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<bold>Summary</bold> Cytosolic calcium concentration ([Ca2+]cyt) and heterotrimeric G‐proteins are universal eukaryotic signaling elements. In plant guard cells, extracellular calcium (Cao) is as strong a stimulus for stomatal closure as the phytohormone abscisic acid (ABA), but underlying mechanisms remain elusive. Here, we report that the sole Arabidopsis heterotrimeric Gβ subunit,AGB1, is required for four guard cell Caoresponses: induction of stomatal closure; inhibition of stomatal opening; [Ca2+]cytoscillation; and inositol 1,4,5‐trisphosphate (InsP3) production. Stomata in wild‐type Arabidopsis (Col) and in mutants of the canonical Gα subunit,GPA1, showed inhibition of stomatal opening and promotion of stomatal closure by Cao. By contrast, stomatal movements ofagb1mutants andagb1/gpa1double‐mutants, as well as those of theagg1agg2 Gγ double‐mutant, were insensitive to Cao. These behaviors contrast withABA‐regulated stomatal movements, which involveGPA1 andAGB1/AGG3 dimers, illustrating differential partitioning of G‐protein subunits among stimuli with similar ultimate impacts, which may facilitate stimulus‐specific encoding.AGB1knockouts retained reactive oxygen species andNOproduction, but lostYC3.6‐detected [Ca2+]cytoscillations in response to Cao, initiating only a single [Ca2+]cytspike. Experimentally imposed [Ca2+]cytoscillations restored stomatal closure inagb1. Yeast two‐hybrid and bimolecular complementation fluorescence experiments revealed thatAGB1 interacts with phospholipase Cs (PLCs), and Caoinduced InsP3 production in Col but not inagb1. In sum, G‐protein signaling viaAGB1/AGG1/AGG2 is essential for Cao‐regulation of stomatal apertures, and stomatal movements in response to Caoapparently require Ca2+‐induced Ca2+release that is likely dependent on Gβγ interaction withPLCs leading to InsP3 production.
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Effect of Salinity on DMSP Production in Gambierdiscus belizeanus (Dinophyceae)
Dimethylsulfoniopropionate (DMSP) is produced by many species of marine phytoplankton and has been reported to provide a variety of beneficial functions including osmoregulation. Dinoflagellates are recognized as majorDMSPproducers; however, accumulation has been shown to be highly variable in this group. We explored the effect of hyposaline transfer inGambierdiscus belizeanusbetween ecologically relevant salinities (36 and 31) onDMSPaccumulation, Chla, cell growth, and cell volume, over 12 d. Our results showed thatG. belizeanusmaintained an intracellularDMSPcontent of 16.3 pmol cell−1and concentration of 139 mMin both salinities. Although this intracellular concentration was near the median reported for other dinoflagellates, the cellular content achieved byG. belizeanuswas the highest reported of any dinoflagellate thus far, owing mainly to its large size.DMSPlevels were not significantly affected by salinity treatment but did change over time during the experiment. Salinity, however, did have a significant effect on the ratio ofDMSP:Chla, suggesting that salinity transfer ofG. belizeanusinduced a physiological response other thanDMSPadjustment. A survey ofDMSPcontent in a variety ofGambierdiscusspecies and strains revealed relatively highDMSPconcentrations (1.0–16.4 pmol cell−1) as well as high intrageneric and intraspecific variation. We conclude that, althoughDMSPmay not be involved in long‐term (3–12 d) osmoregulation in this species,G. belizeanusand otherGambierdiscusspecies may be important contributors toDMSPproduction in tropical benthic microalgal communities due to their large size and high cellular content.
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- PAR ID:
- 10459431
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of Phycology
- Volume:
- 55
- Issue:
- 6
- ISSN:
- 0022-3646
- Page Range / eLocation ID:
- p. 1401-1411
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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