Abstract Detail

Wood: Biology of a Living Tissue

Spicer, Rachel [1], Evanich, Daniel [2].

Development of symplasmic networks in woody stems.

Woody stems commonly contain between 5-20% living cells by volume, and up to 80-90% in the specialized stems of select groups (e.g., Adansonia, Adenia). Living parenchyma cells permeate wood in a complex three-dimensional network, creating symplasmic routes between xylem and phloem and linking the stem and leaves. The goal of this talk is to provide an overview of how these networks are established and to highlight key questions that remain about this understudied tissue. Primary xylem parenchyma (PXP) occupies longitudinal strands associated with the proto- and metaxylem and may live for some time after the production of secondary tissue. PXP is derived early in development from tissue beneath the apical meristem in primary shoots, with minimal differentiation. Although PXP is largely unstudied in woody stems, it may be important in leafy shoots where it forms continuous strands that descend from the leaves, enter the stem as leaf traces, and traverse the woody cylinder to join the primary xylem around the pith. In contrast, secondary xylem parenchyma (SXP) makes up the bulk of living cells in wood and is highly differentiated. SXP comprises ray and axial parenchyma, which are derived from two distinct types of initials in the vascular cambium. Axial parenchyma may be specialized in association with vessels, but is also produced at the start or end of the growing season in some temperate zone taxa. Ray parenchyma, although often thought to be specialized in radial transport, is also closely associated with vessels in angiosperms. Distinct ray cells (e.g., upright and procumbent cells) form in many angiosperm species and show taxa-specific distribution patterns but our understanding of their functional roles is limited. Both types of SXP have extreme ranges of longevity (e.g., 2-200 years), with evidence of ray parenchyma outliving vessel-associated axial parenchyma by many years in some species. Important functional roles are filled through the death of SXP, which likely occurs via a form of programmed cell death. Rather than a gradual decline in metabolic activity with age, SXP show an increase in activity shortly before death and are responsible for critical processes that define heartwood formation, including the occlusion of vessels with gums and tyloses, and the synthesis and deposition of phenolic compounds that impart decay resistance to wood. Key questions remaining about the development of these networks include cell fate specification at the vascular cambium, and the the creation of isolated symplasmic domains through plasmodesmatal regulation.

1 - Connecticut College, Botany, 270 Mohegan Avenue, New London, CT, 06320, USA
2 - Cornell University, Section of Plant Biology, School of Integrative Plant Science, Ithaca, NY, 14853, USA

Keywords:
Parenchyma
symplast
xylem
sapwood
heartwood
vascular cambium
plasmodesmata.

Presentation Type: Symposium Presentation
Session: SY09, Wood: Biology of a Living Tissue
Location: Oglethrope Auditorium/Savannah International Trade and Convention Center
Date: Wednesday, August 3rd, 2016
Time: 8:15 AM
Number: SY09002
Abstract ID:538
Candidate for Awards:None