GEL OCCLUSION IN THE XYLEM VESSELS OF CUT ACACIA HOLOSERICEA FOLIAGE STEMS

The short commercial vase life of cut Acacia holosericea foliage is potentially the result of physiologically-mediated xylem vessel occlusion. Xylem-occluding gels are considered to be a defence and wound healing mechanism. In ~45 cm-long cut A. holosericea foliage stems, occluding gel secretions were observed in xylem vessel lumens at the cut end and for up to 35 cm distally from the cut end. The gels were deposited soon after the stems were detached (mechanically wounded) and they apparently matured over time. Early gels were transparent and colourless in reaction with phloroglucinol-HCl (P-HCl). The staining of late gels with P-HCl was typically pink to cherry red, amber and yellow, or light brown to dark brown. The deposition of gels evidently reduced the xylem hydraulic conductance (Kh) of cut A. holosericea foliage stems.