Restoration of seed germination at supraoptimal temperatures by fluridone, an inhibitor of abscisic acid biosynthesis

Fluridone, an inhibitor of ABA biosynthesis, restored the seed germination of lettuce (Lactuca sativa L. cv. Grand Rapids) and many other plant species at supraoptimal temperatures. ABA content in lettuce seeds after imbibition quickly decreased at 23 degrees C, but not at 33 degrees C (a supraoptimal temperature). Fluridone caused a decrease in ABA content at 33 degrees C, which suggests that the maintenance of high ABA content could be responsible for high-temperature inhibition of germination of lettuce seeds. This probably results from an increase in the rate of ABA biosynthesis at the higher temperature. The present study indicates that ABA plays a decisive role in the regulation of seed germination at supraoptimal temperatures.