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Oxalate occurs in many plants, where it is synthesized by the incomplete oxidation of saccharides. Several plant foods such as the root and/or leaves of spinach, rhubarb, and buckwheat are high in oxalic acid and can contribute to the formation of kidney stones in some individuals. Other oxalate-rich plants include fat hen ("lamb's quarters ...
A number of biochemical pathways for calcium oxalate biomineralization in plants have been proposed. Among these is the cleavage of isocitrate, the hydrolysis of oxaloacetate, glycolate/glyoxylate oxidation, and/or oxidative cleavage of L-ascorbic acid. [9] The cleavage of ascorbic acid appears to be the most studied pathway.
Plants normally produce it in small amounts, but some pathogenic fungi such as Sclerotinia sclerotiorum cause a toxic accumulation. [50] Oxalate, besides being biosynthesised, may also be biodegraded. Oxalobacter formigenes is an important gut bacterium that helps animals (including humans) degrade oxalate. [51]
Many plants accumulate calcium oxalate as it has been reported in more than 1000 different genera of plants. [7] The calcium oxalate accumulation is linked to the detoxification of calcium (Ca 2+) in the plant. [8] Upon decomposition, the calcium oxalate is oxidised by bacteria, fungi, or wildfire to produce the soil nutrient calcium carbonate. [9]
Oxalate oxidase （Enzyme Commission number EC 1.2.3.4 [2] ）occurs mainly in plants. It can degrade oxalic acid into carbon dioxide and hydrogen peroxide. [3]Oxalate decarboxylase (OXDC，EC 4.1.1.2) is a kind of oxalate degrading enzyme containing Mn 2+, [4] found mainly in fungi or some bacteria.
Calcium-oxalate-accumulating plants, such as Amaranthus hybridus and Colobanthus quitensis, show a variation of photosynthesis where calcium oxalate crystals function as dynamic carbon pools, supplying carbon dioxide (CO 2) to photosynthetic cells when stomata are partially or totally closed.
Raphides in Epipremnum Devil's ivy (600× magnification). Raphides (/ ˈ r æ f ɪ d i z / RAF-id-eez; singular raphide / ˈ r eɪ f aɪ d / RAY-fyde or raphis) are needle-shaped crystals of calcium oxalate monohydrate (prismatic monoclinic crystals) or calcium carbonate as aragonite (dipyramidal orthorhombic crystals), found in more than 200 families of plants.
This biochemical appendance of the photosynthetic machinery is a means to alleviate the perpetual plant dilemma of using atmospheric CO 2 for photosynthesis and losing water vapor, or saving water and reducing photosynthesis. The function of alarm photosynthesis seems to be rather auxiliary to the overall photosynthetic performance.