High Glycolate Oxidase Activity Is Required for Survival of Maize in Normal Air  

Abstract

A mutant in the maize (Zea mays) Glycolate Oxidase1 (GO1) gene was characterized to investigate the role of photorespiration in C4 photosynthesis. An Activator-induced allele of GO1 conditioned a seedling lethal phenotype when homozygous and had 5% to 10% of wild-type GO activity. Growth of seedlings in high CO2 (1%-5%) was sufficient to rescue the mutant phenotype. Upon transfer to normal air, the go1 mutant became necrotic within 7 d and plants died within 15 d. Providing [1-14C]glycolate to leaf tissue of go1 mutants in darkness confirmed that the substrate is inefficiently converted to 14CO2, but both wild-type and GO-deficient mutant seedlings metabolized [1-14C]glycine similarly to produce [14C]serine and 14CO2 in a 1:1 ratio, suggesting that the photorespiratory pathway is otherwise normal in the mutant. The net CO2 assimilation rate in wild-type leaves was only slightly inhibited in 50% O2 in high light but decreased rapidly and linearly with time in leaves with low GO. When go1 mutants were shifted from high CO2 to air in light, they accumulated glycolate linearly for 6 h to levels 7-fold higher than wild type and 11-fold higher after 25 h. These studies show that C4 photosynthesis in maize is dependent on photorespiration throughout seedling development and support the view that the carbon oxidation pathway evolved to prevent accumulation of toxic glycolate.

Evidence for a Role for NAD(P)H Dehydrogenase in Concentration of CO2 in the Bundle Sheath Cell of Zea mays

“…Nevertheless, since Rubisco turnover in the BSC is essential to the C 4 mechanism, some photorespiration must occur when O 2 is present-consistent with the mutual competition between O 2 and CO 2 at the enzyme active site (Lorimer and Andrews 1973). Indeed, a high level of glycolate oxidase (the initial step in the photorespiratory pathway) is required for survival of Zea mays in normal air (Zelitch et al, 2009). The seeming paradox of a low, O 2 -independent G and occurrence of measureable O 2 -dependent (and CO 2 -reversible) linear electron transport reported here for normal and mutant maize can be addressed in terms of the compartmentation inherent in the MC-BSC model.…”

Maize Source Leaf Adaptation to Nitrogen Deficiency Affects Not Only Nitrogen and Carbon Metabolism But Also Control of Phosphate Homeostasis

“…The contribution of photorespiration to ammonium production is reduced in C 4 plants such as maize but would still be present. Interruption of photorespiration by repression of the glyoxylate oxidase has shown recently that the presence of photorespiration is also essential for survival of C 4 plants (Zelitch et al, 2009). It was proposed that photorespiration is important to avoid accumulation of glycolate to toxic levels, and this protection mechanism would be needed in high-and low-N conditions.…”

Plant Responses to Salt Stress: Adaptive Mechanisms

“…In pea leaf peroxisomes, there are at least two sites of O2 .− generation: the reaction of the enzyme xanthine oxidase in the matrix and an NAD(P)H-dependent O2 .− generating enzyme in the peroxisomal membrane [205]. In addition, H2O2 is produced at a high rate in peroxisomes by the action of different H2O2-producing flavin oxidases, with the photorespiratory glycolate oxydase enzyme being one of the most important H2O2 generators [206]. In peroxisomal membranes from pea leaves, neither the NADH-induced generation of O2 .− nor the lipid peroxidation of membranes was found to be altered by salt stress, and results were similar in NaCl-tolerant and NaCl-sensitive pea plants [190].…”