Morphologic and anatomical observations in the process of ovulate strobilus generation and development in Pinus tabuliformis

In order to accurately grasp the characteristics of the external morphology and the internal anatomy of ovule growth in the process of ovulate strobilus generation and development in Pinus tabuliformis and establish the corresponding relationship between external morphology and internal tissue development, morphological measurement and paraffin section detection were adopted to perform morphology and anatomy observation on ovulate strobilus of P. tabuliformis in Beijing throughout its whole development process from flower bud initiation to seed maturation during 2013-2016. The results indicated that the flower bud of P. tabuliformis in Beijing presented differentiation in the early August of the first year, and the ovulate strobilus primordium formed at the end of September, entered dormancy in winter, and continued to develop in the spring of second year. Ovulate strobilus could be distinguished in morphology in the early April. Around April 10, the ovule cell started differentiation, the longitudinal diameter of ovulate strobilus was about 5.0 mm at this time. The megaspore mother cell formed around April 20 and subsequently made the meiosis to form the functional megaspore. Around May 10, ovulate strobilus caught the pollens from the staminate strobilus, subsequently, the color of cone scales changed from red to green, and then to brown. Simultaneously, the cones grew up slowly, in which the functional megaspore presented several mitosis to form the megagametophyte with 16-32 free nuclei. The ovule entered megagametophyte free nuclei period at the beginning of June, and entered dormancy in winter. At this time, the longitudinal diameter of ovulate strobilus was about 11.0 mm. Until the spring of the third year, the megagametophyte re-developmented, and around April 20, contained thousands of free nuclei. The longitudinal diameter of ovulate strobilus was about 21.0 mm at this time. The ovule entered megagametophyte cellularization period around April 30, and at the beginning of May, the archegonium started development and formed egg cell. At this time, the longitudinal diameter of ovulate strobilus was about 37.0 mm. Until the egg cell matured around May 10, the cellularization process of female gametophyte completed. During the period of the megagametophyte and cone development, the color of cone scales returned to green gradually. Fertilization started around May 20, and the longitudinal diameter of ovulate strobilus was about 45.0 mm at this time. After that, the embryo developed continuously. The longitudinal diameter of ovulate strobilus was about 58.0 mm on July 10. Subsequently, ovulate strobilus atrophied slightly, and the cone scales were gradually subject to lignification and became seed scales. Until the end of October, the cone cracked, its longitudinal diameter was about 53.0 mm, and the seeds matured and were popped up. The ovulate strobilus development of P. tabuliformis in Beijing lasted for 2 years and 2 months from flower bud differentiation, primordium formation, ovule differentiation, megaspore mother cell generation and meiosis, pollination, megagametophyte and archegonium development, egg cell maturation, fertilization, embryonic development to ovulate strobilus and seed maturation.This study provids morphology and anatomy basis for relevant researches on the development of gymnosperms strobilus.