Effect of Seasonal Decrease in Temperature on the Content and Composition of Guayulins in Stems of Guayule (Parthenium argentatum, Gray)

Abstract

The guayulins are a family of sesquiterpene compounds that consist of an isoprenoid nucleus substituted either by trans-cinnamic or p-anisic acid, and are present only in the resinous fraction of the rubber plant guayule (Parthenium argentatum, Gray). While the natural role of the guayulins remains enigmatic, they may serve as a defense function against other plants or herbivores by virtue of the accumulation of cinnamic acid. Prior research has suggested seasonal variation in guayulin content, which has been shown to decrease as winter arrives in two different varieties. In the present study, the effect of guayulins has been evaluated in 13 different accessions cultivated under the same conditions during autumn. A general reduction in guayulin content was found in the stems from all varieties between the September and November harvest, which was accompanied by an increase in the resin content. With respect to individual guayulins, while guayulin A was the most prominent member during most of the year, guayulin C had more prominence when temperature started to decrease. In this seasonal period, the production of each member of the guayulin family in the leaves was very balanced.

Argentatin Content in Guayule Leaves (Parthenium argentatum A. Gray)

“…The leaf resin content from the three guayule accessions studied is similar to the values reported for stem resin content by Gallego et al [20], and is a suitable starting point for its industrial exploitation. Moreover, the resin percentage was consistent with values reported by Dehghanizadeh et al [2] and Rozalén et al [17], who obtained a yield of 9-10% in plants of the same age, and was much greater than the 4% reported in older plants (15-18 years old) by Spano et al [29]. No significant differences in leaf resin content were found between the three accessions under irrigation conditions; however, R1040 resin content was clearly highest under non-irrigation conditions.…”

“…Early studies on the valorization of guayule by-products focused on the extraction of essential and volatile oils from stem resin [ 13 , 14 ], while more recent attention was paid to phenolic compounds [ 7 , 15 , 16 ], particularly hydroxycinnamic and hydroxybenzoic acids, flavones, flavanols and anthraquinones [ 7 , 15 ]. In addition to the stem resin, a significant proportion of total guayulin content is found in leaf tissue, where the four major guayulins (A–D) are observed in a more consistent relationship than in the stem [ 17 ], whereas rubber content in the leaves is discarded [ 18 ].…”