppress Al toxicity completely, leading to the accumulation of H2O2 and consequential protein oxidation in the roots

Indicadores fisiológicos da interação entre deficit hídrico e acidez do solo em cana-de-açúcar Physiological indicators of the interaction between water deficit and soil acidity in sugarcane

O objetivo deste trabalho foi avaliar os indicadores fisiológicos da interação entre deficit hídrico e acidez do solo em plantas jovens de cana-de-açúcar. As plantas foram submetidas a três tratamentos de disponibilidade hídrica, medidos em percentagem de capacidade de campo (CC) - sem estresse (70% CC), estresse moderado (55% CC) e estresse severo (40% CC); e três tratamentos de acidez no solo, medidos em termos de saturação por bases (V) - baixa acidez (V = 55%), média acidez (V = 33%) e alta acidez (V = 23%). O experimento foi realizado em casa de vegetação a 29,7±4,3ºC e 75±10% UR. O delineamento experimental utilizado foi o de blocos ao acaso, em esquema fatorial 3x3, com quatro repetições. Após 60 dias, foram determinados os teores de solutos compatíveis - trealose, glicina betaína e prolina - na folha diagnóstico e o crescimento inicial da parte aérea. Os solutos compatíveis trealose, glicina betaína e prolina são indicadores do efeito da interação dos estresses hídrico e ácido no solo. O acúmulo dos solutos compatíveis nos tecidos foliares das plantas não é capaz de impedir a redução na produção de matéria seca da cana-de-açúcar, resultante do agravamento nas condições de disponibilidade hídrica e de acidez no solo.<br>The aim of this work was to assess the physiological indicators of the interaction between water deficit and soil acidity, in sugarcane. The plants were submitted to three treatments of water availability - no stress (70% of field capacity, FC), moderate stress (55% FC), and extreme stress (40% FC); and three acidity treatments - no acidity [base saturation (V) = 55%], average acidity (V = 33%), and high acidity (V = 23%). The experiment was carried out in greenhouse, with 29.7±4.3ºC and 75±10% RH. The experimental design was in randomized blocks, in 3x3 factorial arrangement, with four replicates. After 60 days, the contents of compatible solutes - trehalose, glycine betaine and proline - in the diagnostic leaf and the initial growth of shoots were determined. The compatible solutes trehalose, glycine betaine, and proline are indicators of the interaction of water and acidity stresses in the soil. The accumulation of compatible solutes in plant foliar tissues can not prevent sugarcane losses in dry matter production, caused by increasing water deficit and soil acidity