Gibberellin A(4/7) and the Promotion of Flowering in Pinus radiata: Effects on Partitioning of Photoassimilate within the Bud during Primordia Diferentiation.

Gibberellin A(4/7) mixture (GA(4/7)), a highly effective promoter of early and enhanced flowering in the Pinaceae, caused a significant reallocation of dry matter and (14)C-photosynthate within terminal buds of Pinus radiata D. Don within 8 days of hormone treatment. Treatment with GA(4/7) to terminal shoots of vigorous, potentially flowering mature grafted propagules reduced the flow of photoassimilated (14)C and dry matter into the terminal bud as a whole, but significantly increased the dry matter and (14)C allocated within the bud to developing long-shoot primordia (potential seed-cone buds). This was accomplished at the expense of the structural tissues, the apical dome region, and the vegetative branch buds. Although GA(3) caused a similar reallocation of dry matter within the terminal bud, it was significantly less effective than GA(4/7) thus appears to have, in addition to any nutrient diversion abilities, a distinct morphogenic function in sexual differentiation.