Floral organs are important for the reproduction of angiosperms. They play an important role in the reproduction, development, and life cycles of plants. The morphology and function of male organs of male-sterile plants are abnormal, manifested mainly in deformed or degenerated stamens, thin and withered anthers, a lack of pollen, or hollow and nonviable pollen. Kaul (2012) proposed that the variants or phenomena underlying male sterility are mainly in structure and function, and include anamorphosis of the androecium, weak vascular bundle formation, abnormal anther wall development, and undehisced anthers. Similarly, during ovule development, any disruption results in immature and infertile ovules. The major features of aborted ovules include malformation or an absence of egg cells, synergid cells, or polar nuclei; the presence of only a developed integument; undeveloped nucellus tissue; and no mature embryo sac. Therefore, double fertilization does not result in the formation of the embryo and endosperm (Akhalkatsi et al., 1999; Casper and Wiens, 1981; Gao et al., 2017).
Lagerstroemia indica is native to Asia and is a deciduous shrub or small tree belonging to the family Lythraceae. It has a long history of cultivation and is an important landscape plant as a result of its gorgeous flowers and high ornamental value. It is widely grown in China, Japan, and North Korea, and has been introduced to some countries in Europe and the Americas for cultivation (Wang et al., 2014). In 2012, its wholesale value was $66 million (U.S. Department of Agriculture, 2014). L. indica has been widely planted for city landscape greening, expressway greening, sand control, and slope protection. In addition, its plants can also be used in medicine, and flavors can be extracted from its flowers. There are ≈55 species in the genus Lagerstroemia, of which 21 species are distributed in China. Currently, there are many cultivars of L. indica in China, most of which were selected based on natural variation in the species in the wild. Our research team accidentally came across an acarpous individual of L. indica in the wild in 2006 (Wang et al., 2014). Compared with normal L. indica, this L. indica bears no fruit after flowering. Its flowering period can last as long as 115 to 132 d, according to 5-year observations by the current team, whereas that of normal L. indica lasts 60 to 80 d (Chen et al., 2012). It has high ornamental value and significant abortion of its floral organs.
The reproduction of L. indica has been investigated. Pacini and Bellani (1986) studied the structure and function of L. indica pollen. They found that L. indica had spherical pollen, with a textured surface and smooth polar faces. However, there are few studies on the reproductive biology of L. indica. The development of its pollen and ovules is poorly studied, and the reproductive characteristics of acarpous L. indica have not yet been reported.
In this study, we examined the categories and characteristics of floral organ abortion in acarpous L. indica and compared differences between fructiferous L. indica and acarpous L. indica. The results of this study may provide a theoretical foundation for research on the molecular mechanisms of the seedless mutations in L. indica, as well as reproductive biology with regard to the mutations.
Akhalkatsi, M., Pfauth, M. & Calvin, C.L. 1999 Structural aspects of ovule and seed development and nonrandom abortion in Melilotus officinalis (Fabaceae) Protoplasma 208 211 223
Aliscioni, S.S., Gotelli, M. & Torretta, J.P. 2018 Structure of the stigma and style of Callaeum psilophyllum (Malpighiaceae) and its relation with potential pollinators Protoplasma 255 1433 1442
Bender, R.J., Santos, R.P., Guerra, D. & Schwarz, S.F. 2017 ‘URS Campestre’ seedless orange: A new mutant with female sterility Sci. Agr. 74 371 377
Casper, B.B. & Wiens, D. 1981 Fixed rates of random ovule abortion in Cryptantha flava (Boraginaceae) and its possible relation to seed dispersal Ecology 62 866 869
Gao, C., Yang, R. & Yuan, D.Y. 2017 Characteristics of developmental differences between fertile and aborted ovules in Camellia oleifera J. Amer. Soc. Hort. Sci. 142 330 336
Gao, C., Yuan, D.Y., Yang, Y., Wang, B.F., Liu, D.M. & Zou, F. 2015 Pollen tube growth and double fertilization in Camellia oleifera J. Amer. Soc. Hort. Sci. 140 12 18
Hu, S.Y. 2005 Reproductive biology of angiosperms. China Higher Education Press, Beijing, China
Hu, S.Y. 2016 The structure of plants-An atlas. China Higher Education Press, Beijing, China
Kaul, M.L.H. 2012 Male sterility in higher plants. Springer–Verlag, Berlin/Heidelberg, Germany
Pacini, E. & Bellani, L.M. 1986 Lagerstroemia indica L. pollen: Form and function, p. 347–357. In: S. Blackmore and I.K. Ferguson (eds.). Pollen and spores: Form and function. Linnean Soc. Symp. Ser. 12. Academic Press, London, UK
Sanders, P.M., Bui, A.Q., Weterings, K., McIntire, K.N., Hsu, Y.C., Lee, P.Y., Truong, M.T., Beals, T.P. & Goldberg, R.B. 1999 Anther developmental defects in Arabidopsis thaliana male-sterile mutants Sex. Plant Reprod. 11 297 322
U.S. Department of Agriculture 2014 2012 Census of horticultural specialties. 16 May 2016. <https://www.agcensus.usda.gov/Publications/2012/Online_Resources/Census_of_Horticulture_Specialties/>
Wang, X., Li, X., Zhang, J., Feng, G., Zhang, S., Huang, L., Zhuo, R. & Jin, L. 2011 Characterization of nine alfalfa varieties for differences in ovule numbers and ovule sterility Austral. J. Crop Sci. 5 447 452
Wang, X.M., Chen, J.J., Zeng, H.J., Qiao, Z.Q., Li, Y.X., Cai, N. & Wang, X.Y. 2014 Lagerstroemia indica ‘Xiangyun’, a seedless crape myrtle HortScience 49 1590 1592