Characterization of resistance to crenate broomrape (Orobanche crenata) in a new small-seeded line of Tunisian faba beans

Orobanche crenata, crenate broomrape, causes major drawbacks in faba bean production in Mediterranean countries. The development of resistant varieties remains the most efficient way to solve this problem. This study was designed to assess the resistance of the breeding line XBJ90.03-16-1-1-1-1 to crenate broomrape, using cv. Bachaar as a susceptible control. Incidence and severity parameters were evaluated in infested fields to values reaching 95% and 4 (on a 1 to 9 scale), respectively, in 'Bachaar', and reaching only 5% and 1.5, in 'XBJ90.03-16-1-1-1-1'. This selected line displayed, at the most, an average of one emerged crenate broomrape individual per plant at crop maturity, whereas 'Bachaar' plants displayed five emerged broomrape individuals under the same conditions. In addition, the seed yield of 'XBJ90.03-16-1-1-1-1' plants was two-fold higher than that of 'Bachaar'. In pot experiments, number and total dry weight of broomrape individuals per plant were significantly higher for 'Bachaar' than for 'XBJ90.03-16-1-1-1-1'. In root chambers, percent germination of broomrape seeds was five-fold lower in the vicinity of 'XBJ90.03-16-1-1-1-1' roots (3%) than close to 'Bachaar' roots (15%). The direct consequence was a limited number of broomrape tubercles per 'XBJ90.03-16-1-1-1-1' plant. Furthermore, tubercle formation on 'XBJ90.03-16-1-1-1-1' roots was delayed by a week compared with the infection process on 'Bachaar' roots. Finally, some features of 'XBJ90.03-16-1-1-1-1' roots were characterized, such as the low amount of exudation of germination stimulant, which, combined with a deep root system, triggers resistance to the parasite.L'orobanche crénelée, Orobanche crenata, occasionne des problèmes majeurs à la production de féverole à petits grains dans la région méditerranéenne. Le développement de variétés résistantes demeure le moyen le plus efficace de résoudre ce problème. Les travaux réalisés visaient à estimer le degré de résistance de la lignée sélectionnée XBJ90.03-16-1-1-1-1 à l'orobanche crénelée, en prenant le cultivar Bachaar comme témoin sensible. Dans des champs infestés, les paramètres d'incidence et de sévérité ont été estimés à 95 % et à 4 (sur une échelle de 1 à 9), respectivement, pour 'Bachaar' et seulement à 5 % et 1,5 pour 'XBJ90.03-16-1-1-1-1'. À maturité des cultures, sur la ligne sélectionnée, on observait tout au plus l'émergence d'un individu d'orobanche par plant en moyenne, comparativement à cinq émergences par plant chez le cv. Bachaar. De plus, le rendement grainier de 'XBJ90.03-16-1-1-1-1' a été deux fois plus élevé que celui de 'Bachaar'. En pot, le cv. Bachaar a montré un nombre et un poids sec total d'orobanche par plant plus élevés que ceux de la lignée XBJ90.03-16-1-1-1-1. En chambre racinaire, le taux de germination des graines d'orobanche a été cinq fois inférieur à proximité des racines des plants de la lignée XBJ90.03-16-1-1-1-1 (3 %) qu'à proximité des racines du cv. Bachaar (15 %), ce qui a résulté en un nombre limité de tubercules d'orobanche par plant de 'XBJ90.03-16-1-1-1-1'. Le développement des tubercules a par ailleurs été retardé d'une semaine chez les racines de cette lignée en comparaison au processus infectieux observable sur les racines de 'Bachaar'. Enfin, nos travaux ont souligné quelques caractéristiques des racines de la lignée XBJ90.03-16-1-1-1-1, incluant leur exsudation peu stimulante qui, en combinaison avec un système racinaire profond, favorise la résistance au parasite

Influence of salicylic acid pre-treatment on cadmium tolerance and its relationship with non-protein thiol production in flax root

