Reproductive Biology Studies On Camptotheca Acuminata Decne

Camptotheca acuminata Decne which belongs to Camptotheca Decne in Nyssaceae is a deciduous broad-leaved and endemic tree of China. It is mainly distributed in the Yangtze River Basin and south-west provinces. It is suitable for growing in warm climate, cold climate are not suited. Camptothecin and 10-hydroxy camptothecin are indole alkaloids in Camptotheca acuminata Decne and have significant anti-tumor activity. So this plant is more and more attention to the plant academic and medical profession. In recent years, the studies of Camptotheca acuminata focus mainly on anti-tumor activity of camptothecin and its derivatives, such as aspects of the development and utilization, But reproductive biology of the Camptotheca acuminata is little studied, especially, there is no reports embryology of Camptotheca acuminata. The aim of present research was to study floral biology and breeding biology. And we also systematically studied the megasporogenesis, microsporogenesis and development of male and female gametophytes, the development of embryo and endosperm in Camptotheca acuminata with the method of paraffin section. By these studies we expect to grasp law of reproductive biology of camptotheca acuminata and enhance fruiting set and provide new materials on reproductive biology for development and utilization of Camptotheca acuminata.1. The inflorescences of Camptotheca acuminataThe inflorescences of C. acuminata were cymes, each of which was composed of 4-6 capitula. Within a cyme, the 3-4 distal capitula were composed of hermaphroditic florets, while the 1-2 proximal capitula were composed of male florets. There were one pistil and ten stamens in each hermaphroditic floret. Each pistil possessed an inferior ovary containing an anatropous ovule. The male florets had normal stamens, but had no pistil. C. acuminata was hemisynchronously dichogamous, and all florets of a capitulum bloomed synchronously. The male phase came first, in which the stamen matured. Then came the female phase, in which the pistil matured. The female phase of capitula in one order overlapped with the male phaseof those in the next order in the same cyme.2. The floral biology of Camptotheca acuminataWe observed the flowering characters of C. acuminata, the results are as follows: Flower primordium forms early in Mary and florets bloom by the end of June and early July. Florescence is about 20-30 days. The toppest capitulum of cyme flowers firstly and then the proximal capitula bloom in the proper order. In florescence, the toppest capitula of the different cyme flower on the same day. After 6-7 days, the proximal capitula bloom and the pistal of the toppest capitulum in the same cyme matures fully at this time. The stamens shed off when the three lobes of stigma of the same capitulum separate from each other and arch outward. But at this time the stamens of proximal capitula have matured and drew out of the corolla. The lower capitula in a cyme bloom follow the same order, but the interval of time is 1 day. After the florescence of C. acuminata, the 2-4 distal capitula in a cyme remain and develop matured fruits. While the others in the same cyme shed off.3. The breeding of Camptotheca acuminataThe outcrossing index(OCI) of C. acuminata is 4. In accordance with Dafni' s standard, C. acuminata is partly self-compatible and also is outcrossing, and insect-assisted during the pollination. Pollen-ovule ratio(P/O) is 7180-7980. Follow Cruden's standard, the breeding system of C. acuminata is obligate outcrossing. At last, we consider the breeding system of C. acuminata is self-compatible and the coexistence of outcrossing by bag test.4. Megasporogenesis and development of female gametophytesThe ovary of C. acuminata is inferior and has one carpel, one ovule. The ovule is anatropous, one integument and tenuinucellate. Megasporogenesis is started from an archesporial cell under the nucellus epidermis. The archesporial cell is different from the other nucellus cells with large volume and dense cytoplasm and a big nuclear. The archesporial cell dose not divide and develops into megaspore mother cell directly. There is two types of megaspore mother cell meiosis in C. acuminata. One is triad in line type. The one dyad cell in micropyle end degenerates when megaspore mother cell finishes meiosisâ… . But the other dyad cell in chalaza end undergoes meiosisâ…¡and develops two megaspores. Another type is four megaspore in line type. Megaspore mother cell undergoes meiosis and forms tetrad. In these two types, there are more triad in line type and rarely tetrad. Normally, the chalazal magaspore functions and undergoes three mitosis to form the femal gametophyte. During development of embryo sac, some nucellus cells on the base keep their own cytoplasms and shapes longer and then become into podium. The inner integument cells grow into endothelium. The three antipodal cells degenerate soon after development. There are two synergids and one egg at the micropylar end which form egg apparatus. Two polar nucleus are located at the center part of the embryo sac and they have different orientations. Before fertilization, two polar nucleus fuse and form secondary nucleus. The primary endosperm nucleus move into chalazal end before mitosis and there are a lot of starch grains around it.5. Microsporogenesis and development of male gametophytesThere are four microsporangiums in C. acuminata. The structure of anther primodium is simple, its outmost layer is epidermis and the inner layers are a group of active meristem cells. Then the antherogenous occurres because the outside cells at four corners divide quickly. A group of archesporial cells are formed interior to epidermis at each corner. The archesporial cells divide periclinally to form primary sporogenous cells and primary parietal cells. Primary parietal cells divide periclinally into four layer cells of the anther wall, which continue to growing and become into epidermis, endothecium(1 layer), middle layer(two layers) and tapetum(1 layer). Some cell layers may divide cotinuously. When anther wall matures fully, there are one epidermis, one endothecium, two or three middle layers, one tapetum from extrovert to introvert. During the meiotic prophase I of microspore mother cells, the nucleus of tapetum divide into several nucleus. The cells of tapetum are glandular and secrete many fat-sphere bodies into pollen sac. The primary sporogenous cells develop into microsporocyte by mitosis. The microsporocyte undergoes simultaneous meiotic division and produces tetrad. The tetrad is tetrahedral arrangement and surrounded by callose. Then the tetrad is separated by callose decomposition and each of them is a microspore which develops into the mature pollen which is 2-cell type. With the spliting of the wall between neighbor anther sacs, the mature pollens are spilled out when the anther matures fully. At this time, the anther wall is consisted of epidermis and endothecium. The development course of male floret is the same as female one and the mature pollen is also 2-cell type. 6. The development of embryo and endospermThe division of zygote is latter than that of endosperm nucleus. There have been a few of endosperm cells at the stage of the zygote dividing. The zygote divides in late July. The apical cell and basal cell are formed by the transverse mitosis of the zygote. Then the apical cell undergoes longitudinal mitosis and the basal cell undergoes transverse mitosis. Then they form 5-celled proembryo. The basal cell divide into suspensor by transverse mitosis laterly. The apical cell forms globular embryo, pear embryo, heart embryo, torpedo embryo and develops mature embryo at last. The development of embryo is Onagrad type.The development of endosperm is nuclear type. The two polar nucleus fuse and form secondary nucleus. After fertilization, the primary endosperm nuclei keep away from the micropylar end and there are many starch grains around it. Then the primary endosperm nuclei starts the first mitosis and develops two endosperm nucleus. One is near to chalaza end and the other approches micropylar end. Then the endosperm nucleus which is in the micropylar end undergoes the longitudinal mitosis and the other one undergoes the transverse mitosis. So there are four nucleus in embryo sac. The endosperm nucleus become endosperm cells after eigth nucleus stage. Endosperm cells are formed from the micropylar end to chalaza end and from outside to inner. At last, the embryo sac is full of the endosperm cells besides the area of embryo. The ergastic material of endosperm cells in the early stage of seed is polysaccharide, protein and lipid by the method of histochemistry. While the endosperm cells in the mature seed mainly contains lipid.The mature fruit of C. acuminata consist of exterior peel, middle peel, inner peel and seed. The cell wall of inner peel cells becomes lignified. There are at the outside of inner peel. Seed is consist of seed capsule, embryo and endosperm and the embryo is the same long as the seed.By our study, we think the important embryonic character of Camptotheca Decne is similar to Nyssa, but is different from Davidia Baill..