Phytoremediation and biofortification potential of Cannabis sativa L.
Date
2019
Authors
Stonehouse, Gavin C., author
Pilon-Smits, Elizabeth, advisor
Pilon, Marinus, committee member
Ippolito, Jim, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Selenium (Se) is a micronutrient, but toxic at high levels. Both Se deficiency and toxicity are problems worldwide. I studied the potential of hemp (Cannabis sativa L.) for Se environmental cleanup (phytoremediation) and for accumulating elevated levels of this healthy micronutrient (Se biofortification). Hemp properties attractive for phytoremediation are fast growth, high biomass, hardiness and economic value. Furthermore, hemp produces highly nutritious seeds, of interest for Se biofortification. The first Chapter of this thesis reviews Cannabis sativa's history, biological attributes and applications, as well as the technologies of phytoremediation and biofortification, and plant Se metabolism. The second Chapter presents experimental data on two hemp studies. The first was a field survey of Se accumulation in hemp grown across Colorado, and in commercial hemp products. The second study involved controlled greenhouse experiments to study hemp Se tolerance, accumulation and metabolism. Hemp field surveys in four naturally seleniferous (Se-rich) agricultural areas in Colorado, U.S.A. found 15-25 µg Se/g in seed (intact or dehulled) and 5-10 µg Se/g dry weight in flowers and leaves. Hemp beer contained 42 µg Se/L. Considering the U. S. recommended daily allowance (RDA) of 55-75 ug Se, one bottle of hemp beer provides 25%, and 4 gram hemp seed (a half tablespoon) provides 100% of the RDA. In controlled greenhouse experiments, hemp was further characterized for Se tolerance, accumulation and Se speciation. Effects of Se on photosynthesis and cannabinoid and terpenoid levels were also analyzed. At the seedling level, hemp showed high selenate tolerance (up to 160 µM) and accumulation (up to 1,400 mg Se/kg shoot dry weight). Mature hemp was completely tolerant up to 40 µM selenate and accumulated up to 200 mg Se/kg DW in leaves, flowers and seeds. Seeds were found to contain free (water-extractable) selenomethionine and methyl-selenocysteine, superior forms for Se biofortification, reported to have anticarcinogenic properties for consumers. Hemp production of medicinal cannabidiol (CBD) and terpenoids was not affected by Se. Selenium enhanced potassium levels in seeds, and thus their nutritional value; other nutrient levels were unaffected. It can be concluded from these studies that hemp shows promise for Se phytoremediation and can produce Se-biofortified dietary products; Se does not affect levels of valuable secondary plant compounds, nor does it negatively affect nutritional quality of seeds. These findings are of significance in view of the widespread and rapidly expanding cultivation of hemp in seleniferous areas across the U.S.A. and Canada.