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

Abstract

The stems and roots of the semiarid shrub guayule, Parthenium argentatum, contain a significant amount of natural rubber. Rubber accumulates in guayule when plants are vegetatively and reproductively dormant, complicating the relationship between growth/reproduction and product synthesis. To evaluate the factors regulating the partitioning of carbon to rubber, carbon assimilation and partitioning were measured in guayule plants that were grown under simulated summer- and winter-like conditions and under winter-like conditions with CO(2) enrichment. These conditions were used to induce vegetatively active and dormant states and to increase the source strength of vegetatively dormant plants, respectively. Rates of CO(2) assimilation, measured under growth temperatures and CO(2) , were similar for plants grown under summer- and winter-like conditions, but were higher with elevated CO(2) . After 5 months, plants grown under summer-like conditions had the greatest aboveground biomass, but the lowest 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 was more than three-fold higher in plants grown under summer- compared with winter-like conditions. Taken together, the results show that guayule plants maintain a high rate of photosynthesis and accumulate non-structural carbohydrates and rubber in the vegetatively dormant state, but emit volatile compounds at a lower rate when compared with more vegetatively active plants. Enrichment with CO(2) in the vegetatively dormant state increased carbohydrate content but not the amount of rubber, suggesting that partitioning of assimilate to rubber is limited by sink strength in guayule.

Transcriptome and gene expression analysis in cold-acclimated guayule (Parthenium argentatum) rubber-producing tissue

“…Another interesting EST in our collection encodes 1,2-beta-fructan 1F-fructosyltransferase, a fructan biosynthesis enzyme (Ritsema and Smeekens, 2003). Inulin, a fructan produced in guayule, is synthesized in high amounts during winter-like conditions and much less during warmer months (Kelly and van Stadem, 1994;Salvucci et al, 2010). In addition to serving as a reserve carbohydrate, fructans appear to have a role in the protection of plants during drought, salt, and cold stress as demonstrated in tobacco (Pilon-Smits et al, 1995).…”

“…There is a well-established negative correlation between temperature and rubber transferase activity and/or rubber accumulation in guayule; that is, cold temperatures induce higher rubber transferase activity (Table 4; Cornish and Backhaus, 2003;Ji et al, 1993) and increase rubber production (Salvucci et al, 2010;Veatch-Bolhm et al, 2007). In this study, in vitro rubber transferase activity in rubber particles harvested from plants between November 2005 and March 2007 showed the expected higher activity during periods of cold night temperature, and the lowest enzyme activity during the warmer months (Table 4).…”

“…No significant difference in gene expression levels was observed for SQS supported by the analysis of variance applied on the 2006-2007 winter samples (Table 5). Salvucci and coworkers analyzed guayule resin accumulation and production of volatile terpenoids and conclude that these metabolites are regulated differently from the accumulation of rubber (Salvucci et al, 2010).…”

A model study on effect of glucose on the basic characteristics and physical properties of natural rubber

“…The use of glucose was established since glucose is the most common carbohydrate as a simple sugar which is the endogenous sugar obtained from NR latex. In addition, glucose is present in latex from other plants such as Parthenium argentatum or Guayule that are also a commercial source of latex [24]. Therefore, the use of glucose in this work is also informative for the rubber from other plants.…”

“…The reasons for using glucose are based on the fact that glucose is one of endogenous sugars obtained from NR latex. It is the most common carbohydrate as a simple sugar (monosaccharide) involved in the biosynthesis pathway of latex from a Hevea tree and other plants [18,24].…”