Ana Maria Magalhães Andrade Lagôa

Superoxide dismutase and ascorbate peroxidase improve the recovery of photosynthesis in sugarcane plants subjected to water deficit and low substrate temperature.

The physiological responses of C4 species to simultaneous water deficit and low substrate temperature are poorly understood, as well as the recovery capacity. This study investigated whether the effect of these abiotic stressors is cultivar-dependent. The differential responses of drought-resistant (IACSP94-2094) and drought-sensitive (IACSP97-7065) sugarcane cultivars were characterized to assess the relationship between photosynthesis and antioxidant protection by APX and SOD isoforms under stress conditions. Our results show that drought alone or combined with low root temperature led to excessive energetic pressure at the PSII level. Heat dissipation was increased in both genotypes, but the high antioxidant capacity due to higher SOD and APX activities was genotype-dependent and it operated better in the drought-resistant genotype. High SOD and APX activities were associated with a rapid recovery of photosynthesis in IACSP94-2094 plants after drought and low substrate temperature alone or simultaneously.

Lead uptake and tolerance of Ricinus communis L.

Phytoextraction is an important technique used for the decontamination of areas polluted by lead. Consequently, an understanding of the physiological responses to tolerance of tropical species subjected to increasing levels of contamination is fundamental before considering their use as phytoextractors in contaminated areas. The objective of this study was to assess the lead (Pb) uptake and the tolerance of Ricinus communis L. The plants were cultivated in nutrient solution in a greenhouse under controlled conditions. Lead was tested at concentrations of 0, 100, 200 and 400 µmol L-1. The experimental set-up was a block design, using a 4 x 1 factorial scheme, with three replicates. Biometric analyses, photosynthesis rates, and Pb content in the nutritive solution as well as in roots and shoots were performed. In conclusion, R. communis L is a hyperaccumulator species for Pb and presents tolerance properties in lead light concentration.

Pb-phytoextraction by maize in a Pb-EDTA treated Oxisol

One of the most viable strategies to restore metal contaminated soils is the introduction of plants specialized in their accumulation or able to tolerate very high metal concentrations. This research evaluated: i. the maize as a Pb-accumulator plant; ii. the effects of EDTA-chelating agent for Pb-uptake by maize; iii. amending effect of EDTA on the soil Pb-availability using different extracts. Treatments consisted of Pb rates (100; 200; 350; 1,200 and 2,400 mg kg -1 ) applied to a Rhodic Hapludox in the form of Pb 3 (NO) 2 with (0.5 g kg -1 ) and without EDTA. Lead concentrations were determined in maize plant shoots. Soil available Pb was obtained using DTPA, Mehlich-3 and saturation solutions methods. Ionic speciation in the soil solution was performed using the software Visual-Minteq. Although a low t value was found (t 1,500 mg kg -1 of Pb) in maize shoots regardless of EDTA addition. Maize plants treated with EDTA had lower dry matter yield, mainly due to toxic levels of Fe and Al of the Oxisol. All extracting solutions were effective to determine available Pb in soil samples, but the saturation extract is a more difficult and time consuming procedure. At low and medium Pb levels, the plants grew less on EDTA, therefore the phytoextration process was less efficient. The addition of EDTA to the soil is not recommended with the purpose of increasing Pb

Trocas gasosas e condutância estomática em três espécies de gramíneas

Avaliou-se, sob condicoes naturais e sem deficiencia hidrica, o comportamento diario das taxas de assimilacao de CO2 (A) e de transpiracao (E), a condutância estomatica (g) e a eficiencia fotossintetica do uso de agua (E/A) em milho (C4), arroz (C3) e trigo (C3). Nas tres especies, a curva de resposta de A em funcao da irradiância (I), apresentou a forma de uma hiperbole retangular, porem em milho nao houve saturacao luminica. A resposta de g em relacao a I apresentou a mesma forma, respondendo E linearmente, nas tres especies. Em relacao a variacao de g, a curva de resposta de A tambem mostrou a forma de hiperbole retangular, enquanto E respondeu linearmente. Devido a resposta diferencial de A e de E, tanto em funcao de I como de g, a razao E/A aumentou com o aumento de I. As especies C3 (arroz e trigo) revelaram valores maiores de E/A que a C4 (milho), em todos os niveis de I e valores de g, indicando melhor adaptabilidade da C4 na limitacao de abertura estomatica.

