閉花受精

閉花受精是一種植物在關閉的花朵內完成自花授粉，並產生種子的有性繁殖方式^[1]。閉鎖花（Cleistogamous Flower, CL）是閉花受精的關鍵，這類花朵不開放，授粉過程在花朵內部自發完成^[2]。閉花受精現象分布在50個科228個屬的約693種植物中，常見於堇菜科、鳳仙花科、禾本科、遠志科以及豆科等植物類群^[3]。

毛葉黃堇（Viola pubescens）的（a）開放花與（b）閉鎖花

分類

閉花受精植物通常分為以下三類^[2]：

• 完全閉花受精：所有花均為閉鎖花，植物不產生開放花。
• 誘導閉花受精：在特定環境條件下誘發閉鎖花的產生。
• 兩型閉花受精（Dimorphic Cleistogamy）：同一植物在不同部位或不同時期同時產生閉鎖花和開放花（Chasmogamous Flower, CH）。

閉鎖花通常具有減少的花冠和雄蕊數量^[4]。相較於開放花鮮艷的花瓣和特殊氣味，閉鎖花花瓣發育不全或完全缺失，通常無色，且雄蕊數量減少，有時雄蕊退化為絲狀或原基狀^[5][6][7]。

假說

關於兩型閉花受精現象，存在多種假說^[2]：

• 繁殖保障：閉鎖花是一種應對開放花授粉失敗的備份機制。在授粉不成功的情況下，閉鎖花可以通過自交保障種子的生產，延長生長季節的有性生殖時間^{[8][9][10][11]}。

• 防止自交衰退：自交後若有害等位基因未能被清除，將增加群體遺傳漂變與自交衰退的風險^[12][13]。閉鎖花主要依靠自交繁殖，而開放花通過異交產生更多具遺傳變異的後代，從而維持後代的遺傳多樣性，以適應環境變化^{[9][14][10][15]}。

• 能量分配：閉鎖花的能量消耗較低，因為它們節省了產生更多花粉、蜜腺體與花瓣的成本；而開放花較大，通常具有吸引傳粉昆蟲的功能，因此需要更多能量^[10][16]。兩型閉花受精可以通過不同花型的比例調整能量分配，以優化其生殖效益^{[9][17][18][19]}。

• 環境異質性：環境因素（如光周期、光強、溫度、土壤營養和水分等）決定了閉鎖花與開放花的產生，環境異質性促進了兩種花型的分化與選擇^{[6][20][21][15]}。

