Change in XET activities,cell wall extensibility and hypocotyl elongation of soybean seedlings at low water potential

In dark-grown soybean (Glycine max [L.] Merr.) seedlings, exposing the roots to water-deficient vermiculite (_w=–0.36 MPa) inhibited hypocotyl (stem) elongation. The inhibition was associated with decreased extensibility of the cell walls in the elongation zone. A detailed spatial analysis showed xyloglucan endotransglucosylase (XET; EC 2.4.1.207) activity on the basis of unit cell wall dry weight was decreased in the elongation region after seedlings were transplanted to low _w. The decrease in XET activity was at least partially due to an accumulation of cell wall mass. Since cell number was only slightly altered, wall mass had increased per cell and probably led to increased wall thickness and decreased cell wall extensibility. Alternatively, an increase in cell wall mass may represent a mechanism for regulating enzyme activity in cell walls, XET in this case, and therefore cell wall extensibility. Hypocotyl elongation was partially recovered after seedlings were grown in low-_w vermiculate for about 80 h. The partial recovery of hypocotyl elongation was associated with a partial recovery of cell wall extensibility and an enhancement of XET activity in the hypocotyl elongation zone. Our results indicate XTH proteins may play an important role in regulating cell wall extensibility and thus cell elongation in soybean hypocotyls. Our results also showed an imperfect correlation of spatial elongation and XET activity along the hypocotyls. Other potential functions of XTH and their regulation in soybean hypocotyl growth are discussed.     

赤霉素诱导甘蔗节间伸长的效应与相关酶活性的关系

以甘蔗品种'新台糖22号'为试验材料,在伸长初期以200 mg/L GA3进行叶面喷施处理,对照喷清水,研究GA3处理后甘蔗节间糖苷酶、过氧化物酶、过氧化氢酶的变化,以揭示赤霉素诱导甘蔗节间伸长与相关酶活性的关系.结果表明:(1)GA3处理的株高在各个时期显著高于对照,而且在处理后7、14和28 d分别比对照提高了17.32%、14.50%和8.35%,GA3处理引起甘蔗植株表现的高度优势一直保持到后期,节间伸长效果主要是在茎的中部(5～10节).(2)GA3处理后α-葡萄糖苷酶和α-甘露糖苷酶的活性较对照显著下降;POD和β-半乳糖苷酶的活性也略有下降;α-半乳糖苷酶、β-N-乙酰氨基已糖苷酶、过氧化氢酶的活性显著提高;β-葡萄糖苷酶的活性也有一定程度提高.由此推测,外源GA3主要通过调节α-葡萄糖苷酶活性、α-甘露糖苷酶、α-半乳糖苷酶、β-N-乙酰氨基已糖苷酶活性和过氧化氢酶,其次是POD、β-半乳糖苷酶和β-葡萄糖苷酶活性,最终达到节间伸长效果.     

野生型和ospk1突变体水稻幼苗根对外源糖分的吸收和响应

植物根系如何响应环境因子变化是植物发育和营养吸收研究的重要科学问题。丙酮酸激酶OsPK1在根部的表达主要在根尖成熟区和根毛区,其表达水平变化有可能影响水稻对外源糖分的吸收。采用日本晴和水稻突变体ospk1,通过改变1/2 MS培养基中蔗糖含量,探索水稻幼苗对外源糖分的吸收和响应。通过GC-MS的方法检测了水稻幼苗叶片、叶鞘和根中蔗糖、葡萄糖、果糖和半乳糖的含量。发现根与培养基中糖分接触能明显提高幼苗中的糖含量。并且这些幼苗的根系长度大于那些不加蔗糖的培养基培养的幼苗,表明外源糖分被吸收后能促进根的伸长。OsPK1表达下调影响了糖代谢和外源糖分的吸收。半定量RT-PCR结果显示,幼苗根与糖分的直接接触明显上调根中OsPIP2;4,OsPIP2;5和OsTIP2;1三个水孔蛋白基因的表达。     

AIMP3/p18 Controls Translational Initiation by Mediating the Delivery of Charged Initiator tRNA to Initiation Complex

Aminoacyl-tRNA synthetase-interacting multifunctional proteins (AIMPs) are nonenzymatic scaffolding proteins that comprise multisynthetase complex (MSC) with nine aminoacyl-tRNA synthetases in higher eukaryotes. Among the three AIMPs, AIMP3/p18 is strongly anchored to methionyl-tRNA synthetase (MRS) in the MSC. MRS attaches methionine (Met) to initiator tRNA (tRNA_i^Met) and plays an important role in translation initiation. It is known that AIMP3 is dispatched to nucleus or nuclear membrane to induce DNA damage response or senescence; however, the role of AIMP3 in translation as a component of MSC and the meaning of its interaction with MRS are still unclear. Herein, we observed that AIMP3 specifically interacted with Met-tRNA_i^Metin vitro, while it showed little or reduced interaction with unacylated or lysine-charged tRNA_i^Met. In addition, AIMP3 discriminates Met-tRNA_i^Met from Met-charged elongator tRNA based on filter-binding assay. Pull‐down assay revealed that AIMP3 and MRS had noncompetitive interaction with eukaryotic initiation factor 2 (eIF2) γ subunit (eIF2γ), which is in charge of binding with Met-tRNA_i^Met for the delivery of Met-tRNA_i^Met to ribosome. AIMP3 recruited active eIF2γ to the MRS-AIMP3 complex, and the level of Met-tRNA_i^Met bound to eIF2 complex was reduced by AIMP3 knockdown resulting in reduced protein synthesis. All these results suggested the novel function of AIMP3 as a critical mediator of Met-tRNA_i^Met transfer from MRS to eIF2 complex for the accurate and efficient translation initiation.     

