Copper distribution and ionic form effects for postharvest treatments of cut Acacia holosericea stems

A short postharvest life is the major constraint associated with cut Acacia flowers and foliage. Treatment with CuSO4 (Cu2+) has previously been shown to improve the longevity of cut Acacia holosericea stems. Towards refining the treatments, a range of Cu2+ and Cu+ salts were assessed for relative efficacy in improving vase life and water relations of A. holosericea. Five hour pulses with the Cu2+ salts CuSO4, CuCl2, (CH3COO)2Cu and Cu(NO3)2 at 2.2 mM gave equally longer vase lives by ∼2.5-fold over deionised water (DIW) and standard tap water (STW) controls. The same Cu2+ salts at 0.5 mM in the vase solution also gave significantly (P < 0.05) improved vase life, relative fresh weight and water uptake compared to the DIW control. For Cu2+ versus Cu+, optimum concentrations with Cu2+ could not be directly compared due to the low solubility of the Cu+ salt CuCl. However, Cu+ from CuCl at 0.415 mM also had positive effects on vase life compared to the DIW control. Thus, both Cu2+ and Cu+ treatments can enhance vase life parameters for cut A. holosericea foliage. The benefits were irrespective of the counter ion and, thus, Cu2+ and Cu+ per se were responsible. The most effective Cu2+ pulse treatment decreased stomatal conductance of phyllodes initially, but did not cause sustained stomatal closure. Cu accumulated to greater levels in basal stem and phyllode tissues than in upper stem and phyllode tissues of cut A. holosericea stems. Possible mechanisms of Cu2+/Cu+ action are discussed