Potassium alleviates over-reduction of the photosynthetic electron transport chain and helps to maintain photosynthetic function under salt-stress.

Potassium ions enhance photosynthetic tolerance to salt stress. We hypothesized that potassium ions, by minimizing the trans-thylakoid proton diffusion potential difference, can alleviate over-reduction of the photosynthetic electron transport chain and maintain the functionality of the photosynthetic apparatus. This study investigated the effects of exogenous potassium on the transcription level and activity of proteins related to the photosynthetic electron-transport chain of tobacco seedlings under salt stress. Salt stress retarded the growth of seedlings and caused an outflow of potassium ions from the chloroplast. It also lowered qP (indicator of the oxidation state of QA , the primary quinone electron acceptor in Photosystem II (PSII) and YPSII (average photochemical yield of PSII in the light-adapted state) while increasing YNO+NF (nonregulatory energy dissipation in functional and nonfunctional PSII), accompanied by decreased expression of most light-harvesting, energy-transduction, and electron-transport genes. However, exogenous potassium prevented these effects due to NaCl. Interestingly, lincomycin (an inhibitor of the synthesis of chloroplast-encoded proteins in PSII) significantly diminished the alleviation effect of exogenous potassium on salt stress. We attribute the comprehensive NaCl-induced downregulation of transcription and photosynthetic activities to retrograde signaling induced by reactive oxygen species. There probably exist at least two types of retrograde signaling induced by reactive oxygen species, distinguished by their sensitivity to lincomycin. Exogenous potassium appears to exert its primary effect by ameliorating the trans-thylakoid proton diffusion potential difference via a potassium channel, thereby accelerating ATP synthesis and carbon assimilation, alleviating over-reduction of the photosynthetic electron transport chain, and maintaining the functionality of photosynthetic proteins.

Association between Antibiotic Exposure and the Risk of Rash in Children with Infectious Mononucleosis: a Multicenter, Retrospective Cohort Study.

Present evidence suggests that the administration of antibiotics, particularly aminopenicillins, may increase the risk of rash in children with infectious mononucleosis (IM). This retrospective, multicenter cohort study of children with IM was conducted to explore the association between antibiotic exposure in IM children and the risk of rash. A robust error generalized linear regression was performed to address the potential cluster effect, as well as confounding factors such as age and sex. A total of 767 children (aged from 0 to 18 years) with IM from 14 hospitals in Guizhou Province were included in the final analysis. The regression analysis implied that exposure to antibiotics was associated with a significantly increased incidence of overall rash in IM children (adjusted odds ratio [AOR], 1.47; 95% confidence interval [CI], ~1.04 to 2.08; P = 0.029). Of 92 overall rash cases, 43 were probably related to antibiotic exposure: two cases (4.08%) in the amoxicillin-treated group and 41 (8.15%) in the group treated with other antibiotics. Regression analysis indicated that the risk of rash induced by amoxicillin in IM children was similar to that induced by other penicillins (AOR, 1.12; 95% CI, ~0.13 to 9.67), cephalosporins (AOR, 2.45; 95% CI, ~0.43 to 14.02), or macrolides (AOR, 0.91; 95% CI, ~0.15 to 5.43). Antibiotic exposure may be associated with an increased risk of overall rash in IM children, but amoxicillin was not found to be associated with any increased risk of rash during IM compared to other antibiotics. We suggest that clinicians be vigilant against the occurrence of rash in IM children receiving antibiotic therapy, rather than indiscriminately avoiding prescribing amoxicillin.

Responses of photosynthesis and antioxidants to simulated acid rain in mulberry seedlings.

Acid rain, which has negative impacts on the vegetation of ecological systems, is widespread in Northern and Southern China. However, relatively little is known about the effects of acid rain on the growth and yield of economically important tree species in China. To address this issue, we studied the responses of mulberry seedlings to simulated acid rain (SAR) at different pH values. At pH 4.5, SAR induced increased antioxidant activities, total antioxidant capacity, and the accumulation of reactive oxygen species (OFR) relative to controls. However, the growth of the seedlings under SAR treatments at pH 4.5 and pH 5.6 was greater than controls. No significant differences in photosynthesis and chlorophyll a fluorescence quenching parameters were observed between the SAR treatments at pH 4.5 and pH 5.6 and controls. However, the SAR treatment at pH 3.5 resulted in altered leaf surface characteristics and changes to chloroplast ultrastructure, together with an increase in membrane electrical conductivity and an accumulation of OFR and malondialdehyde. In contrast, leaf antioxidant enzyme activities were decreased, together with electron transport parameters and photosynthesis. Taken together, these results show that the effects of acid rain on the growth and leaf physiology of mulberry seedling are dependent on pH. Moreover, mulberry seedlings had a high tolerance to acid rain at pH 4.5.