參考文獻

1. Kuhn M. Bemerkungen über Vandellia und den Blüten dimorphismus. Bot. Zeitung. 1867, 25: 65–67.
2. Li, Qiaoxia; Li, Youlong; Li, Jigang; Chen, Chenlong; Sun, Kun. Effects of photoperiods on the development of chasmogamous and cleistogamous flowers in <i>Viola monbeigii</i> and <i>V. dissecta</i>. Biodiversity Science. 2024, 32 (6): 23484. doi:10.17520/biods.2023484.
3. Culley, Theresa M.; Klooster, Matthew R. The Cleistogamous Breeding System: A Review of Its Frequency, Evolution, and Ecology in Angiosperms. The Botanical Review. 2007-01, 73 (1): 1–30. doi:10.1663/0006-8101(2007)73[1:TCBSAR]2.0.CO;2.
4. Uphof, J. C. Th. Cleistogamic flowers. The Botanical Review. 1938-01, 4 (1): 21–49. doi:10.1007/BF02869833.
5. Wang, Yunjing; Ballard, Harvey E.; McNally, R. Ryan; Wyatt, Sarah E. Gibberellins are involved but not sufficient to trigger a shift between chasmogamous-cleistogamous flower types in Viola pubescens 1. The Journal of the Torrey Botanical Society. 2013-01, 140 (1): 1–8. doi:10.3159/TORREY-D-12-00044.1.
6. Li, Qiaoxia; Huo, Qingdi; Wang, Juan; Zhao, Jing; Sun, Kun; He, Chaoying. Expression of B-class MADS-box genes in response to variations in photoperiod is associated with chasmogamous and cleistogamous flower development in Viola philippica. BMC Plant Biology. 2016-12, 16 (1). doi:10.1186/s12870-016-0832-2.
7. Li, Q; Li, J; Zhang, L; Pan, C; Yang, N; Sun, K; He, C. Gibberellins are required for dimorphic flower development in Viola philippica.. Plant science : an international journal of experimental plant biology. 2021-02, 303: 110749. PMID 33487338. doi:10.1016/j.plantsci.2020.110749.
8. Le Corff, Josiane. Effects of light and nutrient availability on chasmogamy and cleistogamy in an understory tropical herb, Calathea micans (Marantaceae). American Journal of Botany. 1993-12, 80 (12): 1392–1399. doi:10.1002/j.1537-2197.1993.tb15383.x.
9. Culley, Theresa M. Reproductive Biology and Delayed Selfing in Viola pubescens (Violaceae), an Understory Herb with Chasmogamous and Cleistogamous Flowers. International Journal of Plant Sciences. 2002-01, 163 (1): 113–122. doi:10.1086/324180.
10. Culley, Theresa M.; Klooster, Matthew R. The Cleistogamous Breeding System: A Review of Its Frequency, Evolution, and Ecology in Angiosperms. The Botanical Review. 2007-01, 73 (1): 1–30. doi:10.1663/0006-8101(2007)73[1:TCBSAR]2.0.CO;2.
11. Koontz, SM; Weekley, CW; Haller Crate, SJ; Menges, ES. Patterns of chasmogamy and cleistogamy, a mixed-mating strategy in an endangered perennial.. AoB PLANTS. 2017-11, 9 (6): plx059. PMID 29308127. doi:10.1093/aobpla/plx059.
12. Masuda, Michiko; Yahara, Tetsukazu; Maki, Masayuki. Evolution of floral dimorphism in a cleistogamous annual, Impatiens noli‐tangere L. occurring under different environmental conditions. Ecological Research. 2004-11, 19 (6): 571–580. doi:10.1111/j.1440-1703.2004.00673.x.
13. Ginwal, H. S. Inbreeding depression in Eucalyptus tereticornis Sm. due to cleistogamous flowering. New Forests. 2010-09, 40 (2): 205–212. doi:10.1007/s11056-010-9194-z.
14. Ansaldi, Beth H.; Weber, Jennifer J.; Goodwillie, Carol; Franks, Steven J. Low levels of inbreeding depression and enhanced fitness in cleistogamous progeny in the annual plant Triodanis perfoliata. Botany. 2019-07, 97 (7): 405–415. doi:10.1139/cjb-2019-0022.
15. Sternberger, AL; Ruhil, AVS; Rosenthal, DM; Ballard, HE; Wyatt, SE. Environmental impact on the temporal production of chasmogamous and cleistogamous flowers in the mixed breeding system of Viola pubescens.. PloS one. 2020, 15 (3): e0229726. PMID 32160228. doi:10.1371/journal.pone.0229726.
16. Sternberger, AL; Bowman, MJ; Kruse, CPS; Childs, KL; Ballard, HE; Wyatt, SE. Transcriptomics Identifies Modules of Differentially Expressed Genes and Novel Cyclotides in Viola pubescens.. Frontiers in plant science. 2019, 10: 156. PMID 30828342. doi:10.3389/fpls.2019.00156.
17. Parra-Tabla, V; Munguía-Rosas, M; Campos-Navarrete, MJ; Ramos-Zapata, JA. Effects of flower dimorphism and light environment on arbuscular mycorrhizal colonisation in a cleistogamous herb.. Plant biology (Stuttgart, Germany). 2015-01, 17 (1): 163–8. PMID 25077675. doi:10.1111/plb.12223.
18. Zhang, Li-Hui; Sun, Qi; Zhao, Ji-Min; Zhang, Yan-Wen. Plasticity in the reproductive strategy of a clonal cleistogamous species, Pseudostellaria heterophylla. Plant Ecology. 2018-12, 219 (12): 1493–1502. doi:10.1007/s11258-018-0896-1.
19. Zhang, Jiyu; Wu, Fan; Yan, Qi; John, Ulrik P; Cao, Mingshu; Xu, Pan; Zhang, Zhengshe; Ma, Tiantian; Zong, Xifang; Li, Jie; Liu, Ruijuan; Zhang, Yufei; Zhao, Yufeng; Kanzana, Gisele; Lv, Yanyan; Nan, Zhibiao; Spangenberg, German; Wang, Yanrong. The genome of Cleistogenes songorica provides a blueprint for functional dissection of dimorphic flower differentiation and drought adaptability. Plant Biotechnology Journal. 2021-03, 19 (3): 532–547. PMID 32964579. doi:10.1111/pbi.13483.
20. Seguí, J.; Lázaro, A.; Traveset, A.; Salgado-Luarte, C.; Gianoli, E. Phenotypic and reproductive responses of an Andean violet to environmental variation across an elevational gradient. Alpine Botany. 2018-04, 128 (1): 59–69. doi:10.1007/s00035-017-0195-9.
21. Furukawa, T; Itagaki, T; Murakoshi, N; Sakai, S. Inherited dimorphism in cleistogamous flower production in Portulaca oleracea: a comparison of 16 populations growing under different environmental conditions.. Annals of botany. 2020-03-09, 125 (3): 423–431. PMID 31630158. doi:10.1093/aob/mcz167.