Arbuscular mycorrhizae reduce the response of important plant functional traits to drought and salinity. A meta-analysis study.

We aimed at exploring the plant functional traits whose responses to drought or salinity are altered by the presence of arbuscular mycorrhiza (AM). We performed a meta-analysis across 114 articles spanning 110 plant species or cultivars. We quantified the size effect of AM symbiosis on the stress response of several functional traits, using linear mixed model analysis (LMM). Correlation analysis between functional traits and total biomass responses to stresses were also performed through LMM. The literature search and further selection yielded seven functional traits, extracted from 114 laboratory studies, including 888 observations and 110 plant species/cultivars. Evidence for significant effects of predictor variables (type of stress, AM symbiosis and/or their interaction) on functional trait response were found for leaf area ratio (LAR), root mass fraction (RMF) and root-shoot (R:S) ratio. Our results provided evidence to accept the hypothesis that AM fungal inoculation may reduce the stress response of these plant functional traits by decreasing its magnitude. We also found a weak correlation between stress responses of these traits and total biomass variation. Although our literature search and data collection were intensive and our results robust, the scope of our conclusions is limited by the agronomical bias of plant species targeted by the meta-analysis. Further knowledge on non-cultivable plant species and better understanding of the mechanisms ruling resources allocation in plants would allow more generalised conclusions.

Polyamines and Legumes: Joint Stories of Stress, Nitrogen Fixation and Environment.

Polyamines (PAs) are natural aliphatic amines involved in many physiological processes in almost all living organisms, including responses to abiotic stresses and microbial interactions. On other hand, the family Leguminosae constitutes an economically and ecologically key botanical group for humans, being also regarded as the most important protein source for livestock. This review presents the profuse evidence that relates changes in PAs levels during responses to biotic and abiotic stresses in model and cultivable species within Leguminosae and examines the unreviewed information regarding their potential roles in the functioning of symbiotic interactions with nitrogen-fixing bacteria and arbuscular mycorrhizae in this family. As linking plant physiological behavior with "big data" available in "omics" is an essential step to improve our understanding of legumes responses to global change, we also examined integrative MultiOmics approaches available to decrypt the interface legumes-PAs-abiotic and biotic stress interactions. These approaches are expected to accelerate the identification of stress tolerant phenotypes and the design of new biotechnological strategies to increase their yield and adaptation to marginal environments, making better use of available plant genetic resources.

Defining novel plant polyamine oxidase subfamilies through molecular modeling and sequence analysis.

BACKGROUND: The polyamine oxidases (PAOs) catabolize the oxidative deamination of the polyamines (PAs) spermine (Spm) and spermidine (Spd). Most of the phylogenetic studies performed to analyze the plant PAO family took into account only a limited number and/or taxonomic representation of plant PAOs sequences. RESULTS: Here, we constructed a plant PAO protein sequence database and identified four subfamilies. Subfamily PAO back conversion 1 (PAObc1) was present on every lineage included in these analyses, suggesting that BC-type PAOs might play an important role in plants, despite its precise function is unknown. Subfamily PAObc2 was exclusively present in vascular plants, suggesting that t-Spm oxidase activity might play an important role in the development of the vascular system. The only terminal catabolism (TC) PAO subfamily (subfamily PAOtc) was lost in Superasterids but it was present in all other land plants. This indicated that the TC-type reactions are fundamental for land plants and that their function could being taken over by other enzymes in Superasterids. Subfamily PAObc3 was the result of a gene duplication event preceding Angiosperm diversification, followed by a gene extinction in Monocots. Differential conserved protein motifs were found for each subfamily of plant PAOs. The automatic assignment using these motifs was found to be comparable to the assignment by rough clustering performed on this work. CONCLUSIONS: The results presented in this work revealed that plant PAO family is bigger than previously conceived. Also, they delineate important background information for future specific structure-function and evolutionary investigations and lay a foundation for the deeper characterization of each plant PAO subfamily.

Polyamine catabolism is involved in response to salt stress in soybean hypocotyls.

The possible relationship between polyamine catabolism mediated by copper-containing amine oxidase and the elongation of soybean hypocotyls from plants exposed to NaCl has been studied. Salt treatment reduced values of all hypocotyl growth parameters. In vitro, copper-containing amine oxidase activity was up to 77-fold higher than that of polyamine oxidase. This enzyme preferred cadaverine over putrescine and it was active even under the saline condition. On the other hand, saline stress increased spermine and cadaverine levels, and the in vivo copper-containing amine oxidase activity in the elongation zone of hypocotyls. The last effect was negatively modulated by the addition of the copper-containing amine oxidase inhibitor N,N'-diaminoguanidine. In turn, plants treated with the inhibitor showed a significant reduction of reactive oxygen species in the elongation zone, even in the saline situation. In addition, plants grown in cadaverine-amended culture medium showed increased hypocotyl length either in saline or control conditions and this effect was also abolished by N,N'-diaminoguanidine. Taken together, our results suggest that the activity of the copper-containing amine oxidase may be partially contributing to hypocotyl growth under saline stress, through the production of hydrogen peroxide by polyamine catabolism and reinforce the importance of polyamine catabolism and hydrogen peroxide production in the induction of salt tolerance in plants.