Properties of pullulan-based blend films as affected by alginate content and relative humidity

Pullulan-sodium alginate blend films were prepared and characterized as a function of water activity (a_w). At low a_w, the incorporation of alginate into pullulan film increased the tensile strength and elastic modulus, but decreased the elongation at break of the composite films; the opposite trends were observed at elevated a_w. Above 0.43 a_w, water exerted a typical plasticization effect upon the biopolymer blends. As a_w increased from 0.23 to 0.43, an anti-plasticization effect was observed as tensile strength and elastic modulus increased. The glass transition temperature of all samples decreased substantially as aw increased from 0.23 to 0.84 due to the plasticization effect of water. Within this a_w range, one transition temperature was observed for all film specimens. The stretching vibration band of O-H was investigated using attenuated total reflection Fourier transform infrared spectroscopy to identify the various species of water interacting with the polysaccharide films.     

Multiomic Analysis Reveals Disruption of Cholesterol Homeostasis by Cannabidiol in Human Cell Lines

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Laser tweezers as a biophotonic tool to investigate the efficacy of living sickle red blood cells in response to optical deformation

A laser tweezer technique based on single and/or dual-laser beams is proposed as a biophotonic tool to trap single cells and investigate their biophysical and biomechanical characteristics. Optical deformability and changes in size and cellular morphology of living and nonliving cells can be measured using the proposed technique. Representative results of red blood cell (RBC) optical deformability of 20 homozygous patients with sickle cell disease, including follow-up patients after treating with hydroxyurea (HU) for at least 3 months and 20 healthy control groups, are presented and compared. Shape recovery of deformed RBCs and relaxation time are recorded for each RBC. Results showed that healthy blood and patients treated with HU demonstrate significantly higher optical deformability and degree of optical elongation with morphological change of RBCs than untreated patients. Moreover, the healthy control group and patients treated with HU exhibited faster relaxation time for RBCs than untreated patients. A trapping power that reaches 180 mW caused no observable photo-damage at a wavelength 1064 nm.Supplementary InformationThe online version contains supplementary material available at 10.1007/s12551-021-00790-0.     

The auxin-resistant diageotropica mutant of tomato responds to gravity via an auxin-mediated pathway

 Hypocotyls of the diageotropica (dgt) mutant of tomato (Lycopersicon esculentum Mill.) do not elongate in response to exogenous auxin, but can respond to gravity. This appears paradoxical in light of the Cholodny-Went hypothesis, which states that shoot gravicurvature results from asymmetric stimulation of elongation by auxin. While light-grown dgt seedlings can achieve correct gravitropic reorientation, the response is slow compared to wild-type seedlings. The sensitivity of dgt seedlings to inhibition of gravicurvature by immersion in auxin or auxin-transport inhibitors is similar to that of wild-type plants, indicating that both an auxin gradient and auxin transport are required for the gravitropic response and that auxin uptake, efflux, and at least one auxin receptor are functional in dgt. Furthermore, dgt gravicurvature is the result of asymmetrically increased elongation as would be expected for an auxin-mediated response. Our results suggest differences between elongation in response to exogenous auxin (absent in dgt) and elongation in response to gravistimulation (present but attenuated in dgt) and confirm the presence of two phases during the gravitropic response, both of which are dependent on functional auxin transport. Received: 16 July 1999 / Accepted: 24 September 1999     

Role of extensin peroxidase in tomato (Lycopersicon esculentum Mill.) seedling growth

 It is proposed that inhibition of extensin peroxidase activity leads to a less rigid cell wall and thus promotes cell expansion and plant growth. A low-molecular-weight inhibitor derived from the cell walls of suspension-cultured tomato cells was found to completely inhibit extensin peroxidase-mediated extensin cross-linking in vitro at a concentration of 260 μg/ml. The inhibitor had no effect upon guaiacol oxidation catalyzed by extensin peroxidase or horseradish peroxidase. We have demonstrated that the light-irradiated inhibition of plant growth may be partially offset by inhibition of endogenous extensin peroxidase activity. Overall plant growth was enhanced by up to 15% in the presence of inhibitor relative to control plants. Inhibitor-treated and illuminated tomato hypocotyls grew up to 15% taller than untreated controls. The inhibitor had no effect upon etiolated plants over a 15-d period, suggesting that only low levels of peroxidase-mediated cross-linking can be found in the cell walls of etiolated plants. SDS-PAGE/Western blots of ionically bound protein from both etiolated and illuminated hypocotyls identified a doublet at 57/58.5 kDa which is immuno-reactive with antibodies raised to tomato extensin peroxidase. Levels of the 58.5-kDa protein, determined by SDS-PAGE, were at least threefold higher in illuminated tomato hypocotyls than in etiolated hypocotyls. Three fold higher levels of extensin peroxidase, elevated in-vitro extensin cross-linking activity and 15% higher levels of cross-linked, non-extractable extensin were observed in illuminated tomato hypocotyls compared with etiolated tomato hypocotyls. This suggests that white-light inhibition of tomato hypocotyl growth appears to be mediated, at least partially, by deposition of cell wall extensin, a process regulated by M_r-58,500 extensin peroxidase. Our results indicate that the contribution of peroxidase-mediated extensin deposition to plant cell wall architecture may have an important role in plant growth. Received: 22 July 1999 / Accepted: 11 October 1999