ASGSB 1998 Annual Meeting Abstracts

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INFLUENCE OF SPACEFLIGHT ON PHOTOSYSTEM I (PSI) OF BRASSICA RAPA.   S. Jiao¹, E. Hilaire², and J.A. Guikema^{1 1}Div. Biol, Ackert Hall and ²Dept Plant Pathol, Throckmorton Plant Sciences Center, Kansas State University, Manhattan, KS 66506.

The photosynthetic apparatus contains a number of multisubunit protein complexes, many of which are regulated by environmental conditions. In our study (BPAC), we examined the influence of growth during spaceflight on PSI of Brassica rapa as part of the Collaborative US/Ukrainian Experiment (CUE). Brassica rapa seeds were germinated and grown for 14 days in the controlled environment of the new Plant Growth Facility aboard the space shuttle Columbia. Control plants were grown under the same conditions on Earth. Three hours after shuttle landing, cotyledon leaves were harvested and frozen. Analysis of total Chl and protein showed an increase in both Chl a/b and protein/Chl ratio in the flight samples. Thylakoid membranes from the space samples also showed an increase in protein/Chl ratio, but the change in the Chl a/b ratio was not apparent. Thylakoids contained more Chl and protein by 35% and 32%, respectively, than the ground controls. Determination of electron transport rates showed a 30% decrease in PSI activity for the flight samples. Electrophoretic analysis revealed that intact PSI was reduced in the flight samples, and these decreases were quantified by western blotting. PsaA and PsaB were decreased by 33% and 24%, respectively. In contrast, three LHCI proteins and the D2 protein of PSII were reduced by little more than 10%. This pattern of PSI reduction was also observed in our ongoing photoinhibition experiments. An unidentified 54 kDa thylakoid protein was increased in the flight samples, and in prior experiments, we have observed this peptide during conditions which favor PSI photoinhibition. Taken together, these results suggest that the spaceflight conditions during STS-87 favored a reduced level of PSI activity, and we are uncertain at this point if the reduction was due to a photoinhibition of existing enzyme activity leading to protein turnover or a down-regulation of protein biosynthesis. (Supported by NASA grants NAG10-0142, NAGW-2328, and the Kansas NASA EPSCoR Program)

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