Question

The bacteria which inhabit (栖居于) human beings, particularly the guts (肠道) of those beings, have been found in recent years to be important for fighting off diseases. That something similar happens in other animal species is doubtless true as well. But work by Seon-Woo Lee at Dong-A University and Jihyun Kim at Yonsei University, both in South Korea, suggests that it is not only animals that benefit from such bacterial protection. Their study, just published in Nature Biotechnology, shows that plants do, too.

Crop plants of the nightshade family, such as potatoes and tomatoes, are not immune to a soil bacterium called Ralstonia solanacearum. This enters their roots and spreads through their water-transport systems, causing them to wilt (枯萎). Infection is usually deadly; the disease costs potato farmers alone $1bn a year. A variety of tomato called Hawaii 7996, however, does not suffer from such bacterial wilt. Dr Lee and Dr Kim wondered if the explanation for this exceptionalism lay with other bacteria in the soil.

To test that idea, they grew crops of Hawaii 7996 and a second tomato variety called Moneymaker. Once the plants were established, the researchers analyzed bacteria in the soil around the plants’ roots and found systematic differences that depended on which tomato variety was growing. This observation made their explanation reasonable and likely to be true.

They then transplanted some of their Moneymaker plants into soil that had previously supported Hawaii 7996s, and some of the Hawaiian plants into soil that had been home to Moneymakers. As controls, they similarly uprooted (拔起) individuals of both varieties and replanted them in soil once occupied by the same variety. That done, they exposed all of their plants to R. solanacearum and monitored them over the course of 14 days.

They found the disease progressed almost 30% more slowly in Moneymaker plants grown in “Hawaiian” soil than it did in those Moneymakers that had been replanted into their own soil. In contrast, it progressed rapidly in the normally resistant Hawaiian variety when this was transferred into Moneymaker soil.

Further study revealed that credit for this disease resistance went to a single type of soil bacterium, called TRM1. Dr Lee and Dr Kim therefore cultivated (培育) this bug in their laboratory and used it to treat soil into which Moneymaker plants were then planted. When these were infected with R. solanacearum they proved more resistant than others that had been planted into untreated soil as controls.

These findings suggest to Dr Lee and Dr Kim that the roots of Hawaii 7996 are releasing compounds (化合物) which encourage the growth of TRM1. What those compounds are has yet to be determined. The two researchers’ work, however, seems to suggest something constructive.

1.The author mentions the bacteria inhabiting human beings to introduce ___________.

A. the benefits of bacteria to humans    B. the effects of bacteria on plants

C. the efforts to fight off diseases    D. the reasons for plant diseases

2.What are the two researchers’ findings based on?

A. Comprehensive analyses of how plants are infected.

B. Careful observation of the transplanting process.

C. Controlled experiments on the uprooted individuals of both varieties.

D. Comparison of the progress of the disease in different conditions.

3.According to the study, why are some plants immune to infection?

A. They have better water-transport systems.

B. They are protected by some other bacteria.

C. They are genetically different from others.

D. They have resistance to bacteria when transferred.

4.The two researchers’ work indicates that _____________.

A. new ways will be found to deal with bacterial wilt

B. causes of some plant diseases have been discovered

C. a new chapter of agricultural science and technology has started

D. the composition of the compounds released has been identified

Answer

1. B

2. D

3. B

4. A

【解析】

本文是一篇科普说明文，栖居于人体内的细菌可以帮助人们抵抗疾病，同样的原理细菌也可以帮助动物和植物抵抗疾病。文章对此项研究做了详细说明。

1.推理判断题。根据第一句“The bacteria which inhabit (栖居于) human beings, particularly the guts (肠道) of those beings, have been found in recent years to be important for fighting off diseases. ”可知栖居于人体内的细菌可以帮助人们抵抗疾病，同样的原理细菌也可以帮助动物和植物抵抗疾病。所以作者提及人体内部的细菌正是为了说明细菌对植物也有影响。故B项正确。

2.推理判断题。根据第四段第一句“They then transplanted some of their Moneymaker plants into soil that had previously supported Hawaii 7996s, and some of the Hawaiian plants into soil that had been home to Moneymakers.”可知演讲者把Moneymaker移植到了Hawaii 7996s所种植的土壤里，然后再对植物患病的情况进行研究。说明他们对不同情况下植物疾病发展的过程进行了研究。故D项正确。

3.推理判断题。根据第三段最后两句“Once the plants were established, the researchers analyzed bacteria in the soil around the plants’ roots and found systematic differences that depended on which tomato variety was growing. This observation made their explanation reasonable and likely to be true”可知研究的结果发现的确是土壤里的细菌导致植物免受疾病的影响。故B项正确。

4.推理判断题。根据最后两句“What those compounds are has yet to be determined. The two researchers’ work, however, seems to suggest something constructive.”可知我们可以合成一些化合物来处理由于细菌导致的植物枯萎问题。故A项正确。