Shading in mother plant during seed development promotes subsequent seed germination in soybean.

The effect of shading during seed development on subsequent germination is largely unknown so far. In this study, two soybean seed production systems, monocropping (MC) and maize-soybean intercropping (IC), were employed. Compared to the MC soybean seeds, which received the normal light spectrum, the developing IC seeds were exposed to shade resulting from the taller neighboring maize plants. The IC seeds germinated faster than did the MC seeds, while there was no significant difference in the seed coat thickness. The soluble pro-anthocyanidin concentration in the IC seed coat was significantly lower than that in the MC seed coat, and the change of concentrations of several types of fatty acids in IC seeds was documented, findings which are consistent with the germination evidence. The expression levels of genes involved in abscisic acid (ABA) biosynthesis were down-regulated in IC seeds, while the transcription levels of the genes related to gibberellin (GA) biosynthesis were up-regulated. Consistently, this was also reflected in decreasing ABA concentration and increasing active GA4 concentration in IC seeds, resulting in an increased GA4/ABA ratio. Altogether, shading in mother plant during seed development promoted subsequent seed germination by mediating the biosynthesis of pro-anthocyanidins, fatty acids and phytohormones.