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Abstract-Plant seeds sometimes do not germinate at elevated temperature. The thermoinhibition mecha nisms of seed germination have yet not revealed. Here we describe a chemical approach to improve seed ger mination at high temperature. We compared the temperature response of germination between wild type Arabidopsis thaliana and its T DNA insertion mutant ΔAtGLB3 that lacks a functional gene encoding GLB3, a homologue of bacterial truncated Hb (trHb). Under optimal temperature conditions (e.g. 22°C), the seeds of ΔAtGLB3 and the wild type germinated at a frequency near 100%. In contrast, at 32°C the seeds of ΔAtGLB3 did not germinate while wild type seeds retained the same high germination frequency. The ger mination of ΔAtGLB3 at 32°C was partially restored by supplementation with the nitric oxide specific scavenger 2 (4 carboxyphenyl) 4,4,5,5 tetramethylimidazoline 1 oxyl 3 oxide (carboxy PTIO; cPTIO), 3 (3,4 dihydroxycinnamoyl)quinic acid, bovine serum Hb, or isoprene. The results presented in this study suggest that chemical scavengers for reactive nitrogen species potentially improve seed germination at high temperature. Key words: Arabidopsis thaliana germination hemoglobin high temperature nitric oxide DOI: 10.1134/S1021443710020093Abbreviations: CGA-chlorogenic acid; cPTIO-2 (4 carbox yphenyl) 4,4,5,5 tetramethylimidazoline 1 oxyl 3 oxide; Hbhemoglobin; HSP-heat shock protein; MS-Murashige and Skoog nutrient medium; NOS-NO synthase; RNS-reactive nitrogen species; SNP-sodium nitroprusside.

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Nitric oxide (NO) is a gaseous radical molecule that has long been considered to be a harmful air pollutant produced through anthropogenic activities. The finding in the late 1980s that the gas is synthesized in animal cells by the enzyme nitric oxide synthase (NOS) led to a paradigm shift in bioscience. NO is now recognized as an endogenous signalling molecule involved in diverse physiological processes. Plants and algae also produce NO, but the mechanism of synthesis remains controversial. A number of inhibitor experiments have suggested the presence of NOS‐like activities in plants and algae. To date, however, there is no conclusive evidence for the presence of NOS enzymes in these organisms. This chapter provides an overview of plant NOS research, along with a description of possible arginine‐dependent signal transduction mechanisms in plants.