Studies On Development Of Seed And PCD Of Mesosperm In Ginkgo Biloba L.

Fozhi, Dongtinghuang and Longyan, three important seed-purpose cultivars of Ginkgo biloba L., were selected to sample on schedule 15 d after full blossom for measuring and analyzing the seed development and the related changes of anatomical, ultra-structure and components in following two years, and PCD of mesosperm were also studied. The results were as follows:(1) During development of Ginkgo biloba ,the length ,diameter and weight of seed, increased faster within 60 d after full blossom, which growth rate tended to slow from 80 d after full blossom to ripeness. The main growth days of length and diameter were 56~58 d, and those of single seed weight were 4~9 d more than length and diameter. The main growth days of length and diameter were similar among the three cultivars, but Longyan developed fast, which entered blooming earliest and stop growth earliest, too.Its main growth days of weight were 3~5 d less than those of Fozhi and Dongtinghuang cultivars.(2) The relative components in seed varied during development, water content increased and reached to the maximum on 45~60th d after full blossom, then decreased after that; content of soluble sugar had a top on 45 d after full blossom and raised obviously from 80 d after full blossom to ripeness; starch content increased after full blossom and had a decrease for Dongtinghuang and Longyan on the 100th d; protein content decreased during seed development and reached to the highest level , 20.16%,on 15 d after full blossom, then fell slow on 30-60 d and decreased sharply on 60~100 d, the growth showed stable till harvest; change rules of both calcium and protein were resemble , which inclined to decline during development. The average calcium content from highest to slowest was Fozhi, Longyan , Dongtinghuang in order.(3) The respiratory intensity (RI) of seed had a maximum on 30 d after full blossom, RI fell rapidly from 30 to 60 d and changed little after then till maturity. Difference of cell arrangement and shape of episperm, mesosperm and endopleura became obvious during seed development. Cell size increased, number in unit area decreased. The reduce of Fozhi was in evidence. Cell shape changed from ellipse to round, the ratio of length to width increased obviously and cell changed to long ellipse. Ratio of length to width of endopleura was higher than that of episperm and mesosperm. Among the three cultivars, Longyan differentiated earliest, which structure was apparent at phase II and mesosperm lignified at phase IV.(4) The cells development of seed varied during mesosperm formation in Ginkgo biloba. Karyon shape diversified and began to move to the cell wall 5 d before phase IV,at that time nucleolus existed in the cell and organelle kept intact. Mesosperm cells wall of Fozhi and Dongtinghuang was dyed to blackblue at phase IV. Nucleolus disappeared and karyon condensed,organelle began disaggregation.On 5 d after phase IV,karyotheca disappeared, karyon broke down and the fragment moved to the cell wall. Organelle disaggregated further. DNA ladder was found on phase IV by agar gel electrophoresis after seed DNA was extracted, while the ladder couldn't be seen in phase I to phase III. All these showed the formation of mesosperm of Ginkgo biloba was programmed cell death(PCD).(5) The mesosperm of seed was made up of layers of tracheids , which had different kinds of holes on it, and the changes of shape, size and number of holes were dependent on the cultivars. With the ripening of seed, the number and area of break of tracheids was increasing. The diameter of tracheids was Longyan) Fozhi >Dongtinghuang in order.