Jasmonic acid (JA) and its methyl ester (JA-Me) are able to introduce the accumulation of several specific polypeptides in cut leaf segments of barley. Two of the most prominent JA-induced proteins of
M
r 15 000 and 23 000 have been characterized by isolating and sequencing complete cDNA sequences. While the sequence of the
M
r 23 000 polypeptide shows no similarity to published sequences, the sequence of the
M
r 15 000 polypeptide corresponds to the higher-molecular-weight precursor of a leaf thionin previously characterized.
Transcripts for the M
r 23 000 and M
r 15 000 polypeptides accumulate in leaf segments shortly after the beginning of JA treatment. JA and JA-Me induce the appearance of the two proteins not only in leaf segments but also in intact barley seedlings. However, in seedlings the accumulation of JA-induced proteins occurs much more slowly and requires high concentrations of volatile JA-Me. Thus, in barley it seems unlikely that volatile JA-Me is involved in the interaction between different members of this species, as has been proposed recently for tomato seedlings.
Key words jasmonate-induced proteins (JIPs) - leaf thionin - stress response - barley