Queila Souza Garcia

Reactive oxygen species and seed germination

Reactive oxygen species (ROS) are continuously produced by the metabolically active cells of seeds, and apparently play important roles in biological processes such as germination and dormancy. Germination and ROS accumulation appear to be linked, and seed germination success may be closely associated with internal ROS contents and the activities of ROS-scavenging systems. Although ROS were long considered hazardous molecules, their functions as cell signaling compounds are now well established and widely studied in plants. In seeds, ROS have important roles in endosperm weakening, the mobilization of seed reserves, protection against pathogens, and programmed cell death. ROS may also function as messengers or transmitters of environmental cues during seed germination. Little is currently known, however, about ROS biochemistry or their functions or the signaling pathways during these processes, which are to be considered in the present review.

Comportamento germinativo de três espécies de Vellozia da Serra do Cipó, MG

The objective of this study was to evaluate the germinative behaviour of Vellozia gigantea N.L. Menezes & Mello-Silva, Vellozia glandulifera Goethart & Henrard and Vellozia variabilis Mart. ex Schult. & Schult (Velloziaceae). The germination experiments took place in germination chambers at continuous light and dark, and constant temperatures of 15, 20, 25, 30, 35 and 40oC. The seeds of the studied species presented high percentages of germination in light at 20 to 40oC, and V. glandulifera was the only species that the seeds germinated in the temperature of 15oC. In the dark, the seeds of V. glandulifera germinated at 20 to 40oC, showing germination percentages lower than 30%. The seeds of V. variabilis and V. gigantea germinated in a strict of the dark, presenting elevated germination percentage in higher temperatures (35 to 40oC). The species of Vellozia are positive photoblastic in a wide range of temperatures, which indicates a adaptation of these species to their habitats, once they grow in fields and their seeds might be subjected to high light intensities.

Phylogeny strongly drives seed dormancy and quality in a climatically buffered hotspot for plant endemism.

Background and Aims Models of costs and benefits of dormancy (D) predict that the evolutionarily stable strategy in long-term stable environments is for non-dormancy (ND), but this prediction remains to be tested empirically. We reviewed seed traits of species in the climatically buffered, geologically stable and nutrient-impoverished campo rupestre grasslands in Brazil to test the hypothesis that ND is favoured over D. We examined the relative importance of life-history traits and phylogeny in driving the evolution of D and assessed seed viability at the community level. Methods Germination and viability data were retrieved from 67 publications and ND/D was determined for 168 species in 25 angiosperm families. We also obtained the percentage of embryoless, viable and dormant seeds for 74 species. Frequencies of species with dormant and non-dormant seeds were compared with global databases of dormancy distribution. Key Results The majority of campo rupestre taxa (62·5 %) had non-dormant seeds, and the ND/D ratio was the highest for any vegetation type on Earth. Dormancy was unrelated to other species life-history traits, suggesting that contemporary factors are poor predictors of D. We found a significant phylogenetic structure in the dormancy categorical trait. Dormancy diversity was highly skewed towards the root of the phylogenetic tree and there was a strong phylogenetic signal in the data, suggesting a major role of phylogeny in determining the evolution of D versus ND and seed viability. Quantitative analysis of the data revealed that at least half of the seeds produced by 46 % of the surveyed populations were embryoless and/or otherwise non-viable. Conclusions Our results support the view that long-term climatic and geological stability favour ND. Seed viability data show that campo rupestre species have a markedly low investment in regeneration from seeds, highlighting the need for specific in situ and ex situ conservation strategies to avoid loss of biodiversity.

Phosphorous and sulfur nutrition modulate antioxidant defenses in Myracrodruom urundeuva plants exposed to arsenic.

We investigated if plant nutrition and antioxidant system activation are correlated features of arsenic (As)-tolerance in Myracrodruom urundeuva. Plants were grown for 120 days in substrates with 0, 10, 50 and 100mg Askg(-1) and its As-tolerance was demonstrated. As-concentrations greater than 10mgkg(-1) decreased plant growth and photosynthesis but did not induce plant death. Plants coupled alterations in stomatal conductance and transpiration to avoid As-deleterious effects to the photosynthetic apparatus. As-toxicity in M. urundeuva was due to lipid peroxidation induced by hydrogen peroxide accumulation. Ascorbate peroxidase (APX) and gluthatione peroxidase (GPX) had central roles in hydrogen peroxide (H2O2) scavenging in leaves, and their activities were linked to changes in redox potentials (ascorbate and glutathione pools). APX and GPX inactivation/degeneration led to H2O2 accumulation and related lipid peroxidation. Increased phosphorus (P) and sulfur (S) concentrations in leaves were related to increased APX and GPX activities by stimulating increases in glutathione biosynthesis. We concluded that P and S nutrition were directly linked to As-tolerance in M. urundeuva plants by increasing antioxidant system activities.

