Study On The Reproductive Biology Of Acer Yanjuechi

Acer yanjuechi Fang et P.L.Chiu, a deciduous and ancient relic tree of Aceraceae Acer, is one ofthe2ndgrade protected and endangered plants in China. The results of the survey showed that Aceryanjuechi has the ability of low seed setting and weakly natural regeneration, which may lead to theendangered situation. It is knowed that Acer yanjuechi is of the great value in scientific researches andlandscape application, but it is also a pity that there are few reports about Acer yanjuechi. To find outthe cause of being in danger of Acer yanjuechi, resource distribution, morphological and anatomicalcharacteristics, floral biology, development of female and male gametophyte and seed biology werestudied in this paper. The main results are follows:(1) Ecological Characteristic: Acer yanjuechi is in favor of sunny place, moist climate. There was noseedling under a seed tree beause of its weakly natural regeneration. Acer yanjuechi is a shallow-rootedplant with obvious main and lateral roots and lateral roots basseting. In Anthesis, more tress in sunnyslope flowered than in the shadow and tree in the sun can flower and fruit but can't on the condition oflack of sun. Lack of sun hastened the growth and put off the falling of leaves. All of this showed thatAcer yanjuechi is a neutral, heliophilous plant which needs some light to stimulate the reproductivegrowth.(2) Biological Characteristic: Acer yanjuechi buded in April and flowered in the middle of April.Fructescence was in September to October and there is no leaf in tree by December. Two kinds of buds(leaf buds and flower buds) existed, opening out simultaneously. Two kinds of flowers in Aceryanjuechi, bisexual flower and male flower, growed in a corymbose and terminal cyme. Only maleflowers produce pollen and its number was6times more than bisexual flowers. The style of pollinationis entomophilous and cross. Pollen viability was detected by Invitro culture and staining method of withI₂-KI, TTC, methylene blue. The highest viability index was45.97%by methylene blue method. Thefruit drop occurs frequently and lastingly, which cause the infructescenc expulsion rate up to67.7%andfruit-drop rate87.3%.(3) Development of female and male gametophyte: This paper studied the development of femaleand male gametophyte of Acer yanjuechi by using normal paraffin method. Four pollen sacs make upone anther. The anther wall is of basic type. The endothercium develops fibular thickenings, and thetapetum begins to the glandular type. The cytokinesis of the microspore mother cells in meiosis is of thesimultaneous type. The microspore tetrads is of tetrahedral, and pollen grains are two-celled whenmature.The ovary has two loculus with two anatropous ovules in each and the ovule is bitegminous,crassinucellate on the axile placentation. The megasporocyte divides into four megaspores in line typeafter meiosis and only one megaspore in chalaza end usually is the functional one. The embryo sacbelongs to the polygonum type. Stamens and pistils mature at different times, promotingcross-pollination rather than self-pollination. Abnormal phenomena appear in the whole development offemale and male gametophyte, expecially ovules which may be the main cause of being in danger ofAcer yanjuechi. (4) Biological characteristics: The biological characteristics of the seeds of Acer yanjuechi werestudied in this paper,The result showed that the seeds were flaser and oval and made ofepisperm,endothelium,embryo and cotyledon, but no endosperm. The1000-seed weight of Aceryanjuechi was50.88g and the weight of seed coat account for79.55%. The percentage of empty andpoor seeds weighted63.81%,reflecting the high seed abortion. The viability index of full seeds by TTCmethod was56.67%.The seed coat of Acer yanjuechi has the ability of penetration in a certain degree,which is not the main cause of inhibiting the germination of seeds; The seeds that cannot germinatenaturally has the characteristic of deep dormancy.ï¼›The extractants from outer seed coat and embryo ofAcer yanjuechi by methanol could inhibit the germination of cabbage seeds, showing that the seed itselfhas the germination inhibitors that maybe the main cause of deep dormancy.The endangered cause of Acer yanjuechi could be preliminary summarized as follow: weaklynatural regeneration, much less hermaphroditic flowers than male flowers which drop largely during theflowering period, frequent fruit dropping, high proportion of abnormal fruits, seeds of poor quality.