Investigation of the effects of ABA on alleviating drought stress in Lilium ledebourii Bioss under in vitro condition

The Lilium ledebourii Bioss is an endangered and wild species native to native to forest and moist area of Iran, having a high potential for unique beauty in Iran and world flower market.Water deficit produces a cascade of physiological responses that ends-up in decreased production and reduced crop quality. Some factors involved in plant responses to water stress. Several mechanisms that plants utilize to cope with water stress are mediated by abscisic acid. So, the aims of this study were to assess the effects of ABA in alleviating the adverse effect of polyethylene glycol- indced drought stress in lilium plants under in vitro condition. This study was carried out as factorial based on completely randomised design with 5 replications in tissue culture laboratory of Department of Horticultural Science, Faculty of Agricultural Science, University of Mohaghegh Ardabili. In vitro plantlets derived from hormone- free MS medium were cultured on MS medium containing different concentrations of PEG (0, 15, 30, 60 gr/l) and ABA (0, 1, 10, 100 µm). Vegetative traits such as bulblet number, bulblet fresh weight, plant fresh weight, root length and root number, plantlet fresh weight, leaf and scale number, and also some physiological traits in response to drought stress such as proline, chlorophyll, anthocyanins, phenols and flavonoids content were measured after 70 days from the beginning of the culture. Results showed that application of ABA and PEG into the cultural medium affected all of the studied traits, significantly (p≤0.01). Vegetative parameters of plantlets such as, root number and root length, bulblet fresh weight, bulblet number, bulblet scale, leaf number and plant fresh weight were declined by increasing the severity of drought stress. Application of lower concentrations of ABA (1 and 10 µm) enhanced plant growth rate, but a higher level (100 µm) of this plant hormone reduced growth rate under drought strss. Accumulation of phenolic compounds, anthocyanins, flavonoids and proline in tissues of plantlets subjected to severe drought stress were respectively 5.5, 4.5, 3.15 and 2.15 times more than control. While, there was a cosiderable drop in leaf chlorophyll content of stressed plantlts compared to the control. Moreover, application of ABA into cultural medium under drought stress condition, increased proline content, anthocyainins, flavonoids and phenolic compounds in the leaves. This increased concentrations of these secondary metabolytes and osmolytes might resulted in an increased plantlet growth under drought stress. Accordinig to the results it can be deduced that growth rate and bulblet formation in lilium plantlet were reduced as a result of drought stress. However, using ABA at lower concentrations in cultural medium enhanced plantlet growth rate by increasing secondary metabolites and osmolytes. While, this compound at higher concentrations showed an inhibitory effect on in vitro plantlets.