Lucia Maiuro

Effect of water stress on root meristems in woody and herbaceous plants during the first stage of development

We investigated the effect of water stress on the root system architecture of pine saplings and pea seedlings during the first stage of development. Attention was focused on meristematic tissue situated at the root tip because of the leading role played by the tissue in the planning of root system architecture. The data showed that both species are extremely sensitive and that plants arrest their growth immediately during water stress treatment. When stress treatment was not intense, both species recovered growth but presented modifications in the root system architecture. In pine saplings, the modification in root system architecture was the consequence of fine root meristems not recovering from water stress. The saplings survived by producing new lateral meristems from the cortical tannin zone above the fine root tip. In the case of pea seedlings, the meristematic tissues in the primary root arrested proliferation during water stress although they recovered when the event occurred during the first hours of germination. The response was different when water stress was enforced on older seedlings. In this case, root meristems never completely recovered their proliferation despite the increase in proline content observed in the cells. The modification of root system architecture in pea seedlings depended on the arrest of primary root elongation and the formation of new root laterals. As regards the primary roots, water stress treatment induced along the axis the formation of irregular ‘swellings’ in the cortical zone above the meristematic zone. Anatomical investigations suggested that such swellings may have derived from the changes in elongation direction of derivatives. The formation of new laterals was observed in hydroponic cultures when water stress treatment was enforced slowly and prolonged for a long time. The production of new lateral meristems may have been a similar response of woody and herbaceous plants to water stress conditions. It is not known whether these new meristems present characteristics of resistance to water stress.

Irradiation Treatments to Improve the Shelf Life of Fresh Black Truffles (Truffles Preservation by Gamma-Rays)

The aim of this study was to individuate a method to improve the shelf life of fresh truffles, hypogeous fungi highly prized but very perishable as well. Microbial ecology of fresh products was investigated and the effect of irradiation at different doses on microbial and sensorial parameters was assayed. Data showed that fresh truffles are strongly contaminated from different groups of microorganisms. Irradiation was able to influence their growth, determining an impressive reduction. Treatments at 5 and 10 kGy doses produced the highest microbial decontamination but negatively influenced sensorial parameters. Irradiation at a 1.5 kGy dose was the best solution to improve the shelf life of truffles.

Detection of different microenvironments and Lactobacillus sakei biotypes in Ventricina, a traditional fermented sausage from central Italy

The present study evaluated the physico-chemical and microbiological features of Ventricina, considering for the first time the presence of different compartments deriving from the technology of production. In fact meat pieces (pork muscle and fat cut into cubes of about 10-20cm3), mixed with other ingredients and then stuffed into pig bladder, are still distinguishable at the end of the ripening. They appear delimited on the outside by the casing and inside by thin layers consisting of spices (mainly red pepper powder), salt and meat juices. Our results showed that the exterior (portion of the product in contact with the casing), the interstice (area between the different cubes of meat or fat) and the heart (the inner portion of meat cubes) had distinctive values of pH and aw, and a typical microbial progression, so that they can be considered as different ecological niches, here called microenvironments. The study of lactic acid bacteria population, performed with PCR-DGGE and sequence analysis targeting the V1-V3 region of the 16S rRNA gene (rDNA), highlighted the presence of a few species, including Lactobacillus sakei, Lb. plantarum, Weissella hellenica and Leuconostoc mesenteroides. The RAPD-PCR analysis performed on Lb. sakei, recognised as the predominant species, allowed the differentiation into three biotypes, with that characterised by the highest acidifying and proteolytic activities and the highest ability to grow in the presence of sodium chloride prevailing. This leading biotype, detectable in the interstice during the entire ripening period, was isolated in the microenvironments exterior and heart starting from the 30th d of ripening, and it was the sole biotype present at the end of the ripening. The analysis of microenvironments through the scanning electron microscopy (SEM) evidenced the presence of micro-channels, which could favour the microbial flow from the interstice to the exterior and the heart. Moreover, the SEM analysis allowed the detection of biofilms, recognised as responsible for the correct colonisation of the different meat niches.

Lactobacillus plantarum 29 Inhibits Penicillium spp. Involved in the Spoilage of Black Truffles (Tuber aestivum)

The effect of an antifungal culture of Lactobacillus plantarum to be used in the storage at refrigeration temperature of fresh black truffles was examined. The strain was selected among 29 lactobacilli isolated from foods and evaluated for their viability and acidification activity at 4 °C, as well as for their inhibitory activity against 11 Penicillium strains isolated from truffles stored at refrigeration temperature. Lb. plantarum 29 showed the ability to hold not only the growth of Penicillium isolated from truffles, but also that of P. digitatum DSM 2750, a green mold involved in the spoilage of truffles. The antifungal activity was observed in vitro and in situ, and the sensory characteristics of truffles were preserved during the cold storage.

Nucleus and nucleolus in pea root meristems are affected by variations in moisture content

ABSTRACT This paper examines the morphological and biochemical variations occurring in the nucleus when considerable changes in moisture content take place in the tissue. The tissue used for this investigation was the root meristem of Pisum sativum L. at three different developmental stages: during seed maturation, during seed germination and during a vegetative stage. These different developmental stages were representative of three different degrees of moisture content. Seed maturation represented the case of tissue undergoing desiccation whereas seed germination represented the case of tissue undergoing hydration. PEG-treated seedlings represented the case of a vegetative tissue subjected to water stress. The data demonstrated that when moisture content in root meristems was low, the nucleus underwent a reduction in diameter and a change in chromatin arrangement. The nucleolus shrank considerably in diameter and became less visible. These events were simultaneous to qualitative and quantitative variati...

