The Pharmaceutical Journal
Vol 277 No 7425 p556
4 November 2006

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A global warming agent that has been overlooked more
The fascinating case of the cunning cuscuta more
A matter of definition: can greenhouse gases be called poluutants? more
Politics in practice more

A global warming agent that has been overlooked

Whenever we talk of greenhouse gases and global warming we tend to think of carbon dioxide, which is generated on a vast scale by humans as they pursue their interests without regard to the repercussions they may have on the universe. Carbon dioxide, as we know, is in its turn absorbed into plant structures and recycled.

But we have taken relatively little account of another important gaseous factor, methane. We tend to think of it as something that grazing animals generate and emit as they go about their own activities. However, scientists have found that trees and other plants, apart from absorbing and metabolising carbon dioxide, also give off large quantities of methane.

The quantity of methane produced by plants is not easy to estimate. Criticism has arisen of the way in which small scale laboratory findings have been scaled up to produce an estimate of the total global quantity of methane produced by plants. But, for one thing, we should not assume that all plant matter behaves in the same way.

Research carried out in Australia last year shows that it is important to differentiate between plants that are situated in light places and those that grow in darker environments. Structures such as those in wood or in roots react differently from those exposed to sunlight.

To estimate effects on the global scale is speculative. Satellite measurement of methane has been used to calculate plant emissions and relate them to a global methane budget of 400 to 600 million tonnes of emissions a year across the planet. It has been suggested that plant emissions account for no more than 125 million tonnes annually, compared with a previous estimate of 1345 million tonnes a year.

Further research should reduce the uncertainties surrounding the earth’s methane budget. However, it would be wrong to underestimate the benefits derived from tree planting to offset global warming. The benefits could outweigh by some hundred times any disadvantage arising from methane emissions.

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The fascinating case of the cunning cuscuta

The dodder (Cuscuta spp) has long fascinated botanists. In 1694, John Pechey commented in ‘The Compleat Herbal of Physical Plants’, “This fawning parasite and ungrateful Guest hugs the Herb it hangs upon, with its long Threads and reddish Twigs; and so closely embraces it, that at length it defrauds the hospitable Herb of its Nourishment, and destroys it by its treacherous Embraces.”

Indeed, our own native species is parasitic on thyme, heath, milk vetch and particularly furze, which at times it may cover with its tangled masses of red threadlike stems — there has long been speculation over the method by which it picks on its host plant.

In the 29 September issue of Science a group of investigators from Pennsylvania State University describes how dodder uses chemical clues to find its host. It offers evidence that interaction between plants may be achieved through volatile compounds wafted through the air. Devoid of green foliage and barely able to carry out photosynthesis, cuscuta survives by attaching itself to stems and leaves of host plants and robbing them of their essential nutrients. Once its seeds have fallen into the soil and germinated, the plant uses no roots and is totally dependent on its host.

When seeds of Cuscuta pentagona were reared on an artificial medium on filter paper, their rootless and leafless stems invaded by preference a tomato plant in the vicinity and avoided wheat. It was found that wheat plants emit a volatile compound that repels dodder, whereas tomato and some other plants produce an attractant. Further discoveries may make it possible to use volatiles to control the onset of pests upon valuable crops.

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A matter of definition: can greenhouse gases be called poluutants?

A Clean Air Act was adopted recently by the US and has resulted in a host of arguments and excuses.

The Act in question defines a pollutant as “any substance or matter which is emitted into or otherwise enters into the ambient air. This is taken to include what are nowadays referred to as “greenhouse gases”, but the Environmental Protection Agency has argued that there is a distinction between a “pollutant” and an “air pollution agent” and that greenhouse gases do not fall into the latter category.

Attempts have been made to make it obligatory for greenhouse gas emissions by cars and lorries on the roads to be controlled, but the lawyers continued to argue over definitions.

Many states in the US have been frustrated by the inaction on the part of the president to make any move in the direction of arresting further climate change, and states and cities have tried to make their own contribution towards arresting the dangerous drift towards deterioration. Statements from the EPA have argued that greenhouse gases are not pollutants, but that carbon dioxide produced by human activities needs restricting. This seems rather confused — after all, carbon dioxide and methane are regular participants in normal life on earth, despite being stigmatised as greenhouse gases.

The truth is that an increase in industrial activity worldwide is bound to lead to global warming, and that vastly increased travel activities will inevitably add to the problem. But such is human greed and shortsightedness that no-one is prepared to take the first step to easing the strain on living things on the earth’s surface.

To pick on carbon dioxide as a forbidden product to the neglect of so many other factors in our existence strikes me as foolish, to say the least.

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Politics in practice

“The practical politician, as every connoisseur of ochlocracy knows, is not a man who seeks to inoculate the innumerable caravan of voters with new ideas; he is a man who seeks to search out and prick into energy the basic ideas that are already in them, and to turn the resultant effervescence of emotion to his own uses.” — Henry Louis Mencken (1880–1956), in a 97-page preface to 'The American credo: a contribution toward the interpretation of the national mind', by George Jean Nathan and H. L. Mencken (1920).

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