Effect of Gibberellin and Uniconazole on Mesocotyl Elongation of Dark-Grown Maize under Different Seeding Depths

Seeds of five maize inbred lines, including 3681-4, were treated with gibberellin A(3) (GA(3)) and uniconazole (UCZ) under deep seeding and shallow seeding in order ot elucidate the physiological mechanism of maize mesocotyl eleogation under different seeding depths. GA3 was the most effective at 10(-5) M and the mesocotyl eleongation of 3681-4, 178, Zng 3, Huang C, Han 21 was promoted at this concentration by 60.4%, 44.6%, 42.5%, 24.5% and 44.2% under 20 cm seeding depth, respectively. under 2 cm seeding depth, however, there were no significant differences between mesocotyl length of all inbred lines at any concentration. UCZ treatment at concentrations higher than 10(-5) M, significantly inhibited mesocotyl elongation in all inbred lines under seeding depths of both 20 cm and 2 cm. Interestingly, mesocotyl eleongation of only 3681-4 was significantly inhibited at the concentration of 10(-7) M. These results suggested that mesocotyl elongation was more sensitive to gibberellin A (GA) under deep seeding than under shallow seeding, and that 3681-4 was more sensitive to GA than the other inbred lines. Endogenous gibberellin A(1) (GA(1)) contents in the mesocotyls of 3681-4 and 178 treated with GA(3) and UCZ were accordent with their morphological reponses. GA(3) promoted cess elongation rather than cell division, and that UCZ inhibited both cess eleongation and cell division in 3681-4 and 178.