Hypersonic Methane Rocket-Ramjet Engines for RLV
- Paper number
IAC-04-S.5.12
- Author
Prof. Valeriy Tymoshenko, Institute of Technical Mechanics NASU NSAU, Ukraine
- Year
2004
- Abstract
When cucumber seeds are placed in a horizontal position for germination, resulting seedlings develops a specialized protuberance, termed the peg, on the lower side of the transition zone between the hypocotyl and the root, due to gravistimulation. On the other hand, in our space-flight experiment of STS-95, cucumber seedlings grown under microgravity conditions developed a peg on each side of the transition zone, suggesting that gravistimulation was required for suppressing the peg formation on the upper side of the transition zone. We have shown that exogenous auxin induces peg formation and that content of a free form of auxin, indole-3-acetic acid (IAA), in the upper side of the gravistimulated transition zone is less than that in the lower side. In addition, the decrease in mRNA accumulation of auxin-inducible CsIAA1 gene was detected in the upper side of the transition zone of horizontally-grown cucumber seedlings, whereas the decrease in CsIAA1 transcript level was not found in the transition zone of space-grown seedlings. We have therefore proposed that gravistimulation induces the decrement of IAA in the upper side of the transition zone and thus suppresses the peg formation. To reveal the IAA redistribution upon gravistimulation at the tissue level, we investigated the IAA distribution by immunofluorescence method using anti-IAA antibody. When the excised transition zone was treated with IAA, immunofluorescent signals of IAA were detected at higher intensities than those in the IAA-starved segments. These results indicated that our immunofluorescent analysis was valid for monitoring IAA in the transition zone. In the transition zone of cucumber seedlings grown in a horizontal position, signals of IAA in epidermis and cortex of the upper side were weaker than those of the lower side. Moreover, double staining with anti-IAA antibody and 4’, 6-diamidino-2’-phenylindole revealed that this differential distribution of IAA was mainly observed in cell nuclei. Considering the fact that the nuclear-localized auxin receptors regulate the transcription of auxin-inducible genes, our previous results of the differential expression of CsIAA1 can be explained by this differential accumulation of IAA in the nuclei of transition zone. From these results, it is considered that gravistimulation induces the decrease of IAA in cell nuclei of epidermis and cortex of the upper side of transition zone to suppress CsIAA1 gene expression and peg formation.
- Abstract document
- Manuscript document
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