Methyl jasmonate alters N partitioning,N reserves accumulation and induces gene expression of a32-kDa vegetative storage protein that possesses chitinase activity in Medicago sativa taprootsFre de ric Meuriot a,Carine Noquet a,Jean-Christophe Avice a,*,Jeffrey J.Volenec b,Suzanne M.Cunningham b,Thomas G.Sors b,Se bastien Caillot a and Alain Ourry aa UMR INRA UCBN950Physiologie et Biochimie Ve´ge´tales,Institut de Recherche en Biologie Applique´e,Universite´,14032Caen Cedex,Franceb Department of Agronomy,Purdue University,West Lafayette,IN47907-1150,USA*Corresponding author,e-mail:avice@ibba.unicaen.frReceived27November2002;revised4April2003This study presents the effects of methyl jasmonate(MeJA)on growth,N uptake,N partitioning,and N storage in taproots of non-nodulated alfalfa(cv.Lodi).When compared to untreated plants,addition of100m M MeJA to the nutrient solution for14 days reduced total growth and modified biomass partitioning between shoots and roots in favour of taproots and lateral roots.MeJA decreased N uptake(after7days)and increased N partitioning towards roots after14days.This preferential N partitioning to roots was accompanied by increased N storage in taproots as soluble proteins.Compared to total soluble proteins, VSP accumulation occurred earlier(7days),and was greater (2-fold increase)in plants treated with100m M MeJA.Steady-state transcript levels for two VSPs(32and57kDa)also increased markedly(about4-fold)in roots of plants treated with100m M MeJA.This suggests that MeJA could act directly (transcriptional regulation)or indirectly(via the changes of N partitioning among alfalfa organs)on N storage as soluble pro-teins and in particular,VSPs.Because the deduced amino acid sequence of the32kDa VSP clone reveals high homology with Class III chitinases,we propose that the32kDa VSP may have a role in pathogen defense,in addition to its function as a storage protein.IntroductionMany herbaceous and woody species are regularly exposed to critical growth phases during development, such as initiation of spring growth,grain filling,or regrowth after defoliation.These events often result in plants being confronted with a transient limitation of C and N resources(Chapin et al.1990).In perennial forage legumes such as alfalfa(Medicago sativa L.),photosyn-thetic activity as well as N uptake or symbiotic N2fix-ation(Volenec et al.1996)are severely curtailed during early regrowth after defoliation.Post-clipping shoot regrowth requires the mobilization of C and N resources previously stored in roots(lateral roots and taproot)and crowns(Volenec et al.1996).Studies using13C and15N labelling have shown that C is mainly used to support root and crown respiration(Ta et al.1990,Avice et al. 1996b),while endogenous N pools(mainly represented by taproot soluble proteins and amino acids)were largely used to provide shoots with their N needs during herbage regrowth(Hendershot and Volenec1993,Avice et al.1996a,Barber et al.1996).Four soluble proteins[15 19,32and57(b-amylase)kDa]have been identified in alfalfa taproots(Hendershot and Volenec1993,Avice et al.1996a,Cunningham and Volenec1996,Gana et al. 1998).According to the criteria given by Cyr and Bewley (1990)and Staswick(1994),these proteins possess fea-tures consistent with being vegetative storage proteins (VSP).These particular polypeptides,mainly localized in vacuoles of parenchyma cells of wood rays and barkPHYSIOLOGIA PLANTARUM120:113–123.2004Copyright#Physiologia Plantarum2004 Printed in Denmark–all rights reservedAbbreviations–IRMS,Isotope Ratio Mass Spectrometer;JIP,jasmonate-induced protein;MeJA,methyl jasmonate;N,Nitrogen;PBS, phosphate buffer saline;PGT,phosphate gelatin Tween buffer;PNPP,p-nitrophenyl phosphate;PR protein,pathogenesis-related protein; PVDF,polyvinyldene difluoride.Physiol.Plant.120,2004113
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