Common onion

Onion oil is obtained by steam distillation of the crushed bulbs of the common onion. Allium cepa L. It is an amber-yellow to amber liquid with a strongly pungent, lasting, characteristic onion odor. 

Test organism Hordeum vulgare (barley), Latuca sativa (lettuce), Pancurn miliaceum (millet seeds), Lycopersicon esculentum (tomato), Cucumis sativus (cucumber), Glycine max (soybean), Brassica oleracea (cabbage), Avena sativa (oat), Lolium perenne (perennial ryegrass), Allium cepa (common onion), Daucus carota (carrot), Zea mays (corn). 

FIGURE L Chromosome complements in root tips A) the horse bean, Vida faba B) the tree onion, Allium proliferum (C) the common onion, Allium cepa. Acetic alcohol, Feulgen squash. 

Roots grown from bulbs of the common onion, A, cepa In = 16), are a classical material for chromosome studies and were introduced by Levan (1949) for standardized tests of the effects of chemicals on chromosomes and cell division. The chromosome complement of A. cepa is shown in Fig. 1C. The eight pairs of chromosomes do not vary much in size and many of them are divided by the centromere into arms of nearly equal length. Consequently, many of the chromosome pairs are not easy to distinguish from each other. The greatest difference between the length of the arms is found in the satellite-bearing chromosome. The satellite iself is very small and often difficult to detect (e.g.. Fig. 1C). 

The onion, like the other related vegetables (Allium genus), has long been classified as a member of the Lily family (Liliaceae), but now some botanists place the onion and its close relatives in a new family called the Alliaceae. The common onion is classified as the variety cepa to distinguish it from other varieties of onions such as the shallot, which is the aggregatum variety. Fig. 0-23 shows typical onion bulbs. 

Dimethyl sulfoxide occurs widely at levels of <3 ppm. It has been isolated from spearmint oil, com, barley, malt, alfalfa, beets, cabbage, cucumbers, oats, onion, Swiss chard, tomatoes, raspberries, beer, coffee, milk, and tea (5). It is a common constituent of natural waters, and it occurs in seawater in the 2one of light penetration where it may represent a product of algal metaboHsm (6). Its occurrence in rainwater may result from oxidation of atmospheric dimethyl sulfide, which occurs as part of the natural transfer of sulfur of biological origin (7,8). 

Chemical Designations - Synonyms No common synonyms Chemical Formula (CH3)jS04. Observable Characteristics - Physical State (as normally shipped) Liquid Color. Colorless Odor. No characteristic odor slight, not distinctive weak onion. 

The Fourier Trairsform Infrared (FTIR) spectrum obtained from non-adapted tomato cell walls is very similar to that from the onion parenchyma cell wall (both contain cellulose, xyloglucan and pectin) although there is more protein in the tomato walls (amide stretches at 1550 and 1650 cm-i) (Fig 4). In DCB-adapted tomato cell walls, the spectrum more closely resembles that of either purified pectins or of a commercial polygalacturonic acid sample from Sigma with peaks in common at 1140, 1095, 1070, 1015 and 950 cm-t in the carbohydrate region of the spectrum as well as the free acid stretches at 1600 and 1414 cm-i and an ester peak at 1725 cm-k An ester band at 1740 cm-i is evident in both onion parenchyma and non-adapted tomato cell wall samples. It is possible that this shift in the ester peak simply reflects the different local molecular environment of this bond, but it is also possible that a different ester is made in the DCB-adapted cell walls, as phenolic esters absorb around 1720 cm-i whilst carboxylic esters absorb at 1740 cm-k The... 

Another very common phytochemical isolated was phytol (3,7,11, 15-tetramethyl-2-hexadecen-l-ol), the diterpenoid alcohol which forms the "tail" of chlorophyll. This compound is nearly insoluble in water, but when applied as a 0.1 mM (0.003 wt. %) solution in 0.1% DMS0 it increased onion germination while decreasing germination in sorghum, wheat, and carrot. The germination effects are significant at only the 95% level, but pretreatment studies are planned as part of other terpene chemistry studies at SRRC and LSI). 

The effect of applied plant residues can be positively influenced by an increase of temperature. Mallek et al. (2007) established that dried and milled crop residues of onion (Allium cepa L.) or garlic (A. sativum L.) were able to reduce seed germination of barnyard grass (E. crus-galli (L.) R Beauv.), common purslane (Portulaca oleracea L.), london rocket (Sisymbrium irio L.) during their decomposition in soil, but only at the elevated (39°C) soil temperature. It can support combination of methods for weed control, in this case allelopathy with soil heating treatments (e.g., solarization). 

Symptoms Yellow patches on upper leaf surfaces, with corresponding patches of mold beneath in damp weather. Large areas of a leaf may be infected and the leaf may die. Onions rot in store. Most common in damp and humid growing situations. 

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