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Study of cytokinin role in abiotic stress response
Dobrá, Jana ; Vaňková, Radomíra (advisor) ; Ryšlavá, Helena (referee) ; Brzobohatý, Břetislav (referee)
Plants had to evolve, due to their sessile growth habit, a complex system of defence against adverse environmental conditions. Plant abiotic stress responses are regulated by plant hormones, especially by cytokinins (CKs) and abscisic acid (ABA). In order to evaluate the effect of enhanced stress tolerance on the dynamics of hormones (CKs, auxin and ABA) as well as polyamine levels during the drought and/or heat stress (HS) progression, response of tobacco plants with enhanced level of osmolyte proline was compared with the corresponding wild-type. HS (40řC) caused a transient increase in bioactive CK content, accompanied by decrease of ABA, which indicated stimulation of transpiration, important mechanism to cool down the leaf temperature at the early phase of HS. Simultaneously, a transient increase in spermidine and spermine levels was found, more profound in proline-over-producing transformant. The activities of particular polyamine metabolic enzymes correlated well with their content. Drought stress resulted in the establishment of a gradient of bioactive CKs in favour of the upper leaves, crucial for their preferential protection. Application of HS at the end of drought period strongly enhanced the stress severity, mainly due to additional water loss caused by enhanced transpiration....
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