Determination of Free Proline in Plants.

Proline metabolism has been associated with the induction of reactive oxygen species (ROS), antioxidant enzymes, and the control of cellular redox status. Moreover, proline accumulation is a highly evolutionarily conserved response to diverse abiotic stresses in plants. Thus, proline quantification has been helpful in abiotic stress research as a stress marker.

Competitiveness and Phylogenetic Relationship of Rhizobial Strains with Different Symbiotic Efficiency in : Conversion of Parasitic into Non-Parasitic Rhizobia by Natural Symbiotic Gene Transfer.

In Uruguayan soils, populations of native and naturalized rhizobia nodulate white clover. These populations include efficient rhizobia but also parasitic strains, which compete for nodule occupancy and hinder optimal nitrogen fixation by the grassland. Nodulation competitiveness assays using -tagged strains proved a high nodule occupancy by the inoculant strain U204, but this was lower than the strains with intermediate efficiencies, U268 and U1116.

Draft genome sequence of sp. strain Oc8 isolated from nodule.

In this study, we report the draft genome sequence of sp. strain Oc8, a rhizobium isolated from efficient in , and . The whole genome of the strain Oc8 contains 46 scaffolds, 8,283,342 bp, and 63.

The Role of Nitric Oxide in Nitrogen Fixation by Legumes.

The legume-rhizobia symbiosis is an important process in agriculture because it allows the biological nitrogen fixation (BNF) which contributes to increasing the levels of nitrogen in the soil. Nitric oxide (⋅NO) is a small free radical molecule having diverse signaling roles in plants. Here we present and discuss evidence showing the role of ⋅NO during different stages of the legume-rhizobia interaction such as recognition, infection, nodule development, and nodule senescence.

Selection of Competitive and Efficient Rhizobia Strains for White Clover.

The practice of inoculating forage legumes with rhizobia strains is widespread. It is assumed that the inoculated strain determines the performance of the symbiosis and nitrogen fixation rates. However, native-naturalized strains can be competitive, and actual nodule occupancy is often scarcely investigated.

The Rhizobia- Symbioses: Deeply Specific and Widely Diverse.

The symbiosis between and rhizobia has been long considered very specific and only two bacterial species were recognized as the microsymbionts of : was considered the typical rhizobia for the complex, whereas sp. () was the symbiont for and related species. As discussed in this review, this situation has dramatically changed during the last 15 years, with the characterization of nodule bacteria from worldwide geographical locations and from previously unexplored spp.

Identification of Δ-pyrroline 5-carboxylate synthase (P5CS) genes involved in the synthesis of proline in Lotus japonicus.

Proline accumulation is a common response of plants to different biotic and abiotic stresses. In the model legume Lotus japonicus, osmotic stress-induced proline accumulation is one of the first responses of the plant, converting proline in a reliable stress marker. The main biosynthetic pathway of proline is from glutamate and the reaction catalyzed by the enzyme Δ-pyrroline 5-carboxylate synthase (P5CS) is the rate limiting step.

In vivo and in vitro approaches demonstrate proline is not directly involved in the protection against superoxide, nitric oxide, nitrogen dioxide and peroxynitrite.

Plants accumulate proline under diverse types of stresses, and it has been suggested that this α-amino acid has the capacity to protect against oxidative stress. However, it is still controversial whether its protection is due to the direct scavenging of reactive oxygen species (ROS). To solve this issue and considering that nitrosative stress is directly related with an oxidative stress condition, we evaluated whether proline can protect against nitrosative damage.

Photosynthetic responses mediate the adaptation of two Lotus japonicus ecotypes to low temperature.

Lotus species are important forage legumes due to their high nutritional value and adaptability to marginal conditions. However, the dry matter production and regrowth rate of cultivable Lotus spp. is drastically reduced during colder seasons.

Connecting proline and γ-aminobutyric acid in stressed plants through non-enzymatic reactions.

The accumulation of proline (Pro) in plants exposed to biotic/abiotic stress is a well-documented and conserved response in most vegetal species. Stress conditions induce the overproduction of reactive oxygen species which can lead to cellular damage. In vitro assays have shown that enzyme inactivation by hydroxyl radicals (·OH) can be avoided in presence of Pro, suggesting that this amino acid could act as an ·OH scavenger.

Molecular mechanisms for the reaction between (˙)OH radicals and proline: insights on the role as reactive oxygen species scavenger in plant stress.

