Phenotypic plasticity in Philonotis fontana (Bryopsida: Bartramiaceae)

Abstract

Gametophytes from six populations of the moss Philonotis fontana (Hedw.) Brid. were grown under two light and two water regimes in order to assess the effects of these environmental factors on gametophytic architecture and leaf and leaf-cell dimensions. Both light and water affectedgrowth, but the light treatments had a greater effect, and on more characters, than did the water treatments. Significant population effects under common garden conditions point to genetic variation for several traits, and population × environmental treatment interactions demonstratedgenetic variation for patterns of phenotypic plasticity, i.e. plants differed in their 'norms of reaction'. Variation among populations in leaf dimensions tended to have a strong genetic component (20–30% of the total variation), whereas cell dimensions showed relatively little geneticvariation (<10% of the total).     

Selective inhibition of ATPase activity during contraction alters the activation of p38 MAP kinase isoforms in skeletal muscle

Muscle contractions strongly activate p38 MAP kinases, but the precise contraction‐associated sarcoplasmic event(s) (e.g., force production, energetic demands, and/or calcium cycling) that activate these kinases are still unclear. We tested the hypothesis that during contraction the phosphorylation of p38 isoforms is sensitive to the increase in ATP demand relative to ATP supply. Energetic demands were inhibited using N‐benzyl‐p‐toluene sulphonamide (BTS, type II actomyosin) and cyclopiazonic acid (CPA, SERCA). Extensor digitorum longus muscles from Swiss Webster mice were incubated in Ringer's solution (37°C) with or without inhibitors and then stimulated at 10 Hz for 15 min. Muscles were immediately freeze‐clamped for metabolite and Western blot analysis. BTS and BTS + CPA treatment decreased force production by 85%, as measured by the tension time integral, while CPA alone potentiated force by 310%. In control muscles, contractions resulted in a 73% loss of ATP content and a concomitant sevenfold increase in IMP content, a measure of sustained energetic imbalance. BTS or CPA treatment lessened the loss of ATP, but BTS + CPA treatment completely eliminated the energetic imbalance since ATP and IMP levels were nearly equal to those of non‐stimulated muscles. The independent inhibition of cytosolic ATPase activities had no effect on contraction‐induced p38 MAPK phosphorylation, but combined treatment prevented the increase in phosphorylation of the γ isoform while the α/β isoforms unaffected. These observations suggest that an energetic signal may trigger phosphorylation of the p38γ isoform and also may explain how contractions differentially activate signaling pathways. J. Cell. Biochem. 114: 1445–1455, 2013. © 2013 Wiley Periodicals, Inc.