Absorção de chumbo e potencial de fitorremediação de Canavalia ensiformes L.

Phytoextraction is an important technique used for decontamination of areas polluted by heavy metals. Consequently, understanding the physiological responses in relation to the tolerance of tropical species subjected to increasing levels of contamination is fundamental before considering their use as phytoextractans in contaminated areas. The objective of our study was to assess the potential of Canavalia ensiformes L. for the phytoextraction of lead (Pb). Plants were cultivated with nutrient solution in greenhouse under partially controlled conditions. Pb was tested at concentrations of 100, 200 and 400 µmol.L-1. The experimental set-up was a randomized blocks design, using a 4 x 1 factorial scheme, with three replicates. Follow-ups of physiological symptoms were carried out, determining fresh and dried mass for shoot and root, leaf area, plant height, Pb content in nutrient solution and in roots and shoot of the plants. The samples of shoot and roots and of the nutrient solution were submitted to chemical analysis for the determination of Pb, using dry digestion. The Canavalia ensiformes plants proved to be both accumulators and tolerant to Pb, demonstrating their potential as a phytoextractants.

Trocas gasosas e balanço de carboidratos em plantas de cana-de-açúcar sob condições de estresses radiculares

Although the photosynthetic responses of sugarcane plants to environmental stresses are well documented, the biomass ac- cumulation and the dynamic of carbohydrate reserves under simultaneous exposure of roots to low temperature and drought are not known. This work aims to investigate the effect of water deficit and low substrate temperature stresses, occurring alone or in combination, on the sugarcane IACSP94-2094, a drought-tolerant genotype. As our hypothesis, we assume that this genotype is also tolerant to low substrate temperature, since low temperatures and water deficit occur simultaneously under field conditions. The water deficit alone or in combination with low substrate temperature caused reductions in leaf water potential and CO 2 assimilation, which was not observed in plants subjected only to low substrate temperature. The leaf concentration of non-structural carbohydrates, sucrose and starch increased in plants under root chilling. In plants sub- jected to water deficit, we noticed decreases in leaf starch concentration. The root stresses caused an increase in the total soluble sugar concentration and reduction in starch concentration in sugarcane roots. As the plant biomass accumulation was not affected, even with the impairment of root growth under low substrate temperature, we conclude that the sugarcane genotype IACSP94-2094 presents evidence of tolerance to low root temperature. The maintenance of plant growth was likely associated with the breakdown of leaf and root reserves of starch.

Endophytic bacteria affect sugarcane physiology without changing plant growth

The aim of this study was to evaluate if endophytic bacteria inoculants would be beneficial to the sugarcane varieties IACSP94-2094 and IACSP95-5000, promoting changes in photosynthesis and plant growth. The plants, obtained from mini stalks with one bud, were treated with two bacteria mixtures (inoculum I or II) or did not receive any inoculum (control plants). The inocula did not affect shoot and root dry matter accumulation as compared to the control condition (plants with native endophytic bacteria). However, photosynthesis and electron transport rate (ETR) increased in IACSP94-2094 treated with the inoculum II, whereas the inoculum I enhanced photosynthesis and stomatal conductance in IACSP95-5000. The inoculum II caused increase in leaf sucrose concentration of IACSP94-2094 and decrease in IACSP95-5000 leaves. Leaf nitrogen concentration was not affected by treatments, but bacteria inoculation increased nitrate reductase activity in IACSP95-5000, and the highest activity was found in plants treated with the inoculum II. We can conclude that bacteria inoculation changed sugarcane physiology, improving photosynthesis and nitrate reduction in a genotype-dependent manner, without promoting plant growth under non-limiting conditions.

