Wounding and cold stress increase resin and rubber production of Parthenium argentatum cultivar G711
Introduction
Natural rubber (NR) is a critical material used in thousands of products (Critical Agricultural Materials Act 7 7 7, 2020). Hevea brasiliensis is the world’s major producer of NR but has several disadvantages. The plant grows only in tropical climates under threat by climate change, is vulnerable to diseases (Nyaka Ngobisa et al., 2013, Radziah and Chee, 1989), and produces harmful allergens (Berthelot et al., 2012, Siler and Cornish, 1994). A potential alternative source of NR is Parthenium argentatum A. Gray, commonly called guayule, a perennial shrub that naturally grows in the semi-arid Chihuahuan desert of the SW United States and northern Mexico (Cornish, 2001, Konno, 2011, Lewinsohn, 1991). Guayule plants produce and accumulate cis-1,4-polyisoprene NR in the form of rubber particles in the stembark tissue (Cornish and Wood, 2002).
NR biosynthesis in guayule increases in response to abiotic stress even under field cultivation conditions where the majority of guayule NR synthesis occurs during cold, non-freezing temperatures (Benedict et al., 2008, Hunsaker et al., 2019, Ponciano et al., 2012). Studies using controlled growth conditions demonstrated that subjecting guayule to cold temperature does increase rubber production when plants are grown in soil (Bonner, 1943, Goss et al., 1984) or tissue culture (Dong et al., 2017, Placido et al., 2019, Ponciano et al., 2018). The relationship between abiotic stress and rubber production has also been studied in H. brasiliensis (Tangpakdee, 1998) and Ficus (Kim et al., 2003) and may be a key to rubber biosynthesis mechanisms (Konno, 2011). Notably, wounding stress takes place during tapping of H. brasiliensis to collect the latex. Wounding stress has been shown to increase the expression of the phytohormone jasmonic acid (JA) at the site of injury (Tian et al., 2003), and further, that JA triggers signaling pathways that induce the rubber-producing laticifer cells (Deng et al., 2018, Zhai et al., 2018). In addition, increasing rubber production by exogenous application of phytohormones, such as ethylene (Tungngoen et al., 2009, Zhu and Zhang, 2009), abscisic acid (ABA) (Tungngoen et al., 2011), and JA (Hao and Wu, 2000), has been reported in H. brasiliensis. Ethylene treatment prior to tapping is commonly practiced in H. brasiliensis cultivation.
Previously, a relationship between rubber production and phytohormone (JA and salicylic acid) levels was suggested in guayule (Placido et al., 2019). In essence, decreased JA and elevated salicylic acid were correlated to increased rubber production. To further understand abiotic stress and NR production in guayule, here we investigated the effect of wounding and cold stresses on growth and rubber production in growth-chamber grown guayule plants. Plants were subjected to wounding stress with and without cold treatment. Effects upon the physical traits, phytohormone levels, and resin and rubber content were measured.
Section snippets
Plant growth conditions
Wild-type (G7–11) guayule plants were maintained in tissue culture as previously described (Dong et al., 2013). G7–11 is the source of the AZ-2 germplasm line which is favored by industry for commercialization due to its rapid growth and resiliency (Dierig et al., 1989, Ray et al., 1999). Eight-week-old plantlets were carefully uprooted from the tissue culture medium and transplanted into a pot (6″ diameter x 4.25″ depth) with SS#1 F1P RSI 3.8 CFC CDN planting mix (Sun Gro Horticulture, CA,
Characteristics of guayule plants under wounding and cold treatments
The physical features of the guayule plants were affected by the wounding and cold treatments both individually and in combination (Table 1 and Fig. 1A). Wounding the plants’ stems decreased the overall plant height at both 25 °C and under cold treatment. Unwounded plants subjected to cold treatment alone did not display any height change although these plants did have a significant increase in width. When the total biomass was measured, wounding alone did not have an effect, but cold treatment
Discussion
In this study, we investigated the effects of physical wounding and cold stresses on growth chamber-grown guayule plants. Both cold and wound stresses elicited significant responses in guayule’s metabolism, evident in changes in plant architecture, secondary metabolite production, and phytohormone levels.
Surprisingly, cold treatment did not increase the rubber content under greenhouse/growth chamber conditions for the G7–11 wild-type cultivar used in this study. A previous greenhouse/growth
CRediT authorship contribution statement
Dante F. Placido: Conceptualization, Methodology, Formal analysis, Investigation, Writing – original draft. Colleen McMahan: Conceptualization, Methodology, Writing – review & editing. Charles C. Lee: Conceptualization, Formal analysis, Writing – original draft, Writing – review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was supported by the United States Department of Agriculture CRIS 2030-41000-067-000-D. We would like to thank Chen Dong and Trinh Bolton, USDA-ARS for technical support, and Rebecca Cahoon, Edgar Cahoon, and the Lipidomics Core Facility at University of Nebraska, Lincoln for hormone analysis. Mention of trade names or commercial products in this report is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the United States
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