Onion physiology

As well as the TDF content, the proportion between SDF and IDF is an important nutritional parameter because of the different physiological effects that these exert. Proportions of SDF are characteristically high in fruits and vegetables, although they can differ considerably. SDF is less than 20% of TDF in grape but more than 30% in onion and higher than 50% in fig. 

Many organosulfur compounds undergo biological oxidation at the sulfur atom to yield products which have pronounced physiological activity or serve as intermediates in generating bioactive compounds. Three examples are the lachrymating agent in onions ( ) (1), the oxo intermediate ( ) in metabolic desulfuration of phosphorothionate insecticides to form potent cholinesterase inhibitors (2), and the sulfoxides QJ produced on metabolism of thiocarbamate herbicides (3). 

Stiles et al.43 found artemisinin to inhibit respiration in Lemna minor, but the compound strongly stimulates oxygen uptake by lettuce root tips.6 All mitotic phases of onion root tips are inhibited by the compound, and it induces a low level of abnormal mitotic figures.6 Dayan et al.6 conducted a battery of simple physiological tests with several artemisinin analogues. All phytotoxic compounds had similar effects, indicating a common mode of action. In summary, the mode of action results with artemisinin as a phytotoxin are not definitive. 

The presence of asymmetric carbons in selenomethionine, other a-selenoamino acids, and related compounds produces different chiral enantiomers with different physiological activities. HPLC separation of enantiomers is possible with a range of chiral stationary phases, d- and 1-Selenomethionine enantiomers have been resolved with an a-cyclodextrin stationary phase and other species with a teicoplanin-based chiral phase. Hybrid chiral methodologies based on GC, HPLC, and capillary electrophoresis, coupled with ICP-MS are feasible. Enantiomers of d,l-selenocystine, d,l-selenomethio-nine, and d,l-selenoethionine were examined in a range of commercial dietary supplements using a chiral crown ether stationary phase and ICP-MS detection. Selenium-em-iched onion, garlic, and yeast were analyzed and some of the selenoamino acid enantiomers were identified. l-Fluoro-2, 4-dinitro-phenyl-5-l-alanine amide was used to derivatize enantiomers of selenoamides for enhanced resolution. 

H. D. Rabinowitch and J. L. Brewster in Onions and allied crops, CRC Press, Boca Raton, Florida (US), 1990, Vol. 1 Botany, physiology, and genetic. 

We have studied on physiological, pharmaceutical or therapeutic effects of various edible plants, especially the sulfor-containing compounds from onion 15,16). Our continuous screening for the induction of GST activity in RL34 cells resulted in isolation of MS-ITC from the ethyl acetate (EtOAc) extract of wasabi. In this study, we describe the isolation of MS-ITC from wasabi, and examined the protein levels of GST isozyme induced by MS-ITC. As a result from elucidation of the intracellular redox state of BITC instead of MS-ITC, the isothiocyanate moiety of these food foctors phtys an important role for the induction of phase II enzymes. 

Takahama, U. Hirota, S. (2000). Deglucosidation of quercetin glucosides to the aglycone and formation of antifungal agents by peroxidase-dependent oxidation of quercetin on browning of onion scales. Plant Cell Physiology, 41,1021-1029. 

GIANINAZZI-PEARSON V. and GIANINAZZI S. 1978. Enzymatic studies on the metabolism of vesicular-arbuscular mycor-rhiza. II. Soluble alkaline phosphatase specific to mycorrhizal infection in onion roots. Physiology and Plant Pathology, 1 , 45-53. 

---