Barley Photorespiration Mutants

Photorespiration, the light- and O2_dependent release of CO2 from the leaves of certain species, is regarded as the inevitable consequence of the oxygenase activity of ribulose bisphosphate carboxylase/oxygenase, Rubisco [1]. Some authors have suggested that, inevitable or not, the process may have a useful function [2]. It is an apparently wasteful process: 25% or more of fixed CO2 may be lost and energy is consumed [3]. The metabolic routes involved in the process have long been controversial, particularly regarding the source of photorespiratory CO2 and the reassimilation of photorespiratory NH3 [4]. Mutants of Arabidopsis thaliana with defects at seven steps in photorespiratory metabolism provided evidence to settle some of these controversies [5]. We have isolated a series of barley (Hordeum vulgare L.) mutants, with lesions at additional sites, which provide further insights into photorespiratory metabolism.