The development, physiology, and function of selected plant calcium oxalate crystal idioblasts

Abstract

Oxalic acid is a dicarboxylic acid [(COOH)^], produced in plants through at least five biochemical pathways (Hodgkinson, 1977; Franceschi and Homer, 1980a). Oxalate has been reported to originate in some plants via enzymatic cleavage of oxaloacetate (Chang and Beevers, 1968) and/or ascorbate metabolism (Wagner and Loewus, 1973). However, it is generally accepted that the major intermediate precursors of oxalate in higher plants are glycolate and glyoxalate (Kpodar et al., 1978). These pre cursors may arise from the glycolate pathway (i.e., photorespiration; Tolbert, 1973), the glyoxalate bypass (Romberg and Krebs, 1957) or purine degradation (Huang, 1982). Certain plant pathological fungi oxidize glyoxalate to oxalic acid in the presence of peroxisonal NAD-glyoxalate dehydrogenase (Armentrout et al., 1978) but this system is not found in any higher plant species (Huang, 1982). Salient features of oxalate syn thetic pathways in plant cells provide a necessary background for this dissertation on calcium oxalate crystal idioblast biology. The glycolate pathway Glycolate arises as a result of photosynthesis (Tolbert, 1973) and is the principal substrate of photorespiration (Tolbert, 1973; Zelitch, 1975a,b) as the starting point of the glycolate pathway. Its formation is Og and light dependent and inhibited in high CO^ concentration, although the exact route of its production is not entirely clear (Zelitch, 1971). Glycolic acid is one of the first formed products of photosynthesis in 8 other than 0^. This enzume in barley is somevAiat unstable; all activity may be lost after three hours of dialysis (Kolesnikov et al., 1959). Richardson and Tolbert (1961) found that the activity of glycolate oxidase in spinach is not necessarily restricted to oxidizing glycolate to glyoxylate ^ vivo, but under specific cellular conditions, glyoxylate is oxidized to oxalate. Furthermore, they showed that the flavin-linked enzyme was competitively inhibited by oxalate. They implied that this provided for the regulation of oxalate synthesis. The Michaelis-Menten plots also show that the enzyme had a greater affinity for glycolate than for glyoxylate. Millerd et al. (1963d) found that glycolate oxidase from Oxalis was not affected by the presence of oxalate and had no preferential affinity for glycolate or glyoxylate. It may be that ^ vivo, the activity of glyoxyl ate oxidation may be high if oxalate is removed from the reaction site. A number of fates may befall the glyoxylate produced from photosynthetically derived glycolate in the glycolate oxidase reaction. It may return to the chloroplast to be reduced to glycolate by glycolate reductase (Zelitch, 1953) so that a glycolate-glyoxylate shuttle between the peroxisome and chloroplast is established (Carles and Assailly, 1954). Ifiich of the glyoxylates produced from the oxidation of glycolate is transaminated to glycine in the presence of glutamic acid (Richardson and Tolbert, 1961). Glycine may give rise to serine and CO^ by a hydroxymethyltransferase reaction (Tolbert and Cohan, 1953)....

Biochemical, electrophoretic and immunological characterization of peroxisomal enzymes in three soybean organs

“…A second possible explanation for the difference in urate oxidase distribution in soybean as compared with other plant spedes is that other plant spedes are less tissue-selective than soybean in the production of a peroxisomal urate oxidase. For example, Kausch (1983) was able to detect, by ultrastructural cytochemical analysis, urate oxidase in the unspecialized root and leaf peroxisomes of one plant spedes but not in both types of peroxisomes in several other spedes. Thus, although an easily detectable urate oxidase activity appears to be a characteristic of the spedalized nodule pieroxisomes, it may not be absolutely unique to this specialized peroxisome type, as malate synthase is to the glyoxysome.…”

“…Our study provided no evidence for urate oxidase activity in soybean leaf peroxisomes or glyoxysomes. Urate oxidase activity occurs in unspecialized peroxisomes (Vaughn et al 1982, Huang et al 1983, Kausch 1983, leaf peroxisomes (Kausch 1983), and glyoxysomes (Theimer and Beevers 1971) in a diversity of plant species. There are at least two explanations for the apparent difference between the distribution of urate oxidase as found in this report and previous observations on the more ubiquitous nature of this enzyme.…”