Abstract Detail

Ecophysiology

Tixier, Aude [1].

Long distance Transport and mobilization of remote carbohydrates for the bud break during spring. A case study in walnut.

Sustaining spring growth in trees growing in temperate climates depends on resources previously stored in stems and branches. Carbohydrate demand of developing buds often exceeds locally available storage (diffusional distance), sugars have to be translocated from proximal locations (tree limbs, stems and roots). Both phloem and xylem have abilities to fulfil that mission although it is not yet clear how this transport function is split between the two pathways. In order to address this ambiguity we studied temporal dynamics of carbohydrate availability during bud break in walnut trees (Juglans regia L.) with a phloem girdling experiment. Significant loss of branch carbohydrates during initial bud growth occurred in the proximal part of the branch while availability near the bud remained unaffected or even increased supporting the notion of long distance translocation. A phloem girdling experiment resulted in significant reduction of sugar content in distal locations although an accumulation toward the bud was still present. Girdling increased water content in the distal part of the branch suggesting that water was retained in the girdled branch section because of impaired back flow, a notion supported by an apoplastic dye perfusion experiment that showed a significant drop in distal xylem water transport in girdled stems. Based on our results we propose a new model for spring carbohydrate translocation activity in trees. A short term role reversal in function between xylem and phloem during a period of limited transpiration is observed: xylem supplies sugars and phloem backflows water from branch distal locations (Münch osmotic pump).

1 - uc davis, plant sciences, one shield avenue, Davis, CA, 95616, United States

Keywords:
NSC
Munch flow
xylem
transport.

Presentation Type: Oral Paper
Session: 3, Ecophysiology
Location: 104/Savannah International Trade and Convention Center
Date: Monday, August 1st, 2016
Time: 9:15 AM
Number: 3006
Abstract ID:50
Candidate for Awards:None