侧柏雌球果及其胚珠的发育_英文_

侧柏雌球果及其胚珠的发育_英文_ () 植 物 学 报 2000 , 42 6:564 - 569 Acta B ota nica Si nica 侧柏雌球果及其胚珠的发育 Ξ 张 泉 邢树平 胡玉熹 林金星 ( )中国科学院植物研究所 , 北京 100093 ( () ) 摘要 : 观察了侧柏 Platycladus orientalis L . France胚珠的发育过程及后期球果苞片的结构变化 。在北京 ,雌球 果原基 7 月分化 。通常一个球果有 4 对苞片 ,中部两对可育 ,靠球果顶端一对各产生一枚胚珠 ,其下一对各两枚 。 胚珠的发育顺序是向顶的 ,下部可育苞片腋部的两枚胚珠源于同一原基 。胚珠原基分化成珠心和珠被 ,在发育过 程中 ,珠被逐渐包围珠心 ,最后形成烧瓶状的胚珠 。11 月到次年 1 月 ,球果处于休眠状态 。3 月中旬 ,苞片张开露出 胚珠接受花粉 。传粉后 ,苞片近轴面居间生长迅速 ,形成突起 ,并将苞片推到了水平位置 。成熟果鳞有两组维管 束 ,远轴面维管束延伸至苞片 ,近轴面延伸到居间生长突起 。近轴面维管束发育较晚 ,其木质部朝向远轴面 。 关键词 : 侧柏 ; 胚珠发育 ; 球果发育 ; 苞片结构 () 文章编号 : 057727496 20000620564206 中图分类号 : Q944. 4 文献标识码 : A Cone and Ovule Development in Platycla dus orie ntalis ( Cupressaceae) 3ZHANG Quan , XING Shu- Ping , HU Yu- Xi , L IN J in- Xing ( )Institute of Botany , The Chinese Academy of Sciences , Beijing 100093 , China () Abstract : Seed cone in Platycladus orientalis L . France consists of four or five pairs of decussate bracts. Usually , two pairs of the fertile bracts in the middle of the cone subtend six ovules , which initiate in an acropetal manner . Only one ovule presents on each of the upper fertile bract , while two ovules initiate from a common primordium in the axil of lower bracts. In Beijing , most female cones initiated in J uly. All parts of the cone formed before dormancy , which occurred during November to the next J anuary. After pollination in March , bract morphology changed dramatically ; intercalary growth of the bract base formed a conspicuous pro2 tuberance , in which inverted vascular system developed. Furthermore , ovules on different pairs of bracts initi2 ated in an acropetal manner and two ovules in each lower fertile bract initiated from a common primordium , which was different from the basipetal initiation of ovules and independently formed single ovule as reported by Takaso in Calltris . Key words : Platycladus orientalis ; ovule development ; seed cone development ; bract structure ( ) Platycladus orientalis L . Franco , a monotypic ment with a view to providing some extra data for cone genus belonging to Cupressaceae , is one of the best morphology. known trees in cultivation all over the world. Many mor2 It is now generally accepted that the seed cones of phological and embryological studies have provided evi2 most conifers are compound structures , in which the seed 1 - 3 scale represents a modified branch borne in the axil of a dence for its taxonomic significance. Recently Xing 4 bract scale . In Cupresaceae , the bract and ovuliferous et al investigated the mechanism of pollination in P. scale are fused. However , there is no ovuliferous scale orientalis , and found that the ovule played a positive role in pollen capture by secreting pollination drop . However , other than bract existed in P. orientalis. these studies were largely concerned with the well- estab2 1 Materials and Methods lished cones and little information is available for the early stage of cone development and formation of bract structure P. orientalis were collected peri2 The seed cones of in the mature cone . Therefore , we attempted to investi2 odically throughout the annual cycle from mature plants gate the formation of all parts of the cone and the struc2 growing in Beijing Botanical Garden of the Institute of tural changes of bract in the late stage of cone develop2 Botany , The Chinese Academy of Sciences. All samples Received : 2000201220 Accepted : 2000203223 Foundation item : The Innovative Grant of the Chinese Academy of Sciences. 3 Author for correspondence . E- mail : < linjx @ihw. com. cn > . in this study were fixed in FAA. cones became mature in September , the bracts turned to ( ) be woody and hard , and opened along the edge of the For scanning electron microscopy SEM, the fixed young seed cones were dissected and dehydrated in an al2 2 bracts and exposed the seed for dispersal . The whole de velopmental process was summarized in Table 1 . cohol series , critical-point dried and coated with gold palladium. Observation was made under a Hitachi S- 800 2 . 