マツ類の種間交雑における受精について II

Abstract

本実験は林木育種における交雑育種を進めてゆくうえの基礎資料として, マツ属の種間交雑における交雑不能の原因を究明するために, 受粉後10日目より受精前360日目までの雌性配偶体の発達について調査した｡ その結果を要約するとつぎのとおりである｡ (1) 実験に用いた材料および交雑組合せはつぎのとおりである｡ [Table omitted] (2) 交雑は京都大学農学部演習林本部試験地において1960年5月16日および5月31日に人工交配を行なった｡ 受粉後10日目, 30日目, 以後30日目毎に280日目まで, 280日目から320日目, 330日目, 350日目および360日目まで固定した｡ 材料は球果の中央部の鱗片の胚珠を用いた｡ (3) おのおの交雑組合せによる受粉後10日目より, 40日目, 70日目の胚珠および内乳すなわち雌性前葉体の発達は, 大胞子 (胚嚢) 母細胞の後期の減数分裂から, 大胞子核は分裂をつづけ, 初期の分裂とともに容積を増大し始める｡ さらに胚嚢は空胞化し始め, 生長をつづける｡ 受粉後10日目のP. strobus (♀, 5葉) ×P. strobus (♂, 5葉), P. strobus (♀, 5葉) ×P. Koraiensis (♂, 5葉) およびP. Bungeana (♀, 3葉) ×P. Pinaster (♂, 3葉) の交雑において, 胚珠の先端部に花粉が観察された｡ この時の花粉は発芽の最初の段階である｡ (3) 受粉後100日目, 130日目, 160日目および280日目における胚珠および雌性前葉体の発達は, さらに細胞の分裂と容積の増大をつづけ, 細胞質層の方へ遊離核を押しやる｡ 受粉後280日目においては, 生長がいちじるしく増大し, 求心細胞形成の初期の段階である｡ (4) 受粉後320日目および, 330日目の発達は, 細胞の求心生長をつづけ, 胚珠はやや細長く, 増大する｡ おのおの組合せとも異常なく正常に発達している｡ (5) 受粉後350日目における発達は造卵器形成の段階である｡ 受粉後350日目においてP. strobus (♀, 5葉) ×P. strobus (♂, 5葉) の交雑において, 表面珠孔側に2個の造卵器がみられた｡ また自然受粉のP. strobus (5葉) は他の交雑組合せよりも発達が早く, 胚乳組織もさらに生長し, 珠孔側に3個の造卵器がみられた｡ 受粉後360日目においては, 造卵細胞ならびに卵核形成の段階である｡ P. strobus (♀, 5葉) ×P. excelsa (♂, 5葉) の交雑において2個の造卵器がみられ, 卵細胞の初期の発達がみられる｡ またP. strobus (♀, 5葉) ×P. Pinaster (♂, 2葉) の交雑において3個の造卵器がみられ, やや生長, 分化した造卵細胞がみられた｡ (6) おのおの種間交雑における5葉松×5葉松間の種子稔性はよいが, 5葉×3葉, 2葉の交雑はほとんど不稔を呈している｡ この交雑不能の胚珠および内乳すなわち雌性前葉体の発達は受粉後10日目より受精前360日目, すなわち造卵器および卵細胞形成までの発達は異常なく, 受粉後360日目以後の受精について現在, 材料を固定, 観察を継続中である｡

For the purpose of obtaining basic data for promoting the cross breeding in Pinus, the present study, was made on the development of female gametophyte (endosperm) from 10 days after pollination to 360 days before fertilization in order to clarify the cause of cross impossibility in interspecies crossing. The results are summarized as follws. (1) Materials and cross combinations used in the experiment are as follows. [Table omitted] (2) The crossing experiments were made on May 16 and 31, 1960, at the Head quarters Experimental Forest Station, Faculty of Agriculture, Kyoto University. Materials were fixed 10 days and 30 days after pollination, then at 30-days intervals up to 280 days, and after that 320 days, 330 days, 350 days and 360 days irregulary. Ovules were fixed from central portion only of the cones. (3) The development of ovule and female gametophyte at 10 days, 40 days and 70 days after pollination is a mearly stage of differentiation. The central portion of the nucellus is occupied by an axial row of cells, the lowest of which seemed to be at a later period of division. After that the embryo sac, with its increasing capacity, begins to become vacuolate and the growth continues. In crosses of P. strobus (♀, 5 leaves) X P. strobus (♂, 5 leaves), P. strobus (♀, 5 leaves) X P. Koraiensis (♂, 5 leaves) and P. Bungeana (♀, 3 leaves) X P. Pinaster (♂, 3 leaves) pollen grains were observed at the upper part of an ovule 10 days after pollination and it is the first stage of germination. (4) The ovule and femel gametophyte at 100 days, 130 days, 160 days and 280 days after pollination, still increase in size by the growth and division of cell and 280 days after pollination show marked growth and differentaion, This stage of development is that of the early centripetal growth. (5) The development of 350 days and 360 days after pollination is the stage of formation of archegonia and egg cell. The earlier development of P. strobus (5 leaves) of natural crossing than the other cross combinations and more ovule tisse growth were observed together with three archegonia in the superficial micropylor cell. In crosses of P. strobus (♀, 5 leaves) X P. excelsa (♂, 5 leaves), P. strobus (♀, 5 leaves) X P. strobus (♂, 5 leaves) were observed two archegonia. And also in cross of P. strobus (♀, 5 leaves) X P. Pinasters (♂, 2 leaves) were observed three archegonia. But other cross combinations not formation of the archegonia was detected. (6) In each interspecies between 5 leaves and 5 leaves in Pinus, the seed fertility is good. But seeds obtained from crosses between 5 leaves and 3 leaves or 2 leaves were shrivlled mostly. As to the cross impossiblity of interspecies crossing from 10 days after pollination to 360 days before fertilization, it has been found that the archegonia and egg cell in the female gametophyte (endosperm) develop normally.