Peptide transport in the developing barley grain.

Abstract

AbstractA study was conducted to characterize the import of small peptides into the developing barley (cv. Annabel) grain and demonstrate that HvPTR1, a peptide transporter important to reserve mobilization in the germinating barley grain, is expressed during embryo development. Ears of barley at the appropriate developmental stage after anthesis were cut and placed in 1 ml 5-mM sodium phosphate-citrate buffer (ph 5.0) containing 0.5 µCi [14C]glycyl-sarcosine ([14C]Gly-Sar) at a final concentration of 1 mM. Significant accumulation of [14C]Gly-Sar occurred in the developing grain, indicating that peptides had passed through the transfer region of the nucellus projection. Developing embryos were too insubstantial to analyse until 10 days after anthesis (DAA) and so only data for the whole grain was obtained prior to this. The embryo showed a higher [14C]Gly-Sar accumulation than the endosperm based on fresh weight. Peptide uptake into the embryo peaked between 19 and 23 DAA. Dinitrophenol, an inhibitor of H+-coupled transport, inhibited peptide transport both into the embryo and endosperm of 20 DAA developing barley grain by 70%. HvPTR1 was present in 15 DAA developing grain and in embryo but not endosperm tissue, indicating that HvPTR1 may play a role in nutrient transport during embryo development. HvPTR1 protein was only detectable in the barley embryo and was present as early as 3 DAA, with HvPTR1 protein levels subsequently declining between 20 and 30 DAA. Northern analysis showed that transcript levels of HvPTR1 mRNA were lower in the developing grain than the germinating barley grain. Western blot analysis revealed that the globulin storage protein deposition in the embryo was detected at 19 DAA, much later than the induction of HvPTR1 expression.