Morphology and biochemical characteristics of pistils in the staminate flowers of yellow horn during selective abortion

Yellow horn (Xanthoceras sorbifolia Bunge), an andromonoecious woody plant, has both hermaphrodite and staminate flowers. Both stamens and pistils in hermaphrodite flowers develop normally, but the pistils are aborted and the stamens develop normally in staminate flowers. To investigate the anatomical and biochemical characteristics of the aborted pistils in staminate flowers, anatomical and biochemical assays were carried out. Microstructure, ultrastructure and their histochemistry were analysed. The hypotheses that amylase and endogenous hormones are involved in pistil abortion were tested by comparing the homochronous pistil tissues in both hermaphrodite and staminate flowers. We conclude that pistil abortion occurs at the meiosis stage of megasporocyte cells and programmed cell death in staminate flowers. Simultaneously, we observed that starch grains and protein abundance are of benefit to megasporocyte meiosis. Our study indicates that the low activity of amylase isozymes a3 and a4 will result in insufficient soluble sugars for pistil development. The endogenous hormones gibberellic acid (GA3) and abscisic acid (ABA) in the pistil of both staminate and hermaphrodite flowers at four stages were measured by gas chromatography–mass spectrometry. The results suggested that both ABA and GA3 are related to pistil abortion. In addition, a high ratio of GA3 and ABA exists in the stage of megasporocyte cells until the stage of megasporocyte meiosis I, which affects the normal activity of sucrose invertase and pistil development in staminate flowers. These results suggest that starch grains, proteins and endogenous hormones are important for pistil development and, as well, that pistil abortion in staminate flowers is related to the level of endogenous hormones and the activity of amylase isozymes.