Roles of Gibberellin and Auxin in Promoting Seed Germination and Seedling Vigor in Pinus massoniana

摘要

Masson pine (Pinus massoniana Lamb.) is an important timber species and is widely planted in southern China. A large quantity of seed is required for sowing each year. However, low germination in the nursery has resulted in low seedling yields with a consequent negative impact on the Masson pine afforestation program. The purpose of our study was to determine whether gibberellin (GA(3)) or indole-3-acetic acid (IAA) would be more effective in propagating the species from seeds for afforestation and to elucidate their effects on seed respiration and endogenous hormone levels. Seeds were soaked in GA(3) and IAA solutions of different concentrations at 25 degrees C in the dark for 24 hours, and a germination test was conducted. Seed respiration was measured indirectly by estimating oxygen consumption in a closed system. Endogenous hormone levels were analyzed by gas chromatography/mass spectrometry (GC/MS). The germination test showed that the most significant promotion of seed germination and seedling vigor occurred at 5 x 10(-5) M GA(3) in both varieties and that the effects of IAA were variety dependent. Oxygen-sensing measurements showed that increased metabolism time, critical oxygen pressure, and relative germination time were decreased and the oxygen metabolism rate was increased in IAA-and GA3-treated seeds. GC/MS analysis showed that the application of 5 x 10(-5) M GA(3) decreased the endogenous abscisic acid (ABA) content, but increased IAA and GA(1), levels. Our experiment suggests that exogenous GA(3) improves seed germination and seedling vigor of Masson pine through promoting seed respiration or lowering the ABA level and stimulating IAA and GA(1), biosynthesis.