Anther and gynoecium structure and development of male and female gametophytes of Koelreuteria elegans subsp. formosana (Sapindaceae): Phylogenetic implications

Abstract

Anther and gynoecium structure and embryological information in Koelreuteria and Sapindaceae as a whole remain understudied, as well as the evolution of imperfect flowers in the latter. The aims of this study were to analys in K. elegans subsp. formosana the anther and gynoecium structure and the development of male and female gametophytes in the two floral morphs of putatively imperfect flowers. Standard techniques were applied for LM and SEM. Compared to the normal anther development in staminate flowers, a delayed programmed cell death of tapetum, septum and middle layers on the onset of microspore stage result in indehiscent anthers in the functionally pistillate flowers. Orbicules are reported for the first time in Sapindaceae. Gynoecium development in functionally pistillate flowers is normal, whereas in functionally staminate ones a pistillode with degenerated ovules at the tetrad stage is formed. The pollen tube transmitting tract consists of one layer of epithelial cells with a small lumen in the style and ovary. The anatomy of the latter revealed an axile placentation and complete septum. Reproductive characters of Koelreuteria shared with other Sapindaceae taxa are a secretory binucleate tapetum, simultaneous cytokinesis, unicellular stigmatic papillae, Polygonum type megagametophyte with ephemeral antipodals, and ovules campylotropous, with funicular obturator and amphistomic micropyle. Imperfect flowers in the family are triggered by defective sporophytic tissues impacting on the normal development of microspores and megaspores, disrupting embryological events in staminate and pistillate organs at different developmental stages. Reconstructing ancestral character state under parsimony revealed that two ovules per locule, absence of obturator, presence of hypostase, and binucleate tapetum may be regarded as plesiomorphic for Sapindaceae. These analyses have provided information on the evolution of embryological characters in the family and its phylogenetic significance.

Floral morpho-anatomy and reproductive ecology of Spondias macrocarpa Engl. (Anacardiaceae), a vulnerable neotropical andromonoecious tree

“…In Sapindaceae and Meliaceae, for instance, although some species apparently have male and bisexual flowers, anthers of the bisexual morphotype are empty or have unfertile pollen grains. Sometimes the anthers may not even release pollen grains, remaining indehiscent (Gouvêa et al, 2008;Solís et al, 2010;Rosado et al, 2018;Avalos et al, 2019;Zhou et al, 2019).…”

Morphological Study on the Differentiation of Flower Buds and the Embryological Stages of Male and Female Floral Organs in Lespedeza davurica (Laxm.) Schindl. cv. JinNong (Fabaceae)

“…Embryological characteristics are an important basis for judging the compatibility between plant species and determining the process of plant evolution [ 12 ]. There are 11 species in the genus Gossypium , most of which have an Allium-type embryo sac development type, but one has a Drusa-type embryo sac with 4 to 11 antipodal cells [ 13 ]; after the megasporogenesis of Trichoderma and Dodonaeaeae (both belonging to the family Sapindaceae ), the nucleolus in the embryo sac degenerates in the same way as the integument of the ovule [ 5 ]. It can be seen that the same species have relatively consistent development patterns, and it can be seen that the male and female gametophytes of closely related species may have similar development patterns [ 14 ].…”

“…During the development of microspores of Platycladus arborvitae and kiwifruit, the loss of tapetum and programmed cell death will lead to abnormal meiosis and microspore hollowing, and ultimately abortion [3,4]. During the microsporogenesis of Koelreuteria elegans, it was also found that the programmed death of anther wall cells will lead to the failure of anther dehiscence [5]. Scanning electron microscopy observations of the floral development of Medicago truncatula [6] and Astragalus caspicus [7] revealed that the sequence of floral organ development in each whorl was unidirectional, starting from the back of the flower, with a high degree of overlap.…”

Flower Development of Heterodichogamous Juglans mandshurica (Juglandaceae)

“…Monoecious plant species have separate male and female flowers on the same plants and can therefore undergo self-fertilization when the pollen of staminate flowers contacts the stigma of pistillate flowers, barring other defenses against selfing ( Mao et al, 2017 ; Avalos et al, 2019 ; Hildesheim et al, 2019 ). Heterodichogamy, which is dispersed and reported in 20 genera from 13 families of flowering plants, is one of the evolutionary pathways from monoecy to dioecy, heterodichogamous populations usually contain two sexual morphs, protogynous and protandrous, which are reciprocal ( Meng et al, 2009 ; Liu et al, 2016 ).…”