PLANT CELLS produce far more chemical compounds than are necessary for their basic functions. Basic or primary metabolism refers to all biochemical processes that result in assimilation, respiration, transport, and differentiation.
By and large, primary metabolism is shared by all cells, while secondary metabolism generate diverse and seemingly less essential or non-essential byproducts called secondary products. The secondary products give plants the colours, flavours and smells. These products are sources of fine chemicals, such as drugs, insecticides, dyes, flavours and fragrances, and the phytomedicines found in medicinal plants. Plant pigments, alkaloids, isoprenoids, terpenes, and waxes are some examples of secondary products.
The role of many of the secondary products has been difficult to pinpoint, and initially they were thought to be just waste materials. However, considering their non-motile nature, plants had to develop their own defense system against pathogens and predators, and systems to lure motile creatures for fertilisation and dissemination.
Indeed, many of the secondary products are bacteriocidal, repellent (by bad tastes, and so on), or even poisonous to pests and herbivores. Pigments of flowers give attractive colours for insects that help with fertilisation, or warning colours against predators. Plant pigments also provide protection against environmental harms, such as free radicals and UV irradiation.
One group of these secondary metabolites are the flavonoids. Flavonoids are products of plant metabolism and have different phenolic (benzene-type ring) structures. They are effective antioxidants because of their free radical scavenging properties and because they are chelators of metal ions thus, they may protect tissues against free oxygen radicals and fat oxidation.
Flavonoids, which are found in a variety of fruits and vegetables as well as in tea and red wine, are thought to boost health in part by combating oxidation, a process in which cell-damaging substances called free radicals accumulate. Because of differences in their chemical structure, bioavailability, distribution, and metabolism, different flavonoid compounds may have different effects on human health.
Free oxygen radicals appear to be involved in several pathologic conditions such as:
- development of hardening of the arteries
- different stages of cancer development
- autoimmune destruction of cells in the pancreas leading to diabetes
- mediators of inflammatory damage in asthma and in joints in rheumatoid arthritis
- process leading to cataracts
A study of more than 10,000 people found that those consuming fruits and vegetables rich in different flavonoids, had a reduced risk of overall mortality and of several chronic diseases. Participants filled out a questionnaire and completed an interview to find out what they had eaten during the previous year. Based on average flavonoid contents of foods available in the study area, the researchers estimated each person's flavonoid intake. The researchers tracked the development of disease in the participants for up to 28 years after the initial interview.
The results of this study suggest the presence of a protective association between flavonoid intake and subsequent occurrence of heart disease, stroke, lung and prostate cancer, type 2 diabetes, and asthma. For instance, greater consumption of apples, a main source of quercetin in the study area, and onions, which contain a flavonoid called kaempferol, were both linked to a reduced risk of dying from heart disease. Myricetin, hesperitin, and naringenin were also found to be useful. A lifestyle associated with a high intake of foodstuffs rich in flavonoids appears to reduce the risk of chronic diseases.
Source: <http://www.natural-supplements.org/>
Dr. Sylvia Mitchell, research fellow (Graduate School), Biotechnology Centre, University of the West Indies, Mona, email:smitchel@uwimona.edu.jm
