Density-dependent regulation of rapeseed root development by long-petiole leaves: Mediated by sucrose partitioning and phytohormones

doi:10.1016/j.jia.2026.01.021

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Xiaoyu Huang, Hongxiang Lou, Xiaoqiang Tan, Anda Guo, Dongli Shao, Jie Zhao, Zhenghua Xu, Jing Wang, Bo Wang, Jie Kuai^#, Guangsheng Zhou

MOA Key Laboratory of Crop Ecophysiology and Farming System in the Middle Reaches of the Yangtze River, College of Plant Science and Technology, Huazhong Agricultural University, Wuhan 430070, China

Highlights

— The functional contribution of long-petiole leaves to root growth diminished with increasing planting density.

— Density-dependent metabolic reprogramming and hormonal regulation was observed under LP treatment.

— At low density (D3), LP enhanced SUSY activity to promote sucrose allocation to roots; at high density (D5), LP stimulated invertase and starch remobilization to sustain basal root growth.

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摘要

油菜地上部形态建成和产量形成与根系生长状况密切相关。长柄叶是油菜中出现最早的真叶，在高密度种植条件下，其对根系生长影响机制尚未见报道。因此本试验在高密度直播条件下，设置2个密度(D3: 4.5´10⁵株 hm^-²、D5: 7.5×10⁵株 hm^-² )、2个处理(CK: 不剪叶、LP: 剪去一半长柄叶)的大田试验，同时设置盆栽¹³CO₂饲喂试验，对油菜单株一半长柄叶进行¹³CO₂饲喂，以追踪光合同化物分配。结果表明：与CK相比，LP处理降低了单株叶面积和干重，而增加了根冠比。LP处理增加了苗期至薹期叶面积相对生长率(RER_LA)，D3和D5分别增加了56.01%和19.87%；而降低了苗期至花期的根表面积相对生长率(RERRSA)和根体积相对生长率(RGRRV)，D3密度下分别两年平均降低32.71%和56.98%，D5密度下则两年平均下降32.60%和16.61%。LP处理增加了根中蔗糖合酶(SUSY)活性，提高蔗糖、淀粉和IAA含量，而降低了蔗糖转运蛋白活性。在D3密度下，LP处理降低花期细胞分裂素(CTK)、脱落酸(ABA)与SUT含量，进而抑制侧根生长；此外，LP处理增加了苗期和花期的蔗糖转化酶(INV)活性与蔗糖含量，降低淀粉、SUT与IAA含量，进一步阻碍了侧根的生长。在D5密度下，LP处理显著增加了ABA含量，促进主根的伸长。在两个密度下，角果的¹³C积累量与分配率最高。随着密度增加，营养器官中¹³C积累量下降，种子与茎秆中分配率增加。而根中¹³C分配率从14.5%(D3)下降至11.5%(D5)，这表明随着密度增加，长柄叶片对根部碳分配的贡献逐渐减少，长柄叶对根系生长的调节作用减弱。D3密度下，减去长柄叶数量能够促进蔗糖向根系转运；而在D5密度下，LP处理促进根系中淀粉再分配，以维持根系基础生长。本研究阐明了长柄叶在不同种植密度条件下调节根部形态发育的关键机制，并为协调高密度直接播种油菜种植系统中的根-冠平衡建立了理论依据。

Abstract

The morphological establishment and yield formation of rapeseed are fundamentally dependent on root system development. While long-petiole leaves constitute the earliest true leaves in rapeseed, their regulatory effects on root growth under high-density planting conditions remain unexplored. Field experiments were conducted with two planting densities (D3, 4.5×10⁵ plants ha⁻¹; D5, 7.5×10⁵ plants ha⁻¹) and two leaf treatments (CK: no leaf pruning; LP: removal of 50% long-petiole leaves). A continuous ¹³C-CO₂ labeling experiment was implemented in pot-grown plants to track photoassimilate partitioning, with half of the long-petiole leaves receiving ¹³C-CO₂ pulse labeling. The results indicate that compared with CK, LP treatment reduced per-plant leaf area and dry weight while increasing root-to-shoot ratio. From seedling to bolting stages, LP increased relative expansion rate of leaf area (RER _LA) by 56.01% (D3) and 19.87% (D5), but decreased relative expansion rates of root surface area (RER_RSA) and relative growth rates of root volume (RGR _RV) from seedling to flowering stages, with average annual reductions of 32.71% and 56.98% (D3), and 32.60% and 16.61% (D5), respectively. At the seedling stage, LP treatment enhanced root sucrose synthase (SUSY) activity and elevated sucrose, starch, and indole-3-acetic acid (IAA) concentrations, but reduced sucrose transporter (SUT) levels. By the flowering stage, cytokinin (CTK), abscisic acid (ABA), and SUT contents declined under D3 density, coinciding with inhibited lateral root growth. Furthermore, LP treatment increased invertase (INV) activity and sucrose content at both seedling and flowering stages but diminished starch reserves, SUT activity, and IAA levels, collectively impeding lateral root development. Notably, LP treatment significantly elevated ABA content under D5 density, which stimulated taproot elongation. Siliques exhibited the highest ¹³C assimilation and distribution rates under both planting densities. Elevated density reduced ¹³C-labeled photoassimilate accumulation in vegetative organs but enhanced their allocation to seeds and stems. Root ¹³C distribution rates declined from 14.5% (D3) to 11.5% (D5), demonstrating that the contribution of long-petiole leaves to root carbon allocation diminished with increasing plant density. The regulatory influence of long-petiole leaves on root growth diminished with increasing planting density. At D3, reduced long-petiole leaf count enhanced sucrose translocation to roots, whereas at D5, starch remobilization in roots was prioritized to sustain basal root development. This study elucidates key mechanisms by which long-petiole leaves modulate root morphogenesis under varying densities and establishes a theoretical framework for optimizing root-shoot balance in high-density direct-seeded rapeseed cultivation systems.

Keywords: long-petiole leaves root architecture sucrose partitioning phytohormones ¹³C labeling

Online: 15 January 2026

Fund:

This study was supported by the China Agriculture Research System of MOF and MARA (CARS–12), the Earmarked Fund of Hubei Province of China (2023HBSTX4-03), and the Key Research and Development Program of Hubei Province of China (2023BBB028).

About author: Xiaoyu Huang, Email: hxy08033121@163.com; Correspondence Jie Kuai, Email: kuaijie@mail.hzau.edu.cn

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Xiaoyu Huang, Hongxiang Lou, Xiaoqiang Tan, Anda Guo, Dongli Shao, Jie Zhao, Zhenghua Xu, Jing Wang, Bo Wang, Jie Kuai, Guangsheng Zhou. 2026. Density-dependent regulation of rapeseed root development by long-petiole leaves: Mediated by sucrose partitioning and phytohormones. Journal of Integrative Agriculture, Doi:10.1016/j.jia.2026.01.021

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