LAUSR

Phloem unloading and loading are associated with stem non-structural carbohydrates (NSCs) accumulation and remobilization in rice (Oryza sativa L.). Four rice recombinant inbred lines (R032, R191, R046, and R146) derived from a cross between Zhenshan 97 and Minghui 63 were used to investigate the contributions of stem large and small vascular bundles to NSCs accumulation and translocation. Before heading, the parenchyma cells in stem cortex tissues (PCs) surrounding small vascular bundles had higher starch density than those surrounding large vascular bundles. Moreover, the protein levels of sucrose transporters, cell wall invertase, sucrose synthase, and adenosine diphosphate glucose pyrophosphorylase, as well as the phloem plasmodesma densities were higher in small vascular bundles than those in large vascular bundles. After heading, starch density decreased more in PCs surrounding small vascular bundles than in large vascular bundles. Also, the protein levels of sucrose transporters, α-amylase, sucrose phosphate synthase and sucrose synthase, the phloem plasmodesma densities in small vascular bundles were higher than those in large vascular bundles. The correlations of the number and total cross-sectional area of small vascular bundles with mass and contribution to yield of transferred NSCs were higher than those of large vascular bundles. Our results suggest that small vascular bundles may have higher contributions to pre-anthesis stem NSCs accumulation and post-anthesis translocation than large vascular bundles, which is potentially attributed to the high level of protein and enzyme involved in stem unloading and loading via apoplastic and symplastic pathways. This article is protected by copyright. All rights reserved.