Abscisic acid signalling determines susceptibility of bundle sheath cells to photoinhibition in high light-exposed Arabidopsis leaves

Abstract

The rapid induction of the bundle sheath cell (BSC)-specific expression of ASCORBATE PEROXIDASE2 ( APX2 ) in high light (HL)-exposed leaves of Arabidopsis thaliana is, in part, regulated by the hormone abscisic acid (ABA) produced by vascular parenchyma cells. In this study, we provide more details of the ABA signalling that regulates APX2 expression and consider its importance in the photosynthetic responses of BSCs and whole leaves. This was done using a combination of analyses of gene expression and chlorophyll a fluorescence of both leaves and individual BSCs and mesophyll cells. The regulation of APX2 expression occurs by the combination of the protein kinase SnRK2.6 (OST1):protein phosphatase 2C ABI2 and a Gα (GPA1)-regulated signalling pathway. The use of an ost1-1/gpa1-4 mutant established that these signalling pathways are distinct but interact to regulate APX2 . In HL-exposed leaves, BSC chloroplasts were more susceptible to photoinhibition than those of mesophyll cells. The activity of the ABA-signalling network determined the degree of susceptibility of BSCs to photoinhibition by influencing non-photochemical quenching. By contrast, in HL-exposed whole leaves, ABA signalling did not have any major influence on their transcriptomes nor on their susceptibility to photoinhibition, except where guard cell responses were observed.

Uncoupling High Light Responses from Singlet Oxygen Retrograde Signaling and Spatial-Temporal Systemic Acquired Acclimation

“…This could mean that H 2 O 2 -mediated control of APX2 expression in bundle sheath cells is fundamentally different from that in other leaf tissues (Bechtold et al, 2008). In fact, recent work using differential photosynthetic changes to different chemical treatments demonstrates ABA, APX2, and H 2 O 2 responses are distinct to BSCs compared to mesophyll (Suzuki et al, 2013;Gorecka et al, 2014). In Oryza sativa, altering NADPH/NADP + levels through C 4 -like photosynthesis in BSCs promoted HL stress responses specific to the midvein (Shen et al, 2015).…”

Photosynthesis-dependent H2O2 transfer from chloroplasts to nuclei provides a high-light signalling mechanism

“…High-resolution images of the chlorophyll fluorescence (CF) parameter F v ′/F m ′ (PSII operating efficiency) in epidermal and mesophyll chloroplasts were obtained as described previously 64 using a Micro-FluorCam (Photon System Instruments, Czech Republic). Briefly, a single disc was placed onto the microscope slide, overlaid with a coverslip.…”

The Roles of ROS and ABA in Systemic Acquired Acclimation

“…The ABA-dependent responses to high light stress were found to occur in detached leaves as well as whole plants, suggesting that they are leaf autonomous and do not involve ABA biosynthesis in roots. Gorecka et al (2014) have further observed that ABA signaling mutants have an effect on bundle sheath cell responses in terms of APX2 gene expression and photosynthetic efficiency of these cells, but no effect could be detected at the whole leaf level for any of the signaling mutants in response to high light, despite a series of microarray experiments and extensive physiological analysis. These results suggested that in terms of cell autonomy under high light conditions, systemic responses might be confined to bundle sheath cells and guard cells.…”