The hypothesis that application of exogenous glycine betaine (GB EX ) may attenuate the effects of mild water deficit in leaf gas exchange and lipid peroxidation in Carapa guianensis was examined. For this reason, 110-d old plants were sprayed with 0, 25, and 50 mM GB EX and then subjected to two watering regimes. In the first, irrigation was continuously performed to maintain the soil near to field capacity (watered plants). In the second, irrigation was withheld and water deficit resulted from progressive evapotranspiration (water-stressed plants). Treatment comparisons were assessed when predawn leaflet water potential (Ψ pd ) of stressed plants reached -1.28 ± 0.34 MPa. Regardless of the watering regime, significant (P<0.05) increases in foliar glycine betaine (GB Leaf ) concentration were observed in response to increasing GB EX ; however, such increases were more expressive in stressed plants. The net photosynthetic rate, stomatal conductance to water vapor, and intercellular to ambient CO 2 concentration ratio were significantly lower in water-stressed plants independently of GB EX concentration sprayed on leaves. The application of 25 and 50 mM GB EX caused significant (P<0.05) increases in ascorbate peroxidase (APX) activity in stressed plants, while significant (P<0.05) increases in catalase activity was observed just in the stressed plants treated with 50 mM GB EX . Malondialdehyde concentrations did not differ between watered and stressed plants regardless of GB EX concentration. In conclusion, C. guianensis was able to incorporate GB EX through their leaves and the resulting increases in GB Leaf attenuated lipid peroxidation in stressed plants through positive modulation of APX and CAT activities.

Although Selenium (Se) stress is relatively well known for causing growth inhibition, its effects on primary metabolism remain rather unclear. Here, we characterized both the modulation of the expression of specific genes and the metabolic adjustments in Arabidopsis thaliana in response to changes in Se level in the soil. Se treatment culminated with strong inhibition of both shoot and root growth. Notably, growth inhibition in Se-treated plants was associated with an incomplete mobilization of starch during the night. Minor changes in amino acids levels were observed in shoots and roots of plants treated with Se whereas the pool size of tricarboxylic acid (TCA) cycle intermediates in root was not altered in response to Se. By contrast, decreased levels of organic acids involved in the first part of the TCA cycle were observed in shoots of Se-treated plants. Furthermore, decreased expression levels of expansins and endotransglucosylases/endohydrolases (XHTs) genes were observed after Se treatment, coupled with a significant decrease in the levels of essential elements. Collectively, our results revealed an exquisite interaction between energy metabolism and Se-mediated control of growth in Arabidopsis thaliana to coordinate cell wall extension, starch turnover and the levels of a few essential nutrients.

Leaf spots caused by Colletotrichum sp. decrease photosynthesis rate and hamper the growth of açaí seedlings in nurseries. The objective of the study was to quantify the changes in the photosynthetic performance of açaí leaves inoculated with Colletotrichum sp. through measurements of gas exchange, chlorophyll a fluorescence, and photosynthetic pigments. The rate of net CO 2 assimilation, stomatal conductance, transpiration rate, chlorophyll a and b, ratio of chlorophyll a/b and total chlorophyll decreased, but the intercellular CO 2 concentration increased in inoculated plants compared with non-inoculated plants. Changes in chlorophyll a fluorescence began at 3 days after inoculation (dai) and increased with the number of injuries. The maximum photochemical efficiency ratio (F v /F m) declined sharply as well as other characteristics of chlorophyll a fluorescence, such as the photochemical quenching coefficient, effective quantum yield of PSII, quantum yield of non-regulated energy dissipation, and electron transfer rate. Infection by Colletotrichum sp. reduces the photosynthetic performance due to reduced light capture and assimilation of CO 2 in the mesophyll. Gas exchange and chlorophyll a fluorescence can describe reductions in photosynthetic capacity caused by anthracnose in leaves.

Changes in chloroplastidic pigments, gas exchange and carbohydrate concentrations were assessed during the rapid initial expansion of C. guianensis leaflet. Leaves at metaphyll stage were tagged and assessments were carried out 14, 17, 20, 23, 27, and 31 days later. Pigments synthesis, distribution and accumulation were uniform among leaflet sections (basal, median and apical). Chlorophyll (Chl) a, Chl b, Chl (a+b), and total carotenoids (Car) concentrations were significantly increased after 27 days from metaphyll, and the most expressive increases were parallel to lower specific leaflet area. Chl a/b was lower on day 14 and it was increased on subsequent days. Negative net photosynthesis rate (P N ), and the lowest stomatal conductance (g s ) and transpiration (E) were registered on day 14, following significant increases on subsequent days. The Chl (a+b) and Chl a effects on P N were more expressive until day 20. Intercellular to ambient CO 2 concentration ratio (C i /C a ) was higher on day 14 and lower on subsequent days, and no stomatal limitation to CO 2 influx inside leaflets was observed. Leaflet temperature was almost constant (ca. 35°C) during leaflet development. Sucrose and starch concentrations were increased in parallel to increases in P N . Altogether, these results highlight the main physiological changes during C. guianensis leaflet expansion and they should be considered in future experiments focusing on factors affecting P N in this species.