2 Surface morphology of different stages of the SEM operating at 30 kV. developing cone For histology and vascular analysis the fixed cone Bract initiation was similar to that of leaves in decus2 samples were dehydrated in graded alcohol , embedded in sated manner . The axillary complexes initiated in an acropetal sequence immediately after the formation of μparaffin , cut at 6 - 9 m and stained with haematoxylin bracts , i . e . the ovules subtended by the lower pair of and safranin. fertile bracts initiated earlier than those of the upper pair . 2 Results In J uly , at the axil of each of the lower fertile bracts , two potential ovules differentiated on each of the bract pairs as 2 . 1 Phenology of seed cone development ( ) a broad swelling was observed Fig. 1. Then a furrow P. orientalis usually produced abundant cones orig2 formed radically in the swelling and two ovule primordia inating from some shoot apexes that subsequently trans2 ( ) appeared Fig. 2during which time only one ovule pri2 formed into the reproductive shoot . The transition from mordium initiated at the axil of each upper fertile bract vegetative to reproductive shoot occurred in J uly in Beijing ( ) Fig. 3. It was clearly shown that the acropetal initia2 and the newly formed seed cones could be distinguished tion in different pairs , i . e . , ovules , first arised in the from the vegetative buds by their distinctive curvature . axils of lower fertile bracts. Following this , the ovule pri2 The seed cones were not simultaneously initiated and the mordia enlarged and became hemispherical and all ovules initiation process for the whole plant lasted for about 3 ( ) tended to appear synchronously Fig. 4. Each ovule pri2 weeks. After all parts of the cone formed within two mordium differentiated a collar- like structure around the weeks , the growth of cone turned slower , and finally en2 base of the nucellus , which became the integument , en2 tered dormancy during November to the next J anuary. The ( ) closing nucellus progressively Figs. 5 ,6. As ovule de2 young cone consisted of four or five pairs of decussate veloped , the integument appeared bilaterally symmetrical bracts. Although two or three pairs of fertile bract gener2 because the tallest part of the collar was on the adaxial ally positioned in the middle of the cone , only one ovule ( ) side and the lowest part on the abaxial side Fig. 7. At presented on each of the upper fertile bract , and two last the collar overgrew the nucellus and formed a mi2 ovules in the axil of the lower bract . In other words , there ( ) cropyle Fig. 8. Until then , all parts of the cone were were 6 - 10 orthotropous ovules per cone in total . In our well established , then growth slowed down and entered observation , most of the cones had six ovules , thus the dormancy in winter . At pollination time , the ovule was following description is based on the six-ovule cones. ( ) funnel shaped with a round micropyle Fig. 9. In the middle of March , the curved cones became ( ) After pollination , bract morphology changed dramati2 upright and the bracts opened Fig. 14, the ovules ex2 cally due to the intercalary growth of the bract base and posed and produced pollination drop s ready to receive ( ) pollen. After pollination , the bases of the bracts grew gave rise to a protuberance Fig. 15. With the growth of the protuberance , it drove the bract apex from its original rapidly. The bracts were fleshy and grew close to one an2 vertical position outwards and became horizontal . other so as to enclose the ovules in the cone . When the Ta ble 1 Phenology of seed cone development in Platycladus orientalis Developmental stage Approximate starting month of stage Seed cone initiation Early J uly Cone development August to September Beginning of seed cone dormancy October End of seed cone dormancy Mid- February Pollination Middle March Late March Seed cone closure Cone maturation and seeds shedding September to October 植 物 学 报 566 Acta B otanica Sinica 42 卷 Figs. 1 - 9. SEM photographs of dissected seed cones of Platycladus orientalis at successive stages of development . 