Hormone profiling by LC-QToF-MS/MS in dormant Macadamia integrifolia:: Correlations with abnormal vertical growth

A method for analyzing multiple plant hormone groups in small samples with a complex matrix was developed to initiate a study of the physiology of abnormal vertical growth (AVG) in Macadamia integrifolia (cv. HAES344). Cytokinins (CKs), gibberellins (GAs), abscisic acid (ABA), and auxins were detected in xylem sap and apical and lateral buds using high-performance liquid chromatography quadrupole time-of-flight tandem mass spectrometry (LC-QToF-MS/MS). The extraction method separated compounds with high sensitivity in positive (CKs) and negative (ABA, auxins, GAs) modes of QToF-MS/MS. CK profiles differed in xylem sap and apical and lateral buds irrespective of AVG symptoms. Trans-zeatin riboside (t-ZR) was dominant in sap of normal and AVG trees (similar to 4 and 6 pmol g(-1) FW, respectively). In apical buds isopentenyl adenine (iP) (similar to 30 pmol g(-1) FW) was the most abundant CK, and in lateral buds trans-zeatin (t-Z) (22-24 pmol g(-1) FW) and iP (24-30 pmol g(-1) FW) were the most abundant. t-Z levels of AVG trees were higher in apical buds (13.88 vs. 6.6 pmol g(-1) FW, p < 0.05) and lower in sap (0.16 vs. 0.51 pmol ml(-1), p < 0.005) compared to normal trees. ABA in lateral buds was 1.9 times higher (p < 0.001) in AVG. IAA was below quantification, whereas indole-3-butyric acid (IBA) was consistently present. GA(7) was the dominant GA in apical and lateral buds of all trees (100-150 pmol g(-1) FW). GA(3, 4, & 9) were consistently present at low concentrations (< 12 pmol g(-1) FW) in buds. GAs(1, 3, & 9) were detected in xylem sap at low concentrations (< 0.5 pmol g(-1) FW). Differences in sap amino acids (AA) were also assessed. In sap from AVG trees, asparagine and glutamine increased significantly (p < 0.05) in their contribution to total AA. Potential AVG hormone correlations are discussed.