Thus far, the researchers led by plant biologist Eduardo Blumwald of the University of California, Davis have focused on tobacco, as it is easy to genetically manipulate. They are now trying the same approach in tomatoes, rice and wheat, reports Naturenews, the web portal.
The finding could be important for creating other drought-resistant crops, says Jeffrey Leung, a plant biologist at France's National Centre for Scientific Research in Gif-sur-Yvette, who was not affiliated with the study.
Drought is the major culprit behind crop losses worldwide, and water shortages are expected to become still more important as climate change alters rainfall patterns and increases the proportion of arid land in some key agricultural regions. In many parts of the world, water is already as expensive as fertilizer, says researcher Blumwald.
As absent-minded gardeners know all too well, water-starved plants often cope with the stress by wilting and shedding their leaves. That's believed to be a key part of their survival strategy: they sacrifice older leaves to stay alive just long enough to make seeds.
That approach may boost long-term survival in the wild, but it can be devastating to crop yields, says Blumwald. "Crops adopt the same strategy that those plants in the wild use," he says. "If things go wrong, they put out some seeds and die. But we do not grow crops for that."
In looking at the issue, Blumwald suspected that the drought-induced leaf shedding was genetically programmed, and reasoned that one way to circumvent that programming would be to boost a plant hormone called cytokinin. Cytokinins promote cell division and are found in actively growing plant tissues. Dying tissues, on the other hand, do not make the hormone.
So Blumwald and his colleagues created transgenic tobacco plants that produce a protein that makes cytokinin in stressed tissues. Although ordinary tobacco plants shed their leaves and died if not watered for two weeks, the transgenic plants kept their foliage and revived when watering resumed.
The transgenic plants also suffered only a 12% reduction in yield when watered with 70% less water than normally used. The findings are published this week in Proceedings of the National Academy of Sciences of the USA.
The results are surprising, says Leung, because researchers previously focused on another plant hormone, called abscisic acid, as the key to manipulating drought tolerance. "Genetic screens have turned up hundred of mutants that are altered in drought tolerance," says Leung, "and if there is a link of the mutation to a hormone, it has almost always been abscisic acid."
The new approach may hold advantages, he says, because previous attempts to manipulate abscisic acid yielded plants that were abnormal even under normal growth conditions.
Arie Altman, a plant biologist at the Hebrew University of Jerusalem in Israel, agrees that the work is a significant contribution towards improving drought tolerance in crops. An important next step, he notes, is to test whether the plants are also resistant to salt stress.
"Drought is in most cases connected with salinity," he says. "It is the combination of drought and salinity that is the most crucial problem."