G protein signaling and metabolic pathways as evolutionarily conserved mechanisms to combat calcium deficiency.

Calcium (Ca) deficiency causes necrotic symptoms of foliar edges known as tipburn; however, the underlying cellular mechanisms have been poorly understood due to the lack of an ideal plant model and research platform. Using a phenotyping system that quantitates growth and tipburn traits in the model bryophyte Marchantia polymorpha, we evaluated metabolic compounds and the Gß-null mutant (gpb1) that modulate the occurrence and expansion of the tipburn. Transcriptomic comparisons between wild-type and gpb1 plants revealed the phenylalanine/phenylpropanoid biosynthesis pathway and reactive oxygen species (ROS) important for Ca deficiency responses. gpb1 plants reduced ROS production possibly through transcriptomic regulations of class III peroxidases and induced the expression of phenylpropanoid pathway enzymes without changing downstream lignin contents. Supplementation of intermediate metabolites and chemical inhibitors further confirmed the cell-protective mechanisms of the phenylpropanoid and ROS pathways. Marchantia polymorpha, Arabidopsis thaliana, and Lactuca sativa showed comparable transcriptomic changes where genes related to phenylpropanoid and ROS pathways were enriched in response to Ca deficiency. In conclusion, our study demonstrated unresolved signaling and metabolic pathways of Ca deficiency response. The phenotyping platform can speed up the discovery of chemical and genetic pathways, which could be widely conserved between M. polymorpha and angiosperms.

Evaluation of Hearing Sensitivity in Young Adults With Normal Hearing Using a 40-Hz Auditory Steady-State Response With CE-Chirp.

PURPOSE: The present study aimed to measure hearing sensitivity in young adults with normal hearing using a 40-Hz auditory steady-state response with CE-Chirp and to evaluate the speed and accuracy of this method. METHOD: Twelve young adults (1 man, 11 women; mean age = 22.1 ± 3.1 years) each completed two auditory steady-state response measurement sessions with CE-Chirp. The difference score was calculated at each of the four pure-tone frequencies. The measurement time and residual noise level in all stimulus levels were also determined. RESULTS: The difference scores across the 4 frequencies ranged within ±10 dB (1st: 58% to 71%, 2nd: 54% to 79%), within 20 dB (1st: 79% to 96%, 2nd: 79% to 100%), and ≥ 30 dB (1st: 4% to 17%, 2nd: 0% to 17%). The measurement times for both ears were approximately 20 min in both sessions. There was a significant correlation between the measurement time and the mean residual noise level for pooled frequencies in all stimulus levels (p = .0001249, r = .70). The measurement time was reduced by approximately 50% from conventional auditory steady-state response measurement. CONCLUSION: The results of this preliminary study support the use of this technology as a rapid and accurate method for behavioral auditory threshold evaluation.