Abstract Detail

Anatomy and Morphology

Carvalho, Monica [1], Niklas, Karl [2].

Leaf hydraulic architecture of Populus and Ginkgo.

A major obstacle in understanding phloem hydraulics is the difficulty of quantifying sieve cell pressure potential, sugar translocation rates, and hydraulic conductivity in vivo. One approach to this limitation is to draw biophysical inferences based on a detailed anatomical diagnosis of leaf phloem and how it is physically and metabolically linked to the xylem. Here, we describe and compare the leaf phloem-xylem hydraulic architecture of two topologically distinct leaf-types, i.e., Ginkgo biloba and Populus x canescens used as examples of open-dichotomous and reticulated venation patterns, respectively. Using a combination of electron and light microscopy, we compare the conductive cross-sectional areas and lengths of sieve cells and xylary elements across all vein classes in fully expanded leaves. We show that the conductive area of phloem scales one-to-one with that of xylem in both leaf-types. Sieve cell and xylary conductance volumes also increase toward the base of Ginkgo and Populus leaves, thereby increasing the efficiency of basipetal sugar export. However, in Populus, the total phloem conductive area of minor veins in poplar exceeds that of the major veins and the petiole, whereas the phloem conductive area in the petiole of Ginkgo leaves exceeds that of the total phloem conductive area of the collecting veins near the margin of the leaf. Thus, despite the characteristic fan-shape of the Ginkgo leaf blade, the total phloem conductive area of decreases from the leaf base towards the leaf margin. Our data show that the hydraulic architecture of both leaf-types is consistent with Münch’s pressure-flow hypothesis for phloem export. Using measured parameters, we present a spatially-explicit model for phloem transport to estimate translocation and infer the xylem–phloem interconnectivity required for sugar export. Our model indicates that the functional distinction between major and minor veins in Populus leaves is more redundant and more efficient for export compared to the hydraulic architecture of Ginkgo leaves.

1 - Cornell University, School of Integrative Plant Science, 412 Mann Library Building, Ithaca, NY, 14853, United States
2 - Cornell University, Plant Biology, 412 Mann Library, ITHACA, NY, 14853-5908, USA

Keywords:
Phloem
xylem
Structure-Function
anatomy.

Presentation Type: Oral Paper
Session: 20, Anatomy and Morphology
Location: Fort Worth Ballroom 7/Omni Hotel
Date: Tuesday, June 27th, 2017
Time: 8:00 AM
Number: 20001
Abstract ID:230
Candidate for Awards:Katherine Esau Award,Maynard F. Moseley Award