Abstract
Numerous studies have shown effects of abscisic acid (ABA) on nuclear genes encoding chloroplast-localized proteins. ABA effects on the transcription of chloroplast genes, however, have not been investigated yet thoroughly. This work, therefore, studied the effects of ABA (75 μM) on transcription and steady-state levels of transcripts in chloroplasts of basal and apical segments of primary leaves of barley (Hordeum vulgare L.). Basal segments consist of young cells with developing chloroplasts, while apical segments contain the oldest cells with mature chloroplasts. Exogenous ABA reduced the chlorophyll content and caused changes of the endogenous concentrations not only of ABA but also of cytokinins to different extents in the basal and apical segments. It repressed transcription by the chloroplast phage-type and bacteria-type RNA polymerases and lowered transcript levels of most investigated chloroplast genes drastically. ABA did not repress the transcription of psbD and a few other genes and even increased psbD mRNA levels under certain conditions. The ABA effects on chloroplast transcription were more pronounced in basal vs. apical leaf segments and enhanced by light. Simultaneous application of cytokinin (22 μM 6-benzyladenine) minimized the ABA effects on chloroplast gene expression. These data demonstrate that ABA affects the expression of chloroplast genes differentially and points to a role of ABA in the regulation and coordination of the activities of nuclear and chloroplast genes coding for proteins with functions in photosynthesis.
Highlights
The plant hormone abscisic acid (ABA) is involved in the control of developmental processes, such as seed and bud dormancy
Detached barley leaves have been used for a long time as model system in research on plant hormones (e.g. Becker and Apel, 1993; Lee et al, 1996) and have proved to respond sensitively to plant hormones with respect to chloroplast gene expression (Zubo et al, 2008, 2011b; Zubo and Kusnetsov, 2008)
The expression of most chloroplast genes is repressed by ABA
Summary
The plant hormone abscisic acid (ABA) is involved in the control of developmental processes, such as seed and bud dormancy. ABA biosynthesis is stimulated by stress, especially stresses associated with dehydration (drought, salinity, and cold). It plays major roles in the response of plants to these abiotic stress factors and in the defence against pathogens (reviewed in Cao et al, 2011; Qin et al, 2011). ABA signalling leads to changes in the expression of several thousand nuclear genes and interacts with the signalling networks of other factors such as light (reviewed by Lau and Deng, 2010), sugars (Wingler and Roitsch, 2008) and other hormones
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