Involvement of glutathione and glutathione metabolizing enzymes in Pistia stratiotes tolerance to arsenite.

Glutathione is essential for plant tolerance to arsenic but few studies have focused on the coordination between the enzymes involved in its metabolism. We exposed Pistia stratiotes to four treatments (control, 5, 10 and 20 µM AsIII) for 24 h to evaluate the role of glutathione metabolism in arsenic response and determined the arsenic uptake, growth, membrane integrity, glutathione concentration and enzyme activities (γ-glutamyl-cysteine synthetase, glutathione reductase, glutathione peroxidase, and glutathione-S-transferase). Despite absorbing high concentrations of AsIII, plants maintained growth and cell membrane integrity when exposed to concentrations of up to 10 µM AsIII. The maintenance of these parameters involved glutathione concentration increase due to an increase in its biosynthetic pathway (higher γ-glutamyl-cysteine synthetase). In addition, an increase in the activity of glutathione reductase, glutathione peroxidase and glutathione-S-transferase also contributed to the conserve the cellular homeostasis. However, at the concentration of 20 µM AsIII, the high toxicity of AsIII affected glutathione concentration and glutathione metabolizing enzymes activities, which resulted in drastic decrease in growth and damage to cell membranes. These results showed that not only the glutathione concentration but also the coordination of the enzymes involved in the synthesis, oxidation and reduction pathways of glutathione is essential for AsIII tolerance.

Fruit development, growth, and stored reserves in macauba palm (Acrocomia aculeata), an alternative bioenergy crop.

Main conclusion Macauba palm fruiting is supra-annual, and the fruit growth follows a double sigmoidal trend. The prevailing compound in the mesocarp differs as the fruit ages, oil being the major storage compound. Acrocomia aculeata, macauba palm, is a conspicuous species in the tropical Americas. Because the species is highly productive in oil-rich fruits, it is the subject of domestication as an alternative vegetable oil crop, especially as a bioenergy feedstock. This detailed study first presents the macauba fruit growth and development patterns, morphological changes and accumulation of organic compounds. Fruits were monitored weekly in a natural population. The fruiting was supra-annual, and the fruit growth curve followed a double sigmoidal trend with four stages (S): SI-slow growth and negligible differentiation of the fruit inner parts; SII-first growth spurt and visible, but not complete, differentiation of the inner parts; SIII-growth slowed down and all structures attained differentiation; and SIV-second growth spurt and fruit maturation. In SII, the exocarp and endocarp were the main contributors to fruit growth, whereas the mesocarp and endosperm were responsible for most of the weight gain during SIV. In comparison with starch and oil, soluble sugars did not accumulate in the mesocarp. However, starch was transitory and fueled the oil synthesis. The protective layers, the exocarp and endocarp, fulfilling their ecological roles, were the first to reach maturity, followed by the storage tissues, the mesocarp, and endosperm. The amount and nature of organic compounds in the mesocarp varied with the fruit development and growth stages, and oil was the main and final storage material. The description of macauba fruit's transformations and their temporal order may be of importance for future ecological and agronomical references.