Evidence for intra- and extra-protoplasmic feruloylation and cross-linking in wheat seedling roots.
The sub-cellular feruloylation and oxidative coupling sites of cell wall polysaccharides were investigated in planta by monitoring the kinetics of appearance of arabinosyl- and feruloyl-radiolabelled polysaccharides in the protoplasmic compartment and their secretion in the wall either in the presence or absence of brefeldin A (BFA). By using root apical segments excised from wheat seedlings (Triticum durum Desf.), incubated with trans-[U-(14)C]cinnamic acid, we demonstrated that [14C]ferulate, likely [14C]diferulate, as well as trimers and larger products of ferulate are incorporated into the protoplasmic polysaccharides very rapidly within 1-3 min of [14C]cinnamate feeding. This agrees with the assumption that (glucurono)arabinoxylans [(G)AX] feruloylation and oxidative coupling occur intracellularly, likely in the Golgi apparatus. Simultaneously, polymer bound radioactive hydroxycinnamic acids appeared to be incorporated into the cell wall of root apical segments as early as 2 min after trans-[U-(14)C]cinnamic acid feeding. On the contrary, starting from L-[1-(14)C]arabinose as tracer, the secretion of the pentose-containing polymers into the wall was between 5 to 10 min. These results indicated that (G)AX feruloylation and oxidative coupling occur both intra-protoplasmically and in muro. The occurrence of in muro feruloylation and oxidative coupling was confirmed by the use of BFA a well known inhibitor of secretion. The drug caused a strong inhibition of the synthesis and secretion into the wall of the 14C-pentosyl-labelled polymers as well as of 14C-feruloyl-polymers. In spite of this, the total amount of 14C-feruloyl-polymers incorporated into the wall was only slightly affected by BFA. This indicates the existence of a mechanism involved into secretion of the activated hydroxycinnamoyl precursors to the wall, alternative to that involved in polysaccharide secretion.
Mastrangelo
Lucia Ilenia
LI
Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, Università del Salento, via prov.le Lecce-Monteroni, 73100, Lecce, Italy.
Lenucci
Marcello Salvatore
MS
Piro
Gabriella
G
Dalessandro
Giuseppe
G
D019342:Acetic Acid; D001089:Arabinose / Q000378:metabolism; D001554:Benzene; D002250:Carbon Radioisotopes; D002473:Cell Wall / Q000187:drug effects / Q000378:metabolism; D002854:Chromatography, Paper; D002855:Chromatography, Thin Layer; D002934:Cinnamates / Q000378:metabolism; D003373:Coumaric Acids / Q000378:metabolism*; D003432:Cross-Linking Reagents / Q000494:pharmacology*; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism*; D018517:Plant Roots / Q000187:drug effects* / Q000378:metabolism*; D011108:Polymers; D036226:Seedlings / Q000187:drug effects / Q000378:metabolism*; D013997:Time Factors; D014908:Triticum / Q000187:drug effects / Q000378:metabolism*
D002250:Carbon Radioisotopes; D002934:Cinnamates; D003373:Coumaric Acids; D003432:Cross-Linking Reagents; D011108:Polymers; C029010:cinnamic acid; C004999:ferulic acid; D001089:Arabinose; D001554:Benzene; D019342:Acetic Acid