Submitted to: Journal of Japanese Society of Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 21, 2007
Publication Date: September 1, 2007
Citation: Malik, N.S.A., Bradford, J.M. 2007. Different flower inducing conditions elicit different response for polyamine levels in olive leaves. Journal of Japanese Society of Horticultural Science. 76(3):205-209.
Interpretive Summary: It has been known for a long time that polyamines are involved in the regulation of various plant developmental phenomena, including flowering and fruiting in various plant species. Studies on the role of polyamine in regulating developmental processes in olive cultivars are limited. However, it has been reported that spray application of putrescine resulted in increased fruit set and yield of olives, and in another study increased levels of different polyamines, except putrescine, during flower induction period were observed. In addition, several reports also indicate changes in polyamine levels in response to environmental stress and stimuli including chilling temperatures. Since flowering in olive is attributed to several days of chilling period before flower differentiation, we felt it would be important to determine if the changes observed in polyamines at the time of flowering are resulting from a developmental change or simply the effect of chilling temperatures. Using our locally designed growth chambers, we have previously shown that olive trees can be induced to flower under typical chilling (temperatures below 7.2°C) and non-chilling conditions. Free polyamine levels were determined under chilling and non-chilling conditions that induce flowering in 'Arbequina' cultivar and the results showed that levels of free polyamine in leaves are related to environmental and not due to development change such as transition from vegetative to flowering state. Changes in free polyamine levels within the auxiliary buds, however, may play an important role in flower production in olives.
In various plant species, polyamines have been implicated in regulating developmental phenomenon as well as responses to environmental stimuli. The role of polyamines in regulating developmental phenomenon, such as flowering, in olives is poorly understood, although seasonal changes and temperature effects on polyamine levels have been reported. In this study, levels of free polyamines (putrescine, spermine, and spermidine) in the leaves of trees kept under non-inducing conditions were compared with polyamine levels in trees that were induced to flower under chilling and non-chilling conditions. Putrescine and spermine levels were much higher in leaves kept under inductive chilling conditions compared to control trees kept vegetative, but such increased levels of polyamines did not occur in trees that were induced to flower under non-chilling conditions. These results clearly differentiated between the effects of temperature versus the effect of developmental change on free polyamine levels in olive leaves. The results show that changes in free polyamine levels in leaves bears little relevance to flowering in olives. Free polyamine levels within auxiliary buds increased when vegetative buds transformed into flowering and then declined when buds developed into flowers. Compared to floral buds, immature and mature fruits contained much smaller amounts of polyamines.