عنوان مقاله [English]
Background and objectives: The effects of external application of cytokinins on turfgrass leaves and their effects on mitigation of drought stress have been reported in a few studies. However, the effect of benzyl adenine on the content of non-total structural carbohydrates and water-soluble carbohydrates of tall fescue leaves ( Festuca arundinacea Scherb.) has never been investigated under different drought stresses regime, which is our goals in this experiment.
Material and methods: A one-month study on tall fescue that was clonally propagated and established in greenhouse laid out based on completely randomized design with at least three replications including four levels of irrigation treatments (100%, 75%, 50% and 25% of field capacity). In addition to the aforesaid treatments, pots with the same irrigation treatments, foliar sprayed by 50 µM of 6-benzyladenine every 7 days. For comparison, in drought stressed control plants, foliar application of 6-benzyladenine did not applied.
Results: Plants grown on 25% of field capacity was surprisingly influenced by foliar application of benzyl adenine as such noticeable return of leaves to normal growth condition was seen. Looking into water-soluble carbohydrates showed a many fold increase compared to control plants. This water-soluble carbohydrates increase at 50% and 25% of field capacity is much more noticeable than the other treatments. Although foliar treatment with benzyl adenine did not reduce the increase in soluble sugars production to the level of control plants, but BA-influenced WSCs content reduced by half in 50% and 25% of field capacity treatment. Drought stress has reduced chlorophyll content and leaf Starch. This chlorophyll reduction at 25% of FC, to great extent compensated with 50 50 µM of 6-benzyladenine . The activity of α-amylase and β-amylase augmented upon drought stress treatment in 75% of FC followed by reduction in 50% and 25% of FC.
Conclusion: A drastic reduction in soil water content and then plant water can activate starch-degrading enzymes, leading to an increase in water-soluble carbohydrates which could either maintain leaf cell homeostasis or produce more ATP to help with drought stress tolerance. A part of starch degradation in leaves can be explained by α-amylase and β-amylase activity. The research result indicated that application of 50 μM benzyl adenine significantly reduced the stress intensity applied to the plant. This treatment, to great extent improved chlorophyll content and photosynthesis at 25% of FC and reduced further starch degradation and its conversion to fructose, glucose and sucrose, thereby preserving the plant's carbohydrate resources.
Key words: Cytokinin, Drought stress, Tall fescue, Water soluble carbohydrates