| dc.description.abstracteng | The influence of Fusarium graminearum infection on mycotoxin formation and on the protein composition of emmer and naked barley grains was investigated during grain ripening from milk ripe grains until ripeness and during a storage period of six month.
F. graminearum inoculation affected the protein composition of emmer and naked barley grains from the early grain development on, whereupon emmer and wheat were more affected than naked barley. F.graminearum inoculation led to increased gliadin sub-fractions and decreased glutenin sub-fractions in emmer and wheat grains. However, naked barley proteins also showed increased hordein and hordenin sub-fractions during early grain development. The hordenins and the glutenins were apparently degraded by fungal proteases, particularly at later grain development stages. Furthermore, emmer and wheat grains showed distinct higher toxin contents than naked barley. In naked barley the toxin contents increased with grain ripening, whereas they were rather constant in emmer and wheat.
Furthermore, naked barley and emmer exhibited different toxin spectra in both natural infected and artificially inoculated grains. Natural infected emmer and wheat showed DON and ZEA accumulation, whereas naked barley accumulated only NIV, assuming different Fusarium species may establish depending on the grain variety. After inoculation with DON-producing F. graminearum strains, DON and ZEA accumulated strongly in emmer, wheat and naked barley, whereas NIV was again only detected in the naked barley cultivars.
During storage of mature grains the toxin composition in natural infected grains was hardly changed, whereas in inoculated grains the DON contents in emmer and naked barley cultivars were significantly reduced. Nevertheless, the prolamins and glutelins of natural infected and artificial inoculated grains were significantly affected during storage of six months, particularly at rather warm and humid storage conditions. This effect was also observed in F. graminearum inoculated grains at colder and dryer storage conditions.
Regarding the occurrence of phenolic compounds in emmer and naked barley grains and in the respective hulls, ferulic acid was the major phenolic acid, followed by p-coumaric and caffeic acid in soluble and bound forms. Furthermore, naked barley had higher amounts of cinnamic acid derived phenolics in the grains and particularly in the hulls. However, phenolic acids, especially ferulic acid decreased after F. graminearum inoculation, possibly resulting from inhibition of their biosynthesis by the fungi. Mechanisms in plants depending on antioxidant capacity and the general redox status can interfere with the antioxidant secondary plant metabolites and thus may influence toxin accumulation and resistance to Fusarium infection in cereals. The phenolic compounds in the hull-tissues obviously play an important role in inhibiting pathogen growth and toxin accumulation in emmer and naked barley grains.
Proteomic studies were conducted to analyse the effect of Fusarium inoculation on emmer and naked barley grains during the entire grain ripening and infection-period beginning with early grain development (milk ripe) until plant death. The obtained results allow an overview of molecular mechanisms initiated by F. graminearum infection of emmer and naked barley grains and an insight into the interactions between two cereal grains with F. graminearum during the entire period of grain ripening. Different proteins have been induced depending on the grain ripening stages and the cereal genotype. An inoculation of emmer grains with F. graminearum led to changes of protein expression in all analysed development stages. In the early ripening stages proteins, predominantly related to metabolism and photosynthesis as well as stress-related proteins, like PR-poteins and proteins related to oxidative stress were up regulated. Additionally a spermidine synthase was up regulated at BBCH 75 (milk ripe). During later ripening stages at BBCH 87 and BBCH 97 predominantly stress-related proteins were down regulated. Nevertheless, some stress-related proteins such as peroxidase and chitin binding proteins were increased in abundance after F. graminearum infection, demonstrating some defence strategies were persistent during the whole infection period. The pathogen may profit from the enhanced metabolism, providing nutrients that are beneficial for fungal growth.
In naked barley grains, more proteins were changed in abundance during early grain development after F. graminearum inoculation than in the later grain ripening sages. Protease inhibition played a major role at early milk ripe stage, whereas several pathogenesis related proteins and proteins associated with defence response, such as thaumatin-like proteins and ROS scavenging enzymes were regulated due to F. graminearum infection during the entire infection period. Interestingly, proteins related to nitrogen metabolism were predominantly down regulated in naked barley, whereas proteins related to carbohydrate metabolism were predominantly up regulated in artificially inoculated grains compared to natural infected grains. These results demonstrate that complex mechanisms are initiated by Fusarium infection, which are supposed to be partly adapted to the respective infection strategy of the pathogen. | de |