Fruit Development Of Tapiscia Sinensis

Tapiscia sinensis Oliv.,a kind of deciduous tree that belongs to Staphyleaceae. It is an ancient and characteristic species of China. Tapiscia sinensis is relic plants living during Tertiary Period glaciations. Tapiscia sinensis scatters in the south of Yangtze River and the southwest provinces (autonomous regions) of China. They generally scatter vertically at an elevation of 700-1500m. In Shaanxi province, they mainly locate at the northern slope of Daba Tapa, Ningdong and Ningxi forest zone at the southern slope of Qinling Mountains. In spite of the wide distribution, the species have a relatively bad ability to update themselves. In addition to that, their living environment is continuously damaged. As a result of these, the quantity of this species has sharply declined , and the species even becomes extinct, so Tapiscia sinensis is classified as the III national conservative plant. Currently, the researches on Tapiscia sinensis mainly center on its taxonomy, morphology anatomy, ecology, geobotany, introduction and domestication, breeding and so on, but there are few reports about the embryology characters of this species. The paper takes the flowers and fruits of Tapiscia sinensis as the research materials and has researched on the development process of the flowers and fruits of Tapiscia sinensis by utilizing the paraffin microtomy and semithin section microtomy. The research mainly includes the development processes of embryo and endosperm, pericarp and spermoderm as well as the changes of nucellus and chalaza. The aim of writing the paper is not only to provide the latest research results, but also the biological and theoretic evidences for the explicit explanations on the reproduction and biology characteristics of Tapiscia sinensis, the potential solutions to the "leading to extinction" mechanism of Tapiscia sinensis and the breeding and protection of the species.1. The fruit's shape development of Tapiscia sinensis The hermaphroditic flower of Tapiscia sinensis blossoms at late May every year and its fruit becomes mature during the following late September, the whole development process approximately lasts 17 months. The hermaphroditic flower fertilizes during late May and early June, its ovary grows quickly at this time. At the end of July this year, the receptacle begins to expand and extend downwards; as a result, the receptacle gradually wraps the fruit stem, forming a cucurbit-like sphere structure. Thereafter, the young fruit just enters the dormancy state and its shape remains stable until the late of next March. At the end of March in the coming year, the young dormant fruit starts to grow until the following Mid-May when the shape of the fruit is just like the mature ones. And both expanded receptacle and flower stalk form fruit stem together. Right at the moment, the particular phenomenon that bisexual flowers and fruits occur on the same shoot. When the fruit matures within late September in next year, the wall of ovary develops into pericarp, the exterior epidermis cells develop to epicarp, many layers of parenchyma cells develop into mesocarp in which vascular bundles are distributed. And 1-2 layer rectangular parenchyma cells develop into endocarp.And the mature fruit is a berry-like one with a drupe shape. In detail, the exocarp is thin; the mesocarp and endocarp possess the mahogany fleshy skin. Double integument includes three layer cells respectively. When the fruit matures, cell walls of inner epidermis cells of exterior integument become thick and lithoid obviously, and parenchyma cells of exterior integument multiply and extend. The exterior epidermis cells of inner integument are lithoid, and parenchyma cells of inner integument degenerate rapidly but remain few parenchyma cells. The inner epidermis cells of inner integument degenearate, but some remains of those cell wall exist. At this moment, the exterior integument develops the testa which is brown and fleshy; the inner integument develops the endothelium which is hard.2. The development of the embryo and the endosperm of Tapiscia sinensisThe zygocyte of Tapiscia sinensis divides later then its primary endosperm nucleus. A few of dissociated endosperm nucleus have been formed in the embryo sac when the zygocyte is ready to divide. After that, foot cell and apical cell continue to divide until the muticellular proembryo is formed. With the increase of the number of this cell, the prototype globular embryo is formed. Thereafter, one of the suspensor cells disassembles, meanwhile, all the other cells are dividing from all directions, which results in the formation of globular embryo. The cotyledon anlage appears at the both sides of the globular embryo. It is actually the transition period during which the early heart-shape embryo is developed. With the extension of the cotyledon anlage and embryonic plant, the mature heart-shape embryo is formed. When the mature heart-shape embryo proceeds with the development that leads to the formation of the torpedo stage, the procuticle, meristematic tissue and protocambium have differentiated obviously. After that, the cells further the differentiation in order to form the mature torpedo stage. Due to the continuous extension of the cotyledon and the hypocotyls, the dicotyledonous mature embryo is formed. Therefore, the suspensor of Tapiscia sinensis is undeveloped. During the embryo's development, the suspensor is not involved in the formation of embryonic plant. The development of embryo belongs to the crucifer type .The development of endosperm of Tapiscia sinensis is the nuclear type. After the fertilization, the primary endosperm nuclei starts the first mitosis. The division of primary endosperm nucleus is prior to that of zygote. Until the next Mid-April, the zygote starts to divide. At this moment, the endosperm nuclei has divided several times. Most of endosperm nuclei at early stage are circular or ellipsoid or irregular. They form a layer surround the embryo sac. The embryo sac enlarges quickly along with the increase of endosperm nuclei. Endosperm cells are formed from outside of embryo sac to the center. Finally, the embryo sac is foll of endosperm cells. Then the volume of endospenn cells becomes larger and cytoplasm becomes denser, showing the characters of mature cells. From the stage of the globular embryo on, with the development of embryo, the endosperm cells around the embryo degenerates gradually, which helps to provide the nutrition for the embryo's development.3. The development of chalaza and nucellus cellExcept for the chalaza end, the rest part of nucellus cell gradually disassembles, which helps to provide the nutrition for the embryo sac's development. However, the nucellus cells at the chalaza end split and reproduce, which results in the appearance of an expanded apophysis that keeps its shape until the seed becomes mature during the development process of the fruit in the coming year. The expanded apophysis moves aside continuously, therefore, the expanded apophysis and micropyle are finally vertical to each other, differing from the original position that they are opposite. The surface of the blister chalaza is wrapped by the endothelium; what's more, the suspensor and vascular bundle disperse in the blister chalaza, which helps to enlarge the contact area between expanded apophysis and embryo sac and to enhance the transporting capacity of the materials entering the embryo sac. When the seed matures, the surface of expanded apophysis also is wrapped by the lithoid endothelium.4. The passing winter complex formed when Tapiscia sinensis is dormant after its fertilizationAfter the blossom and fertilization in May, Tapiscia sinensis passes the long winter with its naked ovary (undeveloped young fruit) and develops a set of unique structure to pass the long winter. Secondary protective tissues that are similar to perideum are formed on ovary wall and the surface of receptacle which expands down to surround the fruit stalk. The inflated receptacle and the naked ovary form a "passing winter complex". Abundant starch grains are accumulated in the parenchyma of ovary wall and inflated receptacle. Some cells form mucilaginous locules or develop into idioblasts containing druse crystals or tannin. The special passing winter strategies of Tapiscia sinensis demonstrate its adaptation to environment during the long evolutive process.5. The changes of the stored materials for the fruit of Tapiscia sinensisDuring the passing winter period, the starch grain accumulates in the ovary and receptacle. The accumulating amount of the starch grain gradually increases from July to November at the current year; however, the starch grain remains the same or even decrease from December in this year to March in the coming year. Right from April, the accumulated starch grain disappears rapidly with the development of the fruit. It is found that the outer layer of the ovary wall and the cork layer of the receptacle which only contain some fat material. A abundant of fat accumulates in the mature seed of Tapiscia sinensis.