Effects of gibberellic acid and temperature on growth and root carbohydrates of Delphinium seedlings
2001
Delphinium 'Blue Bird' seedlings were grown in heated (air temperature >15 degrees C) and unheated glasshouses in winter and treated with foliar sprays of gibberellic acid (GA3) or drenched with uniconazole (UZ). The unheated seedlings were exposed to temperatures as low as 5 degrees C. Under both heated and unheated growing conditions, leaf differentiation was retarded by the GA3 application. Leaves of the unheated seedlings showed very little expansion, but the GA3 application stimulated leaf expansion under chilled conditions. Root starch and mannitol decreased and root sucrose increased during cold acclimation. These changes were less in the GA3-treated seedlings than in the non-treated seedlings. The higher starch and mannitol contents in GA3-treated seedlings indicates that the GA3 application inhibits starch and mannitol utilization or conversion to sucrose. Chilling hastened flowering but the GA3 application did not. GA3 application during the chilling period increased spike volume, probably because under chilled conditions, the seedlings to which GA3 was applied expanded their leaves and were able to assimilate more than the seedlings not receiving GA3. These results suggest that exogenous GA3 apparently breaks the rosette by means of rapid enlargement of already differentiated tissues and that the action of exogenous GA3 is, essentially, different from that of the chilling treatment.
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