Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 2/20/2005
Publication Date: 2/20/2005
Citation: Anderson, J.V., Chao, W.S., Horvath, D.P., Jia, Y., Gesch, R.W. 2005. Environmentally-induced shifts in sugar metabolism may affect dormancy status in underground adventitious buds of leafy spurge (Euphorbia esula) [Abstract]. Weed Science Society of America. Page No. 121. Interpretive Summary: Summary: Leafy spurge is a perennial weed that can regenerate new shoots from an abundance of buds located on the root system. Previous studies have indicated that a leaf-derived signal can inhibit root buds from developing into new shoots. This type of growth inhibition is referred to as para-dormancy. Our current models suggest that sugars produced in the leaf may interfere with growth hormones such as gibberillic acid located in the root buds. However, when the above ground plant dies off in the fall, the root buds transition to a new phase of dormancy known as endo-dormancy. During the endo-dormant phase, inhibition of new shoot growth is controlled by internal signals within the root buds. To gain a better understanding of the role that sugars might play in regulating the para- and endo-dormant phases, we monitored seasonal carbohydrate contents in field-grown leafy spurge root buds. Our results show that sugars transported to the root buds are stored mainly as starch during the para-dormant phase. However, stored starch is converted to sucrose during the transition to endo-dormancy. These results may imply a potential signaling role for sugars during the different phases of dormancy in root buds. Studying sugar signaling and metabolism at the molecular level should help to address this hypothesis. Using a genomics approach, correlations between sugar and dormancy status were identified by microarray analyses of seasonal root bud gene expression which highlighted a potential link to AMP-binding proteins and GA signaling. To monitor expression of specific sugar metabolism genes, sequence information from a leafy spurge EST-database was used to design primers for ongoing semi-quantitative RT-PCR experiments.
Technical Abstract: Abstract: Dormancy in underground adventitious buds (crown and root buds) is a key characteristic leading to the persistence of perennial weeds like leafy spurge. During the active growing season, these buds are maintained in a state of para-dormancy by both apical meristem- and leaf-derived signals. Although the meristem-derived signal is clearly auxin, the nature of the leaf-derived signal is not yet fully understood but requires photosynthesis for its production/transport. Current models indicate that the leaf-derived signal could result from antagonistic interplay between leaf-derived sugar and gibberillic acid perception in the buds. To test this model under natural environmental conditions, we monitored the relationship between crown bud carbohydrate content and dormancy status during seasonal development of field-grown leafy spurge. Transition from para- to endo-dormancy in crown buds usually occurred during the later stages of senescence (late Aug. to early Oct.). Sucrose levels increased slowly (10-22 mg/g FW) in para-dormant crown buds from July to Sept., but showed a rapid 4-fold increase during transition to, and maintenance of, endo-dormancy. In contrast, an inverse relationship was observed for starch content in para- and endo-dormant crown buds suggesting that leaf-derived sugars transported to the crown buds were quickly metabolized and stored mainly as starch during para-dormancy. Seasonal hexose levels remained relatively constant ('10 mg/g FW) in crown buds suggesting that when starch was broken down during the transition to endo-dormancy, its conversion to sucrose occurred relatively fast. These results may imply a potential signaling role for sucrose during dormancy transition, as apposed to acting only as a cryoprotectant. Studying sugar signaling and metabolism at the molecular level should help to address this hypothesis. Using a genomics approach, correlations between sugar and dormancy status were identified by microarray analyses of seasonal crown bud gene expression which highlighted a potential link to AMP-binding proteins and GA signaling. To monitor expression of specific sugar metabolism genes, such as AGPase, UGPase, hexokinase, and SuSy, sequence information from a leafy spurge EST-database was used to design primers for ongoing semi-quantitative RT-PCR experiments.