Meta-analysis of the responses of tree and herb to elevated CO2 in Brazil.

The CO2 concentration has increased in the atmosphere due to fossil fuel consumption, deforestation, and land-use changes. Brazil represents one of the primary sources of food on the planet and is also the world's largest tropical rainforest, one of the hot spots of biodiversity in the world. In this work, a meta-analysis was conducted to compare several CO2 Brazilian experiments displaying the diversity of plant responses according to life habits, such as trees (79% natives and 21% cultivated) and herbs (33% natives and 67% cultivated). We found that trees and herbs display different responses. The young trees tend to allocate carbon from increased photosynthetic rates and lower respiration in the dark-to organ development, increasing leaves, roots, and stem biomasses. In addition, more starch is accumulated in the young trees, denoting a fine control of carbon metabolism through carbohydrate storage. Herbs increased drastically in water use efficiency, controlled by stomatal conductance, with more soluble sugars, probably with a transient accumulation of carbon primarily stored in seeds as a response to elevated CO2.

Carbon allocation of Spirodela polyrhiza under boron toxicity.

Pectic polysaccharides containing apiose, xylose, and uronic acids are excellent candidates for boron fixation. Duckweeds are the fastest-growing angiosperms that can absorb diverse metals and contaminants from water and have high pectin content in their cell walls. Therefore, these plants can be considered excellent boron (B) accumulators. This work aimed to investigate the relationship between B assimilation capacity with apiose content in the cell wall of Spirodela polyrhiza subjected to different boric acid concentrations. Plants were grown for 7 and 10 days in ½ Schenck-Hildebrandt media supplemented with 0 to 56 mg B.L-1, the non-structural and structural carbohydrates, and related genes were evaluated. The results showed that B altered the morphology and carbohydrate composition of this species during plant development. The optimum B concentration (1.8 mg B.L-1) led to the highest relative growth and biomass accumulation, reduced starch, and high pectin and apiose contents, together with increased expression of UDP-apiose/UDP-xylose synthase (AXS) and 1,4-α-galacturonosyltransferase (GAUT). The toxic state (28 and 56 mg B.L-1) increased the hexose contents in the cell wall with a concomitant reduction of pectins, apiose, and growth. The pectin content of S. polyrhiza was strongly associated with its growth capacity and regulation of B content within the cells, which have AXS as an important regulator. These findings suggest that duckweeds are suitable for B remediation, and their biomass can be used for bioenergy production.

The Effect of Sugarcane Straw Aging in the Field on Cell Wall Composition.

Cellulosic ethanol is an alternative for increasing the amount of bioethanol production in the world. In Brazil, sugarcane leads the bioethanol production, and to improve its yield, besides bagasse, sugarcane straw is a possible feedstock. However, the process that leads to cell wall disassembly under field conditions is unknown, and understanding how this happens can improve sugarcane biorefinery and soil quality. In the present work, we aimed at studying how sugarcane straw is degraded in the field after 3, 6, 9, and 12 months. Non-structural and structural carbohydrates, lignin content, ash, and cellulose crystallinity were analyzed. The cell wall composition was determined by cell wall fractionation and determination of monosaccharide composition. Non-structural carbohydrates degraded quickly during the first 3 months in the field. Pectins and lignin remained in the plant waste for up to 12 months, while the hemicelluloses and cellulose decreased 7.4 and 12.4%, respectively. Changes in monosaccharide compositions indicated solubilization of arabinoxylan (xylose and arabinose) and ß-glucans (ß-1,3 1,4 glucan; after 3 months) followed by degradation of cellulose (after 6 months). Despite cellulose reduction, the xylose:glucose ratio increased, suggesting that glucose is consumed faster than xylose. The degradation and solubilization of the cell wall polysaccharides concomitantly increased the level of compounds related to recalcitrance, which led to a reduction in saccharification and an increase in minerals and ash contents. Cellulose crystallinity changed little, with evidence of silica at the latter stages, indicating mineralization of the material. Our data suggest that for better soil mineralization, sugarcane straw must stay in the field for over 1 year. Alternatively, for bioenergy purposes, straw should be used in less than 3 months.

Flavonoids from duckweeds: potential applications in the human diet.

Duckweeds are the smallest free-floating flowering aquatic plants. Their biotechnological applications include their use as food, bioenergy, and environmental sustainability, as they can help clean polluted water. The high growth capacity and their chemical properties make them suitable for human health applications. Here we evaluated the ethanolic extracts from five species of duckweeds by HPLC-DAD/MS-MS for chemical characterization. Sixteen compounds were identified and quantified, in which three were chlorogenic acid derivatives and eleven apigenin and luteolin derivatives. We describe for the first time the presence in duckweeds of 5-O-(E)-caffeoylquinic acid (1), 3-O-(E)-coumaroylquinic acid (2), luteolin-7-O-glucoside-C-glucoside (3), 4-O-(E)-coumaroylquinic acid (4), luteolin-6-C-glucoside-8-C-rhamnoside (5), and luteolin-8-C-glucoside-6-C-rhamnoside (6). The flavonoids diversity showed a significant content of luteolin and its derivatives, except for Landoltia punctata that had significant apigenin content. Flavones identified in duckweeds were mostly C-glycosides, which can benefit human diets, and its abundance seems to be related to the higher antioxidant and anticancer capacities of Wolffiella caudata, Wolffia borealis, and Landoltia punctata. Our findings reinforce the idea that duckweeds could be valuable additives to the human diet, and their potential should be further explored.

Correlation of Apiose Levels and Growth Rates in Duckweeds.

The carbon assimilated by photosynthesis in plants can be partitioned into starch, soluble sugars, and cell wall polymers. Higher levels of starch accumulation in leaves are usually correlated with a lower growth capacity. Duckweeds are fast-growing aquatic monocot plants that can accumulate high levels of starch. They are an unusual group because their cell wall has very low levels of lignin while accumulating apiogalacturonan, a pectic polysaccharide that could be involved with boron assimilation. In this work, five duckweed species from different genera (Spirodela polyrhiza, Landoltia punctata, Lemna gibba, Wolffiella caudata, and Wolffia borealis) were cultivated under two light intensities (20 and 500 µmoles of photons m-2 s-1) to evaluate the effects of growth rate on carbohydrate metabolism. A comparative analysis was performed by measuring their relative growth rates (RGR), and their content for starch, as well as soluble and cell wall carbohydrates. We found that the faster-growing species (the Lemnoideae) accumulate lower starch and higher soluble sugars than the slower-growing species within the Wolffioideae. Interestingly, analysis of the cell wall monosaccharides revealed that the slower-growing species displayed lower content of apiose in their walls. Our results indicate that higher accumulation of apiose observed in cell walls of the Lemnoideae species, which likely correlates with a higher proportion of apiogalacturonan, may lead to higher efficiency in the assimilation of boron. This is consistent with the increased RGR observed under conditions with higher apiose in the cell wall, such as higher light intensity. Consistent with their lower growth capacity, the Wolffioideae species we studied shows higher starch accumulation in comparison with the Lemnoideae species. We suggest that apiose levels could be good biomarkers for growth capacity of duckweeds and suggest that boron uptake could be an important factor for growth control in this aquatic plant family.