The yield of the soybean (Glycine max
L.) was comprised of the number of the pods, the number of seeds in a pod, 100-seed weight. It has been reported that soybean seeds taken out of a pod and cultured in well water and a complete nutrient medium containing sucrose was bigger than the seed which continued growing up in a pod (Egli 1990). In rice, some genes like GRAIN SIZE (GS3)
are identified as determinant of seed size (Takano-Kai et al. 2013). This seed size regulation by GS3
was shown to be mediated by controlling cell number in the upper epidermis of the glume (Takano-Kai et al. 2013). Therefore, we hypothesized that the pod limits seeds growth in soybean and focus on pod growth. We measured the pod length (R3-R4 stages) every 2 h until 28 h, and examined expression of pod elongation related genes. Soybean pod elongates at the dawn, and the elongation rhythm is consistent with that of hypocotyl in Arabidopsis thaliana
. From gene expression analysis, the mechanism of this elongation rhythm might be involved in BRU1, which enhances plant growth through cell division and extension. Additionally, it is regulated by two transcription factors, PIF4 and BZR1 involved in light and phytohormone signaling, respectively. These results indicate that soybean pod elongation might be regulated by light signaling.
References: Egli (1990) J. Exp. Bot. 41: 243-248.
Takano-Kai et al. (2013) Breed sci. 63: 77 -85.
Keyword: BZR1, PIF4, pod elongation, day length