Antimicrobial activity of gallic acid against food-related Pseudomonas strains and its use as biocontrol tool to improve the shelf life of fresh black truffles

Refrigeration alone or in combination with other technologies represents the main tool used in the last decades to preserve the freshness of black truffles. This is principally due to the delicateness and vulnerability of this edible hypogeous fungus, so that other invasive preservation practices cannot be adopted. However, the proliferation of some microbial species during the cold storage still represents an unsolved problem. Pseudomonads are among the main spoiler bacteria responsible for the deterioration of refrigerated black truffles. Their growth ability at low temperatures requires the use of additional hurdles to prolong the shelf-life of truffles without altering their major features. The use of natural compounds may represent an alternative system for the biocontrol of this kind of product. Specifically, gallic acid (GA) is a phenolic acid naturally present in different foods, whose effectiveness was in vitro demonstrated against Pseudomonas spp. In our study, we reported the antimicrobial activity expressed by GA not only in vitro, using as target bacteria Pseudomonas putida DSMZ 291T, P. fluorescens DSMZ 50090T, P. fragi DSMZ 3456T and Pseudomonas spp. P30-4, previously isolated from black truffles, but also in situ on fresh black truffles stored at 4°C for 28days. Our results showed Minimum Inhibitory Concentrations (MIC) of 2.5mg/mL GA for all tested strains, except for P. fluorescens DSMZ 50090T, having a MIC corresponding to 5mg/mL GA. The Minimum Bactericidal Concentration (MBC) was 10mg/mL for all strains. The analysis of kinetic parameters showed that the survival declined passing from 2.5 to 10mg/mL GA concentrations, with P. fluorescens confirmed to be the most resistant strain. Moreover, images obtained from Scanning Electron Microscopy revealed that Pseudomonas cells were strongly injured by the treatment with GA at 2.5mg/mL concentration, displaying visible pores on the cellular surfaces, absence of flagella and lysis with loss of cytoplasmic material. The storage test performed on fresh black truffles confirmed in situ the GA antimicrobial activity observed in vitro, with a drastic reduction not only of Pseudomonas spp., but also of the other assessed microbial groups, including Enterobacteriaceae and Eumycetes. Finally, sensory analysis established the absence of off-flavours and the preservation of positive features in black truffles treated with 2.5mg/mL GA and stored for 28 d at 4°C. The results obtained in this study suggest that GA is a potential biocontrol tool to decontaminate and preserve fresh black truffles during refrigerated storage.

Modification of chromatin organisation at low water potential in cultured cells of Solanum tuberosum: Possible involvement of dehydrins

ABSTRACT To understand the mechanisms which enable the nucleus to function under low water potential, the morphology and biochemistry of potato cell nuclei were studied. Conformational modifications were observed in the chromatin of nuclei of cells growing under low water potential. These modifications include a higher number of heterochromatic centres, enlargement of the nuclear diameter, and a different accessibility of DNA to the action of restriction enzymes. Biochemical analyses showed that these chromatin modifications may coincide with quantitative and qualitative variations of several nuclear proteins, some of which may belong to the dehydrin family. We especially focussed our attention on a 45-kDa protein that is heat-stable and is recognised by an antibody raised against the conserved domain of dehydrins. The survival of potato cells in an environment where water availability is low may depend on several simultaneous events regarding the nucleus. The accumulation in the nucleus of specific proteins such as dehydrins could be required to stabilise the chromatin by means of their molecule-salvation action. Further studies are in progress to check whether or not variations in chromatin organisation may be one of the numerous traits that a cell must acquire to become water-stress resistant.

Effect of water stress upon root meristems of pea seedlings: The role of quantitative and qualitative changes in protein patterns

To investigate the effect of water stress on the activity of meristems we used an hydroponics culture of pea seedlings to which polyethilene-glicole (PEG) has been gradually added to give the external water potential of –1.7 MPa. We focused our attention on primary root meristem although the meristematic tissue of plumules has been considered as well. Our data showed that under water stress conditions, meristematic cells from primary root arrest their activity irreversibly, while shoot meristems rapidly recover their activity when the seedlings are placed in a normal water conditions. However, the inhibition of cell division of primary root meristems does not interfere with the development of a complete root apparatus; in fact, lateral roots are still formed during water stress from initials situated in the pericycle zone, which give origin to a meristematic tip. The different sensitivity to water stress shown by meristematic cells situated in primary roots, lateral roots or shoot plumules suggests that the tolerance to water stress in meristematic tissue may depend upon factors related to its developmental stage or to the type of `mother initial’ responsible for forming this tissue. The quantitative and qualitative differences in the content of specific proteins showed between meristems during water stress may support this idea. Some of the proteins examined in our samples have shown a striking immuno-affinity for an antibody raised against a conserved sequence common to all the Dehydrins. The proteins recognised by the anti-Dehydrins antibody accumulated in a considerable amount in meristematic cells of plumules during water stress conditions. Since Dehydrins have been proposed to play a protective role during water stress, it may be speculated that the better tolerance shown by shoot or lateral-root meristems is correlated with the accumulation of these specific proteins.