Growth and Physiological Recovery of Kentucky Bluegrass from Drought Stress as Affected by a Synthetic Cytokinin 6‐Benzylaminopurine

Abstract

ABSTRACTCytokinins (CKs) influence plant adaptation to environmental stresses. The objectives of this study were to (i) examine effects of foliar application of a synthetic CK, 6‐benzylaminopurine (6‐BA), on postdrought recovery and (ii) determine physiological factors involved in postdrought recovery affected by CKs in a perennial grass species. Kentucky bluegrass (Poa pratensis L.) cultivars Midnight (drought tolerant) and Brilliant (drought sensitive) were subjected to drought by withholding irrigation for 15 d and were then rewatered for 10 d in growth chambers. Plants were treated with 25 μM 6‐BA at the time of rewatering. Applying 6‐BA significantly increased endogenous zeatin riboside and isopentenyl adenosine content and decreased abscisic acid (ABA) content in both cultivars previously exposed to drought stress. Foliar 6‐BA application enhanced physiological recovery of plants from drought stress, as demonstrated by the increased leaf relative water content and visual turf quality and decreased electrolyte leakage. The 6‐BA application also significantly improved photosynthetic recovery from drought, as manifested by the increase in net photosynthetic rate, transpiration rate, and stomatal conductance. Foliar application of 6‐BA promoted the production of new tillers. Postdrought recovery affected by 6‐BA application was more pronounced in Midnight than Brilliant, probably because the latter experiences a more sustained leaf water deficit. Our results suggested that CK‐enhanced postdrought recovery of Kentucky bluegrass, particularly in the drought‐tolerant cultivar, was associated with the alteration of CK:ABA balance and promotion of stomatal reopening, resumption of photosynthesis, and new tiller formation on rewatering.