The fungal endophyte Epichloë typhina improves photosynthesis efficiency of its host orchard grass (Dactylis glomerata).

MAIN CONCLUSION: According to the results presented in this paper the fungal endophyte Epichloë typhina significantly improves the growth, PSII photochemistry and C assimilation efficiency of its host Dactylis glomerata. In this paper, we present a comprehensive study of the impact of the endophytic fungi Epichloë typhina on its plant hosts' photosynthesis apparatus. Chlorophyll a fluorescence, gas exchange, immuno-blotting and spectrophotometric measurements were employed to assess photosynthetic performance, changes in pigment content and mechanisms associated with light harvesting, carbon assimilation and energy distribution in Dactylis glomerata colonized with Epichloë typhina. According to the results presented in this study, colonization of D. glomerata results in improved photosynthesis efficiency. Additionally, we propose a new mechanism allowing plants to cope with the withdrawal of a significant fraction of its energy resources by the endophytic fungi. The abundance of LHCI, LHCII proteins as well as chlorophyll b was significantly higher in E+ plants. Malate export out of the chloroplast was shown to be increased in colonized plants. To our knowledge, we are the first to report this phenomenon. Epichloë colonization improved PSII photochemistry and C assimilation efficiency. Elevated energy demands of E+ D. glomerata plants are met by increasing the rate of carbon assimilation and PSII photochemistry.

Progress of snow mould infection in crowns of winter rye (Secale cereale L.) is related to photosynthetic activity during cold acclimation.

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 characteristics 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 CO2 assimilation and electron transport efficiency but did not differ from snow mould susceptible (SMS) line in carboxylation rate of RuBisCO (Vcmax). 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.

The initiation of elongation growth during long-term low-temperature stay of spring-type oilseed rape may trigger loss of frost resistance and changes in photosynthetic apparatus.

The aim of the present investigation was to determine if the loss of frost resistance observed in spring-type oilseed rape during winter may be the effect of the tendency to start elongation growth during the prolonged low-temperature stay. Interactions between elongation growth rate, properties of photosynthetic apparatus and frost resistance were studied under these conditions in spring and winter cultivars of oilseed rape. Both spring and winter cultivars of oilseed rape reached the maximal frost resistance after 6 weeks at +5 degrees C. Photosynthetic apparatus of both cultivars acclimated to functioning in cold. The resistance of winter type plants remained unchanged at the end of the experiment (10 weeks) whereas spring-type plants lost the maximal resistance in subsequent weeks. It was preceded in the 7th week of low-temperature stay by acceleration of elongation growth without an increase in dry matter accumulation. A gradual loss of photosynthetic activity was also observed during this period. It was manifested as a decrease in antenna trapping efficiency, photochemical and non-photochemical fluorescence quenching and actual quantum yield of PSII without affecting apparent quantum yield of PSII. At the 70th day of the experiment, a decrease in CO(2) exchange and dry matter accumulation were even observed. The possible relationships between growth rate and functioning of photosynthetic apparatus are discussed.