Abscisic Acid and Xanthoxin Contents in the Long-Day Plant Lolium temulentum L. In Relation to Daylength

In L. temulentum L., flowering can be inhibited by application of abscisic acid (ABA) close to the shoot apex towards the end of an exposure to a single inductive long day. However, analysis by gas-liquid chromatography showed that the contents of endogenous ABA and xanthoxin in L. temulentum leaves are not consistently changed after an inductive photoperiod. Apex extractions carried out when (±)-ABA application near the apex is most inhibitory to flowering also showed no consistent effect of daylength on the content of ABA which was, however, much higher than in leaves. Thus it is unlikely that induction of flowering in L. temulentum by exposure to long days is due to changes in the endogenous levels of ABA and xanthoxin in the leaves or of ABA in the shoot apex.