Compensation for PSII photoinactivation by regulated non-photochemical dissipation influences the impact of photoinactivation on electron transport and CO2 assimilation

The extent to which PSII photoinactivation affects electron transport (PhiPSII) and CO2 assimilation remains controversial, in part because it frequently occurs alongside inactivation of other components of photosynthesis, such as PSI. By manipulating conditions (darkness versus low light) after a high light/low temperature treatment, we examined the influence of different levels of PSII inactivation at the same level of PSI inactivation on PhiPSII and CO2 assimilation for Arabidopsis. Furthermore, we compared PhiPSII at high light and optimum temperature for wild-type Arabidopsis and a mutant (npq4-1) with impaired capacities for energy dissipation. Levels of PSII inactivation typical of natural conditions (< 50%) were not associated with decreases in PhiPSII and CO2 assimilation at photon flux densities (PFDs) above 150 micromol m(-2) s(-1). At higher PFDs, the light energy being absorbed was in excess of the energy that could be utilized by downstream processes. Arabidopsis plants downregulate PSII activity to dissipate such excess in accordance with the level of PSII photoinactivation that also serves to dissipate absorbed energy. Therefore, the overall levels of non-photochemical dissipation and the efficiency of photochemistry were not affected by PSII inactivation at high PFD. Under low PFD conditions, such compensation is not necessary, because the amount of light energy absorbed is not in excess of that needed for photochemistry, and inactive PSII complexes are dissipating energy. We conclude that moderate photoinactivation of PSII complexes will only affect plant performance when periods of high PFD are followed by periods of low PFD.     

Palmitoylations on murine coronavirus spike proteins are essential for virion assembly and infectivity

Coronavirus spike (S) proteins are palmitoylated at several cysteine residues clustered near their transmembrane-spanning domains. This is achieved by cellular palmitoyl acyltransferases (PATs), which can modify newly synthesized S proteins before they are assembled into virion envelopes at the intermediate compartment of the exocytic pathway. To address the importance of these fatty acylations to coronavirus infection, we exposed infected cells to 2-bromopalmitate (2-BP), a specific PAT inhibitor. 2-BP profoundly reduced the specific infectivities of murine coronaviruses at very low, nontoxic doses that were inert to alphavirus and rhabdovirus infections. 2-BP effected only two- to fivefold reductions in S palmitoylation, yet this correlated with reduced S complexing with virion membrane (M) proteins and consequent exclusion of S from virions. At defined 2-BP doses, underpalmitoylated S proteins instead trafficked to infected cell surfaces and elicited cell-cell membrane fusions, suggesting that the acyl chain adducts are more critical to virion assembly than to S-induced syncytial developments. These studies involving pharmacologic inhibition of S protein palmitoylation were complemented with molecular genetic analyses in which cysteine acylation substrates were mutated. Notably, some mutations (C1347F and C1348S) did not interfere with S incorporation into virions, indicating that only a subset of the cysteine-rich region provides the essential S-assembly functions. However, the C1347F/C1348S mutant viruses exhibited relatively low specific infectivities, similar to virions secreted from 2-BP-treated cultures. Our collective results indicate that the palmitate adducts on coronavirus S proteins are necessary in assembly and also in positioning the assembled envelope proteins for maximal infectivity.     

An Evaluation of Some Commercial Test Papers and Tablets for the Determination of Glucose in Urine

The commercial test papers, Tes-Tape, Clinistix, Uristix and Combistix, and the tablet preparation, Clinitest, were evaluated as indicators of glucose in urine by means of a quantitative automated glucose oxidase procedure for glucose determination. The semiquantitative Tes-Tape yielded very low values on urine specimens when compared with the quantitative method. More reliable results could be obtained with this product if the urine specimens were first treated with a mixed bed resin to remove inhibitors of the glucose oxidase peroxidase system. The qualitative test papers, Clinistix, Uristix and Combistix, yielded responses in closer agreement with the automated data, the best performance being obtained with Clinistix. The semiquantitative Clinitest tablets generally yielded more accurate results on a direct urine test than did Tes-Tape, although the Clinitest tablet is designed to measure total reducing substances rather than glucose alone.     

The Use of Urograph for the Determination of Urea Nitrogen Concentration in Serum and Plasma

The accuracy and precision of Urograph, a commercial preparation of chromatography papers designed for the determination of urea nitrogen in plasma and serum, were assessed. Results of duplicate determinations were compared with those of two acceptable quantitative procedures, (1) automated diacetyl monoxime and (2) modified Van Slyke and Cullen analysis. Values for serum specimens obtained by Urograph were significantly higher than those found by the Autoanalyzer method. The confidence limits for the Urograph procedure ranged from 12.5% for plasma to 26.6% for sera, whereas the corresponding values were 6.9% and 7.0% for Autoanalyzer. This lack of precision with Urograph appeared to be due mainly to the presence of a few strips in which only partial migration occurred. The papers yielded low values following 81/2 months of storage in the refrigerator; the test was temperature-sensitive.