Summary• The role of nitric oxide (NO) and the relationship between NO, hydrogen peroxide (H 2 O 2 ) and mitogen-activated protein kinase (MAPK) in abscisic acid (ABA)-induced antioxidant defense in leaves of maize ( Zea mays ) plants were investigated.• Both ABA and H 2 O 2 induced increases in the generation of NO in mesophyll cells of maize leaves, and H 2 O 2 was required for the ABA-induced generation of NO. Pretreatment with NO scavenger and nitric oxide synthase (NOS) inhibitor substantially reduced the ABA-induced production of NO, and partly blocked the activation of a 46 kDa MAPK and the expression and the activities of several antioxidant enzymes induced by ABA. Treatment with the NO donor sodium nitroprusside (SNP) also induced the activation of the MAPK, and enhanced the antioxidant defense systems.• Conversely, SNP treatment did not induce the production of H 2 O 2 , and pretreatments with NO scavenger and NOS inhibitor did not affect ABA-induced H 2 O 2 production.• Our results suggest that ABA-induced H 2 O 2 production mediates NO generation, which, in turn, activates MAPK and results in the upregulation in the expression and the activities of antioxidant enzymes in ABA signaling.

The 2019 novel coronavirus disease has now swept through the continents and poses a global threat to public health. Several investigations have been conducted to identify whether COVID-19 can be transmitted through the ocular route, and the conclusion is that it is a potential route but remains uncertain. Due to the faceto-face communication with patients, frequent exposure to tears and ocular discharge, and the unavoidable use of equipment which requires close proximity, ophthalmologists carry a high risk of contracting severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Based on 33 articles published by Chinese scholars, guidelines and clinical practice experience in domestic hospitals, we have summarized the Chinese experience through the lens of ophthalmology, hoping to make a contribution to protecting ophthalmologists and patients around the world.

Nitric oxide (NO) is a bioactive molecule involved in many biological events, and has been reported as pro-oxidant as well as anti-oxidant in plants. In the present study, the sources of NO production under water stress, the role of NO in water stress-induced hydrogen peroxide (H2O2) accumulation and subcellular activities of anti-oxidant enzymes in leaves of maize (Zea mays L.) plants were investigated. Water stress induced defense increases in the generation of NO in maize mesphyll cells and the activity of nitric oxide synthase (NOS) in the cytosolic and microsomal fractions of maize leaves. Water stress-induced defense increases in the production of NO were blocked by pretreatments with inhibitors of NOS and nitrate reductase (NR), suggesting that NO is produced from NOS and NR in leaves of maize plants exposed to water stress. Water stress also induced increases in the activities of the chloroplastic and cytosolic anti-oxidant enzymes superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR), and the increases in the activities of anti-oxidant enzymes were reduced by pretreatments with inhibitors of NOS and NR. Exogenous NO increases the activities of water stress-induced subcellular anti-oxidant enzymes, which decreases accumulation of H2O2. Our results suggest that NOS and NR are involved in water stress-induced NO production and NOS is the major source of NO. The potential ability of NO to scavenge H2O2 is, at least in part, due to the induction of a subcellular anti-oxidant defense.

In order to better understand the isomerization between HNC and HCN on icy grain (or comet nuclei) surfaces in the interstellar medium in connection with a Strecker synthesis route to glycine, B3LYP/6-31+G(d,p) calculations have been carried out on the mechanisms of direct proton transfer (PT), where water molecules play a purely solvating role, and indirect PT, where water molecules participate in a proton relay mechanism. In the direct PT mechanism, a rather high-energy barrier exists for isomerization of HNC to HCN. In the much more important indirect mechanism, a concerted PT process is possible for isomerization in the presence of several water molecules. The calculations show that three water molecules bound to HNC and HCN give rise to a ring reaction significantly favoring the isomerization, a mechanism previously found for this reaction by Gardebien and Sevin (J. Phys. Chem. A 2003, 107, 3925). Further quite important solvation effects are included in the present work by addition of explicit solvating water molecules, and by a comparison with Polarizable Continuum Model (PCM) solvation. The final calculated free-energy barrier at 50 K is 3.4 kcal/ mol for the isomerization of HNC to HCN with three water molecules in a ring acting as a bridge for concerted PT and seven explicit solvating water molecules; PCM solvation of this entire system leads to a further free-energy barrier reduction of 0.8 kcal/mol. The back isomerization of HCN to HNC, however, is unlikely, with an estimated free-energy barrier of 9.5 kcal/mol at 50 K. These results imply that, on icy surfaces in the interstellar medium, the isomerization of HNC to HCN occurs relatively easily, and the implications for the Strecker synthesis of glycine are discussed.