Photosynthesis in localised regions of oat leaves infected with crown rust (Puccinia coronata): quantitative imaging of chlorophyll fluorescence

Abstract

Abstract. Localised changes in photosynthesis in oat leaves infected with the biotrophic rust fungus Puccinia coronata Corda were examined at different stages of disease development by quantitative imaging of chlorophyll fluorescence. Following inoculation of oat leaves with crown rust the rate of whole-leaf gas exchange declined. However, crown rust formed discrete areas of infection which expanded as the disease progressed and these localised regions of infection gave rise to heterogeneous changes in photosynthesis. To quantify these changes, images of chlorophyll fluorescence were taken 5, 8 and 11 d after inoculation and used to calculate images representing two parameters; ~u, a measure of PSII photochemical efficiency and AFm/Fm', a measure of non-photochemical energy dissipation (qN). Five days after inoculation, disease symptoms appeared as yellow flecks which were correlated with the extent of the fungal mycelium within the leaf. At this stage, ~l~ was slightly reduced in the infected regions but, in uninfected regions of the leaf, values of ~n were similar to those of healthy leaves. In contrast, qN (AFm/Fm') was greatly reduced throughout the infected leaf in comparison to healthy leaves. We suggest that the low value of qN in an infected leaf reflects a high demand for ATP within these leaves. At sporulation, 8 d after inoculation, Ou was reduced throughout the infected leaf although the reduction was most marked in areas invaded by fungal mycelium. In the infected leaf the pattern of non-photochemical quenching was complex; qN was low within invaded regions, perhaps reflecting high metabolic activity, but was now much higher in uninfected regions of the infected leaf, in comparison to healthy leaves. Eleven days after inoculation "green islands" formed in regions of the leaf associated with the Abbreviations: qP~ = photochemical efficiency of photosystem II; qN = non-photochemical energy quenching; AFm/Fm' = a measure of qN; dai = days after inoculation; IRGA = infra-red gas analyser Correspondence to: J.D. Scholes; FAX: 44 (114)276 0159; E-mail: j.scholes@sheffield.ac.uk fungal mycelium. At this stage, photosynthesis was severely inhibited over the entire leaf; however, heterogeneity was still apparent. In the region not invaded by the fungal mycelium, ~n and qN were very low and these regions of the leaf were highly fluorescent, indicating that the photosynthetic apparatus was severely damaged. In the greenisland tissue, (1)if was lOW but detectable, indicating that some photosynthetic processes were still occurring. Moreover, qN was high and fluorescence low, indicating that the cells in this region were not dead and were capable of significant quenching of chlorophyll fluorescence.

Photosynthetic gas exchange and antioxidative system in common bean plants infected by Colletotrichum lindemuthianum and supplied with silicon

“…The high Si concentration in bean leaves contributed to decreased anthracnose severity even though they were lower than those in rice, which is a known Si accumulator that exhibits Si concentrations of up to 5 dag kg -1 of dry mass of shoot (Datnoff et al, 2007;Dallagnol et al, 2009). It is well known that foliar diseases can dramatically decrease photosynthesis in several crops (Chou et al, 2000;Scholes & Rolfe, 1996;Berger et al, 2007;Dallagnol et al, 2013;Resende et al, 2012). In the present study, infection by C. lindemuthianum on bean leaves caused devastating effects on photosynthetic gas exchange.…”

The role of sugar signaling in plant defense responses against fungal pathogens

“…A deficit of sugars and energy at the infection site may pertain also to autotrophic tissues, since fungal infection of leaf tissues typically causes a reduced rate of photosynthesis. A decrease in photosynthesis has been reported in compatible interactions with biotrophic fungi, i.e., Albugo candida, Puccinia coronata and Blumeria graminis (Chou et al 2000;Scholes and Rolfe 1996;Swarbrick et al 2006) as well as necrotrophic pathogens such as Botrytis cinerea (Berger et al 2004(Berger et al , 2007. The photosynthetic organs of young leaves of sugar beet are particularly sensitive to the infection by Aphanomyces cochlioides (oomycetes) (Chołuj and Moliszewska 2012).…”

Imaging of Chlorophyll a Fluorescence: A Tool to Study Abiotic Stress in Plants

“…This technique has been widely applied in the past during induction of photosynthesis (Bro et al, 1996;Oxborough & Baker, 1997), with changes in carbohydrate translocation (Meng et al, 2001), in response to drought (Meyer & Genty, 1999;West et al, 2005), chilling (Hogewoning & Harbinson, 2007), ozone pollution (Guidi et al, 2007;Guidi & Degl'Innocenti, 2008;Leipner et al, 2001), wounding (Quilliam et al, 2006), high light (Zuluaga et al, 2008) and infection with fungi (Guidi et al, 2007;Meyer et al, 2001;Scharte et al, 2005;Scholes & Rolfe, 1996;Schwarbrick et al, 2006) or virus (Perez-Bueno et al, 2006). With Chl fluorescence imaging is possible to detect an analysis of stress-induced changes in fluorescence emission at very early stage of stress.…”