75 Integrating Membrane Transport with Male Gametophyte ... - TAIR

235 Ethylene Signaling Components Are Involved in Polycyclic Aromatic Hydrocarbon Stress
Responses in Arabidopsis thaliana
Adan Colon-Carmona, Merianne Alkio, David Weisman
University of Massachusetts-Boston
With the growing awareness of hazardous polycyclic aromatic hydrocarbons (PAHs) to humans, the interest in
plant responses to these environmental pollutants is increasing. We studied ethylene signaling in plant PAH stress by 1)
analyzing stress responses of Arabidopsis mutants, defective in different components of the ethylene-signaling pathway,
to the model PAH, phenanthrene; 2) studying ethylene-inducible gene expression in PAH-exposed GUS-reporter plants
and 3) comparing global gene expression changes of PAH- and ethylene-exposed plants. Results: 1) PAH-exposed wild
type plants (wt) had shorter hypocotyls and roots than wt grown on control medium. However, growth of some ethylene
insensitive mutants (etr1-1, ers2-1, ein2, ein6) was even more inhibited by PAH than that of wt, whereas constitutive
ethylene signaling mutants (eto3, ctr1-1, and the triple mutants etr1-6xetr2-3xein4-4 and etr2-3xers2-3xein4-4) generally
appeared resistant to the inhibition of organ elongation, and often even had longer roots on PAH than on control medium.
The mutants did not differ from wt in respect to PAH-induced oxidative stress. However, compared to wt, the rosettes
ctr1-1 and etr1-7 were more reduced in size and more chlorotic, indicating greater PAH sensitivity. 2) After PAHexposure,
GUS expression was slightly induced in chitinase-GUS plants but strongly induced in GSTF2-GUS plants. 3)
DNA microarray analyses (our own, and published data) support the view that parts of the ethylene signaling pathway
are involved in the PAH response, although ethylene signaling pathway as a whole is not switched on. We conclude that
while PAH stress signaling in plants overlaps with other signaling pathways, it involves a unique subset of the known
molecular players as well as unidentified cellular components.
Funded by NSF-IBN 0343856
236 The Magnitude of Phosphate-Starvation Responses is Determined by the Rate of Plant
Growth and Cell Division
Fan Lai, Peter Doerner
Edinburgh University
Plants require adequate and balanced quantities of mineral nutrients for optimal growth, but such conditions are rarely
found in nature. For example phosphate (Pi) is required for RNA and DNA synthesis, phospho-lipids, in intermediate
energy metabolism and to regulate protein function. We examined the relationship between Pi starvation responses and
plant growth. To assess Pi starvation responses, we quantified gene expression responses of a set of Pi-responsive genes.
When plant growth was globally enhanced, e.g. by supply of sugars, Pi starvation responses were enhanced. We examined
whether this was a nutrient-specific effect or caused by altered growth magnitude. When plant growth was selectively
inhibited (e.g by osmotic stress) starvation responses were significantly reduced. Selective growth inhibition (for example
of root growth by elevated nitrogen supply) led to reduced Pi starvation responses in roots. These data show that the
magnitude of Pi starvation responses is determined by the demand for phosphate. We found that the magnitude of cell
proliferation, not cell expansion was responsible for setting phosphate demand. Moreover, starvation responses appear
to be controlled organ autonomously. This is in contrast to previous suggestions that plant phosphate status is sensed
in the shoot (Burleigh and Harrison 1999). We propose a model in which growth control networks regulating meristem
activity and therefore shoot-root mass ratios, which then sets the level of demand for phosphate in plant organs. Altered
allocation of growth potential, e.g. by altering carbon-nitrogen ratios, is independent of phosphate nutritional status and
dominates over phosphate starvation-induced growth responses.
Burleigh, S. H. and M. J. Harrison (1999). Plant Physiology 119: 241-248.