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Decrease in phosphoribulokinase activity by antisense RNA in transgenic tobacco: relationship between photosynthesis, growth, and allocation at different nitrogen levels

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  • Fiona M. Banks
  • Simon P. Driscoll
  • Martin A J Parry
  • David W. Lawlor
  • Jacqui S. Knight
  • John C. Gray
  • Matthew J. Paul
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<mark>Journal publication date</mark>1/03/1999
<mark>Journal</mark>Plant Physiology
Issue number3
Volume119
Number of pages12
Pages (from-to)1125-1136
Publication StatusPublished
<mark>Original language</mark>English

Abstract

To study the direct effects of photosynthesis on allocation of biomass by altering photosynthesis without altering leaf N or nitrate content, phosphoribulokinase (PRK) activity was decreased in transgenic tobacco (Nicotiana tabacum L.) with an inverted tobacco PRK cDNA and plants were grown at different N levels (0.4 and 5 mM NH 4NO 3). The activation state of PRK increased as the amount of enzyme was decreased genetically at both levels of N. At high N a 94% decrease in PRK activity had only a small effect (20%) on photosynthesis and growth. At low N a 94% decrease in PRK activity had a greater effect on leaf photosynthesis (decreased by up to 50%) and whole-plant photosynthesis (decreased by up to 35%) than at high N. These plants were up to 35% smaller than plants with higher PRK activities because they had less structural dry matter and less starch, which was decreased by 3- to 4-fold, but still accumulated to 24% to 31% of dry weight; young leaves contained more starch than older leaves in older plants. Leaves had a higher ion and water content, and specific leaf area was higher, but allocation between shoot and root was unaltered. In conclusion, low N in addition to a 94% decrease in PRK by antisense reduces the activity of PRK sufficient to diminish photosynthesis, which limits biomass production under conditions normally considered sink limited.