Decreased ribulose-1,5-bisphosphate carboxylase-oxygenase in transgenic tobacco transformed with ?antisense? rbcS

Abstract

Abstract. Tobacco (Nicotiana tabacum L.) plants transformed with 'antisense' rbcS to decrease the expression of ribulose-l,5-bisphosphate carboxylase-oxygenase (Rubisco) have been used to investigate the contribution of Rubisco to the control of photosynthesis in plants growing at different irradiances. Tobacco plants were grown in controlled-climate chambers under ambient CO2 at 20~ at 100, 300 and 750 gmol.m 2.s-1 irradiance, and at 28~ at 100, 300 and 1000 Dmol.m 2. s-I irradiance. (i) Measurement of photosynthesis under ambient conditions showed that the flux control coefficient of Rubisco A (CRubisco) was very low (0.01-0.03) at low growth irradiance, and still fairly low (0.24-0.27) at higher irradiance. (ii) Short-term changes in the irradiance used to light-saturated rate of photosynthesis in "sun" leaves; apparently additional factors are co-limiting photosynthetic performance. (iv) Growth of plants at high irradiance led to a small decrease in the percentage of total protein found in the insoluble (thylakoid fraction), and a decrease of chlorophyll, relative to protein or structural leaf dry weight. As a consequence of this change, high-irradiance-grown leaves illuminated at growth irradiance avoided an inbalance between the "light" reactions and Rubisco; this was shown by the low value of CRubisc oA (see above) and by measurements showing that non-photochemical quenching was low, photochemical quenching high, and NADP-malate dehydrogenase activation was low at the growth irradiance. In contrast, when a leaf adapted to low irradiance was illuminated at a higher irradiance, Rubisco exerted more control, non-photochemical quenching was higher, photochemical quenching was lower, and NADP-malate dehydrogenase activation was higher than in a leaf which had grown at that irradiance. We conclude that changes in leaf composition allow the leaf to avoid a one-sided limitation by Rubisco and, hence, overexcitation and overreduction of the thylakoids in high-irradiance growth conditions. (v)'Antisense' plants with less Rubisco contained a higher content of insoluble (thylakoid) protein and chlorophyll, compared to total protein or structural leaf dry weight. They also showed a higher rate of photosynthesis than the wild type, when measured at an irradiance below that at which the plant had grown. We propose that N-allocation in low light is not optimal in tobacco and that genetic manipulation to decrease Rubisco may, in some circumstances, increase photosynthetic performance in low light.

Regulation of Photosynthesis during Leaf Development in RbcS Antisense DNA Mutants of Tobacco

“…These analyses revealed that under high-irradiance conditions, similar to those in the present experiments, Rubisco activity is primarily limiting for photosynthesis but that control is also shared with other factors. Stomatal conductance is one of these factors , and CO 2 diffusion through the aqueous phase of the leaf may be another (Lauerer et al, 1993). Our results are consistent with these conclusions and suggest that the control exerted by Rubisco on photosynthesis is considerable throughout leaf development.…”

“…Because the alterations in stomatal conductance are not accompanied by corresponding changes in Ci, it is unlikely that stomatal aperture plays a central role in controlling photosynthetic activity during WT and antisense leaf development, at least under these conditions (reviewed by Farquhar and Sharkey, 1982). The data in Figure 2, B and C, confirm and extend earlier observations of enhanced stomatal conductances and Ci in first fully expanded leaves of the antisense versus WT plants under high-irradiance conditions (Quick et al, 1991b;Stitt et al, 1991;Lauerer et al, 1993). Figure 3A shows that total Chl contents and the patterns of change in Chl accumulation are similar during WT and antisense leaf development.…”

“…Quantitative flux-control analyses have been conducted on first fully expanded leaves of the Rubisco antisense DNA mutants to assess the control that Rubisco exerts on photosynthesis under a variety of short-term and longterm conditions (Quick et al, 1991a(Quick et al, , 1991b(Quick et al, , 1992Stitt et al, 1991;Lauerer et al, 1993;Masle et al, 1993). These analyses revealed that under high-irradiance conditions, similar to those in the present experiments, Rubisco activity is primarily limiting for photosynthesis but that control is also shared with other factors.…”

“…Because of this variability, the antisense mutants have proven to be an attractive system for quantitative fluxcontrol analyses (Kacser and Porteous, 1987) to assess the control that Rubisco exerts on photosynthesis and plant growth under a variety of short-term and long-term growth conditions (Quick et al, 1991a(Quick et al, , 1991b(Quick et al, , 1992Stitt et al, 1991;Lauerer et al, 1993;Masle et al, 1993). Although these studies have focused on the biochemistry and physiology of mature leaf and whole plant responses to decreases in Rubisco content, little is understood about the impact of Rubisco loss on the regulation of photosynthesis during leaf development.…”

Decreased SBPase activity alters growth and development in transgenic tobacco plants

“…If source strength was the only factor involved in determining the developmental changes observed in the Rubisco antisense plants, then it would be expected that the SBPase antisense plants would display a similar phenotypic response. It has been shown that reductions in Rubisco result in changes in the N status of the leaves therefore it is possible that the changes in leaf development, observed in the Rubisco antisense plants, were due to a change in the C/N balance (Fichtener et al 1993;Masle et al 1993;Matt et al 2002). Further support for this suggestion comes from the finding that nitrogen reallocation occurs in the Rubisco antisense plants grown under low light conditions (Lauerer et al 1993).…”