Decapitation of Arabidopsis floral stem suppresses elongation and any associated rate oscillation. This growth inhibition also appeared after application on intact plants of IAA transport inhibitors such as NPA. A subsequent IAA paste application on the cut surface restored growth and circadian oscillations in extension rate. These results indicate that the upper zone of the inflorescence has a major influence on floral stem extension rate and give a particular importance to auxin. Furthermore, measurement of endogenous contents of IAA and IAA-aspartate conjugate displayed that they were subjected to a circadian rhythm during Arabidopsis floral stem growth. All together, these data point out IAA as an essential factor in circadian growth rhythm regulation of Arabidopsis floral stem.
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