GC-SIM-MS detection and quantification of free indole-3-acetic acid in bacterial galls on the marine alga Prionitis lanceolata (Rhodophyta)

Indole-3-acetic acid (IAA), a plant hormone necessary for terrestrial plant growth and development, was detected and quantified in the marine red alga Prionitis lanceolata Harvey (Halymeniaceae, Gigartinales, Rhodophyta) usin g gas chromatogaphy-selective ion-monitoring mass spectrometry (GC-SIM-MS), This allowed comparison of free IAA levels between the algal thallus and e ubacterially induced galls on this alga characterized by abnormal algal gro wth and cell division and extensive, intercellular microbial proliferation, The levels of free IAA in the P, lanceolata thallus averaged 2.5 (+/-1.1) ng.g(-1) fresh wt. Free IAA levels in galls were more variable, ranging fro m ca, 4 to 39 (8.3 +/- 10.9) ng.g(-1) fresh wt, but were significantly high er overall (P = 0.0022), The identity of the IAA in this marine florideophy cean alga was confirmed by full scan GC-MS analysis of both galls and thall i. The levels of free IAA in P, lanceolata were two to three orders of magn itude higher than those observed previously in the Rhodophyta, The origin o f elevated IAA levels in P, lanceolata galls is unknown because it is possi ble that this compound is produced by either the gall-inducing bacterial sy mbiont or the host alga.