Antonio Trotta

Impact of two fluorescent pseudomonads and an arbuscular mycorrhizal fungus on tomato plant growth, root architecture and P acquisition

The ability of fluorescent pseudomonads and arbuscular mycorrhizal fungi (AMF) to promote plant growth is well documented but knowledge of the impact of pseudomonad-mycorrhiza mixed inocula on root architecture is scanty. In the present work, growth and root architecture of tomato plants (Lycopersicon esculentum Mill. cv. Guadalete), inoculated or not with Pseudomonas fluorescens 92rk and P190r and/or the AMF Glomus mosseae BEG12, were evaluated by measuring shoot and root fresh weight and by analysing morphometric parameters of the root system. The influence of the microorganisms on phosphorus (P) acquisition was assayed as total P accumulated in leaves of plants inoculated or not with the three microorganisms. The two bacterial strains and the AMF, alone or in combination, promoted plant growth. P. fluorescens 92rk and G. mosseae BEG12 when co-inoculated had a synergistic effect on root fresh weight. Moreover, co-inoculation of the three microorganisms synergistically increased plant growth compared with singly inoculated plants. Both the fluorescent pseudomonads and the myco-symbiont, depending on the inoculum combination, strongly affected root architecture. P. fluorescens 92rk increased mycorrhizal colonization, suggesting that this strain is a mycorrhization helper bacterium. Finally, the bacterial strains and the AMF, alone or in combination, improved plant mineral nutrition by increasing leaf P content. These results support the potential use of fluorescent pseudomonads and AMF as mixed inoculants for tomato and suggest that improved tomato growth could be related to the increase in P acquisition.

Effects of arbuscular mycorrhizal colonization and phosphorus application on nuclear ploidy in Allium porrum plants

Arbuscular mycorrhizal (AM) colonization can strongly affect the plant cell nucleus, causing displacement from the periphery to the center of the cell, hypertrophy and polyploidization. The hypertrophy response has been shown in a variety of AM plants whilst polyploidization has been reported only in Lycopersicon esculentum, a multiploid species with a small genome. In order to determine whether polyploidization is a general plant response to AM colonization, analyses were performed on Allium porrum, a plant with a large genome, which is much less subject to polyploidization than L. esculentum. The ploidy status of leaves, complete root systems and four zones of the adventitious roots was investigated in relation to phosphorus content, AM colonization and root differentiation in A. porrum plants grown under two different regimes of phosphate nutrition in order to distinguish direct effects of the fungus from those of improved nutrition. Results showed the presence of two nuclear populations (2C and 4C) in all treatments and samples. Linear regression analyses suggested a general negative correlation between phosphorus content and the proportion of 2C nuclei. The percentage of 2C nuclei (and consequently that of 4C nuclei), was also influenced by AM colonization, differentiation and ageing of the root cells, which resulted in earlier occurrence, in time and space, of polyploid nuclei.

Herbivory induces a ROS burst and the release of volatile organic compounds in the fern Pteris vittata L.

Abstract The arsenic hyper-accumulating fern, Pteris vittata L., was studied to investigate the behavior of lower plants in response to both mechanical (MW) and herbivore wounding (HW). To this end, the cotton leaf worm Spodoptera littoralis was fed on P. vittata and the volatile organic compound (VOC) emission was detected from the ferns head space by using solid phase micro extraction (SPME) and analyzed by GC-MS. Controls were represented by unwounded and MW ferns. The fluorescent probe Amplex red was used to investigate the oxidative burst due to MW and HW by confocal laser scanning microscopy. Ferns responded to herbivore wounding events by emitting the sesquiterpenes (Z)-β-farnesene, (E)-β-farnesene, (Z,E)-α-farnesene, (E,E)-α-farnesene and (E)-nerolidol. An oxidative burst was found close to wounded areas in both MW and HW ferns, and young ferns reacted with a higher H2O2 production after HW. The reported data suggest that lower plants, such as ancient ferns, show two events commonly occurring and reported in many higher and more evolved plants after herbivore attack: an oxidative burst and the emission of volatile terpenoids.

Lipophilic properties of some quaternary ammonium ions and dissociation of −Δ H+ from K+ uptake: A tentative correlation

Abstract The capability of some lipophilic quaternary ammonium ions to substitute to a certain extent for the K + in the active (metabolic-dependent) acid extrusion process in fusicoccin-treated pea root segments was correlated, at least in a semi-quantitative way, with their increasing lipophilicity and size. This finding supports the view of an electric coupling between active H + extrusion and monovalent cation (especially K-ion) uptake.

In vitro interactions between Mentha piperita L. and a non-mycorrhizal endophyte: root morphogenesis, fungus development and nutritional relationships

Abstract Field grown Mentha piperita can be colonized by a fungal endophyte, PGP-HSF, which heavily infects roots and enhances growth of in vitro grown plants. In this work, the time course of fungal development and its morphogenetic effects on plant growth, as well as phosphorus shoot concentration, were analyzed. Fungal infection induced longer shoots and roots and increased adventitious root branching. Microscopic analyses showed that hyphae grew between the walls of rhizodermal cells, produced a progressively thicker sheath and colonized the senescent rhizodermal cells. Plant mechanical defences developed early after the contact between hyphae and rhizodermal cells, and specialized host-fungus interfaces were not observed. Phosphorus concentration was lower in colonized plants than in controls. Our data support a passage of carbon from the plant to the fungus, but no transfer of mineral nutrients from the fungus to the root. The role of PGP-HSF on the enhancement of host growth is discussed.

Nucleus size in the host cells of an Arbuscular Mycorrhizal system: a mathematical approach to estimate the role of ploidy and chromatin condensation

Abstract In order to better understand which are the factors involved in the control of nuclear size, and more precisely, to clarify why nuclear hypertrophy doesn’t always follow genome increase, biological techniques combined with a strict mathematical approach have been applied to study the nuclei of root cortical cells of Lycopersicon escu-lentum Mill cv Early Mech. Tomato is a multiploid plant, with three different levels of DNA content, therefore it is especially suitable to study nucleus size according to genome size. In addition, as arbuscular mycorrhizal colonization strongly affects nucleus organization, part of the plants were inoculated with the arbuscular mycorrhizal fungus Glomus mosseae BEG 12. Quantitative and qualitative nuclear changes have been analyzed in mycorrhizal and non-mycorrhizal roots of tomato, by means of microscopy, immuno-labelling and flow cytometry. The results, supported by mathematical analysis, clearly show that increased ploidy is necessary, but not sufficient, to explain nuclear hypertrophy, in which chromatin decondensation is also involved and related to cell metabolic activity.