Abscisic Acid (ABA) and the Regulation of Seedling Growth Under Stress
Siti Rubiah Zainudin and Kamis Awang
Abstract: Xylem sap abscisic acid (ABA) and leaf ABA of Hopea odorata Roxb. and Mimusops elengi L. were measured under conditions of soil compaction and drought to investigate the role of ABA in the regulation of stomatal conductance. A rapid and substantial increase in xylem sap ABA concentration but not leaf ABA concentration was correlated with soil drying in both species. However, xylem ABA concentration was lower in M. elengi seedlings than in H. odorata seedlings. The increase in xylem sap ABA concentration observed at high soil bulk density was correlated with reduced stomatal conductance. These results suggest that xylem ABA may act as a stress signal in the control of stomatal conductance. Reduced xylem ABA levels may explain the lower urban stress tolerance M. elengi seedlings relative to H. odorata.
Keywords: Hopea odorata; Mimusops elengi; soil compaction; drought; stomata conductance; xylem sap abscisic acid; urban environment.