Effects of diff erent NO 3 − :NH 4 + ratios on the photosynthesis and ultrastructure of lettuce seedlings

Xu Zhu,Rui Yang,Yingyan Han,Jinghong Hao,Chaojie Liu,Shuangxi Fan 한국원예학회 2020 Horticulture, Environment, and Biotechnology Vol.61 No.3

Nitrate nitrogen (NO 3− ) and ammonium N (NH 4+ ) are the two main forms of nitrogen (N). The eff ects of the NO 3− :NH 4+ ratio(0:100, 25:75, 50:50, 75:25, and 100:0) in the nutrient solution on growth, pigment content, photosynthetic parameters, chlorophyll(Chl) precursor content, and chloroplast mitochondrial ultrastructure of lettuce leaves were evaluated to determine theappropriate N ratio for the growth of lettuce. The results showed that a ratio of nitrate to ammonium of 75:25 compared withthe single N form resulted in signifi cantly higher fresh weights in the shoots and the lower parts of the lettuce. The growthrate, as indicated by the CO 2 response curve, was increased because of the carboxylation effi ciency and dark respiration rate(Rday) of the lettuce seedlings, and the diff erence between the light compensation point and CO 2 compensation point wasreduced under single nitrate N treatment. The contents of δ-aminolevulinic acid (ALA), porphobilinogen, uroporphyrinogenIII, protoporphyrin IX, and Mg-protoporphyrin IX in seedlings at 75:25 nitrate:ammonium were higher than those inseedlings under the other treatments. The contents of Chl a and b were also the highest when the ratio of nitrate ammoniumwas 75:25. The chloroplast structure of lettuce leaves was intact, the cell membrane was completely closed to the cell wall,and the organelles were closely arranged on the cell membrane. The chloroplast was spindle-shaped and full of vesicles. The whole mitochondria were rich, the base particles were rich, the base granules were clear and rich, and the mitochondriaexhibited the overall best state with a complete structure, rich sputum, and dense inclusions. The above results show that thenutrient solution with a ratio of nitrate to ammonium of 75:25 was more conducive to Chl synthesis and the promotion ofphotosynthesis and root growth in lettuce seedlings than the other treatments. The single nitrate N nutrient solution reducedChl synthesis and photosynthesis in lettuce seedlings, while the single ammonium N nutrient solution aff ected the growthof lettuce seedlings, resulting in lower growth of lettuce shoots and roots. Therefore, the nutrient solution ratio of nitrate toammonium of 75:25 is the most suitable for the lettuce seedling growth.

Effects of exogenous putrescine on the ultrastructure of and calcium ion flow rate in lettuce leaf epidermal cells under drought stress

Xu Zhu,Lin Wang,Yingyan Han,Chaojie Liu,Shuangxi Fan 한국원예학회 2019 Horticulture, Environment, and Biotechnology Vol.60 No.4

The alleviation eff ects of exogenous putrescine treatment on the ultrastructure of and calcium ion fl ow rate in lettuce ( Lactucasativa L.) leaf cells under drought stress were studied. Lettuce seedlings were treated with foliar sprays of 0.1 mM putrescinefor 8 days, after which drought stress was simulated by using 10% polyethylene glycol 6000. The morphological characteristicsof the seedlings and the calcium ion fl ow rate across stomatal guard cells were subsequently determined, and the leaf cellultrastructure was observed via transmission electron microscopy. Under drought stress, the morphological characteristics of the seedlings decreased, and calcium ion infl ux was predominant in the guard cells. In addition, compared to that under control conditions, the stomatal density under drought stress conditions increased signifi cantly, the open/closed stoma ratio was lower, and the degree of stomatal opening was smaller. Exogenous putrescine sprays eff ectively reduced the stomatal density, increased the degree of stomatal opening, and increased the proportion of open stomata. In addition, the chloroplasts became round in shape, the thylakoid structure became blurry in appearance, the number of starch grains decreased, many osmium granules were produced, and plasmolysis occurred in the mesophyll cells. However, the chloroplasts were elongated, the thylakoid structure was clear, the starch grains were abundant, few osmium granules were produced, and plasmolysis did not occur. The above results show that, by altering the leaf cell ultrastructure as well as the fl ow rate and direction of calcium ions in guard cells, exogenous putrescine eff ectively improves the drought tolerance of lettuce.