Dose-dependent changes in cadmium (Cd) tolerance, non-protein thiol (NP-SH) production and their relationship were investigated in sixteen-day-old flax (Linum usitatissimum L.) seedlings derived from seeds pre-soaked with various salicylic acid (SA) doses and grown hydroponically under increased Cd concentrations (0, 50 and 100 μM CdCl2). The results show that single Cd subjection decreased root elongation as expressed by tolerance index (TI). Moreover, an overproduction of NP-SH was detected in both roots and shoots. These Cd toxicity effects were directly related to the high levels of Cd amounts in flax tissues as expressed by root and shoot Cd bioaccumulation factors (BAF). In addition, Cd-tolerance of roots TI was negatively correlated with changes in root BAF but positively correlated with shoot BAF. However, positive correlation was illustrated between root TI and NP-SH contents. SA considerably reversed the Cd-induced decrease in root growth parameters and TI. Moreover, in Cd-treated plants, SA pre-soaking prevented Cd accumulation in the shoot as consequence of significant decreases in BAF of roots, Cd transport estimated by the translocation factor (TF) and shoot BAF, respectively. Interestingly, SA pre-treatment reduced BAF of roots and shoots, enhanced NP-SH production in roots and decreased it in leaves. These results suggest that SA might play a preventive role in Cd uptake, sequestration and translocation processes based primarily in roots where SA-enhanced NP-SH contribute to the improvement of flax tolerance to Cd stress.Key words: Cadmium, salicylic acid, bioaccumulation, growth, non-protein thiols, Linum usitatissimum

Cadmium stress tolerance in plants: a key role of endogenous and exogenous salicylic acid

Cadmium (Cd) has become one of the major metal stresses which pose a serious threat to plants and animals. In this context, endogenous and exogenous salicylic acid (SA) could play an important role in mitigating the uptake of the Cd ions and providing immunity to plants against the heavy metal stress. SA enhances the resistance capacity of contaminated plants, which, however, depends on the metal concentration and the duration of the treatment. Moreover, SA is considered as a promising signal molecule for improving the efficiency of phytoremediation, and, consequently, growing of safe crops in metal polluted areas. The recent developments in the probable mechanisms by which SA could enhance the tolerance of plants to heavy metals and how it could have an effect on phytoremediation of Cd from contaminated soils are discussed

Cellular and signaling mechanisms supporting cadmium tolerance in salicylic acid treated seedlings

This review spotlights on recent indications that recognizes potential cellular mechanisms that may be involved in the tolerance of salicylic acid (SA)-treated seedlings to the presence of cadmium (Cd) in their environment. It appears probable that SA stimulates signaling systems implicated in plant defense-related actions against Cd-induced oxidative stress. These include mechanisms that reduce uptake of metals into the cytosol by extracellular chelation through extruded ligands and binding onto cell-wall constituents. Cellular chelation of metals in the cytosol by a range of ligands (peptides, phytochelatins (PCs)), or increased efflux from the cytosol out of the cell or into sequestering compartments are also key mechanisms improving tolerance. Free-radical scavenging capacities through the activity of antioxidant enzymes or production of peptides and PCs add another line of defense against the toxic effect of Cd. The SA signaling events can be attributed to the extracellular SA perception model in which reactions between SA and apoplastic proteins result in acute oxidative burst under Cd stress

Physiological and structural modifications in snail medic (Medicago scutellata L.) plants exposed to salinity

Seeds of snail medic (Medicago scutellata L.) were assessed for their response to salt at the germination and seedling stages. NaCl at concentrations 86 and 170 mM decreased the final germination percentage. Embryonic axis length, water content and dry weight of embryonic axis and cotyledons were also reduced by salt treatment. Furthermore, 28-d-old plants were grown hydroponically with different NaCl concentrations (0, 86 and 170 mM). After 7 days of treatment, growth, water content and development of the different organs of M. scutellata plant were affected especially at the highest NaCl concentration (170 mM). However, NaCl did not affect root length and the number of stem shoots but reduced stem length and total leaf area. Salt treatment increased markedly the concentration of Na+ in leaf and root tissues while reduced that of K+ only in root and stem tissues. Lipid peroxidation revealed the damage of the membranes of roots and leaves. Moreover, showed a more intense suberization and lignification at the cambial zone of roots of M. scutellata, were observed under the effect of NaCl

Estimation de la sensibilité et de la tolérance de différents génotypes de féverole (Vicia faba L.) à la plante parasite Orobanche foetida Poiret (Impact du génotype hôte sur les particularités physiologiques et métaboliques du parasite)

