大豆における高収量支持のための栄養貯蔵タンパク質による茎窒素蓄積と種子への動員

The role of stems as a source of nitrogen (N) for the growing seeds has received little attention in soybean. This study evaluated N storage and mobilization from stems to seeds across 42 high-yielding environments under contrasting N supply: a "zero-N" treatment, in which crops relied on soil and biological N fixation, and a "full-N" treatment that received ample N fertilizer. We measured the accumulated N per organ before seed filling and subsequent N mobilization from vegetative organs to the seed. Vegetative storage protein (VSP) abundance in stems was quantified via proteomics. Average yield ranged from 4.2 to 7.3 Mg ha-1, with +11% yield in full-N (6.1 Mg ha-1) compared to zero-N (5.5 Mg ha-1). The full-N treatment resulted in a larger mobilized N from stems (+42%) and leaves (+22%) to seeds than the zero-N treatment, which was attributed to the larger N stored in stems and leaves before seed filling (+37% and +21%, respectively). Among the 5,335 identified proteins at the peak of N accumulation, VSPα (+1.4%) and VSPβ (+0.8%) showed the highest increase in full-N. We conclude that N stored in stems as VSPs before seed filling plays a key role in meeting the seed N demand in high-yielding soybean crops.