Vol. 70 No: 3

Title:
Relationship of Polyamines to Low-Temperature Stress-Induced Flowering of the ‘Washington’ Navel Orange (Citrus Sinensis L. Osbeck)

Authors:
A.G. ALI and CAROL J. LOVATT

pp: 491-498

Abstract:
The objectives of the present study were to quantify the relationship between flowering and leaf polyamine content at the initiation of, and during, a low-temperature floral-induction treatment and to test the ability of canopy sprays of L-arginine (50 mM), putrescine (10 and 20 mM), and spermidine (10 and 20 mM) to enhance the flowering response of the ‘Washington’ navel orange (Citrus sinensis L. Osbeck). Five year old container-grown ‘Washington’ navel orange trees were subjected to four weeks of low-temperature treatment of 8 h days at PFD of 500 µmol m^-2 s^-1 and 10°C and 16 h nights at 7°C. Leaf NH₃-NH₄⁺, putrescine and spermidine concentrations were significantly greater at the end of, or one day after, the low temperature floral-induction treatment, while spermine content decreased. Trees receiving putrescine (20 mM) or spermidine (10 mM) had significantly greater leaf concentrations of spermidine at the initiation of the low-temperature floral-induction treatment. Flower number per tree was positively correlated with leaf spermidine concentration at the initiation of the induction treatment. Arginine and polyamines applied to the foliage at the end of the four week low-temperature treatment generally did not result in a significant increase in leaf polyamine content over control trees. Two exceptions were trees receiving 50 mM arginine or 20 mM spermidine, which resulted in significantly greater leaf concentrations of spermidine one week after application and large, but statistically nonsignificant, increases in flower number per tree of 42% and 87%, respectively. The results provide evidence that spermidine availability at the time of flower initiation and organogenesis might be a factor affecting floral intensity in the ‘Washington’ navel orange.

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