|Libourel, Igor gl|
Submitted to: Plant Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/29/2006
Publication Date: 1/12/2007
Citation: Bethke, P.C., Libourel, I., Aoyama, N., Chung, Y., Still, D.W., Jones, R.L. 2007. The Arabidopsis thaliana aleurone layer responds to nitric oxide, gibberellin, and abscisic acid and is sufficient and necessary for seed dormancy. Plant Physiology. 143:1173-1188. Interpretive Summary: Most plant seeds are dormant when mature and will not sprout. Dormancy is lost with time, and this process may be hastened by certain environmental conditions. Depending on the species, these might include light, a sufficient period of cold, or smoke. A lack of dormancy at planting is desirable for seeds of commercially grown plants, because it leads to rapid, uniform establishment of the seedlings. Dormancy is not desireable in weed species, however, because it increases their persistence in the field. Plant hormones and nitric oxide are intimately involved in establishing, maintaining, and removing seed dormancy. We have found that a layer of cells that surrounds the embryo in seeds of Arabidopsis thaliana is the primary determinant of dormancy in this species. Arabidopsis is a member of the mustard family and is related to such familiar plants as broccoli and Canola. This non-embryonic cell layer was shown to respond to plant hormones and nitric oxide in ways that mirror the response of intact seeds. We conclude that this cell layer imposes a physical constraint on the embryo in dormant seeds that prevents embryo growth. Nitric oxide acts with one of the plant hormones to weaken the structural parts of this tissue so that the embryo can push through and sprouting can occur.
Technical Abstract: Seed dormancy is a common phase of the plant life cycle and several parts of the seed can contribute to dormancy. Whole seeds, seeds lacking the testa, embryos, and isolated aleurone layers of Arabidopsis thaliana were used in experiments designed to identify components of the arabidopsis seed that contribute to seed dormancy and to learn more about how dormancy and germination are regulated in this species. The aleurone layer was found to be the primary determinant of seed dormancy. Embryos from dormant seeds, however, had a lesser growth potential than those from non-dormant seeds. Arabidopsis aleurone cells were examined by light and electron microscopy and cell ultrastructure was similar to that of cereal aleurone cells. Arabidopsis aleurone cells responded to nitric oxide, GA and ABA, with nitric oxide being upstream of GA in a signaling pathway that leads to vacuolation of protein storage vacuoles and ABA inhibiting vacuolation. Molecular changes that occurred in embryos and aleurone layers prior to germination were measured and these data show that both the aleurone layer and the embryo expressed the nitric oxide associated gene AtNOS1, but only the embryo expressed genes for the GA biosynthetic enzyme GA3 oxidase.