Effect of Gibberellic acid (GA) and stratification treatment on embryo ultrastructure of Taxus chinensis var. mairei seed

Seeds of Taxus chinensis var. mairei are known for their deep dormancy that can be broken by a procedure involving variable temperature stratification. Changes of ultrastructure in seed embryo of T. mairei during stratification were investigated with a scan electricity microscope and a transmission electricity microscope. After 4 months of warm stratification, the following cytological changes were observed: an enlargement of the embryo and cotyledon. Two months of warm stratification following the cold treatment induced embryonic cells and apical meristems continued to divide. An abundance of electro-dense matter and a small amount of starch grain and mitochondria appeared, and the lipids in the embryonic cell gradually degraded. After four months of cold stratification treatment, one or two distinct nucleoli in the shoot apical meristem cells were observed, embryo increased in volume, the cotyledon became stretched, the lipids in the embryonic cell disappeared, the number of mitochondria increased, and the Golgi bodies appeared. We concluded that warm stratification with alternating temperatures increased the growth of embryos by cell expansion and enlargement. Cold stratification may induce a response to gibberellic acid and initiated cell division resulting in the release of physiological dormancy and subsequent germination of T. mairei seeds.