This is the VOA Special English Agriculture Report.

    Scientists have discovered more details about how plants use water. Their findings could help to engineer plants that grow better and more effectively in conditions with higher levels of carbon dioxide.

    Plants naturally take in carbon dioxide they need for photosynthesis, the process of changing light energy to chemical energy. The carbon dioxide enters the plants through tiny holes or pores on the surface of leaves.

    However, each time a plant takes in one molecule of carbon dioxide gas, it loses hundreds of water molecules.

    Scientists say plants lose ninety-five percent of the water they take in through these pores. Some plants' pores can tighten to save water during conditions of high carbon dioxide. Other plants are not able to do this as well. Now, scientists know how these tiny pores tighten in plants.

    Julian Schroeder is a professor of biology at the University of California, San Diego. Mister Schroeder says that carbon dioxide levels in the atmosphere are much higher now than they were in the past. However, he says, many plants are not closing their pores in order to hold in more water.

    He and his team have identified proteins that control the tightening of a plant's pores. The proteins are enzymes called carbonic anhydrases. The findings were published last month in the journal Nature Cell Biology. Mister Schroeder believes the enzymes could be changed in some plants to increase their ability to store water.

    The researchers added carbonic anhydrase genes to plants that do not react to higher levels of carbon dioxide. They observed that for every molecule of carbon dioxide taken in by the plants, they lost forty-four percent less water.

    The scientists say the photosynthesis process continued normally in these plants. They say this suggests that changing plants to save more water will not affect plant growth. This method might be used to help engineer food crops that are resistant to extremely dry conditions. The discovery could help farmers meet a growing demand for food as water supplies decrease. However, the scientists say more research is needed.

    这是美国之音特别英语的农业报道节目。

    科学家们已经发现了关于植物如何利用水的更多的细节。他们的发现可能有助于策划植物在较高二氧化碳水平的条件下更好、更有效地生长。

    植物自然地吸收二氧化碳，这是它们进行光合作用--一种将光能改变为化学能的过程--所必需的。二氧化碳通过叶子表面上的微孔或孔隙进入植物。

    然而，每次植物吸收一个二氧化碳气体分子，它失去了数以百计的水分子。

    科学家们称，植物失去了它们通过这些孔隙吸收的水份的百分之九十五。在高二氧化碳的条件下，有些植物的孔隙可以收紧以节约用水。其它的植物则不能够同样地做到这一点。现在，科学家们知道了植物中的这些微小的孔隙是怎样收紧的。

    朱利安 施罗德是圣地亚哥的加利福尼亚大学的一位生物学教授。施罗德先生说，现在大气中的二氧化碳含量比以往高出不少。然而，他说，许多植物都不关闭它们的孔隙以保留更多的水。

    他和他的小组已经确认了控制收紧一种植物的孔隙的蛋白质。这种蛋白质是称作为碳酸酐酶的酶类。这项发现发表在上个月《自然细胞生物学》杂志上。施罗德先生认为，可以在一些植物中改变这种酶来提高它们贮存水的能力。

    研究人员们将碳酸酐酶基因加入到对较高的二氧化碳水平不发生反应的植物中。他们观察到，对于被植物吸收的每个二氧化碳分子来说，它们失去的水少了百分之四十四。

    科学家们说，光合作用过程在这些植物中正常保持。他们说，这表明改变植物来节约更多的水不会影响植物生长。这种方法可能被用来帮助设计耐受极其干旱条件的粮食作物。这项发现可能有助于农民在水的供应减少时满足不断增长的粮食需求。但是，科学家们说还需要进行更多的研究。