Polyamines have been globally associated to plant responses to abiotic stress. Particularly, putrescine has been related to a better response to cold and dehydration stresses. It is known that this polyamine is involved in cold tolerance, since Arabidopsis thaliana plants mutated in the key enzyme responsible for putrescine synthesis (arginine decarboxilase, ADC; EC 4.1.1.19) are more sensitive than the wild type to this stress. Although it is speculated that the over-expression of ADC genes may confer tolerance, this is hampered by pleiotropic effects arising from the constitutive expression of enzymes from the polyamine metabolism. Here, we present our work using A. thaliana transgenic plants harboring the ADC gene from oat under the control of a stress-inducible promoter (pRD29A) instead of a constitutive promoter. The transgenic lines presented in this work were more resistant to both cold and dehydration stresses, associated with a concomitant increment in endogenous putrescine levels under stress. Furthermore, the increment in putrescine upon cold treatment correlated with the induction of known stress-responsive genes, and suggested that putrescine may be directly or indirectly involved in ABA metabolism and gene expression.

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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.

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Saline, alkaline and mixed saline-alkaline conditions frequently co-occur in soil. In this work, we compared these plant stress sources on the legume Lotus tenuis, regarding their effects on shoot growth and leaf and stem anatomy. In addition, we aimed to gain insight on the plant physiological status of stressed plants. We performed pot experiments with four treatments: control without salt (pH = 5.8; EC = 1.2 dSÁm À1 ) and three stress conditions, saline (100 mM NaCl, pH = 5.8; EC = 11.0 dSÁm À1 ), alkaline (10 mM NaHCO 3 , pH = 8.0, EC = 1.9 dSÁm À1 ) and mixed salt-alkaline (10 mM NaHCO 3 + 100 mM NaCl, pH = 8.0, EC = 11.0 dSÁm À1

A protocol for the production of transgenic plants was developed for Lotus tenuis via Agrobacteriummediated transformation of leaf segments. The explants were co-cultivated (for 3 days) with an A. tumefaciens strain harbouring either the binary vector pBi RD29A:oat arginine decarboxylase (ADC) or pBi RD29A:glucuronidase (GUS), which carries the neomycin phosphotransferase II (nptII) gene in the T-DNA region. Following co-cultivation, the explants were cultured in Murashige and Skoog medium supplemented with naphthalenacetic acid (NAA) and benzyladenine (BA) and containing kanamycin (30 lg ml -1 ) and cefotaxime (400 lg ml -1 ) for 45 days. The explants were subcultured several times (at 2-week intervals) to maintain the selection pressure during the entire period. About 40% of the explants inoculated with the pBiRD29:ADC strain produced eight to ten adventitious shoots per responsive explant through a direct system of regeneration, whereas 69% of the explants inoculated with the pBi RD29A:GUS strain produced 13-15 adventitious shoots per responsive explant. The selected transgenic lines were identified by PCR and Southern blot analysis. Three ADC transgenic lines were obtained from 30 infected explants, whereas 29 GUS transgenic lines were obtained from 160 explants, corresponding to a transformation efficiency of 10 and 18.1%, respectively.More than 90% of the in vitro plantlets were successfully transferred to the soil. The increase in the activity of arginine decarboxylase from stressed ADC-Lt19 lines was accompanied by a significant rise in the putrescine level. The GUS transgenic line driven by the RD29A promoter showed strong signals of osmotic stress in the leaves and stem tissues. All of the transgenic plants obtained exhibited the same phenotype as the untransformed controls under non-stress conditions, and the stability of the gene introduced into the cloned materials was established.

Encapsulation-dehydration, encapsulation-vitrification, and vitrification were tested for cryopreservation of Lotus tenuis (Fagaceae) adventitious buds clusters (ABCs) obtained by a direct regeneration system from leaves cultures. Among them, the PVS3-based vitrification procedure was found to be useful for survival and regrowth of the preserved explants. For vitrification, the ABCs were dehydrated in a solution containing 2 M glycerol + 0.4 M sucrose for 25 min at room temperature, submerged in PVS3 solution for 1 h at 0 °C, then immersed in liquid nitrogen for 48 h and rapidly rewarmed. Afterword, the explants were unloaded in MS liquid medium with 1.2 M sucrose for 30 min. The washed tissues were dried superficially on filter paper and cultured in semisolid hormone-free MS medium containing 0.1 M sucrose. All cultures were maintained at 25 °C in the dark for 10 days and transferred to the light conditions. With this procedure, 79 ± 5.3% survival and more than 80% of the plantlets displaying a phenotype similar to the non-treated control after acclimatization. The data settled from ISSR showed no genetic dissimilarities between in vitro regenerants derived from cryopreserved tissues and the non-treated plants. Thus, our results indicate that the use of vitrification-based PVS3 solution offers a simple, accurate, and appropriate procedure for the cryopreservation of L. tenuis adventitious buds.

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