The endogenous contents of indoleacetic acid (IAA) and abscisic acid (ABA) were assayed simultaneously in etiolated squash hypocotyls that had been subjected to water stress applied to squash roots by immersing them in 60 mM polyethylene glycol solution. The growth rate and suction force of the hypocotyl under this water-stress condition were determined for comparison with the two hormone contents.Water stress retarded hypocotyl growth and increased the suction force of hypocotyl cells, as the ABA content increased, by 5-fold of the initial content one day after treatment with polyethylene glycol. The ABA contents thereafter remained high up to day 4. The increase in ABA content was detected in stressed hypocotyl as early as 6 h after treatment, when water stress had not affected hypocotyl growth. When the water stress was terminated one day after treatment began, hypocotyl growth immediately recovered, and the ABA content decreased to the value for unstressed hypocotyls in one day. The IAA content gradually decreased in unstressed hypocotyls, but was maintained at a high value in stressed hypocotyls.Logarithmic concentrations of endogenous ABA (ng/g fr wt) were correlated significantly with the suction force of the hypocotyls (r=0.92) and with the growth rates (r=−0.78). IAA content was correlated neither with the growth rate nor the suction force. These results suggest that the endogenous ABA content was associated with the stunted growth of the etiolated squash hypocotyls produced by water stress but that the endogenous IAA content did not have an important role in growth regulation under water stress condition
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