Brassica vegetables are common components of the diet and have beneficial as well as potentially adverse health effects. Following enzymatic breakdown, some glucosinolates in brassica vegetables produce sulforaphane, phenethyl, and indolylic isothiocyanates that possess anticarcinogenic activity. In contrast, progoitrin and indolylic glucosinolates degrade to goitrin and thiocyanate, respectively, and may decrease thyroid hormone production. Radioiodine uptake to the thyroid is inhibited by 194 lmol of goitrin, but not by 77 lmol of goitrin. Collards, Brussels sprouts, and some Russian kale (Brassica napus) contain sufficient goitrin to potentially decrease iodine uptake by the thyroid. However, turnip tops, commercial broccoli, broccoli rabe, and kale belonging to Brassica oleracae contain less than 10 lmol of goitrin per 100-g serving and can be considered of minimal risk. Using sulforaphane plasma levels following glucoraphanin ingestion as a surrogate for thiocyanate plasma concentrations after indole glucosinolate ingestion, the maximum thiocyanate contribution from indole glucosinolate degradation is estimated to be 10 lM, which is significantly lower than background plasma thiocyanate concentrations (40-69 lM). Thiocyanate generated from consumption of indole glucosinolate can be assumed to have minimal adverse risks for thyroid health.
The pigments of Opuntia ficus-indica fruits, which are derived from the betalain rather than anthocyanin pathway, have an extraordinary range in colour from lime green, orange, red to purple. This is a result from varying concentrations and proportions of about half a dozen betaxanthins and betacyanins. The yellow-orange betaxanthins are derived from spontaneous condensation of betalamic acid with amines or amino acids. The reddish-purple betacyanins are enzymatically formed from betalamic acid and cyclo-dihydroxyphenylalanine (DOPA) yielding betanidin and further glycosylated on either of the two hydroxyls of the cyclo-DOPA moiety. In the present work, degenerated primers were used to obtain partial genomic sequences of two major genes in the biosynthetic pathway for betalains, that is the 4,5-extradiol dioxygenase which forms the betalamic acid responsible for the yellow colour and a putative 5-Oglucosyltransferase which glycosylates betanidin in Dorotheanthus bellidiformis and may be responsible for the red colour. Differences in the genomic DNA between coloured versus non-coloured varieties were not found. Regulatory mechanisms seem to independently control pigmentation of O. ficus-indica fruit tissues for inner core, peel and epidermis. Core pigmentation occurs first and well before fruit maturity and peel pigmentation. Peel pigmentation is fully developed at maturity, presumably related to maximum soluble solids. Epidermal pigmentation appears to be independent of core and peel pigmentation, perhaps because of light stimulation. Similar control mechanisms exist through transcription factors for the major enzyme regulating anthocyanin production in grapes.
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Perhaps the most economically important disease of Opuntia ficus indica fruit cacti in Mexicois the “engrosamiento de cladodios” or macho disease. The symptoms of this disease, whichhas been suggested to be caused by a phytoplasma, are severe stunting of cladodes, flowersand fruits. In the mid-1980s this disease appeared in commercial cactus fruit orchards ofD’Arrigo Bros near Gonzalez, California. It was performed more than 30 PCR-based tests forviruses as well as various extraction methods and polymerase chain reaction (PCR) tests forphytoplasmas but were unable to find any of the known viruses or mycoplasmas in thestrongly symptomatic cactus with this disease. As almost all plant viruses go through areplication phase involving double stranded RNA (dsRNA), a dsRNA extraction wasperformed and a dsRNA species of about 600 bp identified. Then, reverse-transcribed thedsRNA, amplified the resultant cDNA by PCR, and cloned and sequenced the 600 bpfragment that were identified in symptomatic tissue. When this sequence was compared totranslated DNA in the National Center for Biotechnology Information (NCBI) nucleotide database (BLAST analysis) it was most similar to the Tobacco bushy top virus (E score of 2e-39),which is a single stranded RNA virus with no DNA intermediate. Primers made from this 630bp fragment were used to extend this sequence to 2989 sequence. This sequence appears tobe a full-length sequence with three open reading frames (ORF) and is shorter than theclosest class of viruses, the Umbraviruses that can be spread by mechanical transmissionand by aphids. It was not possible to transmit the virus or symptoms mechanically. Over asix-year period using traditional PCR, this virus was found in hundreds of symptomatic cactibut not in non-symptomatic pads. RT-PCR has found low levels of this virus on nonsymptomaticcladodes (3.7 fg) on a symptomatic plant and much higher concentrations(1x102 to 1x105 fg) on symptomatic cladodes from the same plant. Black bean aphids (Aphis fabae), that are the vector for a closely related Umbravirus known as groundnut rosetta virus,have been routinely found on the unopened flowers of cactus. This Umbravirus was found inaphids feeding on symptomatic cladodes. As Umbraviruses cannot infect plants without acompanion Luteovirus, that provides the protein coat for the Umbravirus, degenerateLuteovirus primers were used and a probable incomplete Luteovirus-like 4797 bp sequencewas found on aphids feeding on symptomatic cactus. This Luteovirus was not found inOpuntia cladodes using PCR. A micro RNA assembly of six pooled symptomatic Opuntiasdid not find a contig that spanned the 4797 putative Luteovirus sequence, but somefragments as large as 44 bp were exact matches to the Luteovirus. As Umbraviruses occurthroughout the plant but Luteoviruses only occur in the phloem, lower Luteovirusconcentrations would be expected. Two successive one hour 60°C heat treatmentseliminated these symptoms on new growth that was also PCR negative. A 5839 bpPotexvirus was found in some of these cladodes but its presence was not correlated with anysymptoms. Similar symptomatic cacti in Italy, South Africa and Mexico should be examinedwith these primers and dsRNA to see if similar correlations between presence/absence of thisfragment and symptomatic plants can be obtained. It is suggested that this disease be knownas OSD (Opuntia Stunting Disease).
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