Gas exchanges and carbohydrate metabolism in orangetrees with citrus variegated chlorosis

As trocas gasosas e as concentracoes de sacarose, amido e acucares redutores foram analisadas em folhas de laranjeiras com e sem Clorose Variegada dos Citros (CVC), doenca causada pela bacteria Xylella fastidiosa. Plantas sadias (PS) e plantas doentes (PD) foram avaliadas 20 e 26 meses apos a inoculacao da bacteria, em outubro de 1998 e abril de 1999, respectivamente. Na primeira data de avaliacao, as taxas de assimilacao de CO2 em PS foram maiores do que em PD nas primeiras horas da manha e ao meio-dia, mas na segunda data de avaliacao elas foram maiores em PS durante o dia todo. Na primeira data, houve aumento no conteudo de sacarose de PD as 15 h e 17 h em relacao ao de PS. Na segunda data, PD mostrou maior conteudo de acucares redutores somente no periodo da manha, enquanto o conteudo de sacarose apresentou decrescimo as 15 h. Na segunda data, as concentracoes de amido foram sempre menores em PD, quando comparadas com as de PS. As variacoes de amido podem estar relacionadas com a disponibilidade de energia para atividades metabolicas de PD, uma vez que elas tambem apresentaram taxas de fotossintese mais baixas. Os teores de acucares soluveis nao mostraram qualquer relacao com a doenca ou parâmetros de fotossintese.

Cadmium Accumulation by Jack-Bean and Sorghum in Hydroponic Culture

Among the technologies used to recuperate cadmium (Cd) contaminated soils, phytoextraction are particularly important, where the selection of suitable plants is critical to the success of the soil remediation. Thus, the objectives of this study were to evaluate the responses of jack-bean and sorghum to Cd supply and to quantify Cd accumulation by these species grown in hydroponic culture. The plants were subjected to 0, 15, 30, or 60 μmol Cd L−1 in the nutrient solution, and gas exchange, plant growth and Cd accumulation were measured at 25 days after starting Cd treatments. The Cd supply severely reduced growth of shoots and roots in both species. In jack-bean, Cd decreased photosynthesis by 56–86%, stomatal conductance by 59–85% and transpiration by 48–80%. The concentrations and amounts of Cd accumulated in the plant tissues were proportional to the metal supply in the nutrient solution. Sorghum was more tolerant than jack-bean to Cd toxicity, but the latter showed a greater metal concentration and accumulation in the shoot. Therefore, jack-bean would be more suitable than sorghum for use in Cd phytoremediation programs based on phytoextraction.

Baixa temperatura noturna e deficiência hídrica na fotossíntese de cana‑de‑açúcar

The objective of this work was to evaluate the photosynthetic responses of sugarcane to the simultaneous and isolated effects of low night temperature (TN) and water deficit (DH). After 128 days of planting, plants of the cultivar IACSP94-2094 were subjected to the following treatments: control, without DH and with TN of 20°C (TN20); with DH and TN of 20°C (DH/TN20); without DH and with TN of 12°C (TN12); and with DH and TN of 12°C (DH/TN12). After the period of treatment, plants were irrigated and subjected to TN of 20°C for four more days, for recovery. There were decreases in CO2 assimilation in all treatments. Total recovery of CO2 assimilation was observed only in plants from the treatment TN12. The simultaneous occurrence of low night temperature and water deficit caused a accentuated and persistent effect on stomatal conductance, on the maximum capacity of ribulose‑1,5‑bisphosphate carboxylase, on the electron transport rate, on the efficiency factor, and on the operational efficiency of photosystem II, which resulted in diffusive, biochemical, and photochemical limitations of photosynthesis of sugarcane plants.