Histomorphological changes in shoot apices of Lactuca sativa treated with gibberellic acid

Abstract

Lettuce plants were treated with gibberellic acid (GA3) and uniconazole (UZ; a gibberellin synthesis inhibitor) to investigate the influence of GA3 on cell division frequency in the shoot apical meristem (SAM) during stem elongation and flower initiation in lettuce (Lactuca sativa) grown in a greenhouse. GA3 (0.1 mM) was sprayed on the surface of outer leaves and uniconazole solution (0.86 mM) was applied to the soil. GA3 increased cell division frequency in the peripheral zone and the rib meristem of shoot apices, and this was associated with the stimulation of stem elongation. UZ treatment decreased cell division frequency in the peripheral zone, rib meristem and subapical pith, and this was associated with restricted stem elongation. Treatment with UZ and GA3 together induced minor stem elongation. Flower induction occurred 3 d earlier in the GA3 and UZ+GA3 treatments than in the control, while the UZ treatment delayed flower initiation for more than 9 d relative to the control.

Keywords

• bolting
• floral initiation
• histone h4 gene
• in situ hybridization
• lettuce
• stem elongation