Inositol 1,4,5-trisphosphate and Ran expression during simulated and real microgravity.
In order to gain further insight into the signal transduction pathway concerning gravitropism, we studied the expression profiles of mRNA in etiolated sunflower (Helianthus annuus L.) seedlings. Differential-display reverse transcriptase PCR product assayed by capillary electrophoresis revealed the small GTPase Ran, regulating nuclear import and export of proteins. Parallel analysis of inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) release by a highly advanced system of metal-dye detection combined with high-performance liquid chromatography provided evidence that the second messenger Ins(1,4,5)P3 is modulated by changes of the gravity vector. Investigations by fast clinorotation and sounding rockets established a positive correlation between the Ins(1,4,5)P3 level and the expression rate of Ran mRNA during simulated and real microgravity. Since an asymmetric distribution of auxin during graviresponse is suggested to induce differential cell elongation, additional information on the perception and transduction pathways was achieved by auxin stimulation experiments. While we were able to demonstrate an auxin-dependent production of Ins(1,4,5)P3, the expression of Ran mRNA was not affected by auxin. Finally, besides the phosphoinositide system as one element of the signal transduction chain linking graviperception to graviresponse, a Ran-mediated interaction model of extracellular microgravity signal perception and intercellular transduction pathway is proposed.
Kriegs
B
B
Institute for Molecular Physiology and Biotechnology of Plants, University of Bonn, Bonn, Federal Republic of Germany.
Theisen
R
R
Schnabl
H
H
D002851:Chromatography, High Pressure Liquid; D019075:Electrophoresis, Capillary; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D018522:Gravitropism; D018466:Gravity Sensing; D006368:Helianthus / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D018546:Hypocotyl / Q000378:metabolism; D007210:Indoleacetic Acids / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D010937:Plant Growth Regulators / Q000494:pharmacology; D011523:Protoplasts / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012399:Rotation; D036226:Seedlings / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013026:Space Flight; D013997:Time Factors; D014893:Weightlessness; D018474:Weightlessness Simulation; D020931:ran GTP-Binding Protein / Q000378:metabolism*
D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D012333:RNA, Messenger; D015544:Inositol 1,4,5-Trisphosphate; D020931:ran GTP-Binding Protein