Kate of oxalate biosynthesis from glycolate and ascorbic acid in spinach leaves

Abstract

The contribution of glycolate as a precursor of oxalate in newly expanding spinach leaves was compared with that of L-ascorbic acid (ASA). Detached spinach leaves were fed with [2-14C]glycolate and [1-1~C]ASA. Using the values of the rate of photorespiratory glycolate synthesis and the incorporation of glycolate-~C into oxalate, the rate of oxalate biosynthesis via glycolate amounted to 34 ~g g-1 fr wt h -1 under light conditions. When the values of incorporation of ASA-14C into oxalate and the turnover rate of ASA were used, the rate of oxalate biosynthesis via ASA in light and darkness, amounted to 1.6 and 2.9 #g g-1 fr wt h -1, respectively. Glycolate was found to be more efficient as a precursor of oxalate than ASA in newly expanding spinach leaves.Key Words: glycolate, L-ascorbic acid, oxalate biosynthetic rate, photorespiration, spinach.Spinach is an edible plant species belonging to the family Chenopodiaceae. Oxalate accumulates in spinach leaves and a high-oxalate diet can increase the risk of formation of calcium oxalate stones in kidneys (Hodgkinson 1978) and may also affect calcium absorption (Liebman and Doane 1989). Plants which produce calcium oxalate are known to induce a painful sensation in the mouth when eaten (Perera et al. 1990). Oxalate may, therefore, contribute to the harsh taste of spinach and it is thus necessary to produce spinach with a low oxalate content. Many attempts have been made to reduce the level of oxalate in spinach leaves with regard to nitrogen and inorganic ion availability as well as other growth conditions (Watanabe et al. 1987;lwanami 1989;Zhang et al. 1990). However, oxalate biosynthesis has not been well documented. We therefore investigated the biosynthesis of oxalate to obtain information about the possibility of reducing the production of oxalate in spinach. Glyoxylate, glycolate, and ASA are the precursors of oxalate as indicates by feeding experiments in many plants (Chang and Beevers 1968;Seal and Sen 1970;Yang and Loewus 1975;Williams et al. 1979;Chang and Huang 1981). The major part of glyoxylate may be produced from glycolate in the peroxisomes in green spinach leaves. The presence of a barrier to glyoxylate transportation in peroxisomal membranes, and compartmentation have been reported (Liang and Huang 1983;Heupel et al. 1991). As external application of glyoxylate for metabolic studies is not suitable, we compared the contribution of glycolate Abbreviations: ASA, k-ascorbic acid; fr wt, flesh weight; mol wt, molecular weight. or ASA as a precursor of oxalate biosynthesis in spinach leaves. MATERIALS AND METHODSUsing the values of the rate of photorespiratory glycolate synthesis and the incorporation of glycolate-14C into oxalate, the rate of oxalate biosynthesis via glycolate was calculated as follows:Rate of glycolate synthesisX incorporation of glycolate-14C into oxalate X tool wt of oxalate/mol wt of glycolate, (formula 1) and the following formula was used to calculate oxalate biosynthesis via ASA using the values of ASA-~4C incorporation into oxalate...

Identification of long needle crystals and distribution of oxalate salts inNarcissuscv. ‘Garden Giant’

“…Oxalate salts accumulate in various species of higher plants, such as spinach (Goh and Vityakon 1989;Prokakis and Gonzalez 1990;Kameno et al 1991;Kleczkowski et al 1991;Fujii et al 1993;Takebe et al 1995a,b;Watanabe et al 1995), begonia (Sasaki 1963), Phaseolus vulgaris (Zindler-Frank et al 1989; Barnabas and Arnott 1991), plum and cherry (Sanchez-Alonso and Lachica 1988), and rice seedlings (Ivanov et al 1991). Oxalic acid has been considered to be a by-product of plant metabolism.…”

“…Oxalic acid has been considered to be a by-product of plant metabolism. Fujii et al (1993) suggested that oxalate biosynthesis in spinach leaves is related to photorespiration and that glycolate was an important precursor of oxalate. Furthermore, the rate of oxalate synthesis via glycolate depends on the age of the leaves (Fujii et al 1993).…”

“…Fujii et al (1993) suggested that oxalate biosynthesis in spinach leaves is related to photorespiration and that glycolate was an important precursor of oxalate. Furthermore, the rate of oxalate synthesis via glycolate depends on the age of the leaves (Fujii et al 1993). However, not all C 3 plants accumulate oxalate, and Watanabe et al (1995) suggested that the glycolate oxidizing enzyme in spinach, an oxalate accumulator, may differ from the enzyme oxidizing glyoxylate in the non-accumulator C 3 plant, Brassica campestris L.…”

Raphides in Food ? An Unsafe Menu

“…Different precursor use by the different parts of a plant remains to be explored. Biosynthetic pathways have been very well reviewed at length in several recent works [53,[71][72][73][74][75][76] so we are merely summarizing the key findings and focusing on amelioration in the next section. The synthesis of ascorbate, a precursor of calcium oxalate takes place in the vacuoles of idioblast cells itself.…”

“…The major precursors are ascorbate, glycolate, glyoxylate, oxaloacetate and isocitrate [53,[71][72][73][74][75]. Different precursor use by the different parts of a plant remains to be explored.…”