Character isation of xylem conduits and their possible role in limiting the vase life of cut Acacia holosericea (Mimos aceae) foliage stems

Abstract

EarlydesiccationlimitsthevaselifeofAcaciacutflowersandfoliageandmaybeattributabletopoorhydraulic conductivity(K h)ofthecutstems.AcaciaholosericeaA.Cunn.exG.Donhasbeenadoptedasthetestspeciestoinvestigate the postharvest water relations of the genus Acacia. To understand potential constraints on Kh, xylem conduits in cut A.holosericeastemswereanatomicallycharacterisedbylightandscanningandtransmissionelectronmicroscopy.Vessels with simple perforation plates and tracheids were the principal water conducting cells. Bordered vestured intervessel pits werepresentinxylemvesselelements.Themajorityofconduits(89%)wereshortat1–5cmlong.Only2%were15–16cmin length.Meanxylemconduitdiameterwas77 0.9mmandthediameterprofileshowedanormaldistribution,with29%of diametersintherangeof70–80mm.Simpleperforationplatescanofferrelativelylowresistancetowaterflow.Ontheother hand,borderedvesturedpitsandshortxylemconduitscanconfercomparativelyhighresistancetowaterflow.Overall,the presence of bordered vestured pits, together with a high proportion of short xylem conduits and high stomatal densities (232 2mm– 2)onunifacialphyllodes,couldcontributetoearlydehydrationofA.holosericeacutfoliagestemsstandingin vasewater.FurtherresearchwillrelatetheseanatomicalfeatureswithchangesinKhandtranspirationofcutfoliagestems.