Abstract
Polar auxin transport (PAT) is a major determinant of plant morphology and internal anatomy with important roles in vascular patterning, tropic growth responses, apical dominance and phyllotactic arrangement. Woody plants present a highly complex system of vascular development in which isolated bundles of xylem and phloem gradually unite to form concentric rings of conductive tissue. We generated several transgenic lines of hybrid poplar (Populus tremula x alba) with the auxin-responsive DR5 promoter driving GUS expression in order to visualize an auxin response during the establishment of secondary growth. Distinct GUS expression in the cambial zone and developing xylem-side derivatives supports the current view of this tissue as a major stream of basipetal PAT. However, we also found novel sites of GUS expression in the primary xylem parenchyma lining the outer perimeter of the pith. Strands of primary xylem parenchyma depart the stem as a leaf trace, and showed GUS expression as long as the leaves to which they were connected remained attached (i.e., until just prior to leaf abscission). Tissue composed of primary xylem parenchyma strands contained measurable levels of free indole-3-acetic acid (IAA) and showed basipetal transport of radiolabeled auxin ((3)H-IAA) that was both significantly faster than diffusion and highly sensitive to the PAT inhibitor NPA. Radiolabeled auxin was also able to move between the primary xylem parenchyma in the interior of the stem and the basipetal stream in the cambial zone, an exchange that was likely mediated by ray parenchyma cells. Our results suggest that (a) channeling of leaf-derived IAA first delineates isolated strands of pre-procambial tissue but then later shifts to include basipetal transport through the rapidly expanding xylem elements, and (b) the transition from primary to secondary vascular development is gradual, with an auxin response preceding the appearance of a unified and radially-organized vascular cambium.
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Claims 11
Claim · model-written summary
GUS expression occurred distinctly in the cambial zone and developing xylem-side derivatives.
PopulusNot reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Distinct GUS expression in the cambial zone and developing xylem-side derivatives”
e1“hybrid poplar (Populus tremula x alba)”
Claim · model-written summary
GUS expression was found in primary xylem parenchyma at the pith perimeter.
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“novel sites of GUS expression in the primary xylem parenchyma lining the outer perimeter of the pith”
e1“hybrid poplar (Populus tremula x alba)”
Claim · model-written summary
Primary xylem parenchyma leaf traces showed GUS expression while connected leaves remained attached.
- Organ / stage
- leaf tracee0
- Outcome
- GUS expressione0
- Qualifier
- as long as the leaves to which they were connected remained attachede0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Strands of primary xylem parenchyma depart the stem as a leaf trace, and showed GUS expression as long as the leaves to which they were connected remained attached (i.e., until just prior to leaf abscission)”
e1“hybrid poplar (Populus tremula x alba)”
Claim · model-written summary
Primary xylem parenchyma strands contained measurable free IAA.
- Organ / stage
- primary xylem parenchyma strandse0
- Outcome
- measurable levels of free indole-3-acetic acid (IAA)e0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Tissue composed of primary xylem parenchyma strands contained measurable levels of free indole-3-acetic acid (IAA)”
e1“hybrid poplar (Populus tremula x alba)”
Claim · model-written summary
Radiolabeled auxin moved basipetally in primary xylem parenchyma faster than diffusion.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“showed basipetal transport of radiolabeled auxin ((3)H-IAA) that was both significantly faster than diffusion”
e1“hybrid poplar (Populus tremula x alba)”
Claim · model-written summary
Basipetal transport of radiolabeled auxin was highly sensitive to NPA.
- Treatment
- PAT inhibitor NPAe0
- Outcome
- basipetal transport of radiolabeled auxin ((3)H-IAA)e0
- Direction
- highly sensitivee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“showed basipetal transport of radiolabeled auxin ((3)H-IAA) that was both significantly faster than diffusion and highly sensitive to the PAT inhibitor NPA”
e1“hybrid poplar (Populus tremula x alba)”
Claim · model-written summary
Radiolabeled auxin moved between primary xylem parenchyma and the cambial-zone basipetal stream.
- Outcome
- move between the primary xylem parenchyma in the interior of the stem and the basipetal stream in the cambial zonee0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Radiolabeled auxin was also able to move between the primary xylem parenchyma in the interior of the stem and the basipetal stream in the cambial zone”
e1“hybrid poplar (Populus tremula x alba)”
Claim · model-written summary
Ray parenchyma cells were proposed to mediate auxin exchange between the two streams.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“an exchange that was likely mediated by ray parenchyma cells”
e1“Radiolabeled auxin was also able to move between the primary xylem parenchyma in the interior of the stem and the basipetal stream in the cambial zone”
e2“hybrid poplar (Populus tremula x alba)”
Claim · model-written summary
Leaf-derived IAA was proposed first to delineate isolated pre-procambial strands.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“channeling of leaf-derived IAA first delineates isolated strands of pre-procambial tissue”
e1“hybrid poplar (Populus tremula x alba)”
Claim · model-written summary
Leaf-derived IAA transport was proposed later to shift into expanding xylem elements.
- Outcome
- basipetal transport through the rapidly expanding xylem elementse0
- Qualifier
- leaf-derived IAAe1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“then later shifts to include basipetal transport through the rapidly expanding xylem elements”
e1“channeling of leaf-derived IAA first delineates isolated strands of pre-procambial tissue but then later shifts to include basipetal transport through the rapidly expanding xylem elements”
e2“hybrid poplar (Populus tremula x alba)”
Claim · model-written summary
The transition from primary to secondary vascular development was interpreted as gradual, with auxin response before a unified cambium appears.
- Outcome
- transition from primary to secondary vascular development is graduale0
- Qualifier
- auxin response preceding the appearance of a unified and radially-organized vascular cambiume0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the transition from primary to secondary vascular development is gradual, with an auxin response preceding the appearance of a unified and radially-organized vascular cambium”
e1“hybrid poplar (Populus tremula x alba)”
The same questions in other papers
class · physiology: hormones · Populus (poplar)Results agree
1 paper in the same direction as this paper
- negative
Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.