Carlos Antônio Ferreira de Sousa

The metabolic response of plants to oxygen deficiency

As plantas, em condicoes naturais ou experimentais, podem ser submetidas a disponibilidade de O2 que varia desde os teores normais (normoxia), passando pela deficiencia (hipoxia) ou ate mesmo pela ausencia (anoxia). Varios processos metabolicos sao afetados pela deficiencia de O2, porem os eventos mais estudados sao aqueles relacionados a respiracao e ao metabolismo de N. Na ausencia de um aceptor eletronico terminal na cadeia de transporte de eletrons, o ciclo do acido tricarboxilico passa a funcionar parcialmente e em ambas as direcoes. Ocorre a acidificacao do citosol e o piruvato, produto da glicolise, e transformado em lactato e etanol, que representam as principais reacoes fermentativas das plantas. A alanina e o terceiro mais importante produto do metabolismo anaerobico, sendo resultante de altas taxas de interconversao entre os aminoacidos em que as transaminases, tais como alanina aminotransferase, desempenham um papel importante. O acumulo de alanina sob anaerobiose parece ser independente da fonte de N: NO3-, NH4+ ou N2 e o seu papel precisa ser esclarecido. Da mesma forma, ainda nao esta completamente entendido como o NO3- exerce seu efeito benefico sobre a tolerância radicular a hipoxia em plantas encharcadas. Tais aspectos do metabolismo de N colocam desafios interessantes para as futuras pesquisas sobre as respostas das plantas a deficiencia de oxigenio.

Induced over-expression of AtDREB2A CA improves drought tolerance in sugarcane

Drought is one of the most challenging agricultural issues limiting sustainable sugarcane production and, in some cases, yield losses caused by drought are nearly 50%. DREB proteins play vital regulatory roles in abiotic stress responses in plants. The transcription factor DREB2A interacts with a cis-acting DRE sequence to activate the expression of downstream genes that are involved in drought-, salt- and heat-stress response in Arabidopsis thaliana. In the present study, we evaluated the effects of stress-inducible over-expression of AtDREB2A CA on gene expression, leaf water potential (ΨL), relative water content (RWC), sucrose content and gas exchanges of sugarcane plants submitted to a four-days water deficit treatment in a rhizotron-grown root system. The plants were also phenotyped by scanning the roots and measuring morphological parameters of the shoot. The stress-inducible expression of AtDREB2A CA in transgenic sugarcane led to the up-regulation of genes involved in plant response to drought stress. The transgenic plants maintained higher RWC and ΨL over 4 days after withholding water and had higher photosynthetic rates until the 3rd day of water-deficit. Induced expression of AtDREB2A CA in sugarcane increased sucrose levels and improved bud sprouting of the transgenic plants. Our results indicate that induced expression of AtDREB2A CA in sugarcane enhanced its drought tolerance without biomass penalty.

Erythrina speciosa (Leguminosae-Papilionoideae) under soil water saturation: morphophysiological and growth responses.

BACKGROUND AND AIMS Erythrina speciosa is a Neotropical tree that grows mainly in moist habitats. To characterize the physiological, morphological and growth responses to soil water saturation, young plants of E. speciosa were subjected experimentally to soil flooding. METHODS Flooding was imposed from 2 to 4 cm above the soil surface in water-filled tanks for 60 d. Non-flooded (control) plants were well watered, but never flooded. The net CO(2) exchange (A(CO2)), stomatal conductance (g(s)) and intercellular CO(2) concentration (C(i)) were assessed for 60 d. Soluble sugar and free amino acid concentrations and the proportion of free amino acids were determined at 0, 7, 10, 21, 28 and 45 d of treatments. After 28, 45 and 60 d, dry masses of leaves, stems and roots were determined. Stem and root cross-sections were viewed using light microscopy. KEY RESULTS The A(CO2) and g(s) were severely reduced by flooding treatment, but only for the first 10 d. The soluble sugars and free amino acids increased until the tenth day but decreased subsequently. The content of asparagine in the roots showed a drastic decrease while those of alanine and gamma-aminobutyric increased sharply throughout the first 10 d after flooding. From the 20th day on, the flooded plants reached A(CO2) and g(s) values similar to those observed for non-flooded plants. These events were coupled with the development of lenticels, adventitious roots and aerenchyma tissue of honeycomb type. Flooding reduced the growth rate and altered carbon allocation. The biomass allocated to the stem was higher and the root mass ratio was lower for flooded plants when compared with non-flooded plants. CONCLUSIONS Erythrina speciosa showed 100 % survival until the 60th day of flooding and was able to recover its metabolism. The recovery during soil flooding seems to be associated with morphological alterations, such as development of hypertrophic lenticels, adventitious roots and aerenchyma tissue, and with the maintenance of neutral amino acids in roots under long-term exposure to root-zone O(2) deprivation.

