No abstract

Our dependency on reduced carbon for energy has led to a rapid increase in the search for sustainable alternatives and a call to focus on energy densification and increasing biomass yields. In this study, we generated a uniquely stabilized plant structural protein (cysteine [Cys]-oleosin) that encapsulates triacylglycerol (TAG). When coexpressed with diacylglycerol O-acyltransferase (DGAT1) in Arabidopsis (Arabidopsis thaliana), we observed a 24% increase in the carbon dioxide (CO 2 ) assimilation rate per unit of leaf area and a 50% increase in leaf biomass as well as approximately 2-, 3-, and 5-fold increases in the fatty acid content of the mature leaves, senescing leaves, and roots, respectively. We propose that the coexpression led to the formation of enduring lipid droplets that prevented the futile cycle of TAG biosynthesis/lipolysis and instead created a sustained demand for de novo lipid biosynthesis, which in turn elevated CO 2 recycling in the chloroplast. Fatty acid profile analysis indicated that the formation of TAG involved acyl cycling in Arabidopsis leaves and roots. We also demonstrate that the combination of Cys-oleosin and DGAT1 resulted in the highest accumulation of fatty acids in the model single-cell eukaryote, Saccharomyces cerevisiae. Our results support the notion that the prevention of lipolysis is vital to enabling TAG accumulation in vegetative tissues and confirm the earlier speculation that elevating fatty acid biosynthesis in the leaf would lead to an increase in CO 2 assimilation. The Cysoleosins have applications in biofuels, animal feed, and human nutrition as well as in providing a tool for investigating fatty acid biosynthesis and catabolism.

No abstract

Black pigmented leaves are common among horticultural cultivars, yet are extremely rare across natural plant populations. We hypothesised that black pigmentation would disadvantage a plant by reducing photosynthesis and therefore shoot productivity, but that this trait might also confer protective benefits by shielding chloroplasts against photo-oxidative stress. CO2 assimilation, chlorophyll a fluorescence, shoot biomass, and pigment concentrations were compared for near isogenic green- and black-leafed Ophiopogon planiscapus ‘Nigrescens’. The black leaves had lower maximum CO2 assimilation rates, higher light saturation points and higher quantum efficiencies of photosystem II (PSII) than green leaves. Under saturating light, PSII photochemistry was inactivated less and recovered more completely in the black leaves. In full sunlight, green plants branched more abundantly and accumulated shoot biomass quicker than the black plants; in the shade, productivities of the two morphs were comparable. The data indicate a light-screening, photoprotective role of foliar anthocyanins. However, limitations to photosynthetic carbon assimilation are relatively small, insufficient to explain the natural scarcity of black-leafed plants.