RESUMO
Halophytes are potential gene sources for genetic manipulation of economically important crop species. This study addresses the physiological responses of a widespread halophyte, Prosopis strombulifera (Lam.) Benth to salinity. We hypothesised that increasing concentrations of the two major salts present in soils of central Argentina (Na2SO4, NaCl, or their iso-osmotic mixture) would produce distinct physiological responses. We used hydroponically grown P. strombulifera to test this hypothesis, analysing growth parameters, water relations, photosynthetic pigments, cations and anions. These plants showed a halophytic response to NaCl, but strong general inhibition of growth in response to iso-osmotic solutions containing Na2SO4. The explanation for the adaptive success of P. strombulifera in high NaCl conditions seems to be related to a delicate balance between Na(+) accumulation (and its use for osmotic adjustment) and efficient compartmentalisation in vacuoles, the ability of the whole plant to ensure sