Effect of Putrescine on Rooting of Yew Cuttings, an Ornamental Shrub in Danger of Extinction

IntroductionYew or English yew (Taxus baccata L.) from the family of Taxaceae is an ornamental shrub that is used in various industries. Root induction and formation process at the base of stem cuttings of yew is slow. This species is in danger of extinction. Stimulation of rooting in cuttings causes the plant to grow faster. Polyamines are a group of plant growth regulators that play a variety of roles, including cellular differentiation and development and stimulation of adventitious root production. Some yew habitats have been destroyed because of neglect, destruction, livestock and ineffective exploitation. The yew is propagated by seeds or through cutting and grafting. Propagation of yew through seed is difficult and obtained plants show non-uniformity. Therefore, vegetative propagation is used to produce plants similar to the mother plant. The proliferation of the plant through leafy stem cutting is one of the most famous and the best propagation methods due to the preservation of the genetic structure and uniformity. Increasing the rooting capacity of trees and shrub cuttings is being carried out with a variety of plant growth regulators around the world. Putrescine has shown a better response in compare with other polyamines. The stimulation effect of exogenous application of polyamines, especially putrescine, was shown on the rooting of several plants’ cutting. Literature evaluation showed that there is not any study on the effect of polyamines on the rooting of the yew stem cuttings. Therefore, the aim of this research was to improve the rooting conditions of difficult-to-root cuttings with different concentrations of putrescine (a type of polyamine). Materials and MethodsIn order to investigate the effect of different concentrations of putrescine, an experiment was performed based on a completely randomized block design with 4 replications. Treatments included 0 (as a control), 500, 1000, 2000, 3000, 4000 and 5000 mg.l–1 of putrescine concentrations. In October, 25 cm of the end of the shoot of 5-years-old mother plants were cut and used as hardwood cuttings. The cuttings diameter was 2.5-3 mm. The lower ends of the shoot cuttings were kept at different concentrations of putrescine for 10 seconds and then placed in the cultivation bed. In this study, root percentage, number of roots, root length, stem length, shoot number, leaf number and survival percentage of cuttings were measured. Cuttings cultivation bed was perlite, cocopeat and peat moss. To prevent possible contamination, the bottom of the cuttings were immersed in a 2/1000 fungicide solution of Berdofix a week befor cutting preparation. Results and DiscussionThe results of analysis of variance showed that different concentrations of putrescine on all traits were significant at 1% probability levels. The results of mean comparison showed that the largest number of roots (6.50 per plantlet) and the highest root length (7.70 cm per plantlet) were observed in cuttings treated with 500 mg.l–1 putrescine. The highest number of shoots (5.50 per plantlet) and the highest rooting percentage (97.50) were obtained in cuttings treated with 2000 mg.l–1 of putrecine. The maximum number of leaves (41.25 per plantlet) was counted in cuttings treated with 3000 mg.l–1 of putrescine. Yew can be propagated successfully by stem cuttings. Natural conditions propagation and in vitro propagation beside cryopreservation are effective approaches to conserve plants particularly those putted in the red list. Plant growth regulators have an effective role in increasing the rooting of difficult-to-root cuttings of trees and shrubs. The exogenous use of polyamines as a new group of hormones stimulated root production in some cuttings. Peach × almond hybrid cuttings treated with 2 mM putrescine for 5 min showed the highest rooting percentage, root number and root length with the best quality. Putrescine is capable to influences on other plant growth regulators and has less toxicity than most of them. Polyamines stimulate cellular division in dissection place cells of cuttings such as cambium and phloem. The exogenous application of these compounds, especially putrescine during the root formation phase resulted in an increase in endogenous putrescine, endogenous auxin and peroxidase enzyme activity. In the cutting of the leafy stem of Corylus avellana L., the use of putrescine stimulated rooting. The study, like the present study, confirmed that putrescine can be useful for increasing rooting percentage and root quality. Putrescine had an effective role in the rooting of the stem cuttings. The present study revealed that the lowest root number was counted in cuttings that were not treated by putrescine (control). Polyamines (spermine, spermidine and putrescine) increased rooting percentage and root growth by stimulating root cell division (increased mitotic index of tip root cells) in regenerated pine (Pinus virginiana Mill.) seedlings. Polyamine biosynthesis and antioxidant enzymes activity were increased during root induction and formation. The exogenous application of spermidine in the apple (Malus prunifolia) stem cutting stimulated rooting by changing the concentration of some hormones. Spermidine regulated the expression of genes involved in the production of auxins. The study aimed to investigate the cellular-molecular effect of polyamines on the structure and development of roots in Arabidopsis showed that these organic compounds adjusted the size of the root meristematic zone during the effect on both symptomatic accumulations of hormones and reactive oxygen species (ROS). The same and different results are presented with the present findings by some other researchers. The main cause of these different results is the difference in the amount and balance of endogenous hormones, including polyamines in different species. Plant genotype, type of cuttings, cutting age, environmental factors, nutritional status especially type and amount of carbohydrates in the plant, the transfer rate of these carbohydrates from leaves to roots, the presence and the amount of phenolic compounds, nitrogen compounds, phonological stages and cutting season also play an effective role in these differences.