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Abstract Detail



Xylem apoplast-symplast interactions

North, Gretchen [1], Lynch, Frank [2], Maharaj, Franklin [3], Fukui, Kyle [1].

Foliar absorption and transport of water in a tank bromeliad.

For tank bromeliads, which essentially lack elongated stems and absorbing roots, the leaf is the major supplier and consumer of water. After collecting in the tank formed by the leaf bases, water enters primarily through specialized epidermal trichomes, then travels through the hydrenchyma, mesophyll , and bundle sheath cells before entering the xylem. The xylem consists of one rank of parallel veins roughly centered between the two leaf surfaces, linked by relatively infrequent lateral (commissary) veins. Measurements of leaf hydraulic conductance together with calculations of axial (xylem) conductance and results from a model based on leaky-cable theory suggest that axial and radial conductance (between the xylem and the leaf surface) co-limit water transport through the leaf blade above the tank region. For Guzmania lingulata, a shade tolerant species, measured hydraulic conductance for the leaf blade was extremely low, comparable to that for epiphytic ferns and other seedless vascular plants, yet not as low as would be predicted on the basis of its wide interveinal distances. Tracer dyes as well as results from the model implied a strong role for extravascular transport through both the apoplast and symplast, with the properties of the leaf base (the tank region) and the leaf blade being quite distinct. When the leaf base was removed and tracer dyes were supplied directly to the xylem of the cut leaf, uptake of both apoplastic and symplastic tracers occurred more slowly than when tracers were supplied to the sealed leaf with tank region present or to the tanks of intact plants. Aquaporin inhibitors reduced water uptake more strongly when applied to the tank than when supplied to the cut leaf, implying a greater role for the symplast in water uptake than in axial transport and outward radial flow. In both the tank region and in the leaf blade, laterally elongated cells in the hydrenchyma or mesophyll formed cross-links between the veins and were tightly joined to bundle sheath cells around the veins. Such cells have been called “extended bundle sheath” cells or paraveinal mesophyll in some species in the Fabaceae, and preliminary work has shown them to occur in other monocots with widely spaced parallel veins. Such cells may serve to expedite extravascular water flow through both apoplast and symplast of the leaves of tank bromeliads as well as other species.

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1 - Occidental College, Biology, 1600 Campus Rd, Los Angeles, CA, 90041, USA
2 - Occidental College, Mathematics, 1600 Campus Rd, Los Angeles, CA, 90041, USA
3 - Occidental College, Biochemistry, 1600 Campus Rd, Los Angeles, CA, 90041, USA

Keywords:
Bromeliaceae
leaf hydraulic conductance
epiphyte
xylem
paraveinal mesophyll.

Presentation Type: Symposium or Colloquium Presentation
Session: C3
Location: Belle-Chasse/Riverside Hilton
Date: Monday, July 29th, 2013
Time: 10:15 AM
Number: C3009
Abstract ID:745
Candidate for Awards:None


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