Holbrook Lab - Whole Plant Biology

RACHEL SPICER

parenchyma physiology
Living parenchyma cells in secondary xylem (= wood) serve critical functions in carbohydrate storage, wound response, and exchange of material between xylem and phloem. They also have amazing lifespans, ranging from 2 to over 200 years depending on the species. I have been studying the aging process in xylem parenchyma by measuring respiration rates at different tissue ages, and by considering the effects of within-stem gas composition (e.g., stems are typically high in CO2 and low in O2) on parenchyma metabolism and cell longevity.

senescence and PCD in woody tissue
After a certain number of years 'in service', xylem parenchyma cells die following a suite of coordinated activities (e.g., the synthesis of secondary compounds and/or formation of tyloses), and this process drives the transition from sapwood to heartwood. I have been studying the process of cell death during this transition and considering whether it is plausible that these cells die of O2 deprivation deep within the stem, or whether the process might be a form of programmed cell death (PCD) in plants.

reaction wood development & hydraulic consequences
Reaction wood forms in response to mechanical stress and allows any axis of a woody plant to maintain a specific orientation within a gravitational field. Because it is mechanically specialized, reaction wood may come at a hydraulic 'cost' to a plant. Work toward my M.S. included a study of compression wood (the type of reaction wood formed in conifers) and its hydraulic limitations. Of greater interest to me now are specific aspects of compression wood development, including hormonal control of cellular differentiation in the cambial zone, and detection by cells of their orientation with respect to gravity.

microscopic wood identification
I first became interested in xylem structure and function during a course on wood identification that stressed microscopic wood ID. Looking for specific characteristics of pitting between ray cells and tracheids, patterns of axial parenchyma in angiosperms, and the presence or absence of certain cell types, you can more accurately identify many woods than you could using a hand lens. Identification of wood in furniture and historical and archaeological artifacts remains an interest (and hobby) of mine.

vascular cambium and secondary growth
In a broader sense, my research interests are centered around woody stem development and the link between xylem structure and function. This includes the physiology and evolution of the vascular cambium, the role of hormonal signals in xylem development and ultimately senescence, and the ways in which xylem (and phloem!) structure affects long distance transport. I think that the amazing longevity of some woody plants, coupled with their continuous growth and accumulation of mass, makes them particularly interesting models in development.

	parenchyma physiology Living parenchyma cells in secondary xylem (= wood) serve critical functions in carbohydrate storage, wound response, and exchange of material between xylem and phloem. They also have amazing lifespans, ranging from 2 to over 200 years depending on the species. I have been studying the aging process in xylem parenchyma by measuring respiration rates at different tissue ages, and by considering the effects of within-stem gas composition (e.g., stems are typically high in CO2 and low in O2) on parenchyma metabolism and cell longevity.
	senescence and PCD in woody tissue After a certain number of years 'in service', xylem parenchyma cells die following a suite of coordinated activities (e.g., the synthesis of secondary compounds and/or formation of tyloses), and this process drives the transition from sapwood to heartwood. I have been studying the process of cell death during this transition and considering whether it is plausible that these cells die of O2 deprivation deep within the stem, or whether the process might be a form of programmed cell death (PCD) in plants.
	reaction wood development & hydraulic consequences Reaction wood forms in response to mechanical stress and allows any axis of a woody plant to maintain a specific orientation within a gravitational field. Because it is mechanically specialized, reaction wood may come at a hydraulic 'cost' to a plant. Work toward my M.S. included a study of compression wood (the type of reaction wood formed in conifers) and its hydraulic limitations. Of greater interest to me now are specific aspects of compression wood development, including hormonal control of cellular differentiation in the cambial zone, and detection by cells of their orientation with respect to gravity.
	microscopic wood identification I first became interested in xylem structure and function during a course on wood identification that stressed microscopic wood ID. Looking for specific characteristics of pitting between ray cells and tracheids, patterns of axial parenchyma in angiosperms, and the presence or absence of certain cell types, you can more accurately identify many woods than you could using a hand lens. Identification of wood in furniture and historical and archaeological artifacts remains an interest (and hobby) of mine.
	vascular cambium and secondary growth In a broader sense, my research interests are centered around woody stem development and the link between xylem structure and function. This includes the physiology and evolution of the vascular cambium, the role of hormonal signals in xylem development and ultimately senescence, and the ways in which xylem (and phloem!) structure affects long distance transport. I think that the amazing longevity of some woody plants, coupled with their continuous growth and accumulation of mass, makes them particularly interesting models in development.