A druse is a group of crystals of
calcium oxalate,[1] silicates, or carbonates present in plants, and are thought to be a
defense against herbivory due to their toxicity. Calcium oxalate (Ca(COO)2, CaOx) crystals are found in
algae,
angiosperms and
gymnosperms in a total of more than 215 families. These plants accumulate oxalate in the range of 3–80% (w/w) of their dry weight[2][3] through a
biomineralization process in a variety of shapes.[4]Araceae have numerous druses, multi-crystal druses and needle-shaped
raphide crystals of CaOx present in the tissue.[5] Druses are also found in leaves and bud scales of Prunus, Rosa,[6]Allium, Vitis, Morus and Phaseolus.[7][8]
Formation
A number of biochemical
pathways for calcium oxalate biomineralization in plants have been proposed. Among these are 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.[10][11][12][13] The specific mechanism controlling this process is unclear but it has been suggested that a number of factors influence crystal shape and growth, such as proteins, polysaccharides, and lipids or macromolecular membrane structures.[14][15][16] Druses may also have some purpose in calcium regulation.
^Zindler-Frank E. (1976). "Oxalate biosynthesis in relation to photosynthetic pathways and plant productivity: a survey". Z. Pflanzenphysiol. 80 (1): 1–13.
doi:
10.1016/S0044-328X(76)80044-X.
^McNair JB (1932). "The interrelation between substances in plants: essential oils and resins, cyanogen and oxalate". Am J Bot. 19 (3): 255–271.
doi:
10.2307/2436337.
JSTOR2436337.
^Li XX, Franceschi VR (1990). "Distribution of peroxisomes and glycolate metabolism in relation to calcium oxalate formation in Lemna minor L.". Eur J Cell Biol. 51 (1): 9–16.
PMID2184039.
^Horner HT, Wagner BL (1980). "The association of druse crystals with the developing stomium of Capsicum annuum (Solanaceae) anthers". Am J Bot. 67 (9): 1347–1360.
doi:
10.2307/2442137.
JSTOR2442137.
^Arnott HJ, Webb MA (1983). "Twin crystals of calcium oxalate in the seed coat of the kidney bean". Protoplasma. 114 (1): 23–34.
doi:
10.1007/BF01279865.
S2CID180834.