title: Rubisco activities, properties, and regulation in three different C4 grasses under drought.
abstract: In C4 plants, water deficit may decrease photosynthetic CO2 assimilation independently of changes in stomatal conductance, suggesting decreased turnover by ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). The activity and biochemistry of Rubisco was studied in three different C4 grasses: Paspalum dilatatum, Cynodon dactylon, and Zoysia japonica. The objectives were to characterize the C4 Rubisco in these species and to identify factors associated with decreased photosynthetic rates caused by drought. Rubisco isolated from each of the three C4 grasses was characterized by smaller specificity factors (SC/O), larger Michaelis-Menten constants for CO2 (Kc) and O2 (Ko), and larger maximum carboxylation velocities (Vc) than Rubisco from wheat, which can be rationalized in terms of the CO2-rich environment of C4 Rubisco in the bundle sheath. During leaf dehydration the quantity and maximum activity of Rubisco remained unchanged but the initial and total activities declined slightly, possibly due to increased inhibition. Tight-binding inhibitors were present in the light but were more abundant in the dark, especially in Z. japonica, and increased in quantity with drought stress. The inhibitor from darkened leaves of Z. japonica was identified as 2-carboxyarabinitol-1-phosphate (CA1P). Consistent with the presence of CA1P, the total activity of Rubisco was decreased after 12 h darkness in Z. japonica. Ribulose-1,5-bisphosphate (RuBP) in the leaves decreased with drought stress, to quantities approximating those of Rubisco catalytic sites. The magnitude of the decrease in RuBP suggested that, at least in C. dactylon and Z. japonica, it could contribute to the drought-induced decrease in photosynthesis.
authors.affiliation: Centro de Engenharia Biológica and Departamento de Biologia Vegetal, Universidade de Lisboa, Faculdade de Ciências, Campo Grande, 1749-016 Lisboa, Portugal. elizabete.carmosilva@gmail.com
authors.forename: A Elizabete
authors.initials: AE
authors.lastname: Carmo-Silva
authors.forename: Alfred J
authors.initials: AJ
authors.lastname: Keys
authors.forename: P John
authors.initials: PJ
authors.lastname: Andralojc
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Powers
authors.forename: M Celeste
authors.initials: MC
authors.lastname: Arrabaça
authors.forename: Martin A J
authors.initials: MA
authors.lastname: Parry
mesh_terms: D055864:Droughts; D015971:Gene Expression Regulation, Enzymologic / Q000528:radiation effects; D018506:Gene Expression Regulation, Plant / Q000528:radiation effects; D007700:Kinetics; D008027:Light; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006109:Poaceae / Q000201:enzymology* / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects; D012273:Ribulose-Bisphosphate Carboxylase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D010940:Plant Proteins; D012273:Ribulose-Bisphosphate Carboxylase