Studies on Pollen Morphology, Pollen Vitality and Preservation Methods of Gleditsia sinensis Lam. (Fabaceae)

In seed plants, pollen is of great importance for sexual reproduction as a male gametophyte containing genetic information [1]. Pollen viability is a prerequisite for successful pollination, playing an important role in fertilization and fruit setting of flowering plants [2,3], embryo development [4,5], seed quality [6,7] and breeding efficiency. Due to this importance, researchers have conducted many studies on pollen, such as the pollen development process [8], electron microscopy palynology [9], pollen viability detection and pollen preservation methods [10,11], signal transduction and related regulation during pollen tube growth [12,13,14]. All studies above are indispensable for plant cross breeding from practice to theory [15].

Gleditsia sinensis Lam. (Fabaceae) belongs to genus Gleditsia in Fabaceae, which is an endemic species widely distributed in China [16,17]. It is an ideal tree for economic forest, timber forest, shelterbelt and landscaping because of its tall and beautiful shape, strong resistance and barren resistance. The extract of saponin and pod is an excellent Chinese medicinal material [18] and industrial raw material [19], which has high application value and broad prospect. G. sinensis belonged to androdioecy, and its bisexual flowers are functionally female, with most stamens aborted [20] and with a breeding system dominated by outcrossing [21]. In this respect, the fruit and seed set are almost entirely dependent on the pollens provided by male plants during synchronous flowering. Dioecious plants have been under great reproductive pressure due to frequent occurrences of missed flowering periods, lack of pollinators, and imbalanced sex ratios in recent years [22,23]. This necessitates the conservation of pollen resources. In the past, studies of G. sinensis focused mostly on its medicinal components [18], cultivation techniques [24], germplasm resource investigation [25] and stress physiology [26,27] while only a few studies examined its reproductive process [28] like the pollen morphology observed [29] and observation of flowering characteristics [30]. In contrast, pollen-related research of G. sinensis is fragmented and largely unknown, which is not conducive to the popularization and application of this plant.