No abstract

In hulless barley, H 2 S mediated increases in H 2 O 2 induced by putrescine, and their interaction enhanced tolerance to UV-B by maintaining redox homeostasis and promoting the accumulation of UV-absorbing compounds. This study investigated the possible relationship between putrescence (Put), hydrogen sulfide (H2S) and hydrogen peroxide (H2O2) as well as the underlying mechanism of their interaction in reducing UV-B induced damage. UV-B radiation increased electrolyte leakage (EL) and the levels of malondialdehyde (MDA) and UV-absorbing compounds but reduced antioxidant enzyme activities and glutathione (GSH) and ascorbic acid (AsA) contents. Exogenous application of Put, H2S or H2O2 reduced some of the above-mentioned negative effects, but were enhanced by the addition of Put, H2S and H2O2 inhibitors. Moreover, the protective effect of Put against UV-B radiation-induced damage to hulless barley was diminished by DL-propargylglycine (PAG, a H2S biosynthesis inhibitor), hydroxylamine (HT, a H2S scavenger), diphenylene iodonium (DPI, a PM-NADPH oxidase inhibitor) and dimethylthiourea (DMTU, a ROS scavenger), and the effect of Put on H2O2 accumulation was abolished by HT. Taken together, as the downstream component of the Put signaling pathway, H2S mediated H2O2 accumulation, and H2O2 induced the accumulation of UV-absorbing compounds and maintained redox homeostasis under UV-B stress, thereby increasing the tolerance of hulless barley seedlings to UV-B stress.

Cobalamins comprise a group of cobalt-containing organometallic cofactors that play important roles in cellular metabolism. Although many cobalamin-dependent methyltransferases (e.g., methionine synthase MetH) have been extensively studied, a new group of methyltransferases that are cobalamin-dependent and utilize radical chemistry in catalysis is just beginning to be appreciated. In this Concept article, we summarize recent advances in the understanding of the radical-based and cobalamin-dependent methyltransferases and discuss the functional and mechanistic diversity of this emerging class of enzymes.

No abstract