Sodininkystė ir daržininkystė - Sodininkystės ir daržininkystės institutas

GA 3concentration was significantly higher in 80 and 240 µg m -3 treatments,though it was 3 times lower in 160 µg m -3 ozone treatment. Zeatin amount washigher in all variants than in control; ABA and IAA contents were higher in80 and 240 µg m -3 treatments, but lower in 160 µg m -3 treatment, comparedwith control. Calculations of phytohormone balance showed, that GA 3/IAAratio was significantly the lowest and ABA/IAA ratio was the highest in the160 µg m -3 treatment.Discussion. Plants face a continuously changing environment. In order tocomplete their life cycle and maintain a sufficient level of fitness to reproduce,they need to adapt to abiotic and biotic conditions (Baier et al., 2005). Stressresponses are likely to be the end-products of complex interplay between amultitude of hormonal and non-hormonal signals (Hare et al., 1997). Shiftsin hormonal balance accompanying environmental stress do not necessarilyindicate a role in adaptation at the genetic level, though plant hormones arethe main regulators of physiological processes and stress response. ABA,salicylic acid (SA), ethylene, and jasmonic acid (JA) are important indetermining the degree of plant ozone sensitivity and O 3-lesion initiation,propagation and containment (Kangasjarvi et al., 2005).The changes in abscisic acid concentrations under different ozone levelcould be attributed to ozone lesion development. Literature facts show, thatABA contents increase fivefold upon wounding (Taylor et al., 2001). However,according to our results, ABA is distributed unequally: the increase in 80 and240 µg m -3 treatments could be associated with mechanical damage of planttissue and the decrease in 160 µg m -3 treatment could be the result of severerstress. According to Kacperska (2004), the mild environmental stress is assistedby an increased supply of abscisic acid, which is involved in the activation of thepathways that enable the adjustment of plant growth and metabolism to thestressful conditions, i.e. allowing acclimation. Severe or suddenly acting stressorsresult in irreversible injuries and cell death and increased synthesis of jasmonatesand ethylene, which antagonizes ABA functions occurs (Kacperska, 2004).Usually studies of hormonal influences on stress physiology have beendominated by investigations of the role of ABA in plant responses tosuboptimal environmental conditions (Hare et al., 1997). Though the balanceof other hormones also should be highlighted. Significant differences in zeatincontents marks its role in physiological reaction to ozone stress. The leastzeatin concentration in 160 µg m -3 treatment and literature facts (Hare et al.,1997; Szekacs et al., 2000) confirm previous assumption about the strongestozone stress. Cytokinins regulate plant cell cycles, delay senescence; an increasedcytokinin level improves the resistance of plants to environmental stress.Therefore the decrease of its concentration in 160 µg m -3 treatment is a goodindicator of the reduced resistance or susceptibility of radish to necrotic diseases(Szekacs et al., 2000). Auxins (indolyl-3-acetic acid, IAA) are the retardants ofabscission. The decrease in IAA contents, which in our results decreasesgradually with increasing ozone concentration, can induce cell separation anddefoliation (Taylor et al., 2001). Although there is no reasonable literature174