Study On Sexual Reproduction Characteristic Of Scutellaria Tsinyunensis C.Y.Wu Et S. Chow, An Endangered Plant Endemic To Chongqing

Scutellaria tsinyunensis C. Y. Wu et S. Chow (Lamiaceae) is an endangered plant species endemic to Jinyun Mountain Chongqing China. This study focused on floral biology, flowering phenology, Fructification situation, breeding system, male and female gametophytes development of the plant by using yield observation, pollen germination determinate its viability, stigma receptivity test, pollen-ovule ratio, out-crossing index, pollen transfer experiment, and classical paraffin sectioning techniques. And the Pearson correlation analysis between weather condition and some growth or reproduction index were done to identify possible weak points that might contribute to its rarity and impede its conservation. The results show as followings:(1) The plant has a terminal raceme, which with 30-50 opposite flowers; the floral display and floral design of S. tsinyunensis has a type of pollination syndrome fit for insects but no sectary. Bombus and Syrphidae are the main pollinators, which visit the flowers twice one day. P/O ratios are 7618±390, indicated that the breeding system was Xenogamy, and the plant may be a self-incompatibility species demonstrated by the pollen transfer experiments. The pollen viability is 76.3±2.78% and only about 74.19% stigma have receptivity in the first day of flowering, and go down and down in the follows.(2)The flowering period of the plant is April to May, and the population duration is about 14 to 28 days; the duration of individual plants lasts 21±9.3 days, the opening of single flower could lasted 3.9 days. The duration difference among populations is significant at 0.05 levels, and the shortest one is Shaolong-Temple population. The Onset date difference among populations is significant at 0.01 levels, but according to the curve of open flower proportion, the blossoming process and flowering phenology among populations are similar, all of them have a single peak, and the Median dates among populations are much closed, which indicate the plant has a Mass-flowering Pattern. The correlation analysis show that:the correlation between fruit number and Onset date or the Synchrony Index of plant are not significant, while there is positive significant correlation between duration and fruit number(r= 0.558, p<0.01); The weather condition during flower opening time is vital to fructify success of flowers, the more sunny days in duration the more probability of flower fructification is (r=0.813, p<0.05).(3)The largest leaf at the terminal side of plant, and there is positive significant correlation among maximum leaf area, stem basal diameter, fruit number and flower number. The fruit develop rapidly after fructified:the surface of fruit changed about six days later, the fruit shape changed to ovoid about ten days later, and it changed to black nutlet about twenty-five days later. The regression equation of the nutlet diameter and growth time is y=1.058+0.047x (r= 0.633, p<0.01). The shield grows rapidly within five days after fructified, and it is important to primary dispersion of the nutlet.(4) The dynamic condition of plant growth, inflorescence development and blossoming process all indicate that the reproduction strategy of S. tsinyunensis prefers to sexual reproduction. Most plants produced a relatively big mean number of ovules (128.4), and the flowering rate is 80.7%±16.0%, but relatively few of these formed seeds (19.58%). In decreasing importance, ovules in fruits were lost to predation, seed abortion, and lack of fertilization. The Shaolong-Temple population has the lowest plant number and plant density, and these indexes of this population all are the lowest among the four populations:plant flower number, plant ovule production, plant fruit setting rate, plant seed setting rate and plump seed number. Besides, these items all have significant difference between Shaolong-Temple population and others (p<0.05, respectively), but there is no significant difference among the other three.(5) The structure of apical merits accord with Tunica-corpus construction. The development of anther wall follows the dicotyledonous type. The tappetum is partly originated from the primary parietal layer and partly derived from the ground tissues of the connective, and it with quadrinucleate cell belongs to glandular type. Cytokinesis of microsporocyte meiosis is simultaneous type and the microspore tetrad belongs to tetrahedral type. Its mature pollens were 2-celled. The ovary is two carpals, tetra ocular, one ovule in each locale, axial placenta, the ovule is unitegminal, tenuinucellar and anatropous. Cytokinesis in the megaspore mother cell accompanies meiosis and form a linear tetrad. The development of the embryo-sac is the Polygonal type, and with endothelium appeared. There is micronucleus in the developing microspore, but it should not be considered as an important factor respect for the low seeding rate.Above all, beside the sexual interference and relatively low pollen viability and stigma receptivity, population size, weather condition limit to pollination and no enough pollinator visits respect for the low fruit and seed setting rate. Considered low fruit set number and extremely low percentage of seed germination (only about 3%), fertility decreasing have occurred in all the population of the species. Conservation measure such as artificial cultivation should be done immediately.