Decrease in phosphoribulokinase activity by antisense RNA in transgenic tobacco. Relationship between photosynthesis, growth, and allocation at different nitrogen levels
Fm. Banks et al., Decrease in phosphoribulokinase activity by antisense RNA in transgenic tobacco. Relationship between photosynthesis, growth, and allocation at different nitrogen levels, PLANT PHYSL, 119(3), 1999, pp. 1125-1136
To study the direct effects of photosynthesis on allocation of biomass by a
ltering photosynthesis without altering leaf N or nitrate content, phosphor
ibulokinase (PRK) activity was decreased in transgenic tobacco (Nicotiana t
abacum L.) with an inverted tobacco PRK cDNA and plants were grown at diffe
rent N levels (0.4 and 5 mM NH,NO,). The activation state of PRK increased
as the amount of enzyme was decreased genetically at both levels of N. At h
igh N a 94% decrease in PRK activity had only a small effect (20%) on photo
synthesis 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 pho
tosynthesis (decreased by up to 35%) than at high N. These plants were up t
o 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 sh
oot and root was unaltered. In conclusion, low N in addition to a 94% decre
ase in PRK by antisense reduces the activity of PRK sufficient to diminish
photosynthesis, which limits biomass production under conditions normally c
onsidered sink limited.