Sapwood Senescence: A Program of Cell Death Leading to the Formation of Heartwood in Large Woody Stems

EPA Grant Number: U915847
Title: Sapwood Senescence: A Program of Cell Death Leading to the Formation of Heartwood in Large Woody Stems
Investigators: Spicer, Rachel
Institution: Harvard University
EPA Project Officer: Lee, Sonja
Project Period: August 1, 2000 through August 1, 2003
Project Amount: $102,000
RFA: STAR Graduate Fellowships (2000) RFA Text |  Recipients Lists
Research Category: Fellowship - Forestry , Academic Fellowships , Biology/Life Sciences , Ecological Indicators/Assessment/Restoration


This research is designed to test the hypothesis that: (1) the death of xylem parenchyma cells during the transition from sapwood to heartwood is a form of programmed cell death; and (2) the lowered oxygen content in stems associated with heartwood formation is due to the local cessation of water flow.


The experimental approach used in this research includes molecular techniques, fluorescence microscopy, and plant physiology methods. First, to test the hypothesis that parenchyma cell death is a form of programmed cell death (PCD), the TUNEL assay will be adapted to tissue sections of xylem parenchyma. The TUNEL assay detects the cleavage of nuclear DNA, a hallmark of PCD, by labeling the free 3'-OH ends of DNA with a fluorescent marker to be viewed with a microscope. Using TEM, morphological changes in parenchyma cells that are typical of plant PCD will be observed. Using another fluorescent stain specific for nuclei, radial profiles of parenchyma cell survival in species with different anatomies and sapwood longevities will be determined. Finally, by inserting oxygen microelectrodes into stems at different depths and monitoring sapflow simultaneously, it will be possible to see to what extent oxygen content varies with water flow rate, and whether the local concentrations of oxygen are so low as to be consistent with the hypothesis of death by anoxia. Much of this work will be on four northeastern tree species that represent a broad range of xylem anatomies: white pine, hemlock, beech, and red oak. The TUNEL assay also will be performed on hybrid poplar from commercial plantations in Oregon.

Expected Results:

The goal of this research is to demonstrate that parenchyma cell death is an active process, forming part of a developmental program that regulates sapwood senescence.

Supplemental Keywords:

sapwood, heartwood, parenchyma, programmed cell death., RFA, Scientific Discipline, Geographic Area, Ecosystem Protection/Environmental Exposure & Risk, Ecology, exploratory research environmental biology, Genetics, wildlife, Ecosystem/Assessment/Indicators, Chemical Mixtures - Environmental Exposure & Risk, Ecosystem Protection, State, Forestry, Ecological Effects - Environmental Exposure & Risk, Ecological Effects - Human Health, Regional/Scaling, Pacific Northwest, Biology, Exp. Research/future, Futures, Ecological Indicators, sapwood senescence, white pine, Oregon, xylem parenchyma, plants, beech, heartwood, red oak, hemlock, DNA, parenchyma, programmed cell death (PCD)

Progress and Final Reports:

  • 2001
  • 2002
  • Final