Gynodioecy in Trichilia (Meliaceae) and a peculiar case of male sterility due to tapetal necrotic cell death

• Published in: Revista brasileira de botânica 2022-03, Vol.45 (1), p.449-462
• Main Authors: Gama, Rebeca Laino, El Ottra, Juliana Hanna Leite, Pirani, José Rubens, Demarco, Diego
• Format: Article
• Language: English
• Subjects: Anthers; Biomedical and Life Sciences; Bisexuality; Botany; Cell death; Dimorphism; Electron microscopy; Females; Flowers; Germination; Gynodioecy; Hermaphroditism; Life Sciences; Male sterility; Males; Meliaceae; Ovaries; Ovules; Plant reproductive structures; Plant Systematics/Taxonomy/Biogeography; Pollen; Pollination; Polygamy; Reproductive system; Seed germination; Seeds; Sexual dimorphism; Stamens; Stigmas (botany); Structural Botany - Original Article; Trichilia
• ISSN: 1806-9959; 0100-8404; 1806-9959
• DOI: 10.1007/s40415-021-00746-4

Flowers of Meliaceae are traditionally described as bisexual, but functionally unisexual flowers have been reported for many genera. For Trichilia , several reproductive systems have been previously reported: subdioecy, gynodioecy, polygamy and hermaphroditism. The aim of this study was to analyze the occurrence of floral dimorphism and sexual-functional aspects of the flower of Trichilia claussenii . Structural and developmental analyses of flowers of Trichilia claussenii were performed using light and electron microscopy. In addition, male and female function of flowers was investigated through pollen viability and stigma receptivity tests, hand pollination and seed germination. Two floral morphotypes were identified in Trichilia claussenii : one morphologically male with a reduced gynoecium and the other morphologically female with anthers which do not release pollen. In the supposedly male flower, anthers are well developed and produce viable pollen grains. A conspicuous nectary disk differentiates at the base of the gynoecium, and the ovary has small ovules; however, our study proved that this ovary develops into a fruit, which contains viable seeds. In contrast, the supposedly female flower has larger gynoecium and ovules, and the nectary is smaller and inconspicuous. The stamens of female flowers have inviable pollen grains due to a tapetal necrotic product that keeps them united into an amorphous mass within the anthers. Male flowers are geitonogamous. Our results demonstrate that Trichilia claussenii exhibits subtle sexual floral dimorphism with female flowers and bisexual flowers distributed in different individuals. Our results indicate that male sterility occurs in only one morphotype; therefore, the species is gynodioecious.