【单选题】{{B}}Text 2{{/B}}
Researchers have long known that stressing plants can force them to take defensive action, often ramping up the production of protective chemicals that, for example, make them more resistant to insect attack. It has become common practice to stress such plants into increasing their yields. This is usually clone using physical stress elicitors (诱导子), including bits of the micro-organisms that normally attack the plants, or irritants made from metallic compounds such as copper chloride. These are effective, but they come at a cost. Most elicitors are toxic to plants and can build up in tissues, making it necessary to occasionally "clean" a plant of the chemicals so they keep having the same effect.
Recently, research groups at the University ofArizona in Tucson found that the application of an electric current to the hairy roots of the poisonous herb Hyoscyamus muticus stimulated the production of the herb’s toxin hyoscyamine (天仙子胺). This unpublished finding inspired Hans VanEtten, also of the University ofArizona, and his colleagues to test sub-lethal levels of electrical currents on other plants, to assess electricity’s potential to elevate chemical production.
The researchers exposed eight different plant species (ranging from Japanese pagoda tree seedlings to pea plants) to weak electrical currents of 30 milliamps. Seven of the plants increased their production o{ defensive chemicals. The average boost of chemical production was 20 times, they report inBiotechnology Progress. One plant, a type of alfalfa, increased its chemical yield by 168 times. These values are very similar to those achieved using chemical elicitors, and seem to have no lethal effects-just a negative effect on growth. The treatment can be used over and over again without the build-up of any unwanted material.
The useful compounds would be very easy to harvest: they simply pour out into solution if the plants are grown hydroponically. "The fact that we can use electricity instead of toxic materials to elicit chemical production is very exciting because it means we get to look at how these chemicals form without having to constantly add and remove toxins from the system," says VanEtten. "This is a really novel and creative approach that I’ve never seen before," says plant metabolic engineer Fabricio MedinaBolivar fromArkansas State University in Jonesboro. "The possibilities for using electricity with plants in this way are absolutely tremendous. "
B．It can be used time and again.
C．It can boost chemical production.
D．It has no adverse impacts on the growth of plants.
网考网参考答案：D
网考网解析：
[解题思路] 文章第四段谈到了使用电能的优缺点。倒数第二句提到have no lethal effects-just a negative effect on growth(没有致命的影响，只是对生长有副作用)，[D]表示对植物生长没有副作用，与原文冲突，故[D]符合题目要求。本句还提到这个值和那些使用化学诱导子达到的值非常接近，即[A]所表述内容。[B]与最后一句The treatment can be used over and over again表述一致。第四段的数字说明电刺激能够促进化学品的生产，故[C]正确。 document.getElementById("warp").style.display="none"; document.getElementById("content").style.display="block"; 查看试题解析出处>>
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