Research article Progress of snow mould infection in crowns of winter rye (Secale cereale L.) is related to photosynthetic activity during cold acclimation E. Pociecha a, * , F. Janowiak b , E. Dubas b , I. _ Zur b , K. Tokarz b, c , I. Kolasi  nska d , A. P1a _ zek a a Department of Plant Physiology, University of Agriculture in Krakow, Podlu _ zna 3, 30-239 Kraków, Poland b Institute of Plant Physiology, Polish Academy of Sciences, Niezapominajek 21, 30-239 Kraków, Poland c Department of Botanyand Plant Physiology, University of Agriculture in Krakow, Al. 29 Listopada 54, 31-425 Krakow, Poland d Department of Plant Genetics and Breeding, Institute of Plant Breeding and Acclimatization, Radzików, 05-870 Blonie, Poland article info Article history: Received 13 February 2013 Accepted 20 May 2013 Available online 7 June 2013 Keywords: Abscisic acid Cold acclimation Microdochium nivale Photosynthesis Phytopathogenesis Total soluble carbohydrates abstract Resistance to snow mould is a feature determined by multiple genes. Therefore, determining the phenotype of resistant plants is difficult as it requires an investigation over a long period of time from cold acclimation through pathogenesis. The aim of the present study was (i) to determine the charac- teristics of the resistant genotype and (ii) to clarify the connections between photosynthesis during cold acclimation and then pathogenesis caused by Microdochium nivale. Two inbred lines of winter rye (Secale cereale L.) differing in their susceptibility to snow mould were used in the study. After cold acclimation snow mould resistant (SMR) line was characterised by higher values of CO 2 assimilation and electron transport efficiency but did not differ from snow mould susceptible (SMS) line in carboxylation rate of RuBisCO (V cmax ). Higher soluble carbohydrate accumulation, due to higher photosynthesis intensity, as well as an ABA increase at 5 days post infection (DPI) in leaves and crowns were found in SMR line during the pathogenesis period. Callose deposition was found around non- infected bundle sheets and in cortex cells at 5 DPI (at the same time point as ABA peak) only in SMR line, which probably prevented the infection of leaf initials. Early leaf initials infection in SMS line may be responsible for inhibiting leaf growth and plant regeneration after stress cessation. The results show different physiological and biochemical characteristics of the investigated lines, which can be applied in the selection of resistant genotypes and identifying genomic regions responsible for metabolic pathways increasing pathogen resistance. Ó 2013 Elsevier Masson SAS. All rights reserved. 1. Introduction Winter rye (Secale cereale L.) is the most frost resistant cereal but simultaneously it is the most susceptible to Microdochium nivale causing pink snow mould. Recovery after freezing stress as well as after pathogen attack depends on the survival of crowns, which are the reservoir of soluble carbohydrates used for regrowth after stress cessation [1]. It has been previously demonstrated that crowns are crucial for the survival of the plant. The increase in enzyme antioxidant activity in crowns, but not in leaves, has been correlated with snow mould resistance [2]. High intensity of photosynthesis during cold acclimation makes it possible to accumulate large reserves utilized later for frost tolerance and pathogen defence processes. Plants which accumulate high amounts of carbohydrates during winter (e.g. winter plants) increase their photosynthetic activity during cold acclimation [3]. Plants possess various abilities of adaptation of the photosynthetic apparatus to cold. In field conditions the reaction of photosynthetic apparatus could be modified by environmental factors including deacclimation and the presence of a snow cover [4], though plants with higher tolerance to cold-induced photo- inhibition are often more frost resistant [3,5]. Sugars such as glucose, fructose, and sucrose are not only sources of energy in defence response against pathogens but they are also signalling molecules in plants. The major product of photosynthesis and the main form of carbohydrate transport is sucrose [6] whose synthesis is catalyzed by invertases and sucrose synthases. Invertases can affect many processes, among others biosynthesis and perception hormones such as ABA. In addition, both ABA and sugars can be effectors of sucrose synthesis genes [6]. Therefore, an effective defence response to stress is the result of coordinated interaction of sugars and hormones such as ABA. * Corresponding author. Tel.: þ48 12 425 33 01. E-mail address: rrchilmo@cyf-kr.edu.pl (E. Pociecha). Contents lists available at SciVerse ScienceDirect Plant Physiology and Biochemistry journal homepage: www.elsevier.com/locate/plaphy 0981-9428/$ e see front matter Ó 2013 Elsevier Masson SAS. All rights reserved. http://dx.doi.org/10.1016/j.plaphy.2013.05.033 Plant Physiology and Biochemistry 70 (2013) 360e367