Difference in Effectiveness of Various Gibberellins on Shoot Elongation and Flower Formation in Pharbitis nil Chois

Abstract

Various C₂₀-gibberellins, A₁₈, A₃₈, A₂₃, A₂₈ and A₂₇, and various C₁₉-gibberellins, A₁ A₂, A₃, A₄, A₅, A₇, A₈, A₉, A₂₀, A₂₁ and A₂₂ were applied to the cotyledonary plumule of Pharbitis nil Chois., cv. Kidachi which was subjected subsequently to an inductive dark period of relatively short duration. Their promotive activities were examined in shoot elongation as well as flower formation. The order in the promoting activity of these C₂₀-gibberellins except GA₂₇ and GA₃ at 0.05μg dosage on both the shoot elongation and the flower formation was observed as follows: A₃_??_A₃₈36_??_A₂₃_??_A₁₈_??_A₂₈=water control. At 0.5μg dosage the same order in the shoot elongation was observed, but the order in the activity on the flower formation was observed as follows: A₃₈>A₃=A₂₃=A₁₈_??_A₂₈=water control. The order in the promotive activity of various C₁₉-gibberellins and GA₂₇ at 0.5μg dosage on both of the responses was observed as follows: A₃>A₁=A₇>A₅>A₂=A₄_??_A₂₀>A₂₂>A₉_??_A₈=A₂₁=A₂₇= water control. At 0.5μg dosage the same order in growth activity on the shoot elongation was also observed, but the order in the activity on the flower formation was observed as follows: A₂=A₄=A₅>A₁=A₇_??_A₃=A₂₀>A₂₁>A₉=A₈=A₂₇=water control. The gibberellins which have growth promotive activity were always active in flowering, and the opposite was also true. The discrepancy in the order of highly active gibberellins at high dosage between the growth promotive activity and the flower promotive activity may be due to the fact that flower promotive activity at high dosage somewhat decreases, irrespective of highly promotive activity in shoot elongation.