Effect of the stratification temperature and humidity on the germination and endosperm metabolism of Tilia miqueliana seeds

Abstract

In this study, a germination test was conducted using the seeds of Tilia miqueliana, a rare tree species in China. The seeds were treated with H₂SO₄, H₂SO₄-gibberellic acid (GA₃), or H₂SO₄-magnetically treated water (MTW)-GA₃ and then incubated in wet sand at a constant temperature (i.e., 5 °C, 10 °C, 15 °C, 20 °C, or 25 °C) or at alternating temperatures (i.e., 15 °C/25 °C or 5 °C/25 °C/5 °C). Additionally, the effect of relative humidity (RH) on seed germination was assessed (i.e., at 40 % or 50 % RH). These analyses revealed that the optimal temperature and RH for H₂SO₄-MTW-GA₃ treated T. miqueliana seed germination were 15 °C and 50 % RH, respectively. T. miqueliana produces deeply dormant woody seeds. During dormancy release following H₂SO₄-MTW-GA₃ treatment, consistent with the observed metabolic enzyme activities, the contents of protein and fat showed a downward–upward–downward trend, whereas the sugar and starch contents showed an upward–downward trend. Hence, the H₂SO₄-MTW-GA₃ treatment enhanced the conversion of glycogen, starch, protein, and fat to nutrients and energy, while also increasing the activities of diverse metabolic enzymes. Furthermore, the abundance of different hormones promoting seed dormancy release peaked at different time points. Specifically, the GA content peaked before the trans-zeatin-riboside (ZR) content, which may be related to the different mechanisms by which various hormones induce dormancy release.