Ezzeddine Zid

Enhanced salt tolerance of tomatoes by exogenous salicylic acid applied through rooting medium.

In Tunisia, like in the other countries of the Mediterranean, tomato is ranked among the important vegetables in the economic sphere. Tunisia ranks as the first consumer of this vegetable in the world. However, tomatoes are exposed to multiple environmental stresses. In particular, salinity is the most stressful limiting factor to productivity. Salt tolerance of the tomato is susceptible to be ameliorated by genetic and physiologic ways. Salicylic acid (SA), a plant phenolic, is now considered as a hormone-like endogenous regulator, and its role in the defense mechanisms against biotic and abiotic stressors has been well documented. So, the aim of this study was to investigate the impact of exogenous application of SA (0.01 mM) on growth, nutritional behavior, and some metabolic parameters (total chlorophyll, soluble sugars, proline, and proteins) of tomato plants cv. Moneymaker exposed to NaCl (100 mM). Our results showed that the application of 0.01 mM SA to tomato plants via root drenching attenuate the depressive effect of salinity on plants. This amelioration results in stimulation of growth and development of plant. Under stress conditions, SA-treated plants exhibited more accumulation of photosynthetic pigments and K(+) contents. Thus, SA induces an increase in soluble sugars in roots and leaves; also, we noted the increase of proteins only in roots. Overall, the adverse effects of salt stress tomato plants were alleviated by the exogenous application of SA at vegetative stage, which upregulated nutrition and the accumulation of some organic solutes and osmoprotectors such sugars, proline, and proteins. So salicylic acid can be greatly used to enhance salt tolerance of tomato plants.

Tolérance à la salinité d'une poaceae à cycle court : la sétaire (Setaria verticillata L.)

The responses of growth, development, and nutrition to salt stress are examined in short-cycle Setaria verticillata. For these, two experiments are led. The first intended to study the effects of various concentrations of NaCl on the parameters of growth and nutrition during the vegetative phase. Fifteen-day-old platelets were grown on commercial peat irrigated with pure NaCl solutions (0 to 300 mM). After three weeks of culture, the plants were collected and divided into roots and shoots. The fresh and dry matter masses of the various bodies are given. The second experiment was intended to study the effect of different concentrations of NaCl on crop plants until maturity. The culture was led under the same conditions as the preceding one, but for three months until the end of the cycle (production and maturation of the seeds). At harvest, the plants were separated in roots, shoots, and grains. During all the development cycle, Setaria vertillata was very sensitive to salinity. The concentration of NaCl that caused an important reduction of dry weight production was about 75 mM. Dry matter deposition was more diminished in roots than shoots. The reduction of the production of growth observed seems associated with a higher accumulation of Na(+) in shoots and with a deficit alimentation of organs in K(+). During the reproductive phase, salt affects the components of the output and induces variability on the level of the production of biomass as significant as that noted during the phase of vegetative growth. Lastly, the capacity of germination of seeds was strongly dependent on the salt concentration of the culture medium of the plants mothers, a total loss of viability appearing on crop plants collected in the presence of NaCl 300 mM.

Physiology of salt tolerance in Atriplex halimus L.

Atriplex halimus is a common shrub in Tunisia, which represents a palatable food for sheep and camels. Furthermore, its halophytic behavior makes it a model for the study of mechanisms of salt tolerance in plants. We present here results obtained on Atriplex halimus var. halimus. In this species, the germination of seeds is very sensitive to salinity, since low concentrations of sodium chloride (50 mM) in the medium delayed the germination and reduced the capacity of the seedlings to emerge. Germination was completely inhibited, but reversibly, by NaCl concentrations up to 200 mM. Nevertheless, after the development of the radicle and the emergence of the cotyledons, which occurred 5 days after the imbibition of the seeds, the seedlings were able to tolerate this high concentration of NaCl and their growth was stimulated by salt. Also, 1-month-old plantlets, grown in a hydroponic medium, showed an optimal growth on 50-200 mM NaCl, and tolerated NaCl concentrations up to 300 mM. Our results indicate that, in Atriplex halimus, salt tolerance is acquired at an early vegetative stage of the plant development, and is related to: (i) the absorption and transport to shoots of high quantities of Na+ and Cl- and their use in the osmotic adjustment, (ii) the efficiency of the vacuolar compartmentation of these ions, which prevents the ionic damage of the cytoplasm, and (iii) the aptitude of whole plant to ensure a sufficient supply of K+, by maintaining a high selectivity for this essential nutriment, in spite of large amount of Na+ in the medium.

Salt sensitivity and K/Na selectivity in Setaria verticillata

We have studied the effect of salinity on the development and mineral nutrition of Setaria verticillata, a summer wild graminaceae. Measurement of biomass deposition in different organs showed that Setaria is very sensitive to salinity. Even the lowest NaCl concentration of 50 mM caused a significant reduction of dry weight production for both roots and aerial parts. At concentrations higher than 50 mM, dry matter deposition was more diminished in roots than shoot, resulting in higher shoot/root ratios. The tissues of plants grown in the presence of NaCl contained high concentrations of Na and Cl, with an excess of the former ion as compared to the latter, especially in the shoots. The aptitude of the plants for K vs. Na discrimination was estimated from the K/(K+Na) ratio in tissues. The values of this ratio were similar in roots and shoots, suggesting that the former organs controlled the K/Na selectivity of the latter. The K/(K+Na) ratio diminished as the concentration of NaCl in the medium was augmented, but it remained systematically higher than in the medium. This indicates that, even at the highest NaCl concentrations, the plants conserved a significant control on their K/Na nutrition. However, there was a striking parallelism between the inhibition of the growth and the decrease of K/(K+Na) ratio in tissues in response to increasing NaCl concentrations in the medium. We hypothesize that sensitivity of Setaria to NaCl is strongly dependent on the inhibiting effect of NaCl on K nutrition.

Étude comparative de la croissance et de la nutrition minérale chez deux céréales (blé et orge) cultivées sous contrainte saline

Abstract The growth and mineral nutrition were investigated in seedlings of two cereals, durum wheat and barley, cultivated in nutritive solutions containing 0 or 100 mM NaCl. Salt decreased total dry weight of the two cereals. However, barley differed from wheat by a higher salt tolerance of the shoots. Na+ uptake and transport increased in the presence of NaCl, but Na+ accumulation in young leaves was lower in wheat than in barley. Barley was also distinguished by a good ability to sequestred Na+ inside the vacuole, which might play a role in osmotic adjustement under saline conditions.

L'acide salicylique améliore la tolérance de la tomate cultivée (Solanum lycopersicum) à la contrainte saline

Abstract The effect of the salicylic acid (SA) on the salt tolerance was examined in tomato plants cv Rio Grande. Young plants resulting from sowing were cultivated during twelve days in room air—conditioned and on nutritive mediums enriched with NaCl 100 mM and SA 0.1 mM. A control was also prepared without SA. The growth of the aerial parts was reduced by 36% in the presence of NaCl and only 21% when SA was added to the medium. The roots were not very sensitive to NaCl. It was observed a decrease in the K+ content of the various organs. The addition of SA attenuates the deficit in K+ and decreases the accumulation of Na+ and Cl− in the leaves. These results suggest that SA improves salt tolerance of tomato by ensuring a better K+ supply and by limiting the transport of Na+ and Cl− in the leaves.