The technological exploitation of palladium or palladium nanoparticles (PdNPs) is increasing, and their wider usage relates to an unwanted release of pollutants into the environment, raising public health concerns about the infiltration of palladium into the consumption chain. This study focuses on the effect of spherical gold-cored PdNPs of 50 ± 10 nm diameter stabilized by sodium citrate on the interaction between an oilseed rape (Brassica napus) and the fungal pathogen Plenodomus lingam. Pretreatment of B. napus cotyledons with PdNPs suspension 24 h before but not 24 h after inoculation with P. lingam resulted in a decrease in the extent of disease symptoms; however, this effect was caused by Pd2+ ions (35 mg l-1 or 70 mg l-1). Tests to determine any direct antifungal activity on P. lingam in vitro demonstrated that the residual Pd2+ ions present in the PdNP suspension were responsible for the antifungal activity and that PdNPs themselves do not contribute to this effect. Brassica napus plants did not show any symptoms of palladium toxicity in any form. PdNPs/Pd2+ slightly increased the chlorophyll content and the transcription of pathogenesis-related gene 1 (PR1), indicating the activation of the plant defence system. We conclude that the only toxic effect of the PdNP suspension was on P. lingam via ions and that PdNPs/Pd2+ did not have any deleterious effect on the B. napus plants.

• Keywords
• Brassica napus, Leptosphaeria maculans, Palladium, Plenodomus lingam, nanoparticle, plant defence,
• Publication type
• Journal Article MeSH

Natural compounds isolated from macroalgae are promising, ecofriendly, and multifunctional bioinoculants, which have been tested and used in agriculture. Ulvans, for instance, one of the major polysaccharides present in Ulva spp. cell walls, have been tested for their plant growth-promoting properties as well as their ability to activate plant immune defense, on a large variety of crops. Recently, we have characterized for the first time an arabinogalactan protein-like (AGP-like) from Ulva lactuca, which exhibits several features associated to land plant AGPs. In land plant, AGPs were shown to play a role in several plant biological functions, including cell morphogenesis, reproduction, and plant-microbe interactions. Thus, isolated AGP-like proteins may be good candidates for either the plant growth-promoting properties or the activation of plant immune defense. Here, we have isolated an AGP-like enriched fraction from Ulva lactuca and we have evaluated its ability to (i) protect oilseed rape (Brassica napus) cotyledons against Leptosphaeria maculans, and (ii) its ability to activate immune responses. Preventive application of the Ulva AGP-like enriched fraction on oilseed rape, followed by cotyledon inoculation with the fungal hemibiotroph L. maculans, resulted in a major reduction of infection propagation. The noticed reduction correlated with an accumulation of H2O2 in treated cotyledons and with the activation of SA and ET signaling pathways in oilseed rape cotyledons. In parallel, an ulvan was also isolated from Ulva lactuca. Preventive application of ulvan also enhanced plant resistance against L. maculans. Surprisingly, reduction of infection severity was only observed at high concentration of ulvan. Here, no such significant changes in gene expression and H2O2 production were observed. Together, this study indicates that U. lactuca AGP-like glycoproteins exhibit promising elicitor activity and that plant eliciting properties of Ulva extract, might result not only from an ulvan-originated eliciting activities, but also AGP-like originated.

• Keywords
• Arabinogalactan proteins, Ulva lactuca, elicitor, hemibiotrophic fungus, plant defense, plant immunity,
• Publication type
• Journal Article MeSH