Nov. 30, 2004 Researchers at the University of California, Riverside report the development of technology that increases the tolerance of grains crops to drought by decreasing the amount of an enzyme that is responsible for producing the plant hormone ethylene.
UCR Biochemist Daniel R. Gallie led the research, funded by the U.S. Department of Agriculture, the National Science Foundation and the California Agricultural Experiment Station. The findings will be published in the December issue of The Plant Journal in a paper titled ACC Synthase Expression Regulates Leaf Performance and Drought Tolerance in Maize.
Ethylene is vital in regulation of plant responses to environmental stresses, such as flooding and drought, and to attack by pathogens. But often, ethylene initiates leaf death in response to adverse conditions, sacrificing less essential parts of a plant to protect the growing tip, responsible for producing flowers, the reproductive organs of plants. Gallie said that he and his research team have examined the role of ethylene during plant growth and development since 1997.
In the most recent study, conducted by UCR researchers and Pioneer Hi-Bred International, an Iowa-based developer and supplier of seed to farmers, the authors targeted ACC synthase, an enzyme required for the production of ethylene, screening thousands of plants for naturally occurring mutants that were deficient in the enzyme.
The researchers isolated several such plants, and one in particular that produced substantially lower levels of the hormone. Leaves from this mutated plant remained functional and maintained photosynthetic function longer than non-altered plants.
In addition, the plants were more resistant to the effects of adverse environmental conditions. Surprisingly, by reducing the level of ethylene, all the leaves of the altered plants contained higher levels of chlorophyll and leaf protein, and functioned better than control leaves.
"Thus, they are better able to survive conditions of drought and remain productive," said Professor Gallie, who led a research team that included UCR Colleague Todd E. Young and Robert B. Meeley, of Pioneer Hi-Bred. "Erratic rainfall and conditions of drought have plagued farmers from time immemorial, and are responsible for substantial losses in crop yield when they do occur."
For several years, Gallie said, a number of studies on global climate have predicted an increase in global temperature, and regional conditions of drought, which may have already begun.
"Increasing drought tolerance in crops is highly valuable to U.S. and world agriculture now, and will be even more critical as our environment continues to change as a consequence of global warming," said Gallie.
The findings by Gallie and his research team suggest that ethylene controls the level of leaf function under normal growth conditions, as well as during adverse environmental conditions.
Gallie's research with corn opens the door to producing crops better able to withstand periodic losses in rainfall, including grains, which are the most important direct source of food for livestock and for a majority of humans.
"Our discovery will assist farmers who depend on rainwater for their crops during those years when rainfall is low, particularly those who grow crops in arid areas, such as exists in many developing [is he is okay with this change] countries," said Gallie. "As global warming continues to change our own environment in the U.S., our work will be important in helping U.S. farmers continue to produce the food we need even as our climate becomes unpredictable."
Future inquiries will most likely focus on how ethylene may regulate other aspects of plant growth and development, such as during flower development and root growth, Gallie added.
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