Les objectifs sont d évaluer le degré de sensibilité et de tolérance de différents génotypes de féverole à O. foetida, de caractériser les mécanismes impliqués dans cette résistance et d estimer l impact du génotype hôte sur la force de puits du parasite qui conditionne son développement après fixation. Ce pathosystème a été cultivé au champ, en pot et in vitro. Le génotype Bachaar est pris comme témoin de forte sensibilité. Des cinq génotypes testés, le génotype XBJ90.03-16-1-1-1 se révèle le moins sensible et le plus productif sous infestation, au champ comme en pot. Ce génotype se caractérise par une faible activité stimulante de ses exsudats racinaires vis-à-vis de la germination des graines du parasite et par un nombre réduit de tubercules portés par ses racines. La cinétique d infection de ces génotypes a été décrite en condition d infestation artificielle in vitro. Les génotypes classés comme moyennement résistants au champ présentent in vitro des orobanches avec un développement ralenti après fixation, notamment sur le génotype XBJ90.03-16-1-1-1. La croissance du parasite, sous le contrôle des activités invertases solubles, est limitée spécifiquement sur les racines de ce génotype par le faible potentiel osmotique de ses racines et par la carence en azote organique de sa sève phloémienne. Le génotype de féverole n influe pas sur le fonctionnement général d O. foetida. Le potassium constitue le principal agent osmotique du parasite. Parmi les solutés organiques, les hexoses occupent une place majeure dans les tiges. Par contre, les tubercules privilégient une accumulation d amidon et d acides aminés principalement sous la forme asparagine/aspartate. Asparagine/aspartate, glutamine/glutamate, alanine, sérine et acide gamma amino butyrique sont les principales formes azotées prélevées par le parasite chez la féverole. Un schéma d utilisation de ces composés par l orobanche basé sur le couple Asparagine synthétase/ aspartate oxaloglutarate aminotransférase est proposé.This work aim to evaluate some sensitivity and tolerance degrees of various faba bean genotypes to O. foetida, to characterize mechanisms involved in resistance and finally to estimate the impact of the host genotype on the parasite sink strength which controls parasite development following attachment to the host roots. Cultures were performed under field, pot and in vitro conditions. The genotype Bachaar was used as the control of high sensitivity. Among the five tested genotypes, XBJ90.03-16-1-1-1 was the less sensitive and the most productive under infestation in both field and pot assays. The root exudates of this genotype displayed low stimulatory activity for orobanche seed germination. Consequently, few tubercles developed on roots. The infection process of all these genotypes was followed in vitro. In comparison to Bachaar, the genotypes known as moderately resistant genotypes under field conditions limited growth of orobanche tubercles under in vitro conditions, especially the genotype XBJ90.03-16-1-1-1. Growth of the parasite should be mediated by soluble invertase activities and restricted following attachment to XBJ90.03-16-1-1-1 roots by the low osmotic potential of the infected roots in addition to the organic nitrogen deficiency of the host phloem sap. On the other hand, the faba bean genotype did not influence the osmoregulation process of O. foetida. Potassium was by far the major osmotically active compound in orobanche. Among the organic solutes, hexoses were accumulated highly in the growing stems. In contrast, tubercles displayed higher contents in starch and free amino acids, mainly in asparagine and aspartate. In parallel, asparagine/aspartate, glutamine/glutamate, alanine, serine and gamma amino butyric acid were identified as the main nitrogen compounds in the host phloem exudates. The key role of the enzymes asparagine synthetase and aspartate oxaloglutarate aminotransferase in the utilization of these host-derived amino acids is proposed in O. foetida parasitizing faba bean.NANTES-BU Sciences (441092104) / SudocSudocFranceF

Exogenous salicylic acid protects phospholipids against cadmium stress in flax (Linum usitatissimum L.)

Salicylic acid (SA) promotes plant defense responses against toxic metal stresses. The present study addressed the hypothesis that 8-h SA pretreatment, would alter membrane lipids in a way that would protect against Cd toxicity. Flax seeds were pre-soaked for 8 h in SA (0, 250 and 1000 µM) and then subjected, at seedling stage, to cadmium (Cd) stress. At 100 µM CdCl2, significant decreases in the percentages of phosphatidylcholine (PC), phosphatidylglycerol (PG), phosphatidylethanolamine (PE) and monogalactosyldiacylglycerol (MGDG) and changes in their relative fatty acid composition were observed in Cd-treated roots in comparison with controls. However, in roots of 8-h SA pretreated plantlets, results showed that the amounts of PC and PE were significantly higher as compared to non-pretreated plantlets. Additionally, in both lipid classes, the proportion of linolenic acid (18:3) increased upon the pretreatment with SA. This resulted in a significant increase in the fatty acid unsaturation ratio of the root PC and PE classes. As the exogenous application of SA was found to be protective of flax lipid metabolism, the possible mechanisms of protection against Cd stress in flax roots were discussed.This research was supported by a Grant no. 2397 from the Ministry of Higher Education, Scientific Research and Technology in Tunisia.Peer reviewe