No abstract

No abstract

Thirty-month-old 'Pêra' orange trees grafted on 'Rangpur' lemon trees grown in 100 L pots were submitted to water stress by the suspension of irrigation. CO2 assimilation (A), transpiration (E) and stomatal conductance (g s) values declined from the seventh day of stress, although the leaf water potential at 6:00 a.m. (psipd) and at 2:00 p.m. (psi2) began to decline from the fifth day of water deficiency. The CO2 intercellular concentration (Ci) of water-stressed plants increased from the seventh day, reaching a maximum concentration on the day of most severe stress. The carboxylation efficiency, as revealed by the ratio A/Ci was low on this day and did not show the same values of non-stressed plants even after ten days of rewatering. After five days of rewatering only psi pd and psi2 were similar to control plants while A, E and g s were still different. When psi2 decreases, there was a trend for increasing abscisic acid (ABA) concentration in the leaves. Similarly, stomatal conductance was found to decrease as a function of decreasing psi2. ABA accumulation and stomatal closure occurred when psi2 was lower than -1.0 MPa. Water stress in 'Pera´ orange trees increased abscisic acid content with consequent stomatal closure and decreased psi2 values.

The effects of ethephon as a sugarcane ripener are attributed to ethylene. However, the role of this phytohormone at the molecular level is unknown. We performed a transcriptome analysis combined with the evaluation of sucrose metabolism and hormone profiling of sugarcane plants sprayed with ethephon or aminoethoxyvinylglycine (AVG), an ethylene inhibitor, at the onset of ripening. The differential response between ethephon and AVG on sucrose level and sucrose synthase activity in internodes indicates ethylene as a potential regulator of sink strength. The correlation between hormone levels and transcriptional changes suggests ethylene as a trigger of multiple hormone signal cascades, with approximately 18% of differentially expressed genes involved in hormone biosynthesis, metabolism, signalling, and response. A defence response elicited in leaves favoured salicylic acid over the ethylene/jasmonic acid pathway, while the upper internode was prone to respond to ethylene with strong stimuli on ethylene biosynthesis and signalling genes. Besides, ethylene acted synergistically with abscisic acid, another ripening factor, and antagonistically with gibberellin and auxin. We identified potential ethylene target genes and characterized the hormonal status during ripening, providing insights into the action of ethylene at the site of sucrose accumulation. A molecular model of ethylene interplay with other hormones is proposed.

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. Lead uptake and tolerance of Ricinus communis L. Pontencial fitoextrator de Ricinus communis L. para chumbo:A fitoextração é uma técnica remediadora importante para áreas contaminadas por chumbo (Pb), sendo importantes os estudos que relacionam a tolerância de espécies de clima tropical, desenvolvidas em níveis crescentes de contaminação, com a sua fisiologia, para que possam ser cultivadas como fitoextratoras em áreas contaminadas. Este trabalho teve o objetivo de estudar a espécie Ricinus communis L. como potencial fitoextratora de Pb. As plantas foram cultivadas em solução nutritiva, em casa de vegetação, sob condições semi-controladas. Testaram-se as concentrações 0, 100, 200 e 400 µmol Pb L -1 . Os experimentos foram instalados em blocos ao acaso, em esquema fatorial 4 x 1, com três repetições. Foram realizadas análises biométricas e medidas as taxas de fotossíntese, bem como as concentrações de Pb na solução nutritiva, nas raízes e na parte aérea das plantas. Concluiu-se que R. communis L é uma espécie hiperacumuladora e apresenta tolerância ao Pb em baixas concentrações.Palavras-chave: chumbo, fitorremediação, mamona, metal pesado