Phosphorus improves arsenic phytoremediation by Anadenanthera peregrina by alleviating induced oxidative stress.

Due to similarities in their chemical behaviors, studies examining interactions between arsenic (As)—in special arsenate—and phosphorus (P) are important for better understanding arsenate uptake, toxicity, and accumulation in plants. We evaluated the effects of phosphate addition on plant biomass and on arsenate and phosphate uptake by Anadenanthera peregrina, an important Brazilian savanna legume. Plants were grown for 35 days in substrates that received combinations of 0, 10, 50, and 100 mg kg−1 arsenate and 0, 200, and 400 mg kg−1 phosphate. The addition of P increased the arsenic-phytoremediation capacity of A. peregrina by increasing As accumulation, while also alleviating As-induced oxidative stress. Arsenate phytotoxicity in A. peregrina is due to lipid peroxidation, but not hydrogen peroxide accumulation. Added P also increased the activity of important reactive oxygen species-scavenging enzymes (catalase and ascorbate peroxidase) that help prevent lipid peroxidation in leaves. Our findings suggest that applying P represents a feasible strategy for more efficient As phytoremediation using A. peregrina.

Tissue-specific hormonal profiling during dormancy release in macaw palm seeds.

Little is known about the control exerted by hormones in specific tissues during germination and post-germinative development in monocot seeds, whose embryos have complex structures and can remain dormant for long periods of time. Here the tissue-specific hormonal profile of macaw palm (Acrocomia aculeata) seeds overcoming dormancy and seedling during initial development was examined. Endogenous hormonal concentrations were determined in the cotyledonary petiole, haustorium, operculum, endosperm adjacent to the embryo and peripheral endosperm of dry dormant seeds, imbibed seeds trapped in phase I of germination, and germinating (phase 2 and phase 3) seeds 2, 5, 10 and 15 days after sowing. Evaluations were performed on seeds treated for overcoming dormancy by removal of the operculum and by immersion in a gibberellic acid (GA3 ) solution. Removal of the operculum effectively helped in overcoming dormancy, which was associated with the synthesis of active gibberellins (GAs) and cytokinins (CKs), as well as reductions of abscisic acid (ABA) in the cotyledonary petiole. In imbibed seeds trapped in phase I of germination, exogenous GA3 caused an increase in active GAs in the cotyledonary petiole and operculum and reduction in ABA in the operculum. Initial seedling development was associated with increases in the CK/auxin ratio in the haustorium and GA levels in the endosperm which is possibly related to the mobilization of metabolic reserves. Increases in salicylic acid (SA) and jasmonic acid (JA) concentrations were associated with the development of the vegetative axis. Hormones play a crucial tissue-specific role in the control of dormancy, germination and initial development of seedlings in macaw palm, including a central role not only for GAs and ABA, but also for CKs and other hormones.

Efeito da luz e da temperatura na germinação de sementes de quatro espécies de Xyris L. (Xyridaceae) ocorrentes na Serra do Cipó, MG, Brasil

As especies do genero Xyris sao tipicas de solos brejosos ou umidos, sendo bastante frequentes nos campos rupestres de Minas Gerais. O objetivo deste estudo foi investigar o comportamento germinativo de sementes de X. cipoensis Smith & Downs, X. longiscapa A. Nilsson, X. platystachia A. Nilsson e X. trachyphylla Mart. sob diferentes condicoes de luz e temperatura. Os experimentos de germinacao foram realizados em câmaras de germinacao nas temperaturas constantes de 15, 20, 25, 30, 35 e 40oC, sob luz e escuro continuos, e nas alternâncias de 25-15, 30-15, 30-20, 35-15, 35-20 e 35-25oC, onde as temperaturas mais altas referem-se ao periodo de luz, sob fotoperiodo de 12 horas. As quatro especies de Xyris apresentam sementes pequenas e sensiveis a luz, com resposta nula de germinacao no escuro. As sementes de X. cipoensis germinaram em faixa mais estreita de temperatura (20 a 30oC), apresentando alta porcentagem de germinacao na temperatura constante de 20oC. A faixa de 15 a 30oC foi favoravel a germinacao das sementes de X. longiscapa, X. platystachia e X. trachyphylla, apresentando baixo percentual de germinacao a 15oC. As temperaturas alternantes nao favoreceram a germinacao em relacao as temperaturas constantes.

