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Notes:
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Polyamines are known to play important roles
in plant stress tolerance but it has been difficult to determine
precise functions for each type of polyamine and their
interrelationships. To dissect the roles of putrescine from
the higher polyamines spermidine and spermine, we generated
transgenic rice plants constitutively expressing a
heterologous S-adenosylmethionine decarboxylase (SAMDC)
gene from Datura stramonium so that spermidine and
spermine levels could be investigated while maintaining a
constant putrescine pool. Whereas transgenic plants
expressing arginine decarboxylase (ADC) produced higher
levels of putrescine, spermidine and spermine, and were
protected from drought stress, transgenic plants expressing
SAMDC produced normal levels of putrescine and showed
drought symptoms typical of wild type plants under stress,
but the transgenic plants showed a much more robust
recovery on return to normal conditions (90% full recovery
compared to 25% partial recovery for wild type plants). At
the molecular level, both wild type and transgenic plants
showed transient reductions in the levels of endogenous
ADC1 and SAMDC mRNA, but only wild type plants
showed a spike in putrescine levels under stress. In transgenic
plants, there was no spike in putrescine but a smooth
increase in spermine levels at the expense of spermidine.
These results confirm and extend the threshold model for
polyamine activity in drought stress, and attribute individual
roles to putrescine, spermidine and spermine.
This work was supported by grant AGL2004-00444 from the Ministerio de Ciencia y Tecnologia (MEC, Spain) to T. Capell. A. Peremarti is funded by a MEC FPI fellowship (BES-2005-8900); L. Bassie is funded by a Juan de la Cierva fellowship; T. Capell is a tenure-track scientist of the Ramón y Cajal Programme; P. Christou is an ICREA researcher, all at the UdL |
