VOA慢速英语2009年-Agriculture Report - Scientists Help Cut t

This is the VOA Special English Agriculture Report.

We talked last week about when and how to prune¹ plants. Today we tell you about some new understanding of why cutting the main branch of a plant or tree can lead to better development.

The findings are from researchers on two continents. Professor Prezemyslaw Prusinkiewicz of the University of Calgary in Canada led the research with scientists from Britain and Sweden. Their study appears in the Proceedings² of the National Academy of Sciences.

Researchers have known since the nineteen thirties that the actively³ growing tip of a plant releases a hormone⁴ called auxin. This hormone flows down the main stem. Scientists say the auxin has an indirect effect on buds on the side of the stem to prevent branching.

These buds themselves also produce auxin. The research suggests that to grow, they have to be able to export the hormone into the main stem. But the flow from the stem tip prevents them from doing this. The researchers wanted to find out how this blocking happens.

Professor Prusinkiewicz is on sabbatical leave in Australia, but he sent us an e-mail suggesting a simple way to understand the process. Think of a major road crowded with traffic. So many cars are on the main road that the cars on the side roads cannot enter.

The stem is like the crowded main road. The new research shows that the buds on the side cannot export their auxin into the main stem because it is too full. But if that main shoot is pruned⁵, other buds below it can start exporting. They are no longer inhibited⁶ from growing.

Ottoline Leyser from the University of York says that after a plant is pruned, all the inhibited shoot tips compete with each other to grow. In doing this, the branches influence each other's growth. Nearby shoot tips are more likely to affect each other than those that are far apart from each other.

Professor Leyser says the strongest branches grow best, wherever they may be on the plant. The study found that the main shoot grows the best of all not because of its position at the top of the plant, but mostly because it got there first.

And that's the VOA Special English Agriculture Report, written by Jerilyn Watson. Transcripts⁷ and MP3s of our reports, including last week's advice about pruning⁸, can be found at voaspecialenglish.com. You can also post comments. We invite you to share your own experiences -- good or bad -- with pruning plants and trees. I'm Steve Ember.

1 prune   

n.酶干；vt.修剪，砍掉，削减；vi.删除

参考例句：

• Will you prune away the unnecessary adjectives in the passage?把这段文字中不必要的形容词删去好吗？
• It is our job to prune the side branches of these trees.我们的工作就是修剪这些树的侧枝。

2 proceedings   

n.进程，过程，议程；诉讼(程序)；公报

参考例句：

• He was released on bail pending committal proceedings. 他交保获释正在候审。
• to initiate legal proceedings against sb 对某人提起诉讼

3 actively   

adv.积极地，勤奋地

参考例句：

• During this period all the students were actively participating.在这节课中所有的学生都积极参加。
• We are actively intervening to settle a quarrel.我们正在积极调解争执。

4 hormone   

n.荷尔蒙，激素，内分泌

参考例句：

• Hormone implants are used as growth boosters.激素植入物被用作生长辅助剂。
• This hormone interacts closely with other hormones in the body.这种荷尔蒙与体內其他荷尔蒙紧密地相互作用。

5 pruned   

v.修剪（树木等）( prune的过去式和过去分词 )；精简某事物，除去某事物多余的部分

参考例句：

• Next year's budget will have to be drastically pruned. 下一年度的预算将大幅度削减。 来自《简明英汉词典》
• The roses had been pruned back savagely. 玫瑰被狠狠地修剪了一番。 来自《简明英汉词典》

6 inhibited   

a.拘谨的，拘束的

参考例句：

• Boys are often more inhibited than girls about discussing their problems. 男孩子往往不如女孩子敢于谈论自己的问题。
• Having been laughed at for his lameness,the boy became shy and inhibited. 那男孩因跛脚被人讥笑，变得羞怯而压抑。

7 transcripts   

n.抄本（ transcript的名词复数 ）；转写本；文字本；副本

参考例句：

• Like mRNA, both tRNA and rRNA are transcripts of chromosomal DNA. tRNA及rRNA同mRNA一样，都是染色体DNA的转录产物。 来自辞典例句
• You can't take the transfer students'exam without your transcripts. 没有成绩证明书，你就不能参加转学考试。 来自辞典例句

8 pruning   

n.修枝，剪枝，修剪v.修剪（树木等）( prune的现在分词 )；精简某事物，除去某事物多余的部分

参考例句：

• In writing an essay one must do a lot of pruning. 写文章要下一番剪裁的工夫。 来自《现代汉英综合大词典》
• A sapling needs pruning, a child discipline. 小树要砍，小孩要管。 来自《现代汉英综合大词典》