NEWS FROM
PHYSIOLOGIA PLANTARUM
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Published monthly on behalf of SPPS by Wiley-Blackwell.
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DNA methylation is a marker of flowering
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Induction of flowering in azalea (Rhododendron spp.) is associated with changes in DNA methylation levels and these epigenetic alterations seem to be markers of floral bud development. This was shown by Maria Jesus Canal from Universidad de Oviedo in Spain in an experiment where manipulations of photoperiod and temperature were used to promote flowering. Within days after the shift from long days to short days there was a substantial decrease in overall DNA methylation, eventually amounting to almost 50%. Subsequently, however, methylation increased sharply and climbed to a level approximately 25% above the initial value. This pattern of fluctuations in the DNA methylation level followed floral development and was consistent between different cultivars and plants grown under various flower induction conditions. The authors suggest that measurements of DNA methylation can be used as a marker of flower development in commercial production of azalea and probably also other ornamentals.
Read full article here: Meijon et al (September 2011) Physiologia Plantarum 143: 82
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NEWS IN BRIEF
FROM OTHER JOURNALS
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Two hormones control the Venus flytrap
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Source: Escalante-Péreza et al (13 September 2011) PNAS 108: 15492
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Orchids adapt to bees - not vice versa
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Source: Ramirez et al (23 September 2011) Science 333: 1742
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Organic food: Is it really good for you?
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Consumers love organic food, but is it really good for you? From www.onlinedegree.net
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With an estimated global market of $57 billion and a market share of approximately 4%, organic food is highly valued among consumers worldwide. Even facing a financial crisis and a price premium of 10-40%, consumption of organic food show an annual growth of 8%, which is about the double of conventionally produced food. The figures vary considerably between products and countries - e.g. the organic share of fruits and vegetables are almost an order of magnitude higher than on meats, and the same relative difference holds true between individual EU member states - but the general picture is clear: organic is hot!
The consumers' passion for organic food is reflected in a Belgian survey of consumer perception from 2009. It demonstrated that the vast majority of consumers believe that organic food is healthier, more nutritious and contains less harmful microbes and mycotoxins than conventional food - and this overall trend is independent of education, age, gender or how much organic food the responder actually bought.
Public perception of organic food
From Hoefkens et al. (2009) British Food Journal 111: 1062 | Organic vs. conventional | Agree | Disagree | Neutral | | Healthier | 84% | 7% | 9% | | More nutrients | 62% | 20% | 8% | | Less harmful microbes and mycotoxins | 53% | 20% | 27% |
Paradoxically, however, this unanimous praise of organic food is not based on scientific knowledge. Only limited research has been carried out in this area, but the results seem to indicate that while organically grown crops contain more secondary metabolites, they might not always be to the benefit of consumers.
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Many plants - like cannabis - are well known and highly valued for their content of secondary metabolites. From golem13.fr
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Unlike primary metabolites - e.g. amino acids and most carbohydrates and lipids - that are essential to life, plants contain huge amounts of secondary metabolites. As the name implies, they serve to meet the plant's secondary requirements and empower it to survive competition, provide defence and facilitate reproduction. Without them, the plant is not immediately threatened but in the long term it will eventually fare worse. At least 100,000 different secondary metabolites from plants have been identified to date and far more are believed to exist.
Ranging from disease preventing antioxidants like flavonoids over powerful narcotics like cocaine to lethal toxins like ricin from castor bean, the secondary metabolites come in many flavors - both good and bad. Their natural purpose can be to serve as chemical warfare against insects and other herbivores, as colorful shields that protect from sunlight or as irresistible scents that attract pollinators. In many cases they are extremely specialized in their action, and e.g. the powerful heart drug digitoxin from foxglove (Digitalis) is a highly specific sodium-potassium ATPase inhibitor.
Examples of plant secondary metabolites
From www.biologyreference.com | Class | Example | General effect | Typical uses | | Alkaloids | Nicotine (coffee beans); atropin (deadly nightshade) | Interfere with neurotransmission | Stimulants; drugs | | Glucosinolates | Sinigrin (cabbage) | Enzyme inhibitors etc. | Aromatics; potential cancer therapy | | Terpenoids | Menthol (mint); β-carotene (carrot) | Block ion transport; antioxidants | Local anestehtics; disease prevention | | Phenolics | Anthocyanin (tomato); urushiol (poison ivy) | Antioxidants; allergens | Disease prevention; allergic dermatitis |
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Organic crops produce more secondary metabolites to cope with biotic and abiotic stress. From www.ourbreathingplanet.com
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Since many of the secondary metabolites are defense related chemicals induced by biotic and abiotic stress, their concentration in the plants depends on growing conditions. This has led several scientists to look for chemical differences between crops grown under conventional and organic regimes. The two crop management systems differ in terms of the fertilisers and plant protection methods used, and, generally speaking, the better the plant is taken care of, the less secondary metabolites it needs for its own protection. In a recent review, a meta-analysis of published comparisons suggests that organically grown crops have a 12% higher content of secondary metabolites. Most of the difference stems from a higher content of defence related chemicals (amounting to 16%), while antioxidants like carotenoids and vitamin C only amount to a 6% increase.
It is, however, difficult to translate these chemical differences into health effects, since the secondary metabolites can have both beneficial and harmful effects. A few studies have compared the health effects of organic vs. conventional feed in laboratory animals. Though it is difficult to draw conclusions from the experiments, since they are not systematic and only look to short term effects, there seems to be some indication that organic feed activates the immune system and improves reproductive ability. One difference that seems to be consistently found in most analysis, however, is a lower protein content in organic food, and this can obviously have a negative nutritional effect.
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The house sparrow (Passer domesticus) prefers conventional wheat over organic. From www.fotolibra.com
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The lower protein content in organic vs. conventional crops is believed to be the reason why a recent experiment found that birds prefer conventional wheat over its organic counterpart. Both wild garden birds and captive birds consumed more conventional than organic wheat when given free choice, but interestingly it took them about one week to distinguish between the two food types. The authors proposed that the birds need some time to 'learn' which is the better food, and this time lag might also explain why other studies have shown contradictory results.
The authors also tested for the presence of the mycotoxin DON in the two kinds of wheat. DON is a potent toxin produced by Fusarium spp. fungi, and it is known that both birds and mammals try to avoid food containing the mycotoxin. In this experiment, DON content varied considerably between samples (sometimes there was more mycotoxin in conventional than organic wheat and sometimes vice versa) and it did not correlate with consumption.
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Fusarium spp. infects cereals and produce mycotoxins that can render the crop toxic. Photo by Jafar Razzaghian, from www.bioforsk.no
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It has been suggested that since fungicides are not used in organic farming, the organic crops might be more heavily infested with mycotoxin producing fungi and this has prompted several researchers to look for the presence of mycotoxins in crops grown under conventional and organic management. A Korean study from 2011 showed that among 5 mycotoxins only one, nivalenol, was present at significantly higher concentrations in organic vs. conventional rice. A similar Polish study from 2009 on wheat showed that the mycotoxins DON and T-2 was consistently present in 13 organically grown cultivars albeit in low concentrations, while the same cultivars grown by conventional means contained high levels of one of the mycotoxins in 4 of the cultivars and none or very little in the rest.
To sum up, it is assumed that organically grown crops contain higher concentrations of plant secondary metabolites that might be both more beneficial and harmful, but at the present time it can not be concluded what net effect this can have on human health. It should be kept in mind, however, that organic crops contain fewer residual amounts of pesticides and that they at least in this respect can be said to be more healthy than conventional crops.
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