Seasonal effects on the relationship between photosynthesis and leaf carbohydrates in orange trees

To understand the effect of summer and winter on the relationships between leaf carbohydrate and photosynthesis in citrus trees growing in subtropical conditions, 'Valencia' orange trees were subjected to external manipulation of their carbohydrate concentration by exposing them to darkness and evaluating the maximal photosynthetic capacity. In addition, the relationships between carbohydrate and photosynthesis in the citrus leaves were studied under natural conditions. Exposing the leaves to dark conditions decreased the carbohydrate concentration and increased photosynthesis in both seasons, which is in accordance with the current model of carbohydrate regulation. Significant negative correlations were found between total non-structural carbohydrates and photosynthesis in both seasons. However, non-reducing sugars were the most important carbohydrate that apparently regulated photosynthesis on a typical summer day, whereas starch was important on a typical winter day. As a novelty, photosynthesis stimulation by carbohydrate consumption was approximately three times higher during the summer, i.e. the growing season. Under subtropical conditions, citrus leaves exhibited relatively high photosynthesis and high carbohydrate levels on the summer day, as well as a high nocturnal consumption of starch and soluble sugars. A positive association was determined between photosynthesis and photoassimilate consumption/exportation, even in leaves showing a high carbohydrate concentration. This paper provides evidence that photosynthesis in citrus leaves is regulated by an increase in sink demand rather than by the absolute carbohydrate concentration in leaves.

HEPATOTOXICITY ASSESSMENT OF THE AZO DYES DISPERSE ORANGE 1 (DO1), DISPERSE RED 1 (DR1,) AND DISPERSE RED 13 (DR13) IN HEPG2 CELLS

During the dyeing process in baths approximately 10 to 15% of the dyes used are lost and reach industrial effluents, thus polluting the environment. Studies showed that some classes of dyes, mainly azo dyes and their by-products, exert adverse effects on humans and local biota, since the wastewater treatment systems and water treatment plants were found to be ineffective in removing the color and reducing toxicity of some dyes. In the present study, the toxicity of the azo dyes disperse orange 1 (DO1), disperse red 1 (DR1), and disperse red 13 (DR13) was evaluated in HepG2 cells grown in monolayers or in three dimensional (3D) culture. Hepatotoxicity of the dyes was measured using 3-(4,5-dimethylthiazol-2yl)2,5-diphenyltetrazolium (MTT) and cell counting kit 8 (CCK-8) assays after 24, 48, and 72 h of incubation of cells with 3 different concentrations of the azo dyes. The dye DO1 only reduced the mitochondrial activity in HepG2 cells grown in a monolayer after 72 h incubation, while the dye DR1 showed this deleterious effect in both monolayer and 3D culture. In contrast, dye DR13 decreased the mitochondrial activity after 24, 48, and 72 h of exposure in both monolayer and 3D culture. With respect to dehydrogenase activity, only the dye DR13 diminished the activity of this enzyme after 72 h of exposure in both monolayer and 3D culture. Our results clearly demonstrated that exposure to the studied dyes induced cytotoxicity in HepG2 cells.