Expressing an RbcS antisense gene in transgenic Flaveria bidentis leads to an increased quantum requirement for CO2 fixed in photosystems I and II

• Published in: Plant physiology (Bethesda) 1997-11, Vol.115 (3), p.1163-1174
• Main Authors: Siebke, K, Caemmerer, S. von, Badger, M, Furbank, R.T
• Format: Article
• Language: English
• Subjects: ACTIVIDAD ENZIMATICA; ACTIVITE ENZYMATIQUE; ATP; Bioenergetics; Biological and medical sciences; C4 plants; CARBON DIOXIDE; CHEMICAL COMPOSITION; Chlorophylls; Chloroplasts; COMPOSICION QUIMICA; COMPOSITAE; COMPOSITION CHIMIQUE; CONTENIDO PROTEICO; DIOXIDO DE CARBONO; DIOXYDE DE CARBONE; ECHANGE GAZEUX; ELECTRON TRANSFER; ENZYMIC ACTIVITY; EQUATIONS; EXPRESION GENICA; EXPRESSION DES GENES; FEUILLE; Fluorescence; FOTOSISTEMAS; Fundamental and applied biological sciences. Psychology; GAS EXCHANGE; GENE EXPRESSION; GENETIC VARIATION; HOJAS; INTERCAMBIO DE GASES; LEAVES; LIGHT; LIGHT INTENSITY; LUMIERE; Luminous intensity; LUZ; MATEMATICAS; MATHEMATICAL MODELS; MATHEMATICS; MATHEMATIQUE; MEASUREMENT; MEDICION; MESURE; Metabolism; MODELE MATHEMATIQUE; MODELOS MATEMATICOS; NET ASSIMILATION RATE; OXIDOREDUCTIONS; OXIRREDUCION; OXYDOREDUCTION; Photosynthesis; Photosynthesis, respiration. Anabolism, catabolism; PHOTOSYSTEM I; PHOTOSYSTEM II; PHOTOSYSTEME; PHOTOSYSTEMS; Plant physiology and development; PLANTAS TRANSGENICAS; PLANTE TRANSGENIQUE; Plants; PROTEIN CONTENT; PROTEINAS; PROTEINE; PROTEINS; Protons; RIBULOSE-BISPHOSPHATE CARBOXYLASE; RUBISCO; TENEUR EN PROTEINES; TRANSGENIC PLANTS; VARIACION GENETICA; VARIATION GENETIQUE; WILD STRAINS
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.115.3.1163

It was previously shown with concurrent measurements of gas exchange and carbon isotope discrimination that the reduction of ribulose-1,5-bisphosphate carboxylase/oxygenase by an antisense gene construct in transgenic Flaveria bidentis (a C4 species) leads to reduced CO2 assimilation rates, increased bundle-sheath CO2 concentration, and leakiness (defined as the ratio of CO2 leakage to the rate of C4 acid decarboxylation; S. von Caemmerer, A. Millegate, G.D. Farquhar, R.T. Furbank [1997] Plant Physiol 113: 469-477). Increased leakiness in the transformants should result in an increased ATP requirement per mole of CO2 fixed and a change in the ATP-to-NADPH demand. To investigate this, we compared measurements of the quantum yield of photosystem I and II (phi(PSI) and phi(PSII)) with the quantum yield of CO2 fixation (phi(CO2)) in control and transgenic F. bidentis plants in various conditions. Both phi(PSI)/phi(CO2) and phi(PSII)/phi(CO2) increased with a decrease in ribulose-1,5-bisphosphate carboxylase/oxygenase content, confirming an increase in leakiness. In the wild type the ratio of phi(PSI) to phi (PSII) was constant at different irradiances but increased with irradiance in the transformants, suggesting that cyclic electron transport may be higher in the transformants. To evaluate the relative contribution of cyclic or linear electron transport to extra ATP generation, we developed a model that links leakiness, ATP/NADP requirements, and quantum yields. Despite some uncertainties in the light distribution between photosystem I and II, we conclude from the increase of phi(PSII)/phi (CO2) in the transformants that cyclic electron transport is not solely responsible for ATP generation without NADPH production