Allan Klynger da Silva Lobato

Relationships between leaf pigments and photosynthesis in common bean plants infected by anthracnose

Abstract The objective of this study was to: first, evaluate the infection effects caused by Colletotrichum lindemuthianum pathogen (race 2047) on photosynthetic pigments and gas exchanges in Phaseolus vulgaris plants (cv. Mexico 222); and, second, determine infection effects on leaf pigments and their consequences on photosynthesis rate. A completely randomized design with a factorial scheme was used, combining two treatments (control and inoculated) and three evaluation periods (4th, 8th and 12th day). Carotenoid levels presented decreases of 28.3% and 35% during the 8th and 12th day after infection, when control and inoculated plants were compared. Correlation analysis demonstrated the direct relationship between carotenoids and photosynthesis rate (r = 0.84). Total chlorophyll in infected plants had progressive reductions of 6.4%, 20.6% and 21.3% on the 4th, 8th and 12th day, respectively, when treated and untreated plants were compared. Total chlorophyll with photosynthesis (r = 0.85) also revealed a significant and linear correlation. The photosynthetic rate in infected plants decreased by 22%, 49.9% and 77.3% on the 4th, 8th and 12th days after the inoculation, respectively. Anthracnose infection also induced negative effects concerning stomatal conductance, transpiration, photosynthesis and water use efficiency. Our results demonstrate that leaf pigment reduction as a result of pathogens was the main cause of lower gaseous exchanges in infected plants.

Tolerance to waterlogging in young Euterpe oleracea plants

This study investigated whether gas exchange and the present content of antioxidant compounds can contribute to the survival of Euterpe oleracea plants in environments of frequent waterlogging. A factorial randomised, experimental design included two distinct water conditions (waterlogging and control) and five evaluation times (0, 6, 12, 18, and 24 d). Gasexchange parameters, leaf temperature, electrolyte leakage, and contents of antioxidant compounds were measured. Waterlogging did not promote significant alterations in net photosynthetic rate and transpiration, and stomatal conductance was reduced only after 18 d. Malondialdehyde and glutathione contents did not significantly change during waterlogging. Additionally, electrolyte leakage was significant only after 18 d of waterlogging. Thus, this study revealed that maintenance in gas exchange and antioxidant compounds might contribute to the survival of E. oleracea plants in environments exposed to waterlogging.

Silicon mitigates oxidative stress and has positive effects in Eucalyptus platyphylla under aluminium toxicity

The tolerance to metal toxicity, such as aluminium, can be induced by the formation of Al-Si complexes. Therefore, the aim of this research is to determine the contribution of Si on nutrient concentrations, compounds linked to oxidative stress, photosynthetic pigments and gas exchange and to determine if Si can improve the tolerance mechanism of young Eucalyptus platyphylla plants exposed to Al toxicity. The experimental setup was completely randomized with four treatments (0, 1.6 mmol/L Al, 2.0 mmol/L Si and 1.6 mmol/L Al + 2.0 mmol/L Si; being described as the control, Al toxicity, Si and Al toxicity + Si, respectively). The treatment with Si attenuated the negative effects of Al on nutrient concentrations by reducing superoxide, hydrogen peroxide, malondialdehyde and electrolyte leakage. Pigments and gas exchange exhibited beneficial effects after Si application, with positive interactions also being detected between Si-Al. Therefore, this study demonstrates that Si reduced the oxidative stress and improved the tolerance mechanism of young E. platyphylla plants exposed to Al toxicity.

Growth, phosphorus status, and nutritional aspect in common bean exposed to different soil phosphate levels and foliar-applied phosphorus forms

This study aimed to investigate the effect of the foliar application of phosphite and phosphate on growth, phosphorus (P) status, and nutritional aspect of common bean (Phaseolus vulgarisxa0cv. Radiante) plants grown under different soil phosphate levels.xa0Experiment was organized in factorial scheme completely randomized using 2 soil phosphate levels (Pi-starved and Pi-sufficient plants), combined with 3 nutrient sources supplied via foliar application (KH2PO3, KH2PO4, and KCl used as control), and 2 foliar application numbers (single and two applications). In this study were measured root dry weight, shoot dry weight, and root to shoot ratio, as well as shoot P concentration, root P concentration, accumulated P in shoot, accumulated P in root, P uptake efficiency, P utilization efficiency, P translocation,xa0and macro and micronutrients in shoot.xa0Common bean growth under limiting phosphate availability in soil exhibited lower biomass yield and higher concentration of nutrients in shoot tissues. The results exhibit foliar-applied KH2PO3xa0causes harmful effects in phosphate-starved common bean. Either one or two foliar sprays of KH2PO4xa0were not sufficient to affect the growth and nutrition of the common bean plants, regardless of soil P status. n n xa0 n n Key words:xa0Phaseolus vulgaris, phosphorus, phosphate and phosphite anions, foliar application.

Tolerance to water deficit in cowpea populations resulting from breeding program: detection by gas exchange and chlorophyll fluorescence

Cowpea is a crop that exercises social, economic and nutritional importance on the population of several countries due to grain production. This study aimed to (1) evaluate the effect of water deficit stress on gas exchange and chlorophyll fluorescence parameters in six populations, and (2) identify the better population to select plants for tolerance to water deficit stress, derived from crosses of the cowpea cultivars cultivated under irrigation and water deficit conditions. The experimental design was completely randomized composed of six populations, with two parents P1 and P2, and F1, F2, BC1 and BC2 generations derived from the cross between BR3-Tracuateua (sensitive to drought) and Pingo de ouro-1-2 (tolerant to drought). F2 generations showed higher values of net photosynthetic rate, stomatal conductance and water-use efficiency when these populations were exposed to water deficit. In case of chlorophyll fluorescence parameters under water deficit stress, F2 populations showed better results for effective quantum yield of PSII, photochemical quenching and apparent electron-transport rate, while lower values of non-photochemical quenching, relative energy excess at the PSII level and ratio between the apparent electron-transport rate and net photosynthetic rate. Our results on gas exchange and chlorophyll fluorescence revealed that the better performance under water deficit conditions was found in F2 generation, and this validated the breeding strategy used in this program aiming tolerance to water deficit, was successful.

