Photorespiratory N donors, aminotransferase specificity and photosynthesis in a mutant of barley deficient in serine: glyoxylate aminotransferase activity

Abstract

A mutant of Hordeum vulgare L. (LaPr 85/84) deficient in serine: glyoxylate aminotransferase (EC 2.6.1.45) activity has been isolated. The plant also lacks serine: pyruvate aminotransferase and asparagine: glyoxylate aminotransferase activities. Genetic analysis of the mutation strongly indicates that these three activities are all carried on the same enzyme protein. The mutant is incapable of normal rates of photosynthesis in air but can be maintained at 0.7% CO2. The rate of photosynthesis cannot be restored by supplying hydroxypyruvate, glycerate, glutamate or ammonium sulphate through the xylem stream. This photorespiratory mutant demonstrates convincingly that photorespiration still occurs under conditions in which photosynthesis becomes insensitive to oxygen levels. Two major peaks and one minor peak of serine: glyoxylate aminotransferase activity can be separated in extracts of leaves of wild-type barley by diethylaminoethyl-sephacel chromatography. All three peaks are missing from the mutant, LaPr 85/84. The mutant showed the expected rate (50%) of ammonia release during photorespiration but produced CO2 at twice the wild-type rate when it was fed [(14)C]glyoxylate. The large accumulation of serine detected in the mutant under photorespiratory conditions shows the importance of the enzyme activity in vivo. The effect of the mutation on transient changes in chlorophyll a fluorescence initiated by changing the atmospheric CO2 concentration are presented and the role of the enzyme activity under nonphotorespiratory conditions is discussed.

Peroxisomal Malate Dehydrogenase Is Not Essential for Photorespiration in Arabidopsis But Its Absence Causes an Increase in the Stoichiometry of Photorespiratory CO2 Release

“…Studies on various photorespiratory mutants have not consistently agreed on the way that potential CO 2 release steps may be altered. Studies with a barley mutant deficient in Ser:glyoxylate aminotransferase demonstrated significantly elevated release of labeled CO 2 from exogenously supplied glyoxylate (Murray et al, 1987). In contrast, a HPR barley mutant (Murray et al, 1987) showed little evidence for an increased CO 2 release, even though there was considerable photosynthesis in air.…”

“…Studies with a barley mutant deficient in Ser:glyoxylate aminotransferase demonstrated significantly elevated release of labeled CO 2 from exogenously supplied glyoxylate (Murray et al, 1987). In contrast, a HPR barley mutant (Murray et al, 1987) showed little evidence for an increased CO 2 release, even though there was considerable photosynthesis in air. A barley mutant deficient in catalase (Kendall et al, 1983) showed no evidence for increased CO 2 release, while an Arabidopsis transgenic plant with antisense reduction in the levels of the 2-oxoglutarate/ malate translocator (Schneidereit et al, 2006) showed a significant increase in G.…”

Serial Analysis of Gene Expression Study of a Hybrid Rice Strain (LYP9) and Its Parental Cultivars

“…AGT1, localized in peroxisomes of Arabidopsis, is a key photorespiratory enzyme that has the highest specific activity with the Ser:glyoxylate aminotransferase reaction (Liepman and Olsen, 2001). Previous studies have shown that plant mutants lacking Ser:glyoxylate aminotransferase activity were not viable when grown in the atmospheric condition but survived when photorespiration was suppressed by increasing CO 2 concentration in a growing environment (Somerville and Ogren, 1980;Murray et al, 1987). The enhancement of photorespiratory pathway severely diminishes the efficiency of CO 2 assimilation and the yield of C 3 -crops (such as rice, wheat, soybean [Glycine max], and potato [Solanum tuberosum]) and improvement of crop yield of C 3 plants can be achieved in an atmosphere containing elevated CO 2 level, resulting in increased CO 2 assimilation and suppressed photorespiration (Reynolds et al, 2000).…”

Tansley Review No. 112

“…More recently, in transformed tobacco, the underexpression of catalase has been shown to be associated with an increased CO # compensation point, whereas the reverse was observed in plants overexpressing the enzyme (Brisson et al, 1998). By contrast, labelling experiments in the catalasedeficient barley mutant produced no evidence for increased CO # release in conditions promoting high rates of photorespiration (Kendall et al, 1983), even though increased CO # release can occur in barley lacking sufficient aminotransferase activity to keep pace with glyoxylate production (Murray et al, 1987). Further work is required to resolve the apparent discrepancy between the results in barley and tobacco (Kendall et al, 1983 ;Brisson et al, 1998).…”