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.

    這是美國之音特別英語的農業報道節目。

    科學家們已經發現了關于植物如何利用水的更多的細節。他們的發現可能有助于策劃植物在較高二氧化碳水平的條件下更好、更有效地生長。

    植物自然地吸收二氧化碳，這是它們進行光合作用--一種將光能改變為化學能的過程--所必需的。二氧化碳通過葉子表面上的微孔或孔隙進入植物。

    然而，每次植物吸收一個二氧化碳氣體分子，它失去了數以百計的水分子。

    科學家們稱，植物失去了它們通過這些孔隙吸收的水份的百分之九十五。在高二氧化碳的條件下，有些植物的孔隙可以收緊以節約用水。其它的植物則不能夠同樣地做到這一點。現在，科學家們知道了植物中的這些微小的孔隙是怎樣收緊的。

    朱利安 施羅德是圣地亞哥的加利福尼亞大學的一位生物學教授。施羅德先生說，現在大氣中的二氧化碳含量比以往高出不少。然而，他說，許多植物都不關閉它們的孔隙以保留更多的水。

    他和他的小組已經確認了控制收緊一種植物的孔隙的蛋白質。這種蛋白質是稱作為碳酸酐酶的酶類。這項發現發表在上個月《自然細胞生物學》雜志上。施羅德先生認為，可以在一些植物中改變這種酶來提高它們貯存水的能力。

    研究人員們將碳酸酐酶基因加入到對較高的二氧化碳水平不發生反應的植物中。他們觀察到，對于被植物吸收的每個二氧化碳分子來說，它們失去的水少了百分之四十四。

    科學家們說，光合作用過程在這些植物中正常保持。他們說，這表明改變植物來節約更多的水不會影響植物生長。這種方法可能被用來幫助設計耐受極其干旱條件的糧食作物。這項發現可能有助于農民在水的供應減少時滿足不斷增長的糧食需求。但是，科學家們說還需要進行更多的研究。