Optimization of ultrasonic-assisted extraction of polysaccharides from Hemerocallis citrina and the antioxidant activity study.

The present study discussed the optimization of the ultrasonic-assisted extraction of polysaccharides from daylily polysaccharides (DPs). The extracted crude polysaccharides were further separated and purified, and the antioxidant activities including 1,1-diphenyl-2-111 picrylhydrazyl (DPPH) radical scavenging, 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS) radical scavenging, hydroxyl radical scavenging, and ferric-reducing antioxidant power (FRAP) activities of the obtained fractions were also evaluated. The results showed that the optimal ultrasonic-assisted extraction parameters with DPs yield of 15.25 ± 1.13% were water to powder ratio of 25 ml/g, extraction power of 694 W, extraction temperature of 71°C, extraction time of 38 min, and three times extraction. By DEAE Sepharose Fast Flow column, four water-soluble polysaccharide fractions (DP-1, DP-2, DP-3, and DP-4) were successfully obtained. Monosaccharide component analysis showed that the four obtained fractions were all hetero-polysaccharides that mainly contained rhamnose, arabinose, fructose, galactose, glucose, galacturonic acid, and glucuronic acid in different molar ratios. All the four DP fractions did show obvious antioxidant activities in vitro, and the DP-3 component had relatively high ABTS free radical scavenging activity. Overall, our research showed that DPs could provide cheap raw materials for the development of natural antioxidants in medicines, functional foods, and even cosmetics. PRACTICAL APPLICATION: This article deals with the optimization of the ultrasonic-assisted extraction of polysaccharides from daylily and its antioxidant activities. The results showed that the optimal ultrasonic-assisted extraction yield of DPs was 15.25 ± 1.13%. By DEAE Sepharose Fast Flow column, four water-soluble polysaccharide fractions were successfully obtained, and all the four DP fractions did show obvious antioxidant activities in vitro. Daylily polysaccharides could provide cheap raw materials for the development of natural antioxidants in medicines, functional foods, and even cosmetics.

Photoinhibition-like damage to the photosynthetic apparatus in plant leaves induced by submergence treatment in the dark.

Submergence is a common type of environmental stress for plants. It hampers survival and decreases crop yield, mainly by inhibiting plant photosynthesis. The inhibition of photosynthesis and photochemical efficiency by submergence is primarily due to leaf senescence and excess excitation energy, caused by signals from hypoxic roots and inhibition of gas exchange, respectively. However, the influence of mere leaf-submergence on the photosynthetic apparatus is currently unknown. Therefore, we studied the photosynthetic apparatus in detached leaves from four plant species under dark-submergence treatment (DST), without influence from roots and light. Results showed that the donor and acceptor sides, the reaction center of photosystem II (PSII) and photosystem I (PSI) in leaves were significantly damaged after 36 h of DST. This is a photoinhibition-like phenomenon similar to the photoinhibition induced by high light, as further indicated by the degradation of PsaA and D1, the core proteins of PSI and PSII. In contrast to previous research, the chlorophyll content remained unchanged and the H2O2 concentration did not increase in the leaves, implying that the damage to the photosynthetic apparatus was not caused by senescence or over-accumulation of reactive oxygen species (ROS). DST-induced damage to the photosynthetic apparatus was aggravated by increasing treatment temperature. This type of damage also occurred in the anaerobic environment (N2) without water, and could be eliminated or restored by supplying air to the water during or after DST. Our results demonstrate that DST-induced damage was caused by the hypoxic environment. The mechanism by which DST induces the photoinhibition-like damage is discussed below.