Although it has been shown in recent years that plants can see, hear and smell, they are still usually thought of as silent. But now, for the first time, they have been recorded making ultrasonic (超声的) cries when stressed, which researchers say could open up a new field of precision agriculture where farmers listen for water-starved crops.
Itzhak Khait and his colleagues at Tel Aviv University in Israel found that tomato and tobacco plants made cries at frequencies humans cannot hear when stressed by not having enough water or when their stem is cut.
Microphones placed 10 centimetres from the plants picked up sounds in the ultrasonic range of 20 to 100 kilohertz, which the team says insects and some mammals would be able to hear and respond to from as far as 5 metres away. A moth may decide against laying eggs on a plant that sounds water-stressed, the researchers suggest. Plants could even hear that other plants are short of water and react accordingly, they speculate (推断).
On average, drought-stressed tomato plants made 35 sounds an hour, while tobacco plants made 11. When plant stems were cut, tomato plants made an average of 25 sounds in the following hour, and tobacco plants 15. Unstressed plants produced fewer than one sound per hour, on average.
Enabling farmers to listen for water-stressed plants could "open a new direction in the field of precision agriculture", the researchers suggest. They add that such an ability will be increasingly important as climate change exposes more areas to drought.
"The suggestion that the sounds that drought-stressed plants make could be used in precision agriculture seems feasible (可行的) if it is not too costly to set up the recording in a field situation," says Anne Visscher at the royal Botanic Gardens, Kew, in the UK.
She warns that the results can't yet be broadened out to other stresses, such as salt or temperature, because these may not cause sounds. Besides, there have been no experiments to show whether moths or any other animal can hear and respond to the sounds the plants make, so that idea is still based on guesses for now, she says.
Many companies, including McDonald's, are removing artificial colors from their foods. Colors send important signals about food, and companies aren't going to stop using them.
Cheese
Check the packages of most cheeses, and there is likely an ingredient called annatto (胭脂红) listed. The practice dates back to when cheesemakers in England removed the butterfat from milk to make butter. The leftover milk was whiter，so cheesemakers added annatto to create a golden coloring.
Egg Yolks
Many home cooks think darker egg yolks are fresher or more nutritious. But the color may be the result of coloring products in chicken feed. Darker yolks aren't necessarily healthier. The belief that they are healthier is likely rooted in the idea that yolks are darker when hens are fed a diet of fresh plants, which contain the pigments (色素).
Salmon
Bright pink flesh may signal freshness to shoppers eyeing salmon，which is why salmon may have been fed synthetic astaxanthin (虾青素). For example, at Costco, tickets of farmed salmon are saying "Color added through feed".
"People used to get all the coloring all over their fingers. We now kind of laugh at that，" said Richard Matoian, director of a food trade association. Americans, therefore, apparently aren't entirely ready to say goodbye to the artificial colors in various kinds of food. Companies are expected to take new measures in response to customer demand.
A. Without it, cheese would be off-white.
B. But producers know the difference colors can make.
C. It's easy to change yolk colors by simply varying hens' diet.
D. But don't expect your cheeseburgers to look much different.
E. Yolk colors vary when chickens live in different climates as well.
F. Producers are asked to declare on tickets if artificial colors were used.
G. Some companies even offer various shades of pink to help judge flesh colors.
Given the fact that chemical pesticides and artificial fertilisers can fight crop diseases and increase production, they(be) in wide-spread use since the 1950s. When they were first introduced,many farmers considered them as a great way.However, with time (go) by, they have been proved harmful to the environment and people's health if(use) for a long time. (tackle) this problem, some farmers have switched to organic farmingan alternative. And organic food has becomefavorite for many customers. Farmers who grow organic products rely on it that(nature) means could keep their soil fertile and free of disease. Different organic methods have come up, goal is to grow good food while avoiding damage to the environment or to people's health. However, organic farming cannot replace chemical farming(instant) for it's feeding a huge number of people worldwide now. There is still a long way to go before scientists find a suitable(solve) that can serve the high demand for food around the world while protecting the environment.
