Decrease in Phosphoribulokinase Activity by Antisense RNA in Transgenic Tobacco. Relationship between Photosynthesis, Growth, and Allocation at Different Nitrogen Levels1

Abstract

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.The relationship between photosynthesis and growth is a complex one, with growth rate not being well correlated with the rate of photosynthesis on a leaf-area basis . This is because growth also depends on the investment of biomass in growing sinks and investment in leaf area (Chapin et al., 1990;). There have been many thorough investigations of the relationship between photosynthesis, growth, environment, and genotype, but they have not provided definitive information on the relationship between photosynthesis and growth. This is because of the complex interaction between factors, so it has not been easy to decide whether changes in sink growth result from changes in photosynthesis or vice versa. The elucidation of the relationship between photosynthesis and growth requires specific changes in photosynthesis or sink growth independent of other changes. Genetic manipulation of enzymes involved in photosynthesis and/or sink processes provides a means to achieve this. The use of transgenic plants with altered amounts of Rubisco revolutionized the analysis of photosynthesis and its interaction with the whole plant (Quick et al., 1991b;Stitt and Schulze, 1994). However, because Rubisco constitutes such a large proportion of the protein in a leaf (up to 40%;Woodrow and Berry, 1988), a decrease in amounts of Rubisco substantially disrupts the N balance of the plant, making it difficult to establish direct links between photosynthesis and growth and allocation than if there were a more specific alteration in the rate of photosynthesis. What is required is genetic modification of a photosynthetic enzyme that accounts for a fraction of the N content in the leaf.PRK is one such enzyme, accounting for less than 1% of the protein in a leaf (Evans, 1989). Tobacco (Nicotiana tabacum L.) plants were transformed with an inverted cDNA encoding tobacco PRK (Knight and Gray, 1994). First, it was determined that the effect of this modification on photosynthesis under standard growth-chamber conditions was minim...

Long-term effects of simulated acid rain stress on a staple forest plant, Pinus massoniana Lamb: a proteomic analysis

“…This is consistent with the report when plants suffered salt stress (Srivastava et al 2008). However, only significant reduction of PRK had negative effects on photosynthesis and growth (Banks et al 1999). …”

Interactions Between Carbon and Nitrogen Metabolism

“…For plants supplied with optimal N, the calculated data are close to values derived from experiments with excised tobacco leaves supplied with nitrate (Table IB; Morcuende et al 1998). Conversely, calculating the foliar C:N ratio from the proportion of electron flow to nitrate yields a C: N value (6.3) that is similar to measured foliar values in tobacco at optimal N (7.0; Banks et al 1999). Supplying tobacco leaves with sucrose, in concert with nitrate, yielded higher rates ofN assimilation than when nitrate was supplied alone (Morcuende et al 1998).…”

Decrease of phosphoribulokinase activity by antisense RNA in transgenic tobacco: definition of the light environment under which phosphoribulokinase is not in large excess

“…All lines showed the same percentage decrease in PRK activity relative to the wild type (Fig. 6), as when plants were given low nitrogen supply (Banks et al 1999), and there were no dierences in activities of other Calvin cycle enzymes between the lines. Standard error of the mean was less than 11% of the mean.…”

“…Activities of PRK in the lines relative to the wild type under all growth irradiances were as follows: line 1, 6%; line A, 18%; line B, 36%; line 2, 62%; line 3, 75%; line C, 89%; line 4, 100%. Lines on which most work focused were given numbers (as in Banks et al 1999) the others were given letters. Wild-type plants were also analysed and performed exactly the same as line 4.…”