|Canarini, Alberto -|
Submitted to: Physiological Plantarum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 10, 2010
Publication Date: December 1, 2010
Citation: Salvucci, M.E., Barta, C., Byers, J.A., Canarini, A. 2010. Photosynthesis and assimilate partitioning between carbohydrates and isoprenoid products in vegetatively active and dormant guayule: physiological and environmental constraints on rubber accumulation in a semiarid shrub. Physiological Plantarum. 140:368-379. Interpretive Summary: The importance of natural rubber as a global commodity, coupled with concerns about the spread of the South American Leaf Blight to rubber plantations in Asia has spurred a renewed interest in developing alternative sources of natural rubber. Guayule, a desert shrub native to the Chihuahuan desert, has long been regarded as a promising alternative to the rubber tree for production of natural rubber. Germplasm enhancement of guayule, whether by traditional breeding and selection or through molecular approaches to trait improvement, requires a detailed understanding of the physiological and biochemical constraints limiting rubber synthesis. To acquire the needed information, we examined photosynthesis and carbon partitioning in guayule plants grown under simulated summer- and winter-like conditions and also under winter-like conditions with CO2 enrichment to determine the factors regulating the synthesis of rubber. The results showed that guayule plants grown under winter-like conditions have high rates of photosynthesis and use the fixed carbon to make and store carbohydrates and rubber, but not volatile compounds. The findings provide new insights into the physiology of rubber synthesis in guayule that can be used to guide efforts to enhance the commercial value of this plant through genetic and agronomic improvement programs.
Technical Abstract: The stems and roots of the desert shrub guayule, Parthenium argentatum, contain a significant amount of latex that can be used as a source of natural rubber. Photosynthesis and the levels of carbohydrates and volatile isoprenoid products were measured in guayule plants grown under simulated summer- and winter-like conditions to determine the factors regulating carbon partitioning in vegetatively active or dormant plants, respectively. In addition, plants were also grown under winter-like conditions with CO2 enrichment to increase the source strength in the vegetatively dormant state. Rates of CO2 assimilation measured under growth conditions were similar for plants grown under summer- and winter-like conditions, but were higher with elevated CO2. After 5 months, plants grown under summer-like conditions had the highest above-ground biomass, but lower levels of non-structural carbohydrates and rubber. In contrast, the amount of resin in the stems was similar under all growth conditions. Emission of biogenic volatile compounds at 20, 30 and 40°C was more than 3-fold higher in plants grown under summer-like compared with winter-like conditions. Taken together, the results show that in the vegetatively dormant state induced by winter-like conditions, guayule plants maintain a high rate of photosynthesis and accumulate carbon as both non-structural carbohydrates and rubber, but down-regulate volatile emission. Enrichment with CO2 under winter conditions increased carbohydrate content but not the amount of rubber in the stems, suggesting that partitioning of carbon to rubber in guayule is limited by sink strength.