Growth Regulators and the Phytochrome‐Mediated Dormancy of Celery Seeds

Abstract

Seeds of five celery (Apium graveolens L.) cultivars germinated at 15°C in the light or dark but at 22°C only in the light. This light requirement was overcome by treatment with a mixture of the gibberellins GA4 and GA7 (GA4/7) but interactions of cytokinins, daminozide, ethephon, EDTA and N-phenyl-N'-4pyridylurea (NC5392) with GA4/7 were observed. Varietal differences in response to GA4/7 concentration and the requirement for cytokinins were related to the upper temperature limits for germination of the different cultivars. Seeds of cultivars responding to low concentrations of GA4/7 appeared to contain less natural inhibitor than those requiring either high concentrations of GA4/7 or cytokinin in addition to low GA4/7. The cytokinin requirement for germination was partially removed by leaching the seeds with water. Interaction studies with applied hormones indicated that in seeds incubated in the light inhibition by abscisic acid was partially alleviated by N^-benzyladenine but not by GA4/7 application. The implications of these results are discussed in relation to the involvement of natural plant hormones in the dormancy mechanism of celery seeds.

Possible control of gibberellin-induced release of temperature-dependent primary dormancy in seeds of celery (Apium graveolens L.) by transmembrane ion fluxes

“…Conversely, 18-C-6 an ionophore which has been shown to have major effects on K+ fluxes [7, 211 , inhibited GA,,-induced germination but was ineftective in the presence of BA (Table 4). These and previous data [4, 181 are highly suggestive that the availability of gibberellins to exert their primary action on germination [3,27] is in some way controlled by transmembrane ion exchange and that this in turn may be regulated via a cytokinin/inhibitor interaction [13,27].…”

“…From previous experiments [27] it is clear that in darkness there is a threshold temperature above which GA4,, treatment becomes ineffective although this is dependent on the concentration of GA@, and the cultivar used (Figure 1). Although ethephon treatment restores the effect of G&,,, many other compounds are equally effective [14,24,271, indicating that the mechanism involved may not be specifically dependent on ethylene.…”

“…Celery (Apium graveolens L.) seeds possess an innate or primary dormancy which is modified by both temperature and light [27] and which for the purposes of this report is termed 'thermodormancy'. The seeds exhibit classical phytochrome (red/far red) reversal effects [25 J .…”

Comparative effects of gibberellins and an N-substituted phthalimide on seed germination and extension growth of celery (Apium graveolens L.)

“…seeds is characterised by a failure to germinate above 16-18°C in the dark or 22-27°C in the light, the exact temperatures depending on the cultivar examined [7] . This 'thermodormancy' may contribute to the difficulties encountered in the establishment of glasshouse-and field-grown crops .…”

“…Ethephon is used in the commercial seed soak treatment because it enhances the effect of gibberellin in breaking dormancy [7] . Other chemicals including daminozide may be similarly, though not as consistently, effective as ethephon [6] .…”