PLANT PHYSIOLOGY , Vol 103, Issue 2 535-542, Copyright © 1993 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
Seasonal Variations in Rubber Biosynthesis, 3-Hydroxy-3-Methylglutaryl-Coenzyme A Reductase, and Rubber Transferase Activities in Parthenium argentatum in the Chihuahuan Desert
W. Ji, C. R. Benedict and M. A. Foster
Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843
The rubber content and the activities of enzymes in the polyisoprenoid
pathway in Parthenium argentatum (guayule) were examined throughout the
growing season in field plots in the Chihuahuan Desert. The rubber content
of the plants was low in July and August and slowly increased until
October. From October to December there was a rapid increase in rubber
formation (per plant) from 589.0 mg to 4438.0 mg. The percentage of rubber
in the plants increased from 0.7% (mg/g dry weight) in August and 1.27% in
October to 5.5% in December. The rapid increase in rubber formation may
result from exposing the plants to low temperatures of 5 to 7[deg]C. The
activity of 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) was 21.1 nmol
mevalonic acid (MVA) h-1 g-1 fresh weight in the bark of the lower stems in
June during seedling growth and decreased to 5.1 nmol MVA h-1g-1 fresh
weight in July and 2.9 nmol MVA h-1 g-1 fresh weight in September. From
October to December, the activity increased from 5.0 to 29.9 nmol MVA h-1
g-1 fresh weight. The activity of rubber transferase was 65.5 nmol
isopentenyl pyrophosphate (IPP) h-1 g-1fresh weight in the bark in
September and increased to 357.5 nmol IPP h-1 g-1 fresh weight in December.
The rapid increase in the activities of HMGR and rubber transferase
coincided with the rapid increase in rubber formation. The activities of
MVA kinase and IPP isomerase did not significantly increase in the fall and
winter. A tomato HMGR-1 cDNA probe containing a highly conserved C-terminal
region of HMGR genes hybridized at low stringency with several bands on
blots of HindIII-digested genomic DNA from guayule. In northern blots with
the HMGR-1 cDNA probe at low stringency, HMGR mRNA was high in June and
November, corresponding to periods of high HMGR activity during seedling
growth and rapid increase in rubber formation. The seasonal variations in
rubber formation and HMGR mRNA, HMGR activity, and rubber transferase
activity may be due to low temperature stimulation in the fall and winter
months.
