Submitted to: American Society of Plant Biologists Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: July 24, 2003
Publication Date: July 20, 2003
Citation: Anderson, J.V., Gesch, R.W., Horvath, D.P. 2003. Effects of photoperiod on whole-plant carbohydrate partitioning, crown bud development, and gene expression in leafy spurge (Euphorbia esula L.) [abstract]. American Society of Plant Biologists Annual Meeting. Final Program and Abstract Supplement. p. 95.
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.
Photosynthesis and carbohydrate measurements were obtained from plants in partial root containment grown outdoors in full sun. Leaf photosynthesis was greatest in late May and was relatively stable from June to August before sharply declining between August and October. Between August and October the greatest increase in average crown bud development occurred (6.1 cm as compared to an average of 1.2 cm between June and August). Total nonstructural carbohydrates in aboveground plant tissues followed predictable patterns. Starch and sucrose content steadily rose in crown buds as they developed throughout late summer, while hexoses remained unchanged. Between late September and the end of October, crown bud sucrose increased 3-fold corresponding to a sharp decline in starch. Starch in the stem and leaf also declined by 9- and 6-fold, respectively, between August and October. Gene expression patterns observed in crown buds collected during the growing season will be presented and discussed in relation to photoperiod.