Submitted to: Annals of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/1996
Publication Date: N/A
Interpretive Summary: Light regulates plant growth and development processes including germination, flowering, and seed development. Although the biochemical basis of this regulation remains incompletely understood, we know light can affect the quantity of certain plant hormones. Specific compounds within plants responsible for light perception, photoreceptors, initiate a complex series of biochemical reactions after activated by light. Previous studies suggest members of one family of photoreceptors, the phytochromes, influence the levels of cytokinins, a group of plant hormones involved in cell division. Cytokinins increase dramatically early in seed development, and this regulates the formation of cells that eventually fill with starch to form the grain in wheat and other cereals. Learning how phytochrome interacts with these hormones is important to understanding how seed development can be improved. Plants with altered quantities of phytochrome are useed to study how photoreceptors interact with plant hormones. This study compared cytokinin content of Tibet Dwarf, a wheat with elevated levels of phytochrome A, with that of other wheats which have normal levels of this photoreceptor. In the light, Tibet Dwarf accumulated higher levels of cytokinins than the other wheats. When plants were transferred to a dark chamber, cytokinin levels declined in all the wheats at a similar rate. Future studies to compare responses of this dwarf wheat to light will improve our understanding of the role of these hormones in seed development in cereal crops. This knowledge will be critical to development of varieties in which seed development is more tolerant to certain environmental stresses, including high temperature.
Technical Abstract: The wheat (Triticum aestivum L.) genotype Tibet Dwarf has altered phytochrome-mediated responses compared to other wheats and retains a greater percentage of chlorophyll (Chl) when transferred to dark. To determine whether this elevated Chl retention was related to differences in cytokinin physiology, the endogenous cytokinin content of Tibet Dwarf and four other wheat genotypes was analyzed. Cytokinin content was quantified at three timepoints during light-growth and at four 24-hour intervals after light-grown plants were transferred to a dark chamber. Endogenous cytokinin content was not directly correlated with Chl level during dark growth. Cyclic changes in cytokinin production, based on the content of isopentenyl adenosine-type cytokinins, were observed for each wheat during dark-growth. Compared to four other genotypes, the Tibet Dwarf cycle was offset by 24 h. Tibet Dwarf seedlings also accumulated higher quantities of zeatin riboside-like cytokinins during light growth. When seedling roots were exposed to cytokinin-containing medium, root growth inhibition, a measure of cytokinin sensitivity, was similar in all the wheats. Tibet Dwarf root growth was more sensitive to cytokinins when seeds were imbibed in benzyladenine. These studies also showed that unlike four other wheat genotypes, dark-germinated Tibet Dwarf seedlings do not exhibit shoot elongation.