1. Showing the upper () fertile bracts and the broad swellings arrowat the axil of lower fertile bract initiation , ×250. 2. Initiation of ovule primordium , note the for2 () mation of the furrow arrow, ×200. 3. Initiation of the ovules at the axil of the upper fertile bracts , ×200. 4. Showing the six hemispheri2 cal ovules , ×200. 5. Showing the differentiation of the integument and nucellus from the ovule primordium , ×170. 6. Late stage of ovule initiation , ×150. 7. Showing the bilateral symmetric growth of the integument , ×110. 8. Seed cone at the stage of winter dormancy , ×100. 9. At the proximate stage of pollination , showing lateral ridge of ovule development , ×60. Abbreviations : br , bract ; i , integument ; n , nucellus ; op , ovule primordium ; ov , ovule . Figs. 10 - 15. Longitudinal sections of developing cones of Platycladus orientalis . 10. Differentiation of ovule primordium , ×80. 11. Dif2 ferentiation of integument , ×80. 12. Late development of integument and nucellus of ovules , ×80. 13. Seed cone in the stage of winter dor2 mancy , ×80. 14. Seed cone at pollination stage , showing the opened bract and the conspicuous ovules , ×55. 15. Post- pollination develop2 () ment of the bract , showing the growth of the protuberance arrow, ×50. 植 物 学 报 568 Acta B otanica Sinica 42 卷 Fig. 16. Serial transverse sections of the cone of Platycladus orientalis at late developmental stage . A. At level of upper fertile bracts trace , showing the branched trace . B. At a lower level , showing the vascular trace branching into both up2 per and lower pair of bracts. C. At the level of the lower bracts , showing the branched trace . D. At the base of the cone , showing the vascu2 lar system just as that of the vegetative shoot . Seeds , stippled. Resin canals , dotted out line . Arrows indicate orientation of xylem. tbr , trace of the bract ; pt , trace of the protuberance . Consequently , the bract lied at the back of the protuber2 lower fertile bracts and initiated upwards , which was a ance , the latter acting like a protective structure gradually typical acropetal initiation in different pairs. However , enclosed the seed. Calltris , based on the data of the cone development in 5 2 . 3 Histology and va sculature Takaso and Tomlinsonclaimed that the basipetal initia2 Histological study in this investigation was limited to tion of ovules may be a universal feature of development in localize the intercalary meristems , and to investigate the cone of Cupressaceae . This discrepancy indicated that the origin of the mature vascular system. At the time of ovule initiation pattern of ovules could be a taxonomic feature initiation , the axial bundle ended blindly in the meristem and a general conclusion for a family should be based on a at the base of the bract pairs , only the protoxylem and the broad investigation. protophloem continued into the bracts themselves and It was of interest to note that two ovules initiated from a common primordium at the axil of the lower bracts. there was no vascular tissue associated directly with the However in other species examined , such as Thuja plica2 ( ) ovules Figs. 10 - 13. 6 5 7 The vascular system of the young cone up to the time ta , Calltris and Libocedrus , the ovule usually ini2 of pollination was very similar to that of the vegetative tiated independently , just in the same way as single ovule initiated in the axil of the upper fertile bracts in P. orien2 shoot . Each bract had a single central trace . In the cross 8 section of the internode , there were usually six to eight talis . Takaso and Tomlinsonin their investigation of vascular bundles , four of which were the axial bundles , ( ) cone and ovule ontogeny in Cryptomeria Taxodiaceae and others represented traces to the higher pairs of bracts (reported that four ovules and the associated teeth ovulif2 ( ) ) Fig. 16 ,D. erous scaleinitiated from a common primordium. They interpreted that the large axillary primordium was