Development of peptide transport activity in barley scutellum during germination

The scutella separated from nongerminated grains of barley (Hordeum vulgare L. cv. Pirkka) took up labeled glycylsarcosine (Gly-Sar), glycylglycine, and leucylleucine at a rate of about 2 nanomoles per scutellum per hour. About 55% of the uptake of Gly-Sar (2 millimolar) was due to nonmediated uptake, but the active component was similar to that operating in the scutella from germinating grains (pH optimum about 4.5, Km about 10 millimolar). When the grains were allowed to germinate aseptically on agar, the rate of uptake of Gly-Sar began to increase after a lag of about 5 hours. The increase continued until a maximum value of 70 nanomoles per scutellum per hour (35-fold increase) was attained after 3 days of germination. After this the activity began to decrease slowly. The uptake of glycylglycine and leucylleucine changed in a similar way. When embryo-containing halves of seeds or separated embryos were allowed to germinate for 12 hours on agar containing various inhibitors of RNA and protein synthesis, the increase in the peptide uptake activity was completely or partially inhibited. The increase was not affected by removal of the "embryo proper" or endosperm, or by additions of gibberellic or abscisic acid. Root tips and aleurone layers took up Gly-Sar very slowly; the rate of the mediated component of uptake was less than 1% of the uptake by scutella. The preferential localization of the peptide transport system in the scutellum and its rapid development at the beginning of germination strengthen the earlier conclusion that peptide transport plays an essential role in the mobilization of reserve proteins during germination.