Are polyamines involved in the potassium nitrate-induced flowering in mango?
Protacio C. M.
Author Affiliation: Department of Horticulture, University of the Philippines at Los Baņos College, Laguna, 4031, Philippines.
: 76-83
Abstract : The hypothesis that potassium nitrate-induced flowering in mango is mediated by polyamines was investigated. Extracts prepared from maturing mango leaves (5-9 months after flushing) were analysed for polyamine content by HPLC. Initially, putrescine content was high, and then declined with the approach of the dry season and natural flowering. Hydroxycinnamic acid conjugates of putrescine were not detected in leaf extracts. Putrescine (1-100 mM) and spermidine (5-50 mM) were sprayed on the shoots, with 2% potassium nitrate and water as controls. In trees that responded to potassium nitrate, no flowering was observed in response to polyamine or water application, suggesting that increased polyamine content is not necessary for mango flower initiation. Preliminary evidence suggested that the nitrate was channelled elsewhere, with polyamines acting as transient intermediates. Within an hour from spraying with potassium nitrate, spermidine in the leaves increased 6 times compared with the water control, but declined to the same concentrations in control leaves after 24 h. Flowering was stimulated when cyclohexylamine (20 mM) (an inhibitor of spermidine synthase) was sprayed on to plants simultaneously with potassium nitrate. It is suggested that as spermidine and ethylene biosynthesis have a common precursor, inhibition of spermidine synthase may have favoured ethylene biosynthesis, a compound also known to stimulate flowering in mango.