Nitric Oxide and Regulation of Seed Dormancy

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

Mature seeds of many plants do not sprout readily. This is referred to as dormancy. Plant breeders have attempted to select for crop plants whose seeds remain dormant until harvest, yet sprout readily when planted. They have not been completely successful, and premature sprouting of cereal crops remains a problem. The seeds of many noxious weeds have strong dormancy and sprout erratically throughout the growing season. Weed control is therefore difficult, and this can result in serious reductions in crop yield or quality. Dormancy, however, is essential for the maintenance of natural ecosystems. Seed banks that consist of dormant seeds persist in soils. These seeds may lie dormant for years and will only sprout after receiving appropriate environment cues. There is great interest in how dormancy of crops and wild species is controlled. Environment conditions such as light and temperature, soil nitrates and nitrites, smoke from burning plant material, and pollutants resulting from the burning of fossil fuels are important in breaking dormancy and allowing seeds to sprout. Yet, how dormancy of cultivated or wild plants is established and maintained is unknown. A hypothesis is advanced that nitric oxide gas (NO) has a key role in regulating dormancy in agricultural and natural ecosystems. Experiments are proposed with two plants, Arabidopsis and rice. These experiments will provide insights into dormancy in broad-leaf plants and the grasses. The goals of the research are to uncover the biochemical and molecular mechanisms that underlie dormancy and the response of seeds to NO. The hypothesis to be tested is that Arabidopsis and barley seeds can synthesize NO and that NO can overcome dormancy in the seeds of both species. A role for endogenous NO in regulating germination of these seeds is also indicated by experiments with compounds that can scavenge NO. Removal of NO strengthens seed dormancy and reduces seed sprouting. Support for a role of NO as a natural regulator in seeds has come from experiments showing that Arabidopsis and barley seeds can synthesize NO from nitrite. Experiments are proposed using controlled atmospheres to determine how much NO is required to overcome dormancy in seeds. These experiments will establish when NO is effective as a dormancy-breaking agent, information that will help in the design of gene discovery experiments. Other experiments are proposed to establish how Arabidopsis seeds synthesize NO. A biochemical and molecular/genetic approach will be used to investigate how NO regulates dormancy in Arabidopsis. Advanced molecular biology techniques will be used to monitor gene expression in seeds treated with NO. Seeds showing defects in dormancy will be used to investigate how NO functions in dormancy and to discover what genes are essential for dormancy. The Broader Impacts of this research include the importance for agriculture in understanding how the dormancy of noxious weeds is controlled. In particular, an elucidation of the mechanisms by which NO controls dormancy could lead to the design of strategies of manipulation. The proposal will also provide training opportunities for undergraduate and graduate students, as well as for the training of high school students and K-12 curricular development.