Abstract
Glucosinolates are anti-carcinogenic, anti-oxidative biochemical compounds that defend plants from insect and microbial attack. Glucosinolates are abundant in all cruciferous crops, including all vegetable and oilseed Brassica species. Here, we studied the expression of glucosinolate biosynthesis genes and determined glucosinolate contents in the edible organs of a total of 12 genotypes of Brassica oleracea: three genotypes each from cabbage, kale, kohlrabi and cauliflower subspecies. Among the 81 genes analyzed by RT-PCR, 19 are transcription factor-related, two different sets of 25 genes are involved in aliphatic and indolic biosynthesis pathways and the rest are breakdown-related. The expression of glucosinolate-related genes in the stems of kohlrabi was remarkably different compared to leaves of cabbage and kale and florets of cauliflower as only eight genes out of 81 were expressed in the stem tissues of kohlrabi. In the stem tissue of kohlrabi, only one aliphatic transcription factor-related gene, Bol036286 (MYB28) and one indolic transcription factor-related gene, Bol030761 (MYB51), were expressed. The results indicated the expression of all genes is not essential for glucosinolate biosynthesis. Using HPLC analysis, a total of 16 different types of glucosinolates were identified in four subspecies, nine of them were aliphatic, four of them were indolic and one was aromatic. Cauliflower florets measured the highest number of 14 glucosinolates. Among the aliphatic glucosinolates, only gluconapin was found in the florets of cauliflower. Glucoiberverin and glucobrassicanapin contents were the highest in the stems of kohlrabi. The indolic methoxyglucobrassicin and aromatic gluconasturtiin accounted for the highest content in the florets of cauliflower. A further detailed investigation and analyses is required to discern the precise roles of each of the genes for aliphatic and indolic glucosinolate biosynthesis in the edible organs.
Highlights
IntroductionGlucosinolates, β-thioglucoside-N-hydroxysulfates (cis-N-hydroximinosulfate esters), are sulfur-enriched, anionic secondary metabolites of plants synthesized from amino acids and sugars
Glucosinolates, β-thioglucoside-N-hydroxysulfates, are sulfur-enriched, anionic secondary metabolites of plants synthesized from amino acids and sugars
We explored the genes related to glucosinolate biosynthesis and studied their expression in the edible organs of B. oleracea cultivars
Summary
Glucosinolates, β-thioglucoside-N-hydroxysulfates (cis-N-hydroximinosulfate esters), are sulfur-enriched, anionic secondary metabolites of plants synthesized from amino acids and sugars. They are synthesized in all vegetables and oilseed plants of the order Brassicales [1]. Hydrolysis by the myrosinase enzyme degrades glucosinolates into different bioactive products, mostly isothiocyanates [5,6,7]. Isothiocyanates such as sulforaphane [8,9] and indole-3-carbinol [10] are strongly anti-carcinogenic, whereas phenethyl isothiocyanate inhibits the transformation of carcinogens from one form to another [11,12]. It is important to understand the genetics of biosynthesis and accumulation of health-promoting glucosinolates in order to increase their content for human and animal health and plant protection
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