Photoinduction of kaurene synthetase, an enzyme of the gibberellin biosynthetic pathway, during de-etiolation of pea seedlings Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/db78tg327

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  • Previous investigations have shown that the enzymes catalyzing the biosynthesis of the gibberellin-type of hormones from mevalonic acid in plants are compartmentalized in plastids. Moreover, the activity of one of the key enzymes in the biosynthetic sequence, kaurene synthetase, exhibits markedly enhanced activity when a dark-grown pea seedling undergoes de-etiolation in high-intensity white light. Kaurene synthetase catalyzes the two-step cyclization reaction by which the diterpene ent-kaurene is formed from geranygeranyl pyrophosphate. The purposes of these investigations were to determine whether the effect of light on kaurene synthetase activity is to induce de novo synthesis of enzyme or to activate enzyme already present, and to contribute more detailed information regarding compartmentation of kaurene synthetase in chloroplasts. Excised shoot tips from 10-day old etiolated pea (Pisum sativum cv Alaska) seedlings were incubated in solutions of chloramphenicol, cycloheximide, and lincomycin at different concentrations, during periods of 0, 4, 8, and 12 hours of irradiation with high-intensity white light. Enzyme extracts were prepared from the whole shoot tips, and compared with extracts from non-treated shoot tips for kaurene synthetase activity. The rate of chlorophyll formation was used as a measure of de-etiolation. It was found that, in control samples, kaurene synthetase activity increased the first 8 hours of irradiation and decreased after 12 hours. Chlorophyll content increased steadily up to 12 hours of irradiation. Chloramphenicol and cycloheximide reduced both kaurene synthetase activity and chlorophyll content to a similar magnitude during all periods of irradiation, the reduction being greatest after 8 hours of irradiation. Lincomycin, which has been shown to be a specific inhibitor of the formation of chloroplast ribosomes in detached pea shoot tips, hardly affected kaurene synthetase activity but strongly inhibited chlorophyll formation. On the basis of the combined effects of the three antibioti6s tested, it is tentatively concluded that: (a) the increase in kaurene synthetase activity during de-etiolation is due to photoinduction of de novo synthesis of the enzyme; and (b) kaurene synthetase or its precursor is synthesized on cytoplasmic ribosomes but that the functional enzyme is compartmentalized in chloroplasts. In advancing this tentative interpretation as a working hypothesis, it is acknowledged that other proteins than kaurene synthetase may be found in further research to be involved in the observations here reported.
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  • description.provenance : Approved for entry into archive by Patricia Black(patricia.black@oregonstate.edu) on 2013-10-16T14:19:11Z (GMT) No. of bitstreams: 1 GomezNavarreteGladys1978.pdf: 476786 bytes, checksum: ad22ec0ef29462d877bdeb426d7559b8 (MD5)
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  • description.provenance : Approved for entry into archive by Patricia Black(patricia.black@oregonstate.edu) on 2013-10-15T21:24:43Z (GMT) No. of bitstreams: 1 GomezNavarreteGladys1978.pdf: 476786 bytes, checksum: ad22ec0ef29462d877bdeb426d7559b8 (MD5)
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