Oscar Vicente

Breeding and Domesticating Crops Adapted to Drought and Salinity: A New Paradigm for Increasing Food Production

World population is expected to reach 9.2 × 109 people by 2050. Feeding them will require a boost in crop productivity using innovative approaches. Current agricultural production is very dependent on large amounts of inputs and water availability is a major limiting factor. In addition, the loss of genetic diversity and the threat of climate change make a change of paradigm in plant breeding and agricultural practices necessary. Average yields in all major crops are only a small fraction of record yields, and drought and soil salinity are the main factors responsible for yield reduction. Therefore there is the need to enhance crop productivity by improving crop adaptation. Here we review the present situation and propose the development of crops tolerant to drought and salt stress for addressing the challenge of dramatically increasing food production in the near future. The success in the development of crops adapted to drought and salt depends on the efficient and combined use of genetic engineering and traditional breeding tools. Moreover, we propose the domestication of new halophilic crops to create a ‘saline agriculture’ which will not compete in terms of resources with conventional agriculture.

Responses of five Mediterranean halophytes to seasonal changes in environmental conditions

We have studied the responses to changing environmental conditions of five halophytes in a Mediterranean salt marsh, during a 2-year period. Salt tolerance in succulent dicotyledonous halophytes is mostly dependent on compartmentalisation of toxic ions in vacuoles and biosynthesis of osmolytes for osmotic adjustment – mechanisms that appear to be constitutive in the most tolerant taxa – while monocots avoid excessive ion transport to the plant aerial parts. Contrary to what has been described for salt treatments under artificial conditions, the selected halophytes are not affected by oxidative stress in their natural habitat, and do not need to activate antioxidant defence mechanisms.

Environmentally induced changes in antioxidant phenolic compounds levels in wild plants

Different adverse environmental conditions cause oxidative stress in plants by generation of reactive oxygen species (ROS). Accordingly, a general response to abiotic stress is the activation of enzymatic and non-enzymatic antioxidant systems. Many phenolic compounds, especially flavonoids, are known antioxidants and efficient ROS scavengers in vitro, but their exact role in plant stress responses in nature is still under debate. The aim of our work is to investigate this role by correlating the degree of environmental stress with phenolic and flavonoid levels in stress-tolerant plants. Total phenolic and antioxidant flavonoid contents were determined in 19 wild species. Meteorological data and plant and soil samples were collected in three successive seasons from four Mediterranean ecosystems: salt marsh, dune, semiarid and gypsum habitats. Changes in phenolic and flavonoid levels were correlated with the environmental conditions of the plants and were found to depend on both the taxonomy and ecology of the investigated species. Despite species-specific differences, principal component analyses of the results established a positive correlation between plant phenolics and several environmental parameters, such as altitude, and those related to water stress: temperature, evapotranspiration, and soil water deficit. The correlation with salt stress was, however, very weak. The joint analysis of all the species showed the lowest phenolic and flavonoid levels in the halophytes from the salt marsh. This finding supports previous data indicating that the halophytes analysed here do not undergo oxidative stress in their natural habitat and therefore do not need to activate antioxidant systems as a defence against salinity.

Lithium treatment induces a hypersensitive-like response in tobacco

Treatment of tobacco (Nicotiana tabacum L.) plants with lithium induces the formation of necrotic lesions and leaf curling as in the case of incompatible pathogen interactions. Further similarities at the molecular level include accumulation of ethylene and of salicylic and gentisic acids, and induced expression of pathogenesis-related PR-P, PR5 and PR1 genes. With the exception of PR1 induction, lithium produced the same effects in transgenic tobacco plants that do not accumulate salicylate because of overexpression of the bacterial hydroxylase gene nahG. On the other hand, inhibition of ethylene biosynthesis with aminoethoxyvinylglycine prevented lithium-induced cell death and PR5 expression. These results suggest that lithium triggers a hypersensitive-like response where ethylene signalling is essential.

Responses to salt stress in Juncus acutus and J. maritimus during seed germination and vegetative plant growth

Abstract Responses to increasing salinity, during seed germination and vegetative plant growth, were studied in two related species of Juncus, J. maritimus and J. acutus. In both species, germination was optimal in the absence of salt, reduced by about 50% in the presence of 200 mM NaCl, and completely inhibited by NaCl concentrations above 300 mM. Previous exposure of the seeds to salt, up to 500 mM NaCl, did not affect the germination capacity in J. acutus, and clearly enhanced it in J. maritimus. A concentration-dependent inhibition of plant growth was observed in the presence of NaCl for both species, together with the parallel accumulation of sodium ions in the leaves, as determined by cation exchange HPLC. Regarding the levels of divalent cations, in J. acutus Ca2+ and Mg2+ increased up to about two-fold in plants treated with 500 mM NaCl, as compared to control plants, whereas in J. maritimus they were three- to four-fold higher than in J. acutus in the absence of salt, and did not change significantly with increasing NaCl concentrations. These results suggest that Ca2+ and Mg2+ participate in defence mechanisms against salt stress, which would be constitutive in J. maritimus and salt-inducible in J.acutus.

