ASGSB 1999 Annual Meeting Abstracts

MICRO-g EFFECTS ON DEVELOPMENT AND EXPANSIN GENE EXPRESSION IN THE PEG OF SPACE-GROWN CUCUMBER SEEDLINGS. B.M. Link and D.J. Cosgrove, Dept of Biology, Eberly College of Science, Penn State, University Park.

Expansins are cell wall proteins that are important to plant morphogenesis. We are interested in understanding what role these proteins play in the development of gravity sensitive organs such as the peg of cucumber seedlings. The peg is an organ formed by the developing seedling at the root-shoot transition zone. It is used to help remove the seed coat from the emerging cotyledons, and on earth it always forms on the lower side of the seedling. Previous reports stated that pegs do not form when seedlings are grown on Clinostats.

We flew Burpee Hybrid II cucumber seeds on board the space shuttle (STS-95). They were allowed to develop for 35 or 40 hours before being frozen. The seedlings were examined when they returned to earth, most had developed a single peg. The more developmentally advanced seedlings were observed to form hooks. No signs of gravitropism were observed in the roots. When examined by SEM the pegs of the space flown seedlings were found to have subtle developmental differences compared to ground based controls. RNA was isolated from peg tissue and PCR was used to compare the expression levels of two expansin genes. No differences were found, but five additional expansin genes are currently being studied. These results show that peg and hook formation can occur when the seedlings develop under micro-g conditions.

We will present micrographs showing the morphology of our space flown seedlings and present the results of quantitative PCR experiments assessing mRNA levels of two expansin genes (Cs-EXP3 and Cs-EXP4) that are expressed in the root and the peg tissues. These results will be compared to the results for the ground control (1 g) and clinostat samples. (Supported by NASA)

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