Salinity tolerance has been extensively investigated in recent years due to its agricultural importance. Several features, such as the regulation of ionic transporters and metabolic adjustments, have been identified as salt tolerance hallmarks. Nevertheless, due to the complexity of the trait, the results achieved to date have met with limited success in improving the salt tolerance of rice plants when tested in the field, thus suggesting that a better understanding of the tolerance mechanisms is still required. In this work, differences between two varieties of rice with contrasting salt sensitivities were revealed by the imaging of photosynthetic parameters, ion content analysis and a transcriptomic approach. The transcriptomic analysis conducted on tolerant plants supported the setting up of an adaptive program consisting of sodium distribution preferentially limited to the roots and older leaves, and in the activation of regulatory mechanisms of photosynthesis in the new leaves. As a result, plants resumed grow even under prolonged saline stress. In contrast, in the sensitive variety, RNA-seq analysis revealed a misleading response, ending in senescence and cell death. The physiological response at the cellular level was investigated by measuring the intracellular profile of H2O2 in the roots, using a fluorescent probe. In the roots of tolerant plants, a quick response was observed with an increase in H2O2 production within 5 min after salt treatment. The expression analysis of some of the genes involved in perception, signal transduction and salt stress response confirmed their early induction in the roots of tolerant plants compared to sensitive ones. By inhibiting the synthesis of apoplastic H2O2, a reduction in the expression of these genes was detected. Our results indicate that quick H2O2 signaling in the roots is part of a coordinated response that leads to adaptation instead of senescence in salt-treated rice plants.

Salt tolerance is a complex trait that varies between and within species. H2O2 profiles as well as antioxidative systems have been investigated in the cultured cells of rice obtained from Italian rice varieties with different salt tolerance. Salt stress highlighted differences in extracellular and intracellular H2O2 profiles in the two cell cultures. The tolerant variety had innate reactive oxygen species (ROS) scavenging systems that enabled ROS, in particular H2O2, to act as a signal molecule rather than a damaging one. Different intracellular H2O2 profiles were also observed: in tolerant cells, an early and narrow peak was detected at 5 min; while in sensitive cells, a large peak was associated with cell death. Likewise, the transcription factor salt-responsive ethylene responsive factor 1 (TF SERF1), which is known for being regulated by H2O2, showed a different expression profile in the two cell lines. Notably, similar H2O2 profiles and cell fates were also obtained when exogenous H2O2 was produced by glucose/glucose oxidase (GOX) treatment. Under salt stress, the tolerant variety also exhibited rapid upregulation of K+ transporter genes in order to deal with K+/Na+ impairment. This upregulation was not detected in the presence of oxidative stress alone. The importance of the innate antioxidative profile was confirmed by the protective effect of experimentally increased glutathione in salt-treated sensitive cells. Overall, these results underline the importance of specific H2O2 signatures and innate antioxidative systems in modulating ionic and redox homeostasis for salt stress tolerance.

Biostimulants are gaining increasing interest because of their ability to provide a green and effective strategy towards sustainable crop production. Nonetheless, their mode of action remains often unknown. The object of this work was to unravel the mechanisms through which 4-Vita, a biostimulant plant extract, can mitigate drought stress in tomato. To this aim, tomato plants were treated with two foliar applications of 4-Vita and drought stress imposed to both treated and control plants. Phenomics investigations were coupled to mass spectrometric untargeted metabolomics, and raw data were elaborated by multivariate statistics and pathway analysis. The biostimulant elicited a broad reprogramming of the tomato’s secondary metabolism, including its phytohormones profile, corroborating an improved ability to cope with drought stress. A series of mechanisms could be identified in response to the biostimulant treatment under drought, pointing to the preservation of photosynthetic machinery functionality. The modulation of thylakoid membrane lipids, the increase in xanthins involved in ROS detoxification, and the modulation of chlorophylls synthesis could also be observed. Overall, a series of coordinated biochemical mechanisms were elicited by the biostimulant treatment, supporting the increased resilience to drought stress in tomato.

No abstract

Downy mildew, caused by Plasmopara viticola in grapevine, is one of the most devastating and widespread fungal disease on causing serious harm to grape production. The heavy use of chemical pesticides, necessary to control the pests and pathogens, has caused issues with the resistance, resurgence and residues in food, as well as creating diffuse environmental pollution. In the last decade, biological control started to offer an alternative safe(r) and effective method to control diseases. In this paper, we investigate the potential activity of a plant extract to protect grapevine from downy mildew when used in strategy with a reduced dosage of the conventional fungicides (PPP). Four strategies were tested, with two of them giving the best results. Indeed, the use of LL017 increased the tolerance of the vine against P. viticola compared to its control with the same dosage of PPP, and with an efficacy closer to the full dosage of the PPP. In the tests where the yield was evaluated, the treatment with LL017 always resulted in a higher yield than the respective control with the same dosage of PPP and, in some cases, it gave a higher yield than even the positive control.