Vegetable Breeding and Genetics
Laboratory of I.L. Goldman
Health
Horticulture and human health have been linked for thousands of years. A wealth of folkloric information on the connection between plants and health has been handed down from generation to generation, dictating at least in part the kinds of plants produced and consumed worldwide. In recent years, medical scientists have made great strides toward the development of synthetic pharmaceuticals to treat human disease. These mono-molecular drugs have brought with them a new era in the eradication of disease and the promotion of human health. Nevertheless, at the same time, with the adoption of such drugs, human cultures have relied less on therapies derived primarily from the plants they cultivate, and in particular from food crops.
The goal of work in our laboratory is to study secondary compounds from vegetable crops that may be associated with human health. We are most interested in how genes and horticultural environments interact to produce phenotypes that may be associated with human health. Most of our work has focused on organosulfur compounds from onion, carotenoids from carrot, and betalain pigments and folic acid from table beet.
Medicinal Phytochemicals from Onion
Spiraling interest in oofunctional foodso and their derivative ophytopharmaceuticalso has encouraged collaboration between medical and agricultural scientists to investigate crop plant-based compounds with potential health benefits. These efforts have been fueled by an emerging market for novel agricultural products: medicinally-enhanced crops, designed and bred to contain higher levels of health-promoting compounds. Value-added plant products designed to deliver health benefits to the consumer should generate alternative marketing strategies for agricultural commodities and may provide expanded market opportunities and additional income to farmers and food processors. Our laboratory is among a handful of horticulturally-based research groups in the United States investigating vegetable plant-based phytochemicals with medicinal significance. This area has become a focal point for the Goldman laboratory during the past 10 years, and Dr. Goldman has written several review publications on this subject for a variety of audiences.
Our lab has been investigating horticulturally-based questions surrounding the biological nature of onion-induced antiplatelet activity. For thousands of years, humans have recognized that native compounds in onion plants promote blood circulation, however it was only recently that the mechanism of this enhancement was determined to be the inhibition of platelet aggregation. Platelet aggregation is a major cause of thromboembolic events leading to cardiovascular disease, the leading cause of death in the United States. Dietary intake of onion may thereby decrease cardiovascular risk. Dr. Goldman has teamed up with Dr. B.S. Schwartz, a hematologist from the Department of Medicine, who offered expertise with human platelets and has enabled Goldmanos research group to pursue successful inquiry into this interdisciplinary field. He has also formed an alliance with Dr. John Folts in the Department of Medicine (Cardiology) who has provided expertise with an in vivo coronary thrombosis model. Completing the team are Dr. Kirk Parkin, a food chemist in the Department of Food Science and Dr. Michael Havey, a geneticist from the Department of Horticulture. Together, these scientists obtained a USDA-NRI grant to work collaboratively on various aspects of onion-induced antiplatelet activity.
We have demonstrated substantial variability for antiplatelet strength among Allium species accessions and among cultivated germplasm sources. They have shown the antiplatelet factor is sulfur-dependent and therefore correlated with certain environmental conditions, a finding that was consistent with the biochemistry of the well-characterized sulfur assimilation pathway in onion, through which sulfate is converted into g-glutamyl peptides and ultimately to S-(alk)-en-yl cysteine sulfoxides (ACSOs). Thiosulfinates and other organosulfur compounds with antiplatelet activity are derived from hydrolysis of these ACSOs by the enzyme alliinase. Dr. Goldman and his students also demonstrated that onion-induced antiplatelet activity is likely a serendipitous by-product of a developmentally-regulated flux of organosulfur compounds for control of insect pests. Because organosulfur compounds are thought to be a primary deterrent to insect predators, these compounds cycle through onion plants from old leaf scales to new in protecting the developing bulb and then are shunted to the developing leaves and ultimately to flowers for protection during pollination. This finding demonstrates this unique medicinal character fluctuates dramatically with plant development and is associated likely with a natural flux in defense compounds. Additional research in this area has focused on (1) investigation of the genetic control of onion-induced antiplatelet activity through quantitative trait locus mapping approaches using cloned regulatory genes in the sulfur assimilation pathway as DNA probes; (2) evaluation of the effects of sulfur fertility on onion-induced antiplatelet activity; (3) temporal aspects of thiosulfinate formation and medicinal activity in onion extracts; (4) comparative induction of antiplatelet activity of various Allium thiosulfinates; relationship of onion organosulfur compounds and resistance to onion white rot; and (6) in vivo canine testing of onion extracts and Allium thiosulfinates in a coronary thrombosis model. These studies have suggested that onion extracts, particularly those that are not processed with heat, have significant potential to inhibit in vivo antiplatelet activity. Further research is required to determine if this effect can be obtained from dietary onion intake in humans.
Carotenoids and Tocopherols from Carrot
Carrot roots contain high levels of b-carotene and have long been a significant source (perhaps as much as 20%) of provitamin A in the human diet. Vitamin A may offer significant potential to inhibit carcinogenesis and improve cardiovascular health. Little investigation of carotenoid biosynthesis has been conducted with carrot, in part because of its limitations as an experimental organism. All previous studies on the genetic control of b-carotene synthesis in carrot root tissue have indicated the presence of pigment (i.e. orange roots) is recessive to white or non-pigmented roots. However, Dr. Goldman recently identified and characterized a new recessive gene that causes a 93% reduction in carotenoid content suggesting a new interpretation of carotenoid biosynthesis in carrot roots. This gene, designated rp, likely causes a lesion in the carotenoid biosynthetic pathway and may provide new clues as to the details of this important process in carrot. Recent chromatographic analysis indicates the presence of novel carotenoids in rprp roots that are not present in RPRP roots. Further investigation of these carotenoids and related questions surrounding the carotenoid biosynthetic pathway in carrot are continuing in Dr. Goldmanos laboratory. Through analysis of this mutant, we have determined that carrots produce tocopherols, particularly alpha tocopherol or provitamin E. This has led to projects designed to screen carrot germplasm for both provitamins A and E and to a breeding program focusing on increasing both compounds in carrot. We have also developed a protocol for screening carrot tissue for both compounds simultaneously via HPLC.
Folic Acid from Table Beet
Recommended Daily Allowances (RDA) for folic acid, a B-vitamin responsible for the production of red blood cells and development of fetal neural tubes, has increased substantially in the past two years due to the recognition of widespread damage to fetal brain tissues as a result of deficiencies of this nutrient. In addition, recent epidemiological investigation has shown that folic acid lowers blood homocysteine levels and may be a significant cardiopreventative agent. Despite changes in RDA, variation in native plant folic acid concentration complicates dietary recommendations. Plants from the family Chenopodiaceae such as red beet are among the best vegetable sources of folic acid. Work in Dr. Goldmanos laboratory has focused on developing an understanding of the magnitude of genetic variability and the mechanism of genetic control of folic acid content in red beet germplasm. In a series of journal publications, he and his students have successfully characterized variability for folic acid content in a range of red beet germplasm sources, shown that transgressive segregation is important for folic acid content in wide crosses, and demonstrated developmental patterns of folic acid accumulation in root and shoot tissues.