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

摘要

Cytokinins (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 ??M 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.