Effect of potassium sources on the antioxidant activity of eggplant

Potassium participates in the essential processes in plant physiology, however, the effects of K sources on plant metabolism have been little studied. Also, in certain cases, K sources and concentrations may cause undesirable effects, e.g., soil salinization. The objective was to evaluate the effect of K sources and levels on the enzyme activity of the antioxidant system and protein content in eggplant (Solanum melongena L.) leaves and to determine the most suitable K sources for these physiological characteristics. The experiment was conducted in randomized blocks, in a 2 × 4 factorial design, consisting of two K sources (KCl and K2SO4) and rates (250, 500, 750, and 1000 kg ha-1 K2O), with four replications. The following variables were evaluated: plant height, number of leaves per plant, superoxide dismutase (SOD), catalase (CAT), and leaf protein content. There was an increase in CAT activity with increasing K levels until 30 days after transplanting (DAT), when K2SO4 was applied and until 60 DAT, when KCl was used; after this period, the enzyme activity decreased under both sources. The activity of SOD increased in the presence of KCl, but was reduced with the application of K2SO4. For both K sources, increasing rates reduced the protein content and number of leaves per plant, and this reduction was greater under KCl application. Thus it was concluded that KCl tends more strongly to salinize the soil than K2SO4. Both for KCl and for K2SO4, the increasing rates adversely affected the activities of CAT and SOD and the levels of leaf protein in eggplant. The potential of KCl to reduce the enzyme activity of SOD and CAT, leaf protein content and plant growth of eggplant was stronger than that of K2SO4.

Differential behaviours in two species of Eucalyptus exposed to aluminium

One of the limiting factors in the growth and development of plants is soil acidity due to high aluminium (Al) content. The aim of this research was to determine the micronutrient contents, photosynthetic pigments, gas exchange and morphological parameters, and to explain the possible tolerance mechanisms involved in two species of the genus Eucalyptus that were exposed to low and high aluminium concentrations. The experiment was conducted in a factorial completely randomised design, with two aluminium concentrations, viz., 0.08 (low) and 1.60 (high)xa0mMxa0Al, and two species, i.e., Eucalyptus platyphylla and Eucalyptus grandis. High Al concentration increased the Al contents in E. platyphylla and E. grandis by 104 and 29%, respectively. Significant reductions of Fe, Zn and Mn contents were detected only in E. platyphylla. Reductions on chlorophyll b and total chlorophyll were observed in both the species, which were more intense in the E. platyphylla. Net photosynthetic rate and water use efficiency increased under high Al concentration, whereas stomatal conductance and transpiration rate decreased in E. grandis. Growth characteristics decreased under high Al concentration in E. platyphylla and increased in E. grandis, while opposite response was observed in both species under low Al concentration. Our results described clearly that E. platyphylla is sensitive, while E. grandis is tolerant to Al. The tolerance mechanism of E. grandis can be explained by the maintenance of the iron, zinc and manganese supplies, combined with an increase in the chlorophyll a, net photosynthetic rate and water use efficiency, resulting in the mitigation of the Al effects on growth parameters.

Potential of calcium silicate to mitigate water deficiency in maize

The aim of this study was to evaluate the potential of calcium silicate to mitigate the effects of water deficiency in maize plants yield. A completely randomized factorial design, consisting of five combinations of calcium silicate (0, 25, 50, 75, and 100%) and five different soil moisture levels (30, 70, 100, 130, and 160%), was adopted. The following parameters were evaluated: soil matric potential, xylem water potential, silicon concentration, leaf dry weight, and dry mass production. Matric potential monitoring confirmed that the irrigation depths employed resulted in different environments for maize plant development during the experiment. Confirming the hypothesis of the study, at the lower irrigation depths, the maize production has accompanied the increase in calcium silicate used as corrective up to the proportion of 50%. These results indicate that silicon mitigated the impact of water deficiency in maize plants and increased the xylem water potential.

Antioxidant enzymes efficiently control leaf and root cell damage in young Euterpe oleracea plants exposed to waterlogging

Euterpe oleracea (Mart.), an Amazonian palm, is of economic importance due to the production of energy drinks. Plants exposed to waterlogging are prone to damage at the cellular level and cause irreversible metabolic dysfunctions leading to cell death. This study was aimed to study cell damages and to investigate enzyme activities related to antioxidant system in this specie. The experimental design was in factorial randomized with two water conditions (waterlogging and control) and five evaluation times (0, 6, 12, 18, and 24xa0days). The parameters measured were electrolyte leakage (EL), contents of hydrogen peroxide (H2O2), malondialdehyde (MDA) and glutathione (GSH), and enzymatic activities of catalase (CAT), ascorbate peroxidase (APX) and peroxidase (POX) in leaf and root tissues. Waterlogging did not promote significant modifications in EL, MDA and H2O2 in both the tissues evaluated, and a minor alteration in GSH was observed only in the roots. Significant increases in the activity of CAT, APX and POX were observed in leaf and roots, at early stages. It can thus be concluded that CAT, APX and POX were efficient in controlling EL and MDA in leaf and root of E. oleracea plants under waterlogging.