The accumulation of proline (Pro) and overproduction of reactive oxygen species (ROS) by plants exposed to stress is well-documented. In vitro assays show that enzyme inactivation by hydroxyl radicals ((•)OH) can be avoided in the presence of Pro, suggesting this amino acid might act as a (•)OH scavenger. Although production of hydroxyproline (Hyp) has been hypothesized in connection with such antioxidant activity, no evidence on the detailed mechanism of scavenging has been reported.

Phyllobacterium loti sp. nov. isolated from nodules of Lotus corniculatus.

Strain S658(T) was isolated from a Lotus corniculatus nodule in a soil sample obtained in Uruguay. Phylogenetic analysis of the 16S rRNA gene and atpD gene showed that this strain clustered within the genus Phyllobacterium. The closest related species was, in both cases, Phyllobacterium trifolii PETP02(T) with 99.

Antioxidant and photosystem II responses contribute to explain the drought-heat contrasting tolerance of two forage legumes.

Identification of metabolic targets of environmental stress factors is critical to improve the stress tolerance of plants. Studying the biochemical and physiological responses of plants with different capacities to deal with stress is a valid approach to reach this objective. Lotus corniculatus (lotus) and Trifolium pratense (clover) are legumes with contrasting summer stress tolerances.

Proline does not quench singlet oxygen: evidence to reconsider its protective role in plants.

Plants are commonly subjected to several environmental stresses that lead to an overproduction of reactive oxygen species (ROS). As plants accumulate proline in response to stress conditions, some authors have proposed that proline could act as a non-enzymatic antioxidant against ROS. One type of ROS aimed to be quenched by proline is singlet oxygen ((1)O(2))-molecular oxygen in its lowest energy electronically excited state-constitutively generated in oxygenic, photosynthetic organisms.

Water stress induces a differential and spatially distributed nitro-oxidative stress response in roots and leaves of Lotus japonicus.

Water stress is one of the most severe problems for plant growth and productivity. Using the legume Lotus japonicus exposed to water stress, a comparative analysis of key components in metabolism of reactive nitrogen and oxygen species (RNS and ROS, respectively) were made. After water stress treatment plants accumulated proline 23 and 10-fold in roots and leaves respectively, compared with well-watered plants.

Response to photoxidative stress induced by cold in japonica rice is genotype dependent.

Two japonica rice genotypes, INIA Tacuarí and L2825CA, were analyzed for tolerance to low temperature during early vegetative growth. Effect on photosynthesis, energy dissipation, pigment content, xanthophyll-cycle pool conversion, hydrogen peroxide accumulation, oxidative damage and antioxidant enzyme activities were determined to better understand potential mechanisms for cold tolerance. Photoinhibition was measured using chlorophyll fluorescence and oxidative damage by lipid peroxidation and electrolyte leakage.

Deficiency in plastidic glutamine synthetase alters proline metabolism and transcriptomic response in Lotus japonicus under drought stress.

The role of plastidic glutamine synthetase (GS2) in proline biosynthesis and drought stress responses in Lotus japonicus was investigated using the GS2 mutant, Ljgln2-2. Wild-type (WT) and mutant plants were submitted to different lengths of time of water and nutrient solution deprivation. Several biochemical markers were measured and the transcriptional response to drought was determined by both quantitative real-time polymerase chain reaction and transcriptomics.

Heat stress results in loss of chloroplast Cu/Zn superoxide dismutase and increased damage to Photosystem II in combined drought-heat stressed Lotus japonicus.

Drought and heat stress have been studied extensively in plants, but most reports involve analysis of response to only one of these stresses. Studies in which both stresses were studied in combination have less commonly been reported. We report the combined effect of drought and heat stress on Photosystem II (PSII) of Lotus japonicus cv.

Denitrification ability of rhizobial strains isolated from Lotus sp.

Ten rhizobial strains isolated from Lotus sp. have been characterized by their ability to denitrify. Out of the 10 strains, the five slow-growing isolates grew well under oxygen-limiting conditions with nitrate as a sole nitrogen source, and accumulated nitrous oxide in the growth medium when acetylene was used to inhibit nitrous oxide reductase activity.

Nitrate assimilation in Lotus japonicus.

This paper summarizes some recent advances in the understanding of nitrate assimilation in the model legume Lotus japonicus. First, different types of experimental evidence are presented that emphasize the importance of the root in the nitrate-reducing assimilatory processes in this plant. Secondly, the main results from an ethyl methanesulphonate mutagenesis programme are presented.