Plants react quickly and profoundly to changes in their environment. For example, complete submergence and low light intensities induce differential petiole growth, resulting in upward leaf movement (hyponastic growth) in Arabidopsis thaliana. This thesis deals with the physiological-, genetic- and molecular regulation of hyponastic growth to these stimuli. In addition, we describe how a sudden increase in temperature induces hyponastic growth. Conclusively, we gained comprehensive insight in how these abiotic stimuli interact and use light- and hormonal signals to control hyponastic growth. Because different environmental stimuli induce hyponastic growth with remarkable similar kinetics, we hypothesized that the signal transduction routes converge downstream. We followed unbiased approaches; e.g. a forward genetic mutant screen, QTL analysis, and phenotyping of a large set of natural accessions, to isolate novel genetic components involved in the control of hyponastic growth. Among others, this resulted in the isolation of the core cell-cycle regulator CYCLIN-A2 and the LRR-RLK ERECTA as important factors in the control of hyponastic growth. Next to our study on hyponasty, we describe that light intensity and light quality controls compaction of nuclear chromatin. Evidence is provided that this is mediated by photoreceptor proteins (phyB, cry2) and HISTONE DEACETYLASE 6
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