The plant-growth-promoting actinobacteria of the genus Nocardia induces root nodule formation in Casuarina glauca.

Actinorhizal plants form a symbiotic association with the nitrogen-fixing actinobacteria Frankia. These plants have important economic and ecological benefits including land reclamation, soil stabilization, and reforestation. Recently, many non-Frankia actinobacteria have been isolated from actinorhizal root nodules suggesting that they might contribute to nodulation. Two Nocardia strains, BMG51109 and BMG111209, were isolated from Casuarina glauca nodules, and they induced root nodule-like structures in original host plant promoting seedling growth. The formed root nodule-like structures lacked a nodular root at the apex, were not capable of reducing nitrogen and had their cortical cells occupied with rod-shaped Nocardiae cells. Both Nocardia strains induced root hair deformation on the host plant. BMG111209 strain induced the expression of the ProCgNin:Gus gene, a plant gene involved in the early steps of the infection process and nodulation development. Nocardia strain BMG51109 produced three types of auxins (Indole-3-acetic acid [IAA], Indole-3-Byturic Acid [IBA] and Phenyl Acetic Acid [PAA]), while Nocardia BMG111209 only produced IAA. Analysis of the Nocardia genomes identified several important predicted biosynthetic gene clusters for plant phytohormones, secondary metabolites, and novel natural products. Co-infection studies showed that Nocardia strain BMG51109 plays a role as a "helper bacteria" promoting an earlier onset of nodulation. This study raises many questions on the ecological significance and functionality of Nocardia bacteria in actinorhizal symbioses.

Effects of water deficit on leaves and fruit quality during the development period in tomato plant.

In nature, plants are often exposed to a multitude of environmental constraints that severely limit crop productivity. Water deficit is one of the factors that most affects agricultural production. The aim of this work is to evaluate the effect of water deficit on morphology, development, nutritional behavior, as well as chlorophyll fluorescence and certain important metabolic parameters (soluble sugars, organic acids, starch, carotenoid, and vitamin C) of the cultivated tomato (Solanum lycopersicum cv Plovdiv). In this study, the water supply was reduced by 60% compared to control conditions. The conditions of water deficit showed that the size of the different organs (leaves, fruits) was reduced. A reduction in the number, width, and length of the leaves, respectively, 9%, 36%, and 37%, then the leaf surface was also observed. Reduction of fluorescence (Fo, Fm, and Fv) and total index performance were among the other symptoms of plants with water deficiency. For fruit, we observed a significant decrease in diameter, fresh weight, and moisture content during the cell division period, the cell expansion period, and the fruit ripening period. In contrast, the composition of the Plovdiv fruit changed only during cell division and expansion phase. On the other hand, the water deficit induces an increase in the total carotenoid and vitamin C content of the fruits.. Besides, water deficit induced a reduction of fruit size, moisture content, and production dry matter during different phases of development. Decrease levels of soluble sugars and organic acid but increase in vitamin C and carotenoid content.

Effect of salinity and calcium on tomato fruit proteome.

Salinity is a major abiotic stress that adversely affects plant growth and productivity. The physiology of the tomato in salty and nonsalty conditions has been extensively studied, providing an invaluable base to understand the responses of the plants to cultural practices. However few data are yet available at the proteomic level looking for the physiological basis of fruit development, under salt stress. Here, we report the effects of salinity and calcium on fruit proteome variations of two tomato genotypes (Cervil and Levovil). Tomato plants were irrigated with a control solution (3 dSm(-1)) or with saline solutions (Na or Ca+Na at 7.6 dSm(-1)). Tomato fruits were harvested at two ripening stages: green (14 days post-anthesis) and red ripe. Total proteins were extracted from pericarp tissue and separated by two-dimensional gel electrophoresis. Among the 600 protein spots reproducibly detected, 53 spots exhibited significant abundance variations between samples and were submitted to mass spectrometry for identification. Most of the identified proteins were involved in carbon and energy metabolism, salt stress, oxidative stress, and proteins associated with ripening process. Overall, there was a large variation on proteins abundance between the two genotypes that can be correlated to salt treatment or/and fruit ripening stage. The results showed a protective effect of calcium that limited the impact of salinization on metabolism, ripening process, and induced plant salt tolerance. Collectively, this work has improved our knowledge about salt and calcium effect on tomato fruit proteome.

Salt-stress induced physiological and proteomic changes in tomato (Solanum lycopersicum) seedlings.

Soil salinity is one of the major abiotic stress limiting crop productivity and the geographical distribution of many important crops worldwide. To gain a better understanding of the salinity stress responses at physiological and molecular level in cultivated tomato (Solanum lycopersicum. cv. Supermarmande), we carried out a comparative physiological and proteomic analysis. The tomato seedlings were cultivated using a hydroponic system in the controlled environment growth chamber. The salt stress (NaCl) was applied (0, 50, 100, 150 and 200 mM), and maintained for 14 days. Salt treatment induced a plant growth reduction estimated as fresh-dry weight. Photosynthetic pigments (chlorophyll a, b) content of NaCl-treated tomato plants was significantly decreased as the salinity level increased. Proline accumulation levels in leaf and root tissues increased significantly with increasing NaCl concentration. Relative electrolyte leakage known as an indicator of membrane damage caused by salt stress was increased proportionally according to the NaCl concentrations. Roots of control and salt-stressed plants were also sampled for phenol protein extraction. Proteins were separated by two-dimensional gel electrophoresis (2-DGE). Several proteins showed up- and downregulation during salt stress. MALDI-TOF/MS analysis and database searching of some of the identified proteins indicated that the proteins are known to be in a wide range of physiological processes, that is, energy metabolism, ROS (reactive oxygen species) scavenging and detoxification, protein translation, processing and degradation, signal transduction, hormone and amino acid metabolism, and cell wall modifications. All proteins might work cooperatively to reestablish cellular homeostasis under salt stress, water deficiency, and ionic toxicity.