Biochemical Changes during Fruit and Seed Development in Nanjing Linden (Tilia miqueiana M.)

In China, the wild population of Nanjing Linden (Tilia miqueliana M.) is experiencing a drastic decline, primarily due to high levels of empty seeds. This study aimed to measure the biochemical and physiological changes during fruit and seed development in T. miqueliana to determine the developmental mechanism. The weight method and photosynthetic respiration were used to determine the biological aspects of both fruits and embryos, while transmission electron microscopy and the anthrone colorimetric method were used to determine the endosperm content, including sugar, starch, protein, and fat. Enzyme-linked immunosorbent assays were conducted to determine the levels of endogenous plant hormones such as indole-3-acetic acid (IAA), gibberellic acid 3 (GA3), zeatin riboside (ZR), and abscisic acid (ABA). The nonlinear least-squares method was used to fit the model of nutrient and hormone levels, revealing that fruit size expanded from the 5th to the 65th day and that fruit moisture content exhibited a downward trend, along with a decrease in fruit respiration intensity. Embryos were found to be fully developed between 35 DAF and 65 DAF, while the nutrients in the endosperm, i.e., sugar, starch, protein, and fat, continuously accumulated after 50 DAF. Additionally, ABA, IAA, GA3, and ZR contents were found to synergistically regulate seed development and maturation.