《经济学家》读译参考：蓝玫瑰红紫罗兰－转基因技术让花儿色香俱全(2)

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　　色香俱全方为花

　　Mere colour, however, is for unsophisticated[2] lovers. A truly harmonious Valentine gift should smell beautiful as well. Sadly, commercial varieties of cut rose lack fragrance. This is because there is a trade-off between the energy that plants spend on making the complex, volatile chemicals that attract women and insects alike, and that available for making and maintaining pretty-coloured petals. So, by artificially selecting big, long-lasting flowers, breeders have all but erased another desirable characteristic.

　　然而，颜色之美只能取悦那些初涉尘世的恋人。作为情人节礼物，蓝色的玫瑰再加上迷人的香气，才更为协调。可惜，市售的切花玫瑰都缺少芳香。这是因为，植物合成挥发性复合物（这种复合物对女人和虫子有着同样的吸引力），与形成颜色迷人的花瓣并为之提供养料，两者所耗能量存有一种平衡关系。因此，人工培育时如果注重花瓣大、花期长，就必须“牺牲”人人心仪的芳香。

　　Smell is tougher to implant than colour because it not only matters whether a plant can make odoriferous chemicals, it also matters what it does with them. This was made plain by the first experiment designed to fix the problem. In 2001 Joost Lücker, then a researcher at Plant Research International in Wageningen, in the Netherlands, added genes for a new scent into petunias. Chemical analysis showed that the new scent was, indeed, being made, but unfortunately the flowers did not smell any different. As happens in Florigene's blue carnations and roses, Dr Lücker's petunias dumped the foreign chemical they were being forced to create into cellular waste buckets known as vacuoles. Whereas pigments are able to alter a petal's colour even when they are inside a vacuole, because the cell contents surrounding the vacuole are transparent, smelly molecules must find a route to the sniffer's nose by getting out of the cell and evaporating.

　　在花中加入香味要比加入颜色难，因为前者涉及植物能否合成有味化学物质以及如何处理这些化学物质。第一个设计用于解决该难题的试验充分证明了这一点。2001年，时任荷兰瓦赫宁根（Wageningen）国际植物研究所研究员的朱斯特?吕克尔（Joost Lücker）在矮牵牛中插入了一种新型香味基因。化学分析发现了合成的新型香气物质，但可惜花的气味没有任何变化。跟Florigene培育的康乃馨和玫瑰所遇到的情况一样，吕克尔博士的矮牵牛细胞液泡中被动产生的外来化学物质被当作废物给排泄了。色素即便是位于液泡中，它也能改变花瓣的颜色，这是因为液泡外包绕的细胞内容物是透明的，而气味分子必须穿过细胞并挥发才能为闻者所闻。

　　Like Dr Lücker, Natalia Dudareva, of Purdue University, in Indiana, eschews[3] experiments with roses, since these plants have scents composed of 300 to 400 different molecules. She prefers to understand basic odour science using petunias and snap-dragons, which have about ten smelly chemicals apiece. She has made an encouraging discovery. By studying the many different pathways through which flowers make their fragrances, she has found consistent patterns in the way these pathways are regulated.

　　印第安纳州普渡大学（Purdue University）的娜塔丽娅?都达瑞娃（Natalia Dudareva）跟吕克尔博士一样，也没有用玫瑰做试验，因为这类植物的气味分子组成多达300到400种。她选择矮牵牛和金鱼草作为基础气味科学的研究对象，这两种植物每种只有10个左右的气味分子。结果令人鼓舞——她通过研究花形成香气的多个不同途径发现，这些途径都共用同一调控模式。

　　Such co-ordinated patterns suggest that a type of protein called a transcription factor is involved. Transcriptionfactors switch genes on and off in groups.If Dr Dudareva is right, cut roses have lost their fragrances not because the genes that encode their hundreds of scent molecules have each lost their function, but because the plants no longer make a few transcription factors needed to turn the whole system on.

　　试验表明，这一共用调控模式与一种名为转录因子的蛋白有关。转录因子相当于基因的“开关”。都达瑞娃博士认为，切花玫瑰之所以失去芳香，并非因为香气分子的所有编码基因功能均失活，而是因为在这些切花玫瑰中，几个启动基因转录系统所必须的转录因子停止了合成。

　　This suggests that the task of replacing lost fragrance is more manageable than it seemed at first blush[4]. But even when the transcription factors in question have been identified, the problem of the energetic trade-off with pigmentproduction and longevity will remain. So Dr Dudareva is also measuring how quickly the enzymes in scent-production pathways work, in order to identify bottlenecks and thus places where her metabolic-engineering efforts would best be concentrated.

　　这表明，还原失去的芳香其实并不难。但是即使能鉴定出有关转录因子，与色素形成及寿命之间的能量平衡问题仍不可避免。因此，都达瑞娃博士对气味形成过程中酶催化速度也进行了检测，以期解开制约花香形成的“瓶颈”，进而弄清在哪个位置运用代谢工程技术最为有效。

　　Dr Dudareva's methods may also help to improve the job that flower-scents originally evolved to do—attracting insects that will carry pollen from flower to flower. By modifying the smell of crops such as vanilla, which have specific pollinator species, different insects might be attracted. That could expand the range in which such crops could be grown and thus make some poor farmers richer. A change, then, from making rich but romantic men poorer.

　　都达瑞娃博士的方法还可能有助于改善花香物质的后期作用（即吸引传播花粉的昆虫）。香草等农作物具有特定的传粉昆虫，但对其香味进行修饰后，可吸引不同的昆虫。这样一来，就可以扩大这类农作物的种植面积，从而提高贫苦农民的收入。因为这一改变，农民致富了，浪漫的男士却要“破财”了。