Ternstroemia Gymnanthera
Total Page：16
File Type：pdf, Size：1020Kb
Cryptic Dioecy of Symplocos wikstroemiifolia Hayata (Symplocaceae) and Ternstroemia gymnanthera (Wight & Arn.) Sprague (Pentaphylacaceae) in Taiwan 台灣產蕘花葉灰木與厚皮香之隱性雌雄異株之研究 Yu-Chen Wang (王有禎) and Jer-Ming Hu (胡哲明) Institute of Ecology and Evolutionary Biology, College of Life Science, National Taiwan University Introduction Androdioecy is a rare breeding system in angiosperms. Theoretical models predicted that the condition for the evolution of androdioecy is stringent, and most morphologically androdioecious plants were proved to be cryptically dioecious. In the 2nd edition of the Flora of Taiwan, only two species, Symplocos wikstroemiifolia and Ternstroemia gymnanthera, were documented as morphologically androdioecious. Symplocos wikstroemiifolia had been already proposed to be cryptically dioecious, but for T. gymnanthera the sexual characteristics of its breeding system is unclear. This thesis is aimed to investigate the possibility of the existence of androdioecy in Taiwan and to enhance the knowledge on cryptic dioecy. Reproductive Biology of Symplocos wikstroemiifolia Study Species Flower Morphology Sex Ratios Symplocos wikstroemiifolia (Symplocaceae) is an There were no pollen grains in the anthers of the The sex ratios in the population of Peichatienshan were near 1:1 evergreen shrub or tree species. The male flowers morphologically bisexual flowers in anthesis. in two consecutive years (2007~2008), and no plants altered their usually have 15~20 stamens, but the morphologically sexual expressions. Male flowers Morphologically bisexual flowers bisexual flowers only have about five stamens. Table 1 Sex ratios and male frequencies of the population in 2007 and 2008. M, male plants. B, morphologically bisexual plants. The Morphologically sex ratios are not significantly different from 1:1 (χ2 = 3.84). Male plants bisexual plants 0.05, 1 Year M B Sex Ratio Male Frequency χ2 2 2007 35 30 1:0.86 0.54 0.24 < χ 0.05, 1 2008 24 18 1:0.75 0.57 0.59 < χ2 Figure 2 Anthers of S. wikstroemiifolia. 0.05, 1 Morphologically Inflorescences Unusual Natural Mutants Plant no. 29 Plant no. 189 Plant no. 29 bisexual flowers Two natural mutants, plant no. 29 and plant no. 189, were found in the population. They produced morphologically bisexual flowers and viable pollen grains, Flowers but it is not known whether they have the Figure 3 Flowers of two natural mutants of Figure 4 The stigmas of S. wikstroemiifolia. Figure 1 Inflorescences and flowers of S. female reproductive function because the S. wikstroemiifolia. Note that the styles of Note that the stigmas of plant no. 29 are wikstroemiifolia. stigmas are morphologically different from plant no. 189 are shorter than normal ones smaller than normal ones. normal morphologically bisexual flowers. (see figure 1). Reproductive Biology of Ternstroemia gymnanthera Study Species Pollen Morphology In vitro Pollen Germination Ternstroemia gymnanthera (Pentaphylacaceae) is Pollen grains from male flowers were prolate to prolate- Pollen grains from morphologically bisexual and male flowers of T. an evergreen shrub or tree species. Both male and spheroidal and tricolporate, whereas pollen grains from gymnanthera were cultured in 5% sucrose solution. Only the pollen morphologically bisexual flowers have five sepals, morphologically bisexual flowers were spheroidal and grains from male flowers could produce pollen tubes. Some of the five petals and numerous stamens. Carpels are inaperturate. Morphologically pollen grains from morphologically bisexual flowers released some rudimentary in male but well-developed in Male flowers bisexual flowers substances during the cultured periods, but they never formed pollen morphologically bisexual flowers. tubes. Mean pollen germination rate (%) of the pollen grains from Morphologically morphologically bisexual flowers was significantly different from male Male flowers bisexual flowers flowers (P < 0.0001). Morphologically Male flowers 50% N = 24 bisexual flowers 40% 30% 20% 10% N = 8 0% 1 2 Figure 7 Scanning electron micrographs of pollen (%) rate Germination Figure 5 Flowers of T. gymnanthera. grains from T. gymnanthera. B M Figure 9 Pollen grains that were Figure 10 Mean pollen cultured in 5% sucrose solution after germination rate (± SE) of T. Pollen Number per Flower Pollen Volume 24 hours. The pollen and pollen gymnanthera. B, morphologically The male flowers Means of pollen volume tubes were stained with methylene bisexual flowers. M, male flowers. 600000 N = 10 18000 N = 100 contained significantly more were significantly larger in blue. Bar = 50μm. N, the number of flowers was 16000 pollen grains than the 500000 morphologically bisexual used to conduct pollen ) 3 14000 morphologically bisexual flowers than in male flowers germination experiments. 400000 m 12000 Artificial Pollination flowers. (P < 0.0001). (P < 0.0001). μ ( 10000 Artificial pollination experiments revealed that only the pollen 300000 Figure 6 Mean pollen Figure 8 Mean pollen volume 8000 grains from male flowers could set fruits. Treatments were 2 grain per flower (± SE) of 200000 (± SE) of T. gymnanthera. B, 6000 significantly different (χ = 11.6, P < 0.005). T. gymnanthera. B, N = 11 pollen grains from N = 100 Volume 4000 Table 2 Fruit-sets (%) of artificial Pollen grains Pollen 100000 Flowers Fruits Fruit-sets (%) morphologically bisexual morphologically bisexual 2000 pollination experiments. B, Pollen grains flowers. M, male flowers. B 6 0 0 0 Bisexual M ale flowers. M, pollen grains from 0 Bisexual M ale from the morphologically bisexual plants; N, the number of flowers S 6 0 0 male flowers. N, the number S, pollen grains from the same plant M 7 5 71.4 was used to estimate B M of pollen grains was used to B M (selfing); M, pollen grains from the male pollen grains. estimate pollen volume. plant. Conclusions Based on these evidences, S. wikstroemiifolia and T. gymnanthera are cryptically dioecious species. The morphologically bisexual flowers are actually functionally female. The discovery of mutant plants in S. wikstroemiifolia may imply that some female plants could restore the male reproductive function in some circumstances. Ternstroemia gymnanthera exhibits floral and pollen dimorphism, and pollen grains from female flowers are inaperturate and sterile. In conclusion, no plant species in Taiwan are discovered to be functionally androdioecious so far..