a branch In serial transverse sections of the seed cone at the ( ) complex , and ovules were located on the sprophyll termi2 late developmental stage Fig. 16, the protuberance was nal. As for P. orientalis , it seemed difficult to identify the dominant feature . The new vascular system was dis2 whether the common primordium represented as axillary tinguished by its inverted orientation , i . e . , the xylem ( ) shoot or not . Nevertheless , the results offered hints for oriented abaxially Fig. 16 , A - C. The normal adaxial further investigation towards the revelation of the morpho2 orientation was shown as a trace of bract . This series of strands fused at the base of the bract and attached to the logical nature of the common primordium. ( ) four axial bundles Fig. 16. 3 . 2 Post- pollination development of bract In P. orientalis , intercalary growth of the adaxial 3 Discussion side of the bract exceeded the abaxial side after pollina2 tion. Eventually , a protuberance formed by uneven inter2 3 . 1 Ovule initiation calary growth with earlier bract attached to the back of the P. orien2 Our observation on cone development of protuberance as a curved spine . In many earlier reports , talis provided some new information for understanding of the protuberance was defined as an “ovuliferous cone structure in Cupressaceae where only a few individu2 2 , 3 , 9 , 10 al species have been investigated in detail that could be ”. The scales of Cupressaceae have been a scale5 ,9 ,10 comparatively referred here for discussion. topic for centuries. Many researchersinsisted that From our observation , it was clear that P. orientalis the bract should be a congenital fusion of bracts and an produced several ovules that arised first in the axils of the ovuliferous scale initiated from a single primordium. 3 ] Singh H , Oberoi Y P. A contribution to the life history of However , intercalary growth of the bract determined the Biota orientalis Endl . Phytomorphology . 1962 , 12 : 373 - late development of the inverted vascular supply , which 393. has been extensively referred in interpreting the hypotheti2 () () () 4 ] Xing S- P邢树平, Zhang Q 张泉, Hu Y- X胡玉熹, cal“ovuliferous scale”. Through series of studies , Takaso () ( ) Chen Z- K陈祖铿, Lin J- X 林金星. The mechanism 5 and Tomlinson claimed that no ovule supporting struc2 of pollination in Platycladus orientalis and Thuja occidentalis ( ) ture ovuliferous scale was present in Cupressaceae , ( ) () Cupressaceae. Acta B ot Sin 植物学报, 1999 , 41 :130since the protuberance and the associated bundle devel2 - 132. oped after the main structural features of the cone were es2 5 ] Takaso T , Tomlinson P B. Cone and ovule development in ( ) Callitris Cupressaceae- Callitroideae . B ot Gaz , 1989 , tablished. Our investigation of P. orientalis showed that 150 :378 - 390. the protuberance and inverted vascular bundle developed 6 ] Owens J N , Molder M. Sexual reproduction in western red after pollination , which was in agreement with their con2 ( ) cedar Thuja plicata . Can J B ot , 1980 , 58 : 1376 - clusion. 1393. Tomlinson P B , Takaso T , Cameron E K. Cone develop2 7 ] Ackno wledgements : Many thanks are due to Mr . ( ) ment in Libocedrus Cupressaceae—phenological and mor2XIAO Yin- Hou for assistance with SEM facilities. phological aspects. Amer J B ot , 1993 , 80 :649 - 659. Takaso T , Tomlinson P B. Aspect of cone and ovule ontoge2 8 ] ( ) ny in Cryptomeria Taxodiaceae. Amer J B ot , 1989 , 76 : References : 692 - 705. 1 ] Buchholz L H. The embryogeny of conifers. Duggar B M. Owens J N , Molder M. Cone initiation and development be2 9 ] Proc Fourth Int Congr Plant Sci . Vol . 1. Menasha : Geoge ( fore dormancy in yellow cedar Chamaecyparis nootkaten2 Banta , 1929. 359 - 392. ) sis. Can J B ot , 1974 , 52 :2075 - 2084. 2 ] Martin P C. A morphological comparison of Biota and Thu2 Sporne K R. The Morphology of Gymnosperms. London : 10 ] ja . Proc Penn Acad Sci , 1950 , 24 :65 - 112. Hutchinson , 1971. 144 - 147. () 责任 安全质量包保责任状安全管理目标责任状8安全事故责任追究制幼儿园安全责任状占有损害赔偿请求权 编辑 : 梁 燕