A global analysis of parenchyma tissue fractions in secondary xylem of seed plants.

Hugh Morris,Steven Jansen,Elisabeth Wheeler,Kasia Ziemińska,Esther Fichtler,Jingming Zheng,Mark A F Gillingham,Patrick Cvecko,Lenka Plavcová,Hugo I Martínez‐Cabrera,Daniel J Mcglinn

doi:10.1111/nph.13737

Abstract

Summary Parenchyma is an important tissue in secondary xylem of seed plants, with functions ranging from storage to defence and with effects on the physical and mechanical properties of wood. Currently, we lack a large‐scale quantitative analysis of ray parenchyma (RP) and axial parenchyma (AP) tissue fractions.Here, we use data from the literature on AP and RP fractions to investigate the potential relationships of climate and growth form with total ray and axial parenchyma fractions (RAP).We found a 29‐fold variation in RAP fraction, which was more strongly related to temperature than with precipitation. Stem succulents had the highest RAP values (mean ± SD: 70.2 ± 22.0%), followed by lianas (50.1 ± 16.3%), angiosperm trees and shrubs (26.3 ± 12.4%), and conifers (7.6 ± 2.6%). Differences in RAP fraction between temperate and tropical angiosperm trees (21.1 ± 7.9% vs 36.2 ± 13.4%, respectively) are due to differences in the AP fraction, which is typically three times higher in tropical than in temperate trees, but not in RP fraction.Our results illustrate that both temperature and growth form are important drivers of RAP fractions. These findings should help pave the way to better understand the various functions of RAP in plants.

Highlights

Parenchyma tissue in secondary xylem is composed of living cells variable in their morphology and physiology, which usually have thin walls and are rectangular or square in shape
There was a 29-fold variation in ray and axial parenchyma (RAP) fractions, with total fractions varying from 3.4% in Thuja occidentalis to 99% in Adenia glauca
There was a clear difference between angiosperms and conifers, as we found only significant correlations between RAP and mean annual temperature (MAT), and between RAP and Mean annual precipitation (MAP) for angiosperms

Summary

Introduction

Parenchyma tissue in secondary xylem is composed of living cells variable in their morphology and physiology, which usually have thin walls and are rectangular or square in shape They are produced by fusiform and ray initials of the vascular cambium, which develop into axial parenchyma (AP) strands and ray parenchyma (RP), respectively, and run perpendicular to each other (Fig. 1). Rays provide means for interactions between phloem and xylem (van Bel, 1990; Spicer & Holbrook, 2007; Hearn et al, 2013; Pfautsch et al, 2015), as they stretch from the inner bark across the cambium and into the xylem

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