Sodininkystė ir daržininkystė - Sodininkystės ir daržininkystės institutas

(ABA), jasmonic acid (JA) and gibberellic acid (GA 3) signaling pathways. Thesepathways serve to induce defense-gene expression to minimize lesion formationin plants exposed to ozone, as well as regulating developmental processes(Conklin et al., 2004). It is suggested (Lin et al., 2001), that ascorbic acid, anintegral weapon in the defense against ROS, is involved as a cofactor in thesynthesis of ABA, GA 3and ethylene.Plant hormones play key roles in determining the degree of plant ozonesensitivity, ozone lesion development and ozone-induced cell death. Ethyleneand salicylic acid are needed for the development of the visible O 3lesions.Cell death also triggers ethylene production, which is required for thecontinuing ROS production responsible for the propagation of cell death.Jasmonates counteract ethylene action: limit lesion spread and inhibit celldeath promoters. ABA plays the main role in the stomatal regulation andozone influx; antagonizes ethylene function. Cytokinins are generally consideredto be antagonists of ABA (Hare et al., 1997) and delay ozone-induced leafsenescence (Szekacs et al., 2000).The evidence on the hormonal control of plant O 3responses is strong.Plant hormones do not act independently, but rather in a complex signalingnetwork and their balance is very likely to be largely responsible for the metabolicresponse processes (Conklin et al., 2004). Several publications on ozonephytotoxicity are available (Sanderamann, 1996, 1998; Black et al., 2000; Raoet al., 2001; Mahalingam et al., 2003; Conklin et al., 2004; Baier et al., 2005;Kangasjarvi et al., 2005). These articles are mainly concerned with primaryplant metabolism, whose inhibition by ozone leads to a general reduction ofgrowth and competitive fitness of the plant or only with separate aspects ofthe plant response in molecular level. Though, presently there is nocomprehensive model to predict plant acclimation to ozone exposure. Therole of phytohormones, biochemical and molecular responses are not exploredin detail due to the lack of understanding the regulatory mechanisms andmetabolic signaling under elevated O 3conditions. The impact of ozone isknown to vary between species and cultivars and to be influenced by bothclimatic factors and cultural practices (Black et al., 2000).The aim of this study was to evaluate the exposure of different ozoneconcentrations on phytohormone system in radish (Raphanus sativus L., cv.Þara).Materials and Methods. Investigations were carried out in Laboratory ofPlant Physiology at the Lithuanian Institute of Horticulture, Phytotron complexin 2005. Radish (Raphanus sativus L. cv. Þara) was grown in 5 L tumblers inneutral peat substratum (pH 6-6.5). 30 plants were sown in each tumbler, toget a starting density of ~ 950 plants per m -2 . Plants were germinated andkept in greenhouse for 12 days. Then plants were moved to phytotron chambersand left for 2 days to get accustomed to new environment. Subsequently,generation of ozone was started. Different ozone concentrations weremaintained as follows: 0 (control), 80, 160 and 240 ìg m -3 . Plants were treatedwith ozone 7 h per day and 5 days per week. The ozone concentrations were171