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Much of the medicinal activity induced by vegetable Alliums is derived from a suite of organosulfur compounds formed following hydrolysis of the S-alk(en)yl-l-cysteine sulfoxides (ACSOs). One of these medicinal activities is the inhibition of blood platelet aggregation; a factor that may influence cardiovascular health. Concentrations of ACSOs in the onion bulb ebb-and-fl ow during the vegetative phase, suggesting they act as storage forms of sulfur. To examine whether medicinal efficacy paralleled these changes, I tracked bulb, leaf, and inflorescence-induced antiplatelet activity during reproductive growth of four onion genotypes. Levels of bulb-induced antiplatelet activity dropped sharply for the first 8 weeks following the end of vernalization. Leaf-induced antiplatelet activity also dropped rapidly for the first 4 weeks, but rose precipitously by week 6. The rapid loss in leaf-induced antiplatelet efficacy between week 6 and week 8 suggests a recycling of these organosulfur compounds from the leaves to the developing flower stalk and inflorescence, which would be needed for protection against insect pests. Overall, I found a dramatic decrease in bulb-induced antiplatelet activity concomitant with an initially similar decrease and subsequent increase in leaf-induced antiplatelet activity. These were complemented by the presence of high levels of antiplatelet activity induced by the inflorescence. These data indicate development mediates the medicinal activity induced by onion plants. Furthermore, the flux of antiplatelet activity induced by various plant organs suggests that this medicinal trait is serendipitously associated with the storage and cycling of sulfur in onion plants; perhaps in response to insect predation.
Wisconsin Fast Plants are rapid-cycling versions of various Brassica species amenable to a variety of genetic studies due to their short life cycle and ease of handling. I have recently developed a model system using Brassica rapa L. Fast Plants for teaching the cyclical selection process known as recurrent selection in the context of a course on plant breeding. The system allows for up to three cycles of recurrent selection during a 15-week semester and enables students to gain experience in planting, selection, pollination, and seed harvest during each cycle. Fourteen cycles of replicated, recurrent mass selection for high (H) and low (L) levels of anthocyanin pigment expression in hypocotyl tissue were practiced by students in Horticulture 502 during a period of four semesters. In addition to bi-directional selection; replicated unselected (D) control populations were maintained forcomparative purposes. Over 14 cycles, highly significant gains and losses in hypocotyl pigment production were realized for H and L populations, respectively. Plants in D populations showed no directional response to random selection and therefore did not exhibit genetic drift. Plants in H populations exhibited production of anthocyanin pigment in organs other than hypocotyls, suggesting selection goals could be modified to include pigmentation of specific organs or whole plants. Results from this selection program suggest significant gains from recurrent selection can be visualized through student-based selection activities in the classroom.
The use of cylindrically shaped red beet cultivars for production of processing beets has increased in recent years. Yield and shape of globe-shaped red beet cultivars are determined in part by population density and within-row spacing; thus, it is thought cylindrical cultivars are similarly affected by these factors. The objective of this investigation was to evaluate the effects of population density on shape and size of cylindrical red beet cultivars. Two F1 hybrids and two open-pollinated cultivars were planted in replicated trials consisting of three population densities during 1993 and 1994. Ten traits were measured on a randomly selected sample of beets from each plot. Averaged over genotypes, significant differences among densities were found for percent harvestable beets per plot, length × width, harvest weight, length, and mid-width. Average over genotypes, greater harvest weight, higher percentage of harvestable beets, and greater length, mid-width, and length × width values were found at low density. Average over densities, open-pollinated cultivars exhibited a greater degree of straightness along with lower yield, harvest weight, and percent harvestable beets than their hybrid counterparts. These data demonstrate population density has a differential effect on shape and size of cylindrical beet genotypes.
Pigments in orange carrot tissue, such alpha and beta carotene, are important vitamins in the human diet. Previously identified white or nonpigmented carrot roots, such as those from wild carrot and white derivatives of yellow or orange types, are dominant to the production of pigment, which is recessive. A nonpigmented carrot root was discovered during routine propagation of the inbred line W266 in 1992. Subsequent segregation analysis in the F2 and BC1 generations in three genetic backgrounds demonstrated the lack of pigmentation is due to a single recessive gene (reduced-pigment: rp). Total carotenoid content was reduced 92% in the roots of rprp genotypes compared to RPRP genotypes, however there were no differences in carotenoid content in leaves. Plants carrying rprp also exhibit white-speckled leaves during early stages of development, suggesting rp has an effect on leaf chlorophyll content. This character may prove useful in dissecting the complex inheritance of carotenoids in carrot.
Carrots contribute ≈14% of the total Vitamin A to the human diet in the United States due to the presence of the provitamin A carotenoids α- and β-carotene. We have described a recessive gene (rp) that inhibits carotenoid biosynthesis in carrot by 93%, resulting in whitish-yellow roots. The rp mutation is also associated with relatively high levels of a tocopherol (Vitamin E, 0.61±0.15 mg α-tocopherol/100 g FW). Vitamin E is a powerful antioxidant that must be obtained from the diet. The biosynthesis of a tocopherol in carrot has not been studied in any detail; however, the rp gene may provide clues as to its mechanism. The production of carotenoids and tocopherols is biosynthetically linked by their common precursor, geranylgeranyl diphosphate (GGDP). GGDP is converted into phytoene by phytoene desaturase to produce carotenoids and combined with homogentisic acid to produce tocopherols. Carotenoid and tocopherol profiles for various carrot genotypes are presented alongside a model describing the potential relationship between root carotenoids and tocopherols in carrot. The presence of significant amounts of tocopherols in carrot could significantly raise the nutritional profile of this vegetable.
Few genes have been identified in red beet. A spontaneously occurring dwarf mutant was identified in the late 1970s and again in 1994 in several breeding populations. Mutant plants are characterized by extreme dwarfing of both root and shoot. Young leaves are narrow, thin and strap-like while older leaves are thicker and deeply veined. The shoot axis forms a compressed rosette. Neither the shoot axis nor the root axis of field-grown plants exceeds 3 cm in height. Genetic analysis of F2 and backcross populations revealed the dwarf phenotype is conditioned by a single recessive gene. Several experiments were conducted to determine if the dwarf phenotype was due to a lack of gibberellic acid (GA) production. Exogenous application of GA3 at concentrations ranging from 1 to 1000 ppm on dwarf plants a) following seeding and b) during reproductive growth revealed a linear increase in plant height. Control dwarf plants receiving a water-only treatment were 18% as tall as plants receiving regular application of 1000 ppm GA3. A wild-type phenotype during reproductive growth was recoverable following regular GA3 application.