Reduced sedoheptulose-1,7-bisphosphatase levels in transgenic tobacco lead to decreased photosynthetic capacity and altered carbohydrate accumulation |
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Authors: | Elizabeth P Harrison Nicola M Willingham Julie C Lloyd Christine A Raines |
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Institution: | (1) Department of Biological John Tabor Laboratories, University of Essex, Colchester, CO4 3SQ, UK, GB |
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Abstract: | Transgenic tobacco (Nicotiana tabacum L. cv. Samsun) plants with reduced levels of the Calvin cycle enzyme sedoheptulose-1,7-bisphosphatase (SBPase; EC 3.1.3.37)
were produced using an antisense construct in which the expression of a tobacco SBPase cDNA clone was driven by the cauliflower
mosaic virus (CaMV) promoter. The reduction in SBPase protein levels observed in the primary transformants correlated with
the presence of the antisense construct and lower levels of the endogenous SBPase mRNA. No changes in the amounts of other
Calvin cycle enzymes were detected using Western blot analysis. The SBPase antisense plants with less than 20% of wild-type
SBPase activity were observed to display a range of phenotypes, including chlorosis and reduced growth rates. Measurements
of photosynthesis, using both light-dosage response and CO2 response curves, of T1 plants revealed a reduction in carbon assimilation rates, which was apparent in plants retaining 57%
of wild-type SBPase activity. Reductions were also observed in the quantum efficiency of photosystem II. This decrease in
photosynthetic capacity was reflected in a reduction in the carbohydrate content of leaves. Analysis of carbohydrate status
in fully expanded source leaves showed a shift in carbon allocation away from starch, whilst sucrose levels were maintained
in all but the most severely affected plants. Plants with less than 15% of wild-type SBPase activity were found to contain
less than 5% of wild-type starch levels. The results of this preliminary analysis indicate that SBPase activity may limit
the rate of carbon assimilation.
Received: 23 February 1997 / Accepted: 2 May 1997 |
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Keywords: | : Antisense DNA Calvin cycle Carbon assimilation Nicotiana (transgenic) Sedoheptulose-1 7-bisphosphatase Transgenic plant (tobacco) |
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