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Probing PIP patterns in
The importance of drought for crop productivity
worldwide is again emphasized, this time in a paper by Aroca et al. (La Jolla, CA and Pisa, pp. 1301–1310), reporting an investigation of the effects of drought
on water relations and on aquaporins in Phaseolus vulgaris.
Aquaporins are proteinaceous pores in membranes that permit the diffusion of
water across those membranes; PIP1 and PIP2 are classes of aquaporins located
in the plasma membrane. From the authors’ extensive study we concentrate here
mainly on the effects of drought. After 4 d of withholding water, the water
potential of the rooting medium had dropped from _0.23 to _0.63 MPa. Leaf water status was unaffected but the
transpiration rate was reduced by nearly 80 %. Re-watering the rooting medium
restored its water potential and led to a return to control transpiration rates
in the leaves. Drought also affected root hydraulic conductance (L), which
was reduced to approx. 50 %of control values. Interestingly, in plants
re-watered after drought, L remained at the value observed in droughted plants.
Study of PIPs showed that drought led to increased expression of PIP2.1 (assayed by
Northern blotting of mRNA) and increased levels of PIP1 and PIP2 proteins in
leaves; levels of PIP proteins fell again after re-watering. In roots,
droughted plants showed up-regulation of PIP1.1, PIP1.2 and PIP2.1 (no other PIP genes were assayed) plus decreased levels
of PIP2 protein (correlating with the decrease in L). Protein and mRNA returned to control levels after re-watering.
Interestingly, drought treatment did not lead to an increase in
Professor J. A. Bryant
University of Exeter, UK
j.a.bryant{at}exeter.ac.uk
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