Experimental study on the tension of cables and motion of tunnel element for an immersed tunnel element under wind, current and wave

Wu Hao,Rheem Chang-Kyu,Chen Wei,Xu Shuangxi,Wu Weiguo 대한조선학회 2021 International Journal of Naval Architecture and Oc Vol.13 No.1

The tension of cables and motion response significantly affect safety of an immersed tunnel element in the immersion process. To investigate those, a hydrodynamic scale-model test was carried out and the model experiments was conducted under wind, current and wave loads simultaneously. The immersion standby (the process that the position of the immersed tunnel element should be located before the immersion process) and immersion process conditions have been conducted and illustrated. At the immersion standby conditions, the maximum force of the cables and motion is much larger at the side of incoming wind, wave and current, the maximum force of Element-6 (6 cables directly tie on the element) is larger than for Pontoon-8 (8 cables tie on pontoon of the element), and the flexible connection can reduce the maximum force of the mooring cables and motion of element (i.e. sway is expecting to decrease approximate 40%). The maximum force of the mooring cables increases with the increase of current speed, wave height, and water depth. The motion of immersed tunnel element increases with increase of wave height and water depth, and the current speed had little effect on it. At the immersion process condition, the maximum force of the cables decrease with the increase of immersion depth, and dramatically increase with the increase of wave height (i.e. the tension of cable F4 of pontoons at wave height of 1.5 m (83.3t) is approximately four times that at wave height of 0.8 m). The current speed has no much effect on the maximum force of the cables. The weight has little effect on the maximum force of the mooring cables, and the maximum force of hoisting cables increase with the increase of weight. The maximum value of six-freedom motion amplitude of the immersed tunnel element decreases with the increase of immersion depth, increase with the increase of current speed and wave height (i.e. the roll motion at wave height of 1.5 m is two times that at wave height of 0.8 m). The weight has little effect on the maximum motion amplitude of the immersed tunnel element. The results are significant for the immersion safety of element in engineering practical construction process.

New dammarane-type triterpenoid saponins from Panax notoginseng saponins

Qian Li,Mingrui Yuan,Xiaohui Li,Jinyu Li,Ming Xu,Di Wei,Desong Wu,Jinfu Wan,Shuangxi Mei,Tao Cui,Jingkun Wang,Zhaoyun Zhu 고려인삼학회 2020 Journal of Ginseng Research Vol.44 No.5

Background: Panax notoginseng saponin (PNS) is the extraction from the roots and rhizomes of Panax notoginseng (Burk.) F. H. Chen. PNS is the main bioactive component of Xuesaitong, Xueshuantong, and other Chinese patent medicines, which are all bestselling prescriptions in China to treat cardiocerebrovascular diseases. Notoginsenoside R₁ and ginsenoside Rg₁, Rd, Re, and Rb₁ are the principal effective constituents of PNS, but a systematic research on the rare saponin compositions has not been conducted. Objective: The objective of this study was to conduct a systematic chemical study on PNS and establish the HPLC fingerprint of PNS to provide scientific evidence in quality control. In addition, the cytotoxicity of the new compounds was tested. Methods: Pure saponins from PNS were isolated by means of many chromatographic methods, and their structures were determined by extensive analyses of NMR and HR-ESI-MS studies. The fingerprint was established by HPLC-UV method. The cytotoxicity of the compounds was tested by 3-(4,5-dimethylthiazol-2-yl)-2,5 -diphenyltetrazolium bromide assay. Results and Conclusion: Three new triterpenoid saponins (1e3) together with 25 known rare saponins (4 e28) were isolated from PNS, except for the five main compounds (notoginsenoside R₁ and ginsenoside Rg₁, Rd, Re, and Rb₁). In addition, the HPLC fingerprint of PNS was established, and the peaks of the isolated compounds were marked. The study of chemical constituents and fingerprint was useful for the quality control of PNS. The study on antitumor activities showed that new Compound 2 exhibited significant inhibitory activity against the tested cell lines.