Efficient Accumulation of Amylopectin and Its Molecular Mechanism in the Submerged Duckweed Mutant.

Large-scale use of fossil fuels has brought about increasingly serious problems of environmental pollution, development and utilization of renewable energy is one of the effective solutions. Duckweed has the advantages of fast growth, high starch content and no occupation of arable land, so it is a promising starchy energy plant. A new submerged duckweed mutant (sub-1) with abundant starch accumulation was obtained, whose content of amylopectin accounts for 84.04% of the starch granules. Compared with the wild type (Lemna aequinoctialis), the branching degree of starch in sub-1 mutant was significantly increased by 19.6%. Chain length DP 6-12, DP 25-36 and DP > 36 of amylopectin significantly decreased, while chain length DP 13-24 significantly increased. Average chain length of wild-type and sub-1 mutant starches were greater than DP 22. Moreover, the crystal structure and physical properties of starch have changed markedly in sub-1 mutant. For example, the starch crystallinity of sub-1 mutant was only 8.94%, while that of wild-type was 22.3%. Compared with wild type, water solubility of starch was significantly reduced by 29.42%, whereas swelling power significantly increased by 97.07% in sub-1 mutant. In order to further analyze the molecular mechanism of efficient accumulation of amylopectin in sub-1 mutant, metabolome and transcriptome were performed. The results showed that glucose accumulated in sub-1 mutant, then degradation of starch to glucose mainly depends on α-amylase. At night, the down-regulated ß-amylase gene resulted in the inhibition of starch degradation. The starch and sucrose metabolism pathways were significantly enriched. Up-regulated expression of SUS, AGPase2, AGPase3, PYG, GPI and GYS provide sufficient substrate for starch synthesis in sub-1 mutant. From the 0H to 16H light treatment, granule-bound starch synthase (GBSS1) gene was inhibited, on the contrary, the starch branching enzyme (SBE) gene was induced. Differential expression of GBSS1 and SBE may be an important reason for the decrease ratio of amylose/amylopectin in sub-1 mutant. Taken together, our results indicated that the sub-1 mutant can accumulate the amylopectin efficiently, potentially through altering the differential expression of AGPase, GBSS1, SBE, and BAM. This study also provides theoretical guidance for creating crop germplasm with high amylopectin by means of synthetic biology in the future.

Effect of permanent magnetic field on scale inhibition property of circulating water.

Effect of a permanent magnet field on the scale inhibition property of circulating water was investigated. Orthogonal experiments of L16(45) were performed and analyzed using the range analysis method. The operating parameters included magnetic field intensity, initial concentration of Ca2+ and Mg2+, magnetic treatment time, temperature, and flow velocity. Scale inhibition rate, hardness, relative variation in the proportion of free water molecules, electrical conductivity, and relative variation of molecular energy were chosen as the objectives. In addition, the morphology and the composition of CaCO3 and MgCO3 scale were studied by X-ray diffraction analysis. The optimal conditions were initial concentration of 900 mg/L, magnetic field intensity of 0.5 T, temperature of 303 K, time of 54 h and flow velocity of 0.17 m/s. The nuclear magnetic resonance results demonstrated that the number of hydrogen bonds increased between water molecules and hydrated ions. The magnetic field can promote the increase in the number of hydrogen bonds, which can inhibit the formation of calcium and magnesium carbonate precipitation. Moreover, the ratio of calcite, aragonite and vaterite will be changed at different magnetic field intensities, and the aragonite ratio will reach the peak at the optimum conditions.

Metabolome and transcriptome analyses of the flavonoid biosynthetic pathway for the efficient accumulation of anthocyanins and other flavonoids in a new duckweed variety (68-red).

Duckweed is a kind of aquatic plant with the characteristics of high nutritional value and medicinal benefits. However, most researches focused on the natural germplasms. The underlying metabolic pathway remains to be systematically elaborated in duckweed. In our laboratory, one reddish-purple mutant with high-flavonoids was screened from a mutant library of Spirodela polyrhiza 6068, named 68-red. The content of anthocyanins and proanthocyanidins in 68-red mutant increased by 563.47% and 231.19%, respectively, compared to wild type. It is interesting that cynaroside and orientin content were significantly increased, in contrast, apigetrin and vitexin were decreased in 68-red mutant. Considering this, metabolome and transcriptome were employed to explore the flavonoids biosynthetic pathway. Here, a total of 734 metabolites were identified in the wild type and 68-red mutant. Among which, cyanidin-3-O-glucoside, cyanidin-3-O-galactoside, pelargonidin-3-O-glucoside and pelargonidin-3-O-(6″-O-malonyl)glucoside were significantly accumulated, which were positively correlated with deep reddish-purple of 68-red mutant. In addition, proanthocyanidins (B1, B2, B3, B4, C1, C2), flavonoid and its glycosides (11 luteolin and its glycosides, 14 quercetin and its glycosides, 14 kaempferol and its glycosides, 2 apigenin glycosides) were significantly accumulated, 2 apigenin glycosides were down-regulated in 68-red mutant. The transcriptome data and qRT-PCR indicated that 16 enzyme genes in flavonoids biosynthetic pathway (PAL, C4H, CHSs, F3H, ANS, ANR, F3'Hs, DFRs, LAR, GT1, BZ1) were significantly up-regulated in 68-red mutant. Correlation analysis found that three copies of F3'H gene play important roles in the synthesis of anthocyanins, luteolin and apigenin glycosides. In conclusion, the 68-red mutant is a high quality germplasm resources for food and medical industry. Metabolome and transcriptome provide new insight for exploring the enzyme genes and functional metabolites in duckweed.