Plasma-Activated Water Triggers Rapid and Sustained Cytosolic Ca2+ Elevations in Arabidopsis thaliana

Increasing evidence indicates that water activated by plasma discharge, termed as plasma-activated water (PAW), can promote plant growth and enhance plant defence responses. Nevertheless, the signalling pathways activated in plants in response to PAW are still largely unknown. In this work, we analysed the potential involvement of calcium as an intracellular messenger in the transduction of PAW by plants. To this aim, Arabidopsis thaliana (Arabidopsis) seedlings stably expressing the bioluminescent Ca2+ reporter aequorin in the cytosol were challenged with PAW generated by a plasma torch. Ca2+ measurement assays demonstrated the induction by PAW of rapid and sustained cytosolic Ca2+ elevations in Arabidopsis seedlings. The dynamics of the recorded Ca2+ signals were found to depend upon different parameters, such as the operational conditions of the torch, PAW storage, and dilution. The separate administration of nitrate, nitrite, and hydrogen peroxide at the same doses as those measured in the PAW did not trigger any detectable Ca2+ changes, suggesting that the unique mixture of different reactive chemical species contained in the PAW is responsible for the specific Ca2+ signatures. Unveiling the signalling mechanisms underlying plant perception of PAW may allow to finely tune its generation for applications in agriculture, with potential advantages in the perspective of a more sustainable agriculture.

A glutamate synthase mutant of Bradyrhizobium sp. strain ORS285 is unable to induce nodules on Nod factor-independent Aeschynomene species

The Bradyrhizobium sp. strain ORS285 is able to establish a nitrogen-fixing symbiosis with both Nod factor (NF) dependent and NF-independent Aeschynomene species. Here, we have studied the growth characteristics and symbiotic interaction of a glutamate synthase (GOGAT; gltD::Tn5) mutant of Bradyrhizobium ORS285. We show that the ORS285 gltD::Tn5 mutant is unable to use ammonium, nitrate and many amino acids as nitrogen source for growth and is unable to fix nitrogen under free-living conditions. Moreover, on several nitrogen sources, the growth rate of the gltB::Tn5 mutant was faster and/or the production of the carotenoid spirilloxanthin was much higher as compared to the wild-type strain. The absence of GOGAT activity has a drastic impact on the symbiotic interaction with NF-independent Aeschynomene species. With these species, inoculation with the ORS285 gltD::Tn5 mutant does not result in the formation of nodules. In contrast, the ORS285 gltD::Tn5 mutant is capable to induce nodules on NF-dependent Aeschynomene species, but these nodules were ineffective for nitrogen fixation. Interestingly, in NF-dependent and NF-independent Aeschynomene species inoculation with the ORS285 gltD::Tn5 mutant results in browning of the plant tissue at the site of the infection suggesting that the mutant bacteria induce plant defence responses.

Deciphering Brassica plant defence responses to cabbage white butterfly egg-associated molecular patterns

Brassica plants activate a strong hypersensitive response (HR)-like necrosis underneath eggs of cabbage white butterflies, but their molecular response to eggs is poorly understood. Here, we developed a method to generate egg wash to identify potential insect egg-associated molecular patterns (EAMPs) inducing HR-like necrosis. We found that egg wash, containing compounds from Pieris eggs, induced a similar response as eggs. We show that wash of hatched eggs, of egg glue, and of accessory reproductive glands (ARG) that produce this glue, also induced HR-like necrosis, whereas removal of the glue from eggs resulted in a reduced response. Eggs of Pieris butterflies induced callose deposition, production of reactive oxygen species and cell death in B. nigra and B. rapa leaf tissue, also in plants that did not express HR-like necrosis. Finally, only washes from Pieris eggs induced defence genes and ethylene production, whereas egg wash of a generalist moth did not. Our results indicate that EAMPs are in the egg glue and that the response in B. nigra is specific to Pieris species. Our study expands knowledge on the Brassica-Pieris-egg interaction, and paves the way for identification of EAMPs in Pieris egg glue and corresponding receptor in Brassica spp.

Zinc phosphate protects tomato plants against Pseudomonas syringae pv. tomato

The purpose of this study was to determine whether zinc phosphate treatments of tomato plants (Solanum lycopersicum L.) can attenuate bacterial speck disease severity through reduction of Pseudomonas syringae pv. tomato (Pst) growth in planta and induce morphological and biochemical plant defence responses. Tomato plants were treated with 10 ppm (25.90 µM) zinc phosphate and then spray inoculated with strain DAPP-PG 215, race 0 of Pst. Disease symptoms were recorded as chlorosis and/or necrosis per leaf (%) and as numbers of necrotic spots. Soil treatments with zinc phosphate protected susceptible tomato plants against Pst, with reductions in both disease severity and pathogen growth in planta. The reduction of Pst growth in planta combined with significantly higher zinc levels in zinc-phosphate-treated plants indicated direct antimicrobial toxicity of this microelement, as also confirmed by in vitro assays. Morphological (i.e. callose apposition) and biochemical (i.e., expression of salicylic-acid-dependent pathogenesis-related protein PR1b1 gene) defence responses were induced by the zinc phosphate treatment, as demonstrated by histochemical and qPCR analyses, respectively. In conclusion, soil treatments with zinc phosphate can protect tomato plants against Pst attacks through direct antimicrobial activity and induction of morphological and biochemical plant defence responses.

Nanoelicitors with prolonged retention and sustained release to produce beneficial compounds in wines

Methyl jasmonate (MeJ), an elicitor able to trigger plant defence responses, is a natural and clean alternative to the use of hazardous pesticides. However, the efficient application of MeJ in...

Plasma activated water triggers plant defence responses

Nowadays, one of the main challenges is moving towards an eco-sustainable agriculture, able to preserve the food production through a reduced use of pesticides. Current global food sustenance by intensive agriculture is mainly based on economic crop monocultures and drastically reduces the biodiversity, increasing the yield losses due to the presence of biotic and abiotic stresses. A technology based on plasma activated water (PAW), characterized by the presence in liquid of reactive oxygen and nitrogen species, was tested to try to ensure yield stability also enhancing the plant resistance responses and to promote an eco-sustainable management of plant diseases. In PAW-treated micropropagated periwinkle shoots, periwinkle and grapevine plants, qRT-PCR and small RNAs high-throughput sequencing were used to analyse the differential expression of genes involved in the major plant defence pathways. The results indicate that PAW treatment enhances the plant defence responses and provide an encouraging framework for future applications in plant disease management programs.