UV-B exposure of indoor-grown Picea abies seedlings causes an epigenetic effect and selective emission of terpenes.

Terpenoids are involved in various defensive functions in plants, especially conifers. Epigenetic mechanisms, for example DNA methylation, can influence plant defence systems. The purpose of the present study was to investigate the influence of UV-B exposure on the release of terpenoids from spruce seedlings and on needle DNA methylation. Ten-week-old seedlings grown indoors were exposed to UV-B radiation during 4 h, and the volatile compounds emitted from the seedlings were analysed. Analysis of the volatiles 1, 3, and 22 d after this UV-B exposure showed that bornyl acetate, borneol, myrcene, and limonene contents increased during the first 3 days, while at day 22 the level of emission had returned to the control level. UV-B exposure decreased the level of DNA methylation in needles of young seedlings, reflected in methylation changes in CCGG sequences. Exposure of young seedlings to UV-B radiation might be a way to potentiate the general defensive capacity, improving their ability to survive in outdoor conditions. UV-B-induced defence is discussed in the light of epigenetic mechanisms.

Engineered non-fluorescent Affibody molecules facilitate studies of the amyloid-beta (Aß) peptide in monomeric form: low pH was found to reduce Aß/Cu(II) binding affinity.

Aggregation of amyloid-beta (Aß) peptides into oligomers and amyloid plaques in the human brain is considered a causative factor in Alzheimer's disease (AD). As metal ions are over-represented in AD patient brains, and as distinct Aß aggregation pathways in presence of Cu(II) have been demonstrated, metal binding to Aß likely affects AD progression. Aß aggregation is moreover pH-dependent, and AD appears to involve inflammatory conditions leading to physiological acidosis. Although metal binding specificity to Aß varies at different pH's, metal binding affinity to Aß has so far not been quantitatively investigated at sub-neutral pH levels. This may be explained by the difficulties involved in studying monomeric peptide properties under aggregation-promoting conditions. We have recently devised a modified Affibody molecule, Z(Aß3)(12-58), that binds Aß with sub-nanomolar affinity, thereby locking the peptide in monomeric form without affecting the N-terminal region where metal ions bind. Here, we introduce non-fluorescent Aß-binding Affibody variants that keep Aß monomeric while only slightly affecting the Aß peptide's metal binding properties. Using fluorescence spectroscopy, we demonstrate that Cu(II)/Aß(1-40) binding is almost two orders of magnitude weaker at pH 5.0 (apparent K(D)=51 µM) than at pH 7.3 (apparent K(D)=0.86 µM). This effect is arguably caused by protonation of the histidines involved in the metal ligandation. Our results indicate that engineered variants of Affibody molecules are useful for studying metal-binding and other properties of monomeric Aß under various physiological conditions, which will improve our understanding of the molecular mechanisms involved in AD.