Submitted to: American Society of Plant Biologists Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: March 14, 2010
Publication Date: N/A
Technical Abstract: The stems and roots of the desert shrub guayule, Parthenium argentatum, contain a significant amount of latex, a potential source of natural rubber. To determine the factors regulating carbon partitioning, net photosynthesis (Pn) and the levels of carbohydrates and isoprenoid compounds were measured in guayule plants grown under 30/22 C; 14 h light (summer plants), 18/8 C; 10 h light (winter plants) or 18/8 C; 10 h light, 1000 micro liter per liter CO2 (winter plus CO2 plants). After 6 months, plants grown under summer conditions had the highest above ground biomass, but the ratios of dry/fresh wt and stem/leaf tissue were not affected by growth condition. Pn rates measured under growth conditions were similar for summer and winter plants, but were higher for winter plus CO2 plants. The levels of glucose, fructose, sucrose and inulin in the stem were more than three-fold higher in winter plus CO2 plants compared with summer plants and nearly two-fold higher than in winter plants. The amount of resin in the stems was ~3.5% of the dry wt under all growth conditions. In contrast, the amount of rubber differed; summer, winter and winter plus CO2 plants contained 5.3, 9.3 and 6.9% rubber, respectively. Guayule leaves emitted a suite of volatile compounds dominated by alpha- and beta-pinene. Volatile emission was more than 3-fold higher from summer compared with winter or winter plus CO2 plants at 20, 30 and 40 C. Taken together, the results show that guayule down-regulates volatile emission and accumulates carbon as both fructans and rubber in response to winter-like conditions. 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.