Impatiens balsamina is an annual herb, cultivated as a valued medicinal and ornamental plant all over China. It is also used as a popular dye, and in some places it is referred to as “henna.” For centuries, the aboveground parts of this plant have been used in traditional Chinese medicine for their antimicrobial, antirheumatic, antipruritic, anti-inflammatory, antiallergic, and antitumoral properties, and for the treatment of difficult labor and puerperal pain (Kang et al., 2013; Shin et al., 2015). Many active ingredients have been isolated from I. balsamina, including phenolics, flavanols, anthocyanin pigments, and saponins (Oku and Ishiguro, 2002; Yang et al., 2001). Although metabolites from this plant have been extensively studied (Chua, 2016; Kang et al., 2013; Sakunphueak et al., 2013; Su et al., 2012), reports of detailed studies on anther development, cytological features, and distribution of nutritional reserves in the anthers of I. balsamina are scarce.
The flower, as an important reproductive organ, is believed to be a very complicated part of angiosperms. Specifically, the floral differentiation process and significant structural changes are complex mechanisms. Male reproductive development in higher plants is an intricate biological process that includes the formation of anthers with differentiated tissues, in which microspores and pollen are formed. As the anther morphology becomes established, the anther typically consists of microsporocytes at the center of each anther locule surrounded by four different cell layers: the epidermis, the endothecium, the middle layer, and the tapetum from the outer to the inner. The successful development of pollen grains within the anther requires active cooperation and interaction between the sporophytic and gametophytic molecules (Zhang et al., 2010).
Cell inclusions, especially calcium oxalate crystals are secondary metabolites and biominerals in plants, and are distributed among all taxonomic levels of angiosperms. Calcium oxalate crystals occur in five morphologically different forms, one or more of which are found in most angiosperm families (Franceschi and Horner, 1980; Franceschi and Nakata, 2005). Knowledge of plant crystals consists almost entirely of details of crystal structure, how the crystal forms within the cell, and distribution of crystals in mature organs. Crystal types, their specific distribution, and development are neglected aspects of crystallization. Many plants accumulate crystals of calcium oxalate, but how these crystals form remains unknown (Nakata, 2012, 2015). Since then, crystals of calcium and oxalate have been reported in more than 215 plant families (McNair, 1932).
In this study, the ultrastructure and histochemical changes associated with the various developmental stages of anthers were investigated, with a focus on changes of polysaccharides and lipids, which are nutritional materials. Study on the synthesis and distribution of nutritional constituents in the anthers can provide understanding viability and its role in reproductive fitness. In addition, the features of calcium oxalate crystals in the anthers, representing a nonmolecular synapomorphy were examined to gain insights into the reproductive biology and evolution of I. balsamina.
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