Photorespiration in C4 grasses remains slow under drought conditions

Carmo-Silva, Ana E. and Powers, Stephen J. and Keys, Alfred J. and Arrabaça, Maria Celeste and Parry, Martin A. J. (2008) Photorespiration in C4 grasses remains slow under drought conditions. Plant, Cell and Environment, 31 (7). pp. 925-940. ISSN 0140-7791

Abstract

The CO2-concentrating mechanism present in C4 plants decreases the oxygenase activity of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) and, consequently, photorespiratory rates in air. Under drought conditions, the intercellular CO2 concentration may decrease and cause photorespiration to increase. The C4 grasses Paspalum dilatatum Poiret, Cynodon dactylon (L.) Pers. and Zoysia japonica Steudel were grown in soil and drought was imposed by ceasing to provide water. Net CO2 assimilation (A) and stomatal conductance to water vapour decreased with leaf dehydration. Decreased carbon and increased oxygen isotope composition were also observed under drought. The response of A to CO 2 suggested that the compensation point was zero in all species irrespective of the extent of drought stress. A slight decrease of A as O 2 concentration increased above 10% provided evidence for slow photorespiratory gas exchanges. Analysis of amino acids contained in the leaves, particularly the decrease of glycine after 30 s in darkness, supported the presence of slow photorespiration rates, but these were slightly faster in Cynodon dactylon than in Paspalum dilatatum and Zoysia japonica. Although the contents of glycine and serine increased with dehydration and mechanistic modelling of C4 photosynthesis suggested slightly increased photorespiration rates in proportion to photosynthesis, the results provide evidence that photorespiration remained slow under drought conditions.