Overview of transcriptome changes and phenomic profile of sanitized artichoke vis-à-vis non-sanitized plants.

Plant tissue in vitro culture is increasingly used in agriculture to improve crop production, nutritional quality, and commercial value. In plant virology, the technique is used as sanitation protocol to produce virus-free plants. Sanitized (S) artichokes show increased vigour compared to their non-sanitized (NS) counterparts, because viral infections lead to a decline of growth and development. To investigate mechanisms that control the complex traits related to morphology, growth, and yield in S artichokes compared to NS plants, RNAseq analysis and phenotyping by imaging were used. The role of peroxidases (POD) was also investigated to understand their involvement in sanitized plant development. Results showed that virus infection affected regulation of cell cycle, gene expression and signal transduction modulating cellular response to stimulus/stress. Moreover, primary metabolism and photosynthesis were also influenced, contributing to explain the main morphological differences observed between S and NS artichokes. Sanitized artichokes are also characterized by higher POD activity, probably associated with increased plant growth, rather than strengthening of cell walls. Overall, results show that the differences in development of S artichokes may be derived from the in vitro culture stressor, as well as through pathogen elimination, which, in turn, improve qualitative and quantitative artichoke production.

Multitraits evaluation of a Solanum pennellii introgression tomato line challenged by combined abiotic stress.

Rising daily temperatures and water shortage are two of the major concerns in agriculture. In this work, we analysed the tolerance traits in a tomato line carrying a small region of the Solanum pennellii wild genome (IL12-4-SL) when grown under prolonged conditions of single and combined high temperature and water stress. When exposed to stress, IL12-4-SL showed higher heat tolerance than the cultivated line M82 at morphological, physiological, and biochemical levels. Moreover, under stress IL12-4-SL produced more flowers than M82, also characterized by higher pollen viability. In both lines, water stress negatively affected photosynthesis more than heat alone, whereas the combined stress did not further exacerbate the negative impacts of drought on this trait. Despite an observed decrease in carbon fixation, the quantum yield of PSII linear electron transport in IL12-4-SL was not affected by stress, thereby indicating that photochemical processes other than CO2 fixation acted to maintain the electron chain in oxidized state and prevent photodamage. The ability of IL12-4-SL to tolerate abiotic stress was also related to the intrinsic ability of this line to accumulate ascorbic acid. The data collected in this study clearly indicate improved tolerance to single and combined abiotic stress for IL12-4-SL, making this line a promising one for cultivation in a climate scenario characterized by frequent and long-lasting heatwaves and low rainfall.

Redox regulation in plant programmed cell death.

Programmed cell death (PCD) is a genetically controlled process described both in eukaryotic and prokaryotic organisms. Even if it is clear that PCD occurs in plants, in response to various developmental and environmental stimuli, the signalling pathways involved in the triggering of this cell suicide remain to be characterized. In this review, the main similarities and differences in the players involved in plant and animal PCD are outlined. Particular attention is paid to the role of reactive oxygen species (ROS) as key inducers of PCD in plants. The involvement of different kinds of ROS, different sites of ROS production, as well as their interaction with other molecules, is crucial in activating PCD in response to specific stimuli. Moreover, the importance is stressed on the balance between ROS production and scavenging, in various cell compartments, for the activation of specific steps in the signalling pathways triggering this cell suicide process. The review focuses on the complexity of the interplay between ROS and antioxidant molecules and enzymes in determining the most suitable redox environment required for the occurrence of different forms of PCD.

The efficient physiological strategy of a novel tomato genotype to adapt to chronic combined water and heat stress.

Climate change is increasing the frequency of high temperature shocks and water shortages, pointing to the need to develop novel tolerant varieties and to understand the mechanisms employed to withstand combined abiotic stresses. Two tomato genotypes, a heat-tolerant Solanum lycopersicum accession (LA3120) and a novel genotype (E42), previously selected as a stable yielding genotype under high temperatures, were exposed to single and combined water and heat stress. Plant functional traits, pollen viability and physiological (leaf gas exchange and chlorophyll a fluorescence emission measurements) and biochemical (antioxidant content and antioxidant enzyme activity) measurements were carried out. A Reduced Representation Sequencing approach allowed exploration of the genetic variability of both genotypes to identify candidate genes that could regulate stress responses. Both abiotic stresses had a severe impact on plant growth parameters and on the reproductive phase of development. Growth parameters and leaf gas exchange measurements revealed that the two genotypes used different physiological strategies to overcome individual and combined stresses, with E42 having a more efficient capacity to utilize the limiting water resources. Activation of antioxidant defence mechanisms seemed to be critical for both genotypes to counteract combined abiotic stresses. Candidate genes were identified that could explain the different physiological responses to stress observed in E42 compared with LA3120. Results here obtained have shown how new tomato genetic resources can be a valuable source of traits for adaptation to combined abiotic stresses and should be used in breeding programmes to improve stress tolerance in commercial varieties.

Cytochemical localization of phenol-oxidizing enzymes in lignifying Coleus blumei stems.

