Abstract
AbstractThe dormancy of celery seeds was broken by red light treatment given during imbibition and this effect was reversed by far‐red light. The exact quantitative relationship between the timing and duration of red light treatment and dormancy‐break has not been elucidated. However, the accumulated effect of daily 5 min exposures was greater than a single 5 min exposure on the second day of imbibition. The effects of red light treatment were simulated by treatment with a mixture of the gibberellins A4 and A7 and N6‐‐benzyladenine. A correlation between the requirement for red light and the requirement for exogenous cytokinins in the presence of GA4/7 was demonstrated by using six cultivars with different dormancy characteristics. In order to investigate the role of natural cytokinins in dormancy‐break, quantitative and qualitative changes in cytokinins were measured in celery seeds immediately after red‐light treatments. Rapid increases in n‐butanol‐soluble cytokinins following irradiation were associated with concomitant decreases in water‐soluble cytokinins, suggesting a red light induced cytokinin conversion. Three of the cytokinins present in the n‐butanol fraction of celery seed extracts were chromatographically similar to zeatin, zeatin riboside and N6‐‐A2‐‐isopentenyladenosine (i6Ado). The elution profiles from a PVP column of two others were similar to BA and its riboside. The possibility that these two cytokinins act as specific dormancy‐breaking cytokinins in celery seeds is discussed. There was little evidence of reversal of the cytokinin conversion mechanism by far‐red light exposure.
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