Tracing the opposing assimilate and nutrient flows in live conifer needles.
J Exp Bot
; 74(21): 6677-6691, 2023 11 21.
Article
em En
| MEDLINE
| ID: mdl-37668473
ABSTRACT
The vasculature along conifer needles is fundamentally different from that in angiosperm leaves as it contains a unique transfusion tissue inside the bundle sheath. In this study, we used specific tracers to identify the pathway of photoassimilates from mesophyll to phloem, and the opposing pathway of nutrients from xylem to mesophyll. For symplasmic transport we applied esculin to the tip of attached pine needles and followed its movement down the phloem. For apoplasmic transport we let detached needles take up a membrane-impermeable contrast agent and used micro-X-ray computed tomography to map critical water exchange interfaces and domain borders. Microscopy and segmentation of the X-ray data enabled us to render and quantify the functional 3D structure of the water-filled apoplasm and the complementary symplasmic domain. The transfusion tracheid system formed a sponge-like apoplasmic domain that was blocked at the bundle sheath. Transfusion parenchyma cell chains bridged this domain as tortuous symplasmic pathways with strong local anisotropy which, as evidenced by the accumulation of esculin, pointed to the phloem flanks as the preferred phloem-loading path. Simple estimates supported a pivotal role of the bundle sheath, showing that a bidirectional movement of nutrient ions and assimilates is feasible and emphasizing the role of the bundle sheath in nutrient and assimilate exchange.
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Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Traqueófitas
Idioma:
En
Revista:
J Exp Bot
Ano de publicação:
2023
Tipo de documento:
Article