Effect of post-planting inoculation with Bradyrhizobium sp and mycorrhizal fungi on the growth of Brazilian rosewood, Dalbergia nigra Allem. ex Benth., in two tropical soils

Six months after planting, seedlings of the leguminous treeDalbergia nigra, known as Brazilian rosewood, wereinoculated with a selected Bradyrhizobium strainBHICB-DN 15,either alone or in combination with mycorrhizal fungi to determine their effecton the growth of D. nigra in Atlantic forest andeucalyptussoils. Height growth of D. nigra was similar in both soilsand six months after inoculation Bradyrhizobium did notaffect the D. nigra height growth, but it did improve drymass and especially in the nitrogen content of plants grown in eucalyptus soil.The success of the delayed inoculation with BHICB-DN 15 confirms its competitiveability “vis-à-vis” indigenous soil rhizobia. Co-inoculationof BHICB-DN 15 and mycorrhizal fungi did not increase plant dry weight,nitrogenand phosphorus content or mycorrhizal colonization. These results suggest thatthe BHICB-DN 15 strain had no synergistic relationship with the mycorrhizalfungi or that there was incompatibility between symbionts, in both soils.

Germination characteristics of S yngonanthus seeds ( Eriocaulaceae) in campos rupestres vegetation in south-eastern Brazil

The present study evaluated the size and germination characteristics of seeds of seven species of Syngonanthus (distributed among four sections) that occur in different microhabitats in campos rupestres vegetation in Minas Gerais State, to determine if (1) the germination responses of the various species characterize a single germination pattern for the genus; and (2) there is a correlation between the germination characteristics and the geographic distribution as well as the microhabitat of the different species. The experiments were undertaken with recently collected seeds exposed to a 12-h photoperiod and continuous darkness, at constant temperatures of 10–40°C (at intervals of 5°C) in germination chambers. The results indicated the existence of a pattern of reduced seed size and light requirements for germination within the genus. The geographic distribution of different species of the genus cannot be explained by the responses of seed germination to different temperatures, but suggests some relationship to their edaphic microhabitats. Therefore, germination characteristics of the populations studied may have been selected to colonize specific environments at different soil water conditions.

Ecophysiological response to seasonal variations in water availability in the arborescent, endemic plant Vellozia gigantea

The physiological response of plants growing in their natural habitat is strongly determined by seasonal variations in environmental conditions and the interaction of abiotic and biotic stresses. Here, leaf water and nutrient contents, changes in cellular redox state and endogenous levels of stress-related phytohormones (abscisic acid (ABA), salicylic acid and jasmonates) were examined during the rainy and dry season in Vellozia gigantea, an endemic species growing at high elevations in the rupestrian fields of the Espinhaço Range in Brazil. Enhanced stomatal closure and increased ABA levels during the dry season were associated with an efficient control of leaf water content. Moreover, reductions in 12-oxo-phytodienoic acid (OPDA) levels during the dry season were observed, while levels of other jasmonates, such as jasmonic acid and jasmonoyl-isoleucine, were not affected. Changes in ABA and OPDA levels correlated with endogenous concentrations of iron and silicon, hydrogen peroxide, and vitamin E, thus indicating complex interactions between water and nutrient contents, changes in cellular redox state and endogenous hormone concentrations. Results also suggested crosstalk between activation of mechanisms for drought stress tolerance (as mediated by ABA) and biotic stress resistance (mediated by jasmonates), in which vitamin E levels may serve as a control point. It is concluded that, aside from a tight ABA-associated regulation of stomatal closure during the dry season, crosstalk between activation of abiotic and biotic defences, and nutrient accumulation in leaves may be important modulators of plant stress responses in plants growing in their natural habitat.