Effects of gibberellic acid and temperature on growth and root carbohydrates of Delphinium seedlings

Delphinium 'Blue Bird' seedlings were grown in heated (air temperature > 15 degreesC) and unheated glasshouses in winter and treated with foliar spray s of gibberellic acid (GA(3)) or drenched with uniconazole (UZ). The unheat ed seedlings were exposed to temperatures as low as 5 degreesC. Under both heated and unheated growing conditions, leaf differentiation was retarded b y the GA(3) application. Leaves of the unheated seedlings showed very littl e expansion, but the GA(3) application stimulated leaf expansion under chil led conditions. Root starch and mannitol decreased and root sucrose increas ed during cold acclimation. These changes were less in the GA(3)-treated se edlings than in the non-treated seedlings. The higher starch and mannitol c ontents in GA(3)-treated seedlings indicates that the GA(3) application inh ibits starch and mannitol utilization or conversion to sucrose. Chilling ha stened flowering but the GA(3) application did not. GA(3) application durin g the chilling period increased spike volume, probably because under chille d conditions, the seedlings to which GA(3) was applied expanded their leave s and were able to assimilate more than the seedlings not receiving GA(3). These results suggest that exogenous GA(3) apparently breaks the rosette by means of rapid enlargement of already differentiated tissues and that the action of exogenous GA(3) is, essentially, different from that of the chill ing treatment.