Overexpression of BdMATE Gene Improves Aluminum Tolerance in Setaria viridis

Acidic soils are distributed worldwide, predominantly in tropical and subtropical areas, reaching around 50% of the arable soil. This type of soil strongly reduces crop production, mainly because of the presence of aluminum, which has its solubility increased at low pH levels. A well-known physiological mechanism used by plants to cope with Al stress involves activation of membrane transporters responsible for organic acid anions secretion from the root apex to the rhizosphere, which chelate Al, preventing its absorption by roots. In sorghum, a membrane transporter gene belonging to multidrug and toxic compound extrusion (MATE) family was identified and characterized as an aluminum-activated citrate transporter gene responsible for Al tolerance in this crop. Setaria viridis is an emerging model for C4 species and it is an important model to validate some genes for further C4 crops transformation, such as sugarcane, maize, and wheat. In the present work, Setaria viridis was used as a model plant to overexpress a newly identified MATE gene from Brachypodium distachyon (BdMATE), closely related to SbMATE, for aluminum tolerance assays. Transgenic S. viridis plants overexpressing a BdMATE presented an improved Al tolerance phenotype, characterized by sustained root growth and exclusion of aluminum from the root apex in transgenic plants, as confirmed by hematoxylin assay. In addition, transgenic plants showed higher root citrate exudation into the rhizosphere, suggesting that Al tolerance improvement in these plants could be related to the chelation of the metal by the organic acid anion. These results suggest that BdMATE gene can be used to transform C4 crops of economic importance with improved aluminum tolerance.

A procedure for maize genotypes discrimination to drought by chlorophyll fluorescence imaging rapid light curves

BackgroundPhotosynthesis can be roughly separated into biochemical and photochemical processes. Both are affected by drought and can be assessed by non-invasive standard methods. Gas exchange, which mainly assesses the first process, has well-defined protocols. It is considered a standard method for evaluation of plant responses to drought. Under such stress, assessment of photochemical apparatus by chlorophyll fluorescence needs improvement to become faster and reproducible, especially in growing plants under field conditions. For this, we developed a protocol based on chlorophyll fluorescence imaging, using a rapid light curve approach.ResultsAlmost all parameters obtained by rapid light curves have shown statistical differences between control and drought stressed maize plants. However, most of them were affected by induction processes, relaxation rate, and/or differences in chlorophyll content; while they all were influenced by actinic light intensity on each light step of light curve. Only the normalized parameters related to photochemical and non-photochemical quenching were strongly correlated with data obtained by gas exchange, but only from the light step in which the linear electron flow reached saturation.ConclusionsThe procedure developed in this study for discrimination of plant responses to water deficit stress proved to be as fast, efficient and reliable as the standard technique of gas exchange in order to discriminate the responses of maize genotypes to drought. However, unlike that, there is no need to perform daily and time consuming calibration routines. Moreover, plant acclimation to the dark is not required. The protocol can be applied to plants growing in both controlled conditions and full sunlight in the field. In addition, it generates parameters in a fast and accurate measurement process, which enables evaluating several plants in a short period of time.

Nova abordagem para a fenotipagem de plantas: conceitos, ferramentas e perspectivas (New approach for plant phenotyping: concepts, current tools and perspectives)

As tecnicas tradicionais de fenotipagem de plantas usam caracteristicas facilmente mensuraveis, com base em medidas relacionadas, por exemplo, ao peso e ao tamanho das plantas. Tais medidas podem ser realizadas em qualquer horario, sem protocolo, preparacao previa da amostra ou conhecimentos profundos para a obtencao e interpretacao dos dados. Por isso, sao as mais usadas na experimentacao a campo, embora envolvam metodos destrutivos e sejam altamente demandadoras de tempo, recursos financeiros e mao-de-obra. Em razao dos desafios atuais relacionados a competitividade do mercado de cultivares, a sustentabilidade do agronegocio e as mudancas climaticas globais, os cientistas de plantas tem buscado agregar modernas tecnicas de fenotipagem ao processo de desenvolvimento de novas cultivares. Tais tecnicas devem permitir uma analise ampla, detalhada e precisa da manifestacao das informacoes geneticas do individuo e sua interacao com o meio ambiente, aumentando assim a eficiencia e eficacia do processo de selecao. Consequentemente, as novas tecnicas de fenotipagem tem avancado em escala, precisao, reprodutibilidade e complexidade em relacao as tecnicas tradicionais, principalmente pelo uso de imagens geradas em plataformas automatizadas. Tais plataformas sao constituidas de estacoes para a geracao de imagens que utilizam diferentes tecnicas espectroscopicas, para cobrir diferentes regioes do espectro eletromagnetico. As estacoes mais comuns capturam imagens digitais RGB, de fluorescencia da clorofila, UV/VIS, termograficas e na regiao do NIR, as quais possibilitam a avaliacao do crescimento das plantas, do aparato fotoquimico, dos teores de pigmentos, da temperatura da copa e de diferentes metabolitos encontrado nas plantas. Traditional techniques of plant phenotyping use easily measurable traits, based on measures related for instance to plant weight and size. Such measurements can be made at any time, without protocol, prior sample preparation or deep knowledge for obtaining and interpreting the data. However, they require field experimentation, financial resources and manpower, use destructive methods and are time-consuming. Due to the current challenges related to the competitiveness of the cultivars market, the sustainability of agribusiness and global climate change, plant scientists have sought more specific and dynamics features, which are used to assist in explaining the responses of plants to the environment. To evaluate these characteristics, plant phenotyping has advanced in scale, precision, reproducibility and complexity compared to traditional techniques, especially by using automated platforms images. Such platforms consist of automated imaging stations that use different techniques to cover different regions of the electromagnetic spectrum. The most common imaging stations capture digital RGB, chlorophyll fluorescence, UV/VIS, thermographic and NIR images, which enable the evaluation of plant growth, photochemical apparatus, pigments content, canopy temperature and several metabolites found in plants. Keywords: plant evaluation, spectroscopy, phenotyping platforms, sensors