Inhibition of eukaryotic cell-free protein synthesis by thionins from wheat endosperm

Thionins are polypeptide toxins of about 5000 molecular weight, present in the endosperms of many Gramineae, which modify membrane permeability and inhibit macromolecular synthesis in cultured mammalian cells. Evidence is presented that they inhibit in vitro protein synthesis at micromolar concentrations in cell-free systems derived from wheat germ or from rabbit reticulocytes. Inhibition seems to occur by direct binding of mRNA by the toxin, as judged by the ability of thionins to mediate retention of RNA in nitrocellulose filters and by the dependence of inhibitory concentrations on the amount of exogenous RNA added to the wheat-germ translation system. Commercial preparations of wheat-germ have been found to include some endosperm contamination (up to 15%), which may result in at least partially inhibitory concentrations of the toxin in the cell-free extracts.

Effects of salt stress on the reproductive biology of the halophyte Plantago crassifolia

Floral phenology, pollen quality and seed set of Plantago crassifolia plants, grown in the presence of increasing NaCl concentrations, were studied to test how this Mediterranean halophyte responded to salt stress during the reproductive phase of its life cycle. “Reproductive success” was maximal in plants grown in non-saline conditions, or in the presence of 100 mM NaCl, but it was negatively affected by higher salinities, due to a progressive reduction of pollen fertility, seed set, and seed viability.

Intragenomic diversity and phylogenetic systematics of wild rosemaries (Rosmarinus officinalis L. s.l., Lamiaceae) assessed by nuclear ribosomal DNA sequences (ITS)

Nuclear ribosomal sequences (ITS) were used to study species boundaries and to infer phylogenetic patterns in wild rosemaries (Rosmarinus officinalis, R. eriocalyx, R. tomentosus). Intragenomic polymorphisms (overlapping peaks and in some cases unreadable sequences) were found throughout the sequencing electrophoretograms of most Rosmarinus accessions. Sequencing the cloned ITS products from representative individuals resulted in 25 ribotypes differing at 59 variable sites. Average sequence divergence among clones was 1.75%, and the most divergent sequences differed by 3.48%. No single ribotype was shared between any two-paired species. The highest values of intragenomic divergence were similar in R. officinalis (1.63%) and R. eriocalyx (1.14%–2.12%), and contrast with those shown by R. tomentosus (0.97%). Sequence data suggest that most divergent rDNA sequences within individuals belong to paralogous loci that apparently are not pseudogenes. A detailed inspection of direct and cloned sequences does not show evidence that the intragenomic polymorphism found is due to interspecific hybridization. Phylogenetic analyses of cloned sequences suggested that both R. officinalis and R. tomentosus were monophyletic, whereas R. tomentosus clones were nested within a paraphyletic R. eriocalyx.

In Vitro Pollen Cultures: Progress and Perspectives

Today a number of cell culture and molecular techniques are used or are under development to manipulate sexual reproduction. Protoplast fusion is used not only to create somatic hybrids but also to produce cybrids that regenerate into cytoplasmic male sterile plants. Unreduced gametophytes are selected for polyploidization or distant hybridization. In vitro pollination and in vitro fertilization after isolation of egg and sperm cells are used to overcome pre- and postfertilization crossing barriers (Shivanna and Johri, 1985).

Studies on the activation of the heme-stabilized translational inhibitor of reticulocyte lysates by oxidized glutathione and NADPH depletion.

The translational inhibition produced by addition of oxidized glutathione (GSSG) to hemin-containing reticulocyte lysates and the accompanying phosphorylation of the alpha subunit of the polypeptide chain initiation factor eIF-2 can be prevented or reversed by NADPH generators, including glucose 6-phosphate, deoxyglucose 6-phosphate, fructose 6-phosphate, NADPH itself, and also by dithiols, e.g., dithiothreitol, but not by reduced glutathione (GSH) or other monothiols, e.g., 2-mercaptoethanol. The same is true of the inhibition caused by addition of glutamate dehydrogenase, alpha-ketoglutarate, and NH4+, which may be entirely due to NADPH depletion via the reaction.