title: Thermotolerant guard cell protoplasts of tree tobacco do not require exogenous hormones to survive in culture and are blocked from reentering the cell cycle at the G1-to-S transition.
abstract: When guard cell protoplasts (GCPs) of tree tobacco [Nicotiana glauca (Graham)] are cultured at 32 degrees C with an auxin (1-napthaleneacetic acid) and a cytokinin (6-benzylaminopurine), they reenter the cell cycle, dedifferentiate, and divide. GCPs cultured similarly but at 38 degrees C and with 0.1 micro M +/- -cis,trans-abscisic acid (ABA) remain differentiated. GCPs cultured at 38 degrees C without ABA dedifferentiate partially but do not divide. Cell survival after 1 week is 70% to 80% under all of these conditions. In this study, we show that GCPs cultured for 12 to 24 h at 38 degrees C accumulate heat shock protein 70 and develop a thermotolerance that, upon transfer of cells to 32 degrees C, enhances cell survival but inhibits cell cycle reentry, dedifferentiation, and division. GCPs dedifferentiating at 32 degrees C require both 1-napthaleneacetic acid and 6-benzylaminopurine to survive, but thermotolerant GCPs cultured at 38 degrees C +/- ABA do not require either hormone for survival. Pulse-labeling experiments using 5-bromo-2-deoxyuridine indicate that culture at 38 degrees C +/- ABA prevents dedifferentiation of GCPs by blocking cell cycle reentry at G1/S. Cell cycle reentry at 32 degrees C is accompanied by loss of a 41-kD polypeptide that cross-reacts with antibodies to rat (Rattus norvegicus) extracellular signal-regulated kinase 1; thermotolerant GCPs retain this polypeptide. A number of polypeptides unique to thermotolerant cells have been uncovered by Boolean analysis of two-dimensional gels and are targets for further analysis. GCPs of tree tobacco can be isolated in sufficient numbers and with the purity required to study plant cell thermotolerance and its relationship to plant cell survival, growth, dedifferentiation, and division in vitro.
authors.affiliation: Department of Biology, Willamette University, 900 State Street, Salem, Oregon 97301, USA.
authors.forename: Nathan N
authors.initials: NN
authors.lastname: Gushwa
authors.forename: Derek
authors.initials: D
authors.lastname: Hayashi
authors.forename: Andrea
authors.initials: A
authors.lastname: Kemper
authors.forename: Beverly
authors.initials: B
authors.lastname: Abram
authors.forename: Jane E
authors.initials: JE
authors.lastname: Taylor
authors.forename: Jason
authors.initials: J
authors.lastname: Upton
authors.forename: Chloe F
authors.initials: CF
authors.lastname: Tay
authors.forename: Sarah
authors.initials: S
authors.lastname: Fiedler
authors.forename: Sam
authors.initials: S
authors.lastname: Pullen
authors.forename: Linnsey P
authors.initials: LP
authors.lastname: Miller
authors.forename: Gary
authors.initials: G
authors.lastname: Tallman
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology; D000222:Adaptation, Physiological; D000818:Animals; D001973:Bromodeoxyuridine / Q000378:metabolism; D002453:Cell Cycle / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000737:chemistry / Q000378:metabolism; D009280:Naphthaleneacetic Acids / Q000494:pharmacology; D018515:Plant Leaves / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D011523:Protoplasts / Q000166:cytology* / Q000187:drug effects; D051381:Rats; D016196:S Phase; D013696:Temperature; D013997:Time Factors; D014026:Nicotiana / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism
chemical_list: D018840:HSP70 Heat-Shock Proteins; D009280:Naphthaleneacetic Acids; C034182:1-naphthaleneacetic acid; D000040:Abscisic Acid; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D001973:Bromodeoxyuridine