It is of great significance to develop green solvents for promoting green and sustainable technology. Deep eutectic solvents (DESs) as new extraction solvents are emerging in the search for efficient the extraction of bioactive compounds or drugs. In this study, twelve types of DESs including choline chloride-, betaine-, and l -proline-based DESs were investigated in combination with ultrasonic-assisted extraction (UAE) for the extraction of phenolic compounds from Morus alba L. leaves. Compared with conventional extraction system, DESs composed of choline chloride/citric acid showed more effective extraction yields (22.66 mg/g vs. 15.29 mg/g). The operation conditions were also optimized systematically. In addition, liquid–liquid extraction was an effective approach to recover the major phenolic compounds in the extracts. The recovery and recyclability of DESs were also evaluated. A broad extractability of phenolic compounds in the certain designed DESs systems was observed according to principal component analysis (PCA). The developed DESs can be an alternative procedure for the green and efficient extraction of phenolic compounds from natural sources.
The pollen coat, which forms on the pollen surface, consists of a lipid–protein matrix. It protects pollen from desiccation and is involved in adhesion, pollen–stigma recognition, and pollen hydration during interactions with the stigma. The classical methods used for pollen coat observation are scanning and transmission electron microscopy. In this work, we screened a collection of fluorescence dyes and identified two fluorescent brighteners FB-52 and FB-184. When they were used together with the exine-specific dye, Basic fuchsin, the pollen coat and the exine structures could be clearly visualized in the pollen of Brassica napus . This co-staining method was applied successfully in staining pollen from Fraxinus chinensis , Calystegia hederacea , and Petunia hybrida . Using this method, small pollen coat-containing cavities were detected in the outer pollen wall layer of Oryza sativa and Zea mays . We further showed these dyes are compatible with fluorescent protein markers. In the Arabidopsis thaliana transgenic line of GFP-tagged pollen coat protein GRP19, GRP19-GFP was observed to form particles at the periphery of pollen coat . This simple staining method is expected to be widely used for the studies of the palynology as well as the pollen–stigma interaction.
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