The cytochemical localization of the phenol oxidases, laccase and peroxidase, has been studied in pro-lignifying and lignifying Coleus blumei stem sections using 4-methoxy-alpha-naphthol as substrate. The results illustrated that, for short incubation times, both pro-lignifying and lignifying Coleus sections showed H2O2-dependent phenol oxidase (peroxidase-like) activity in epidermal and vascular tissues, while no detectable H2O2-independent phenol oxidase (laccase-like) activity was found in Coleus tissues. For long incubation times, H2O2-independent phenol-oxidases can also be detected in these tissues, however, this is probably due to the partial capability of intercellular washing fluid Coleus peroxidase to oxidize 4-methoxy-alpha-naphthol in the absence of exogenously added H2O2. This illustrates not only the importance of the substrate used, but also the importance of the incubation time, in the cytochemical localization of phenol oxidizing enzymes.

Galactone-γ-lactone-dependent ascorbate biosynthesis alters wheat kernel maturation.

Kernel development and maturation involve several well-characterised events, such as changes in ascorbate (ASC) metabolism, protein synthesis and storage, programmed cell death (PCD) of starchy endosperm and tissue dehydration. Despite many studies focusing on these events, whether and how they are metabolically related to each other, remains to be elucidated. In the present investigation, the changes in ASC-related metabolism, PCD occurrence, kernel filling and dehydration have been analysed during kernel maturation, over a 3-year period in plants grown under normal conditions and in plants displaying modified ASC synthesis. The obtained results suggest that ASC plays a pivotal role in the network of events characterising kernel maturation. During this process, a decrease in ASC content occurs. When ASC biosynthesis is improved in the kernel, by feeding the plants with its immediate precursor, L-galactone-γ-lactone (GL), the decrease in ASC, observed during kernel maturation, is delayed. As a consequence, ascorbate peroxidase (APX) activity is also enhanced. Moreover, a delay in the ASC decrease permits a delay in PCD occurring in kernel storage tissues and in kernel dehydration. Interestingly, the data emerging from the present investigation suggest that the delay in the decrease in ASC content and APX activity also improves kernel filling. The relevance of the ascorbate-dependent redox regulation for kernel productivity is discussed.

The redox state of the ascorbate-dehydroascorbate pair as a specific sensor of cell division in tobacco BY-2 cells.

The effects of ascorbate (ASC) and dehydroascorbate (DHA) on cell proliferation were examined in the tobacco Bright Yellow 2 (TBY-2) cell line to test the hypothesis that the ASC-DHA pair is a specific regulator of cell division. The hypothesis was tested by measuring the levels of ASC and DHA or another general redox pair, glutathione (GSH) and glutathione disulfide (GSSG), during the exponential-growth phase of TBY-2 cells. A peak in ASC, but not GSH, levels coincided with a peak in the mitotic index. Moreover, when the cells were enriched with ascorbate, a stimulation of cell division occurred whereas, when the cells were enriched with DHA, the mitotic index was reduced. In contrast, glutathione did not affect the mitotic-index peak during this exponential-growth phase. The data are consistent in showing that the ASC-DHA pair acts as a specific redox sensor which is part of the mechanism that regulates cell cycle progression in this cell line.

The multiplicity of enzymatic DNA reduction: a new purification procedure for a DHA reducing protein from potato tubers.

The multiplicity of DHA reducing proteins has been observed by means of a native-PAGE technique in several plant species, thus demonstrating, in accordance with recent literature, that several differently evolved proteins are likely to perform DHA reduction. Moreover, a research strategy coupling the use of native-PAGE with chromatographic separation procedure, tentatively performed in Solanum tuberosum, proved to be a useful tool for the separation and partial identification of the proteins involved in DHA reduction.

A comparative study of glutathione and ascorbate metabolism during germination of Pinus pinea L. seeds.

The ascorbate and glutathione systems have been studied during the first stages of germination in orthodox seeds of the gymnosperm Pinus pinea L. (pine). The results indicate that remarkable changes in the content and redox balance of these metabolites occur in both the embryo and endosperm; even if with different patterns for the two redox pairs. Dry seeds are devoid of the ascorbate reduced form (ASC) and contain only dehydroascorbic acid (DHA). By contrast, glutathione is present both in the reduced (GSH) and in the oxidized (GSSG) forms. During imbibition the increase in ASC seems to be mainly caused by the reactivation of its biosynthesis. On the other hand, the GSH rise occurring during the first 24 h seems to be largely due to GSSG reduction, even if GSH biosynthesis is still active in the seeds. The enzymes of the ascorbate--glutathione cycle also change during germination, but in different ways. ASC peroxidase (EC 1.11.1.11) and glutathione reductase (EC 1.6.4.2) activities progressively rise both in the embryo and in endosperm. These changes are probably required for counteracting production of reactive oxygen species caused by recovery of oxidative metabolism. The two enzymes involved in the ascorbate recycling, ascorbate free radical (AFR) reductase (EC 1.6.5.4) and DHA reductase (EC 1.8.5.1), show different behaviour: the DHA reductase activity decreases, while that of AFR reductase remains unchanged. The relationship between ascorbate and glutathione metabolism and their relevance in the germination of orthodox seeds are also discussed.