Physiologia Plantarum 2011 Copyright © Physiologia Plantarum 2011, ISSN 0031-9317 Nitric oxide as a critical factor for perception of UV-B irradiation by microtubules in Arabidopsis Yuliya A. Krasylenko † , Alla I. Yemets ∗,† , Yarina A. Sheremet and Yaroslav B. Blume Department of Genomics and Molecular Biotechnology, Institute of Food Biotechnology and Genomics, National Academy of Sciences of Ukraine, Kiev 04123, Ukraine Correspondence *Corresponding author, e-mail: yemets.alla@gmail.com; cellbio@cellbio.freenet.viaduk.net Received 25 March 2011; revised 27 August 2011 doi:10.1111/j.1399-3054.2011.01530.x Influence of ultraviolet-B (UV-B) as an abiotic stress factor on plant micro- tubules (MTs) and involvement of nitric oxide (NO) as a secondary messenger mediating plant cell response to environmental stimuli were investigated in this study. Taking into account that endogenous NO content in plant cells has been shown to be increased under a broad range of abiotic stress factors, the effects of UV-B irradiation and also the combined action of UV-B and NO donor sodium nitroprusside (SNP) or NO scavenger 2-(4-carboxyphenyl)- 4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO) on the MTs organiza- tion in different root cells of Arabidopsis thaliana were tested. Subsequently, realization of the MT-mediated processes such as root growth and devel- opment was studied under these conditions. Arabidopsis thaliana seedlings expressing the chimeric gene gfp-map4 were exposed to the enhanced UV-B with or without SNP or c-PTIO pretreatment. The UV-B irradiation alone led to a dose-dependent root growth inhibition and to morphological alterations of the primary root manifested in their swelling and excessive root hair forma- tion. Moreover, dose-dependent randomization and depolymerization of MTs in both epidermal and cortical cells under the enhanced UV-B were found. However, SNP pretreatment of the UV-B irradiated A. thaliana seedlings recovered the UV-B inhibited root growth as compared to c-PTIO pretreat- ment. It has been shown that in 24 h after UV-B irradiation the organization of MTs in root epidermal cells of SNP-pretreated A. thaliana seedlings was par- tially recovered, whereas in c-PTIO-pretreated ones the organization of MTs has not been distinctly improved. Therefore, we suppose that the enhanced NO levels in plant cells can protect MTs organization as well as MT-related processes of root growth and development against disrupting effects of UV-B. Introduction The elevation of solar ultraviolet-B (UV-B, 280 – 315 nm) radiation levels occurs due to the current depletion of the stratospheric ozone layer (Jansen 2002, Frohnmeyer and Staiger 2003) and/or other climate-induced changes Abbreviations – c-PTIO, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide; MTs, microtubules; NO, nitric oxide; ROS, reactive oxygen species; SIMR, stress-induced morphological response; SNP, sodium nitroprusside; UV-B, ultraviolet-B irradiation. † These authors contributed equally to this work. (McKenzie et al. 2011) resulting in various photo- morphogenic responses of plants and a decrease in crop yields. The extent of plant responses to the enhanced UV-B irradiation vary between species and ecotypes (Jansen 2002), as well as the effects of dif- ferent UV-B doses: high fluence UV-B levels induced Physiol. Plant. 2011