Review
The physiological and biochemical responses of guayule to the low temperature of the Chihuahuan Desert in the biosynthesis of rubber

https://doi.org/10.1016/j.indcrop.2007.09.003Get rights and content

Abstract

Guayule (Parthenium argentatum Gray) is a rubber plant indigenous to the Chihuahuan Desert of Northern Mexico and Southwestern Texas. In this review we report the nature of the physiological, cellular and biochemical responses of these plants to the low temperature of the desert in the biosynthesis of rubber.

Studies on rubber formation in guayule in several field plantings support the conclusion that the low temperature of the fall and winter months of the Chihuahuan Desert promotes a rapid increase in rubber biosynthesis. There are definite changes in the cortical parenchyma during the biosynthesis and deposition of rubber. Discrete rubber particles are formed in the parietal and interior cytosol. Following the digestion of the cytosol in the interior of the cell and rubber particle fusion leaves the parenchyma with rubber deposits throughout the cells. The rubber transferase (RT) bound to the washed rubber particles (WRP-RT) catalyzes the formation of different length cis-1, 4-polyisoprene chains that collectively form the rubber polymer. The activities of the WRP-RT and the endoplasmic reticulum 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR) increase with exposure of the plant to low temperature and it is conceivable that these two enzymes play a pivotal role in the biosynthesis of rubber during this period. Thus guayule plants indigenous to the Chihuahuan Desert have developed a genetic system capable of responding to the low temperatures of the fall and winter of the desert culminating in the formation of rubber.

Introduction

Rubber (1,4-cis-polyisoprene) is a natural plant product found in over 2000 plant species but is only sufficiently high enough in Hevea brasiliensis and guayule (Parthenium argentatum Gray) to be of commercial interest. Hevea is a tropical tree grown in Southeastern Asia whereas, guayule is a rubber plant indigenous to 130,000 square miles of the Chihuahuan Desert of Northern Mexico and Southwestern Big Bend area of Texas (McGinnies, 1978). The polymer properties of rubber that determine its industrial use, are similar in both Hevea and guayule, but the cost of rubber production is significantly less in Hevea. This is primarily due to the ease of harvesting the rubber latex by simply tapping the Hevea trees year after year in contrast to the expensive solvent extraction procedure to extract the rubber from the harvested guayule plants. Aqueous extraction procedures (Cornish, 1996, Cornish, 1998) to extract the rubber from ground guayule plants are now available and currently used by the Yulex Corporation to furnish hypoallergenic guayule rubber for medical devices. The expansion of this commercial venture from Arizona to other growing sites may make guayule rubber available to other U.S. industries. The economic success of these expanded ventures is in part determined by the yield of rubber. Guayule is native to the Chihuahuan Desert and has developed the capacity to produce rubber growing in this desert environment. In this review of our work at Texas A&M University, we discuss the physiological, cellular and biochemical responses of the plant to the low temperature of the desert in the biosynthesis and regulation of rubber yield.

Section snippets

Guayule plants indigenous to the Chihuahuan Desert

Guayule plants are indigenous to the Chihuahuan Desert of Northern Mexico and Presidio, Brewster and Pecos Counties of Texas. A native stand of guayule in Brewster County, Texas is shown in Fig. 1. The plants are 0.3–0.6 m in height. In the 1940's strains of guayule were found to contain up to 26% rubber (Guayule, 1977). A stand of guayule plants in field plots at the Texas A&M Experiment Station and the Bridgestone Test Site, Ft. Stockton, TX in Pecos County is shown in Fig. 2. Foster et al.

The effect of low temperature on rubber formation

Bonner (1943) demonstrated that the exposure of guayule plants to 27 °C during the day and 7 °C at night with an 8 h photo period for 4 months in a controlled temperature greenhouse induced a 4-fold increase in rubber formation compared to plants grown at 27 °C for both day and night with an 8 h photoperiod. The optimum night temperature for the induction of rubber biosynthesis was in the neighborhood of 7 °C provided the days were 27 °C. It was also shown that nights at 7 °C combined with days at 7 °C

The effect of low temperature on the ultrastructural changes in the cortical parenchyma

The cellular deposition of rubber in guayule plants has been studied by Ross (1908), Lloyd (1911) and Artschwager (1943). The vascular rays of phloem and xylem contain the majority of deposited rubber in plants older than 1 year. In younger plants the parenchymatous tissue of the pith, primary cortex, epithelial cells of the resin canals and the xylem parenchyma contain a major amount of rubber deposited in the plant. A light photomicrograph of the cross-section of guayule stems of plants 1

The regulation of rubber transferase (RT) bound to rubber particles and 3-hydroxy-3-methylglutanyl coenzyme A reductase (HMGR) by low temperatures of Chihuahuan Desert

Goss et al. (1984) demonstrated that radioactive acetate and mevalonic acid (MVA) were incorporated into rubber in stem slices of cold treated guayule plants compared to stem slices from control plants. Two pivotal enzymes in this acetate-MVA-rubber pathway are RT and HMGR.

Benedict et al. (1986) described the polymerization reaction catalyzed by the washed rubber particle bound RT (WRP-RT) from guayule stem bark. The reaction mixture for the assay of the WRP-RT is given in Table 1. The WRPs are

Discussion

Goss et al. (1984) studied rubber formation in guayule plants growing at 27–32 °C days in the greenhouse and 7° nights in controlled growth chambers. Control plants were grown at 27–32 °C days in the greenhouse and 21–24 °C nights in growth chambers. After 6 months of growth the control and cold-treated plants contained 2.18% and 5.69% rubber, respectively. The stimulation of rubber formation by low night temperature was similar to earlier reports (Bonner, 1943). In other work Bonner, 1950,

Acknowledgements

This work was supported in part by grants from the NSF and The Texas Advanced Technology Program to C.R.B. and The Texas Agricultural Experiment Station to C.R.B. and M.A.F.

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    Current address: Department of Horticultural Sciences, Texas A&M University, College Station, Texas 77845, United States.

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