Apple roots, phlorizin

The hypothesis of Gray and Bonner (31, 32) that 3-acetyl-6-methoxybenzaldehyde, which is found in the leaves of Encelia farinosa and in the soil beneath these plants, is responsible for the suppression of other plant species has not been substantiated by Muller (33, 34). The same is true for the presumed role of trans-cinnamic acid in "soil sickness associated with guayule (Parthenium argentatum), for the amygdalin of peach roots, and for the phlorizin of apple roots or its breakdown products (35), which were thought to be associated with the "soil sickness" of orchards. 

Many allelochemicals are decomposed in soil, either abiotically (37) or by microorganisms (95-100). Obviously, the attainment of active concentrations of allelochemicals in soil depends on the relative rates of addition and inactivation. It is important to understand also that microbial decomposition of allelochemicals does not necessarily result in a decrease in allelopathic activity. In fact, the reverse may be true. Hydrojuglone is oxidized in soil to juglone, a quinone that is inhibitory to some species at a 10 ° M concentration (101). Isoflavonoids produced by red clover are decomposed to even more toxic phenolic compounds (95) and to repeat, amygdalin from peach roots is changed to hydrogen cyanide and benzaldehyde which cause the peach replant problem (88), and phlorizin from apple roots is decomposed to several phenolic compounds that appear to be responsible for the apple replant problem (100). 

Borner (1960) states that soil sickness in fruit culture is a problem of economic importance in Germany. This is a replant problem that involves micro-element depletion and nematodes, but also root residues. As little as 1 g of air-dry root bark of an old apple tree per half liter of nutrient solution reduced root and stem growth of apple seedlings up to 50% within 30 days. Phlorizin, a natural constituent of apple root bark, and its breakdown products, are at least partially responsible for this apple soil sickness. 

Phlonzm is obtained from the root bark of apple pear cherry and plum trees It has the molecular formula C21H24O10 and yields a compound A and D glucose on hydrolysis in the pres ence of emulsin When phlorizin is treated with excess methyl iodide in the presence of potassium carbonate and then subjected to acid catalyzed hydrolysis a compound B is obtained Deduce the structure of phlorizin from this information... 

Phlorizin is a dihydrochalcone. Apart from its common occurrence in rosaceous trees, and especially in the root bark, it is otherwise reported as occurring only in Micromelum teprocarpum, a relative of Citrus. Although present in the seeds, shoots, and leaves of apples, it appears to be entirely absent from the flesh—a fortunate fact in view of its poisonous character. 

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