Maurizio Curadi

Trichoderma harzianum T6776 modulates a complex metabolic network to stimulate tomato cv. Micro-Tom growth

Background and aimsTrichoderma harzianum 6776 is a novel and beneficial tomato fungal isolate. To investigate the mechanisms underlying the T. harzianum 6776-tomato interaction, several physiological and biochemical responses were explored on dwarf tomato plants, cv. Micro-Tom.MethodsGrowth of treated and untreated plants was evaluated by measuring the height and biomass production of plants. The leaf pigment content and sugar partitioning in plant organs were evaluated by biochemical analysis. The photosynthetic parameters were measured by a miniaturized PAM fluorometer and a portable gas-exchange system. The hormonal analysis in root and xylem sap was performed by gas cromatography- mass spectrometry (GC-MS).ResultsT. harzianum 6776 positively affected plant growth, increasing the leaf pigment content and improving the photosynthetic activity at both stomatal and non-stomatal levels. Differences in pigment composition and photosynthetic performance were reflected in the carbohydrate content and their partitioning. In the absence of a pathogen, root and xylem vessel stress and growth-related hormone balance were affected by the interaction with T. harzianum 6776, with an increase in jasmonic and indoleacetic acids and a decrease in salicylic acid content.ConclusionsThis study shows the complex connection between increased hormone accumulation and transport, altered sugar partitioning and enhanced photosynthetic efficiency induced by T. harzianum 6776, and how growth promotion is the result of the combination of these drastic changes in Micro-Tom plants.

Auxin metabolism and transport in an embryogenic cell line of Daucus Carota L

Summary In this paper we analysed the endogenous IAA levels in carrot cell cultures and in cell culture medium. Free IAA and its conjugates (esters and amides) were measured in cell cultures exposed to different concentrations of 2,4-D (nil, 2,3 and- 92 μmol/L). The three culture conditions determine different physiological conditions of the cell cultures: somatic embryogenesis, unorganised growth and growth under stress, respectively. The results indicate that these two types of IAA conjugates account for 60–70 % of total IAA and buffer the variations of free IAA in a sequential manner. Free IAA is in a steady state relationship with the ester conjugates and the increased synthesis of IAA is initially buffered by IAA-amide. When a certain threshold (750 ng/g) is reached inside the cell by the amide, further increments are buffered by ester IAA. Another result coming from this analysis is that the presence of tryptophan alone in the culture medium is sufficient to sustain, metabolically as well as physiologically, the conditions of proliferation, shifting the state of the cell culture from somatic embryogenesis to unorganised growth.

The role of Euglena gracilis paramylon in modulating xylem hormone levels, photosynthesis and water-use efficiency in Solanum lycopersicum L.

β-1,3-glucans such as paramylon act as elicitors in plants, modifying the hormonal levels and the physiological responses. Plant hormones affect all phases of the plant life cycle and their responses to environmental stresses, both biotic and abiotic. The aim of this study was to investigate the effects of a root treatment with Euglena gracilis paramylon on xylem hormonal levels, photosynthetic performance and dehydration stress in tomato (Solanum lycopersicum). Paramylon granules were processed to obtain the linear fibrous structures capable to interact with tomato cell membrane. Modulation of hormone levels (abscisic acid, jasmonic acid and salicylic acid) and related physiological responses such as CO2 assimilation rate, stomatal and mesophyll conductance, intercellular CO2 concentration, transpiration rate, water-use efficiency, quantum yield of photosystem II and leaf water potential were investigated. The results indicate a clear dose-dependent effect of paramylon on the hormonal content of xylem sap, photosynthetic performance and dehydration tolerance. Paramylon has the capability to enhance plant defense capacity against abiotic stress, such as drought, by modulating the conductance to CO2 diffusion from air to the carboxylation sites and improving the water-use efficiency.