Interactive influence of temperature and growth light intensity on rubber accumulation and rubber transferase activity in guayule (Parthenium argentatum Gray)

Interactive effects of low night temperature (15 degreesC) and growth light intensity on rubber particle proteins and rubber transferase activity were investigated in stem bark tissue of guayule (Parthenium argentatum Gray, v ar 11591), a desert shrub of commercial interest as an additional source of natural rubber. Three-year-old guayule plants were subjected to 60 cycles of 30/15 degreesC day/night temperature regime with 12h photoperiod in a co ntrolled environment growth chamber. Plants were also treated with 30/20 de greesC and 30/30 degreesC day/night temperatures for 60 cycles under varyin g day light growth regimes of 450, 900, and 1500 mu Em(-2) s(-1). Rubber pa rticles were extracted and the associated proteins were characterized in st em tissues of guayule. SIDS-PAGE protein profile of the rubber particles sh owed an abundant rubber particle protein (RPP) with a molecular weight of 5 0 kDa. This protein accumulated at higher concentrations after 60 cycles of cold night temperature (15 degreesC) treatment. Rubber transferase (RuT) a ctivity was estimated in the rubber particle fractions at an optimum pH of 7.4. Plants exposed to 60 cycles of 30/15 degreesC temperature showed 80% m ore rubber transferase activity compared to the control plants that were gr own in the field (34/28 degreesC). The results indicate that rubber biosynt hesis in plants treated with 15 degreesC night temperature for 60 cycles wa s superior to that of those grown under natural photoperiod. A radiation of 900 mu Em(-2)s(-1) had a positive effect on guayule plants subjected to 30 /15 degreesC temperature treatment, showing the highest rubber transferase activity compared to the growth light intensities of 450 mu Em(-2)s(-1) or 1500 mu Em(-2)s(-1) under similar temperature regimes. In conclusion, low t emperature modulation of the rubber particle proteins under optimum growth light intensity could enhance the rubber production in guayule plants throu ghout the year and not just restricted to the winter months.