Abstract
Cytokinins (CKs) are phytohormones regulating plant growth and development as well as response to the environment. In order to evaluate their function in heat stress (HS) responses, the effect of CK elevation was determined during three types of HS - targeted to shoots, targeted to roots and applied to the whole plant. The early (30min) and longer term (3h) responses were followed at the hormonal, transcriptomic and proteomic levels in Arabidopsis transformants with dexamethasone-inducible expression of the CK biosynthetic gene isopentenyltransferase (ipt) and the corresponding wild-type (Col-0). Combination of hormonal and phenotypic analyses showed transient up-regulation of the CK/abscisic acid ratio, which controls stomatal aperture, to be more pronounced in the transformant. HS responses of the root proteome and Rubisco-immunodepleted leaf proteome were followed using 2-D gel electrophoresis and MALDI-TOF/TOF. More than 100 HS-responsive proteins were detected, most of them being modulated by CK increase. Proteome and transcriptome analyses demonstrated that CKs have longer term positive effects on the stress-related proteins and transcripts, as well as on the photosynthesis-related ones. Transient accumulation of CKs and stimulation of their signal transduction in tissue(s) not exposed to HS indicate that they are involved in plant stress responses.
Highlights
Due to their sessile character, plants have had to evolve complex systems to sense and respond dynamically to various stress conditions
heat stress (HS)-R was associated with a decrease of tZR content, while the levels of iP and DZR transiently increased after 30 min
Evaluation of the impact of the changed CK/abscisic acid (ABA) ratio showed that CKs are involved in regulation of stomatal aperture and subsequently transpiration
Summary
Due to their sessile character, plants have had to evolve complex systems to sense and respond dynamically to various stress conditions. Integration of environmental stimuli, signal transduction and the stress response is mediated, at least partially, by intensive cross-talk among plant hormones With the exception of abscisic acid (ABA), the mechanism of the hormonal mode of actions in abiotic stress responses needs to be elucidated in more detail. Hormone functions in the HS response can be deduced from the impact of their elevated content on plant stress tolerance. In addition to salicylic acid (SA), a positive effect on HS tolerance was found in the case of cytokinins (CKs), hormones associated predominantly with stimulation of cell division, delay of senescence and stabilization of the photosynthetic machinery (Ha et al, 2012; Stirk et al, 2012; Wang et al, 2012)
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