Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase Activase Deficiency Delays Senescence of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase but Progressively Impairs Its Catalysis during Tobacco Leaf Development

Abstract

Transgenic tobacco (Nicofiana fabacum L. cv W38) plants with an antisense gene directed against the mRNA of ribulose-1,sbiphosphate carboxylase/oxygenase (Rubisco) activase grew more slowly than wild-type plants in a C0,-enriched atmosphere, but eventually attained the same height and number of leaves. Compared with the wild type, the anti-activase plants had reduced CO, assimilation rates, normal contents of chlorophyll and soluble leaf protein, and much higher Rubisco contents, particularly in older leaves. Activase deficiency greatly delayed the usual developmental decline in Rubisco content seen in wild-type leaves. This effect was much less obvious in another transgenic tobacco with an antisense gene directed against chloroplast-located glyceraldehyde-3-phosphate dehydrogenase, which also had reduced photosynthetic rates and delayed development. Although Rubisco carbamylation was reduced in the anti-activase plants, the reduction was not sufficient to explain the reduced photosynthetic rate of older antiactivase leaves. Instead, up to a 10-fold reduction in the catalytic turnover rate of carbamylated Rubisco in vivo appeared to be the main cause. Slower catalytic turnover by carbamylated Rubisco was particularly obvious in high-C0,-grown leaves but was also detectable in air-grown leaves. Rubisco activity measured immediately after rapid extraction of anti-activase leaves was not much less than that predicted from its degree of carbamylation, ruling out slow release of an inhibitor from carbamylated sites as a major cause of the phenomenon. Nor could substrate scarcity or product inhibition account for the impairment. We conclude that activase must have a role in vivo, direct or indirect, in promoting the activity of carbamylated Rubisco in addition to its role in promoting carbamylation.

Low stomatal and internal conductance to CO2 versus Rubisco deactivation as determinants of the photosynthetic decline of ageing evergreen leaves

“…8). Interestingly, in transgenic plants with reduced Rubisco activity due to decreased expression of Rubisco activase, the senescence-related degradation of Rubisco is delayed relative to chlorophyll and other soluble proteins (He et al 1997). Presumably, the persistence of large amounts of Rubisco late into leaf development is a consequence of the reduced carbamylation of the Rubisco pool (He et al 1997); a similar mechanism may be involved in the age-related accumulation of Rubisco in evergreen leaves.…”

Independently Silencing Two Photosynthetic Proteins inNicotiana attenuataHas Different Effects on Herbivore Resistance

“…He et al (1997) have shown that silencing RCA increases RuBPCase content in cultivated tobacco. In order to determine if silencing RCA and RuBPCase influences the accumulation of large subunits of RuBPCase in N. attenuata, we performed a one-dimensional protein analysis of EV, irRCA, and asRUB plants (Fig.…”

“…The degradation and remobilization of the soluble proteins provide an important source of N and sulfur for the other parts of the developing plants (Friedrich and Huffaker, 1980). However, RuBPCase declines faster than RCA (He et al, 1997). Therefore, despite having less RuBPCase, asRUB plants have similar photosynthetic rates as EV plants.…”

“…Therefore, despite having less RuBPCase, asRUB plants have similar photosynthetic rates as EV plants. He et al (1997) showed that the turnover of RuBPCase is repressed by 50% in RCA-deficient plants, which retained more RuBPCase in their older leaves compared with control plants. As a consequence, there is a large increase in the ratio of RuBPCase to soluble protein and a decrease in the ratio of RCA to RuBPCase in the older leaves of RCA-deficient plants (He et al, 1997).…”

“…In Arabidopsis, moderate reductions of RCA decrease growth and aboveground biomass and leaf area (Ilyin et al, 2005). While tobacco plants transformed with RCA expressed in an antisense orientation are slow growing, they eventually attain the same height and leaf number as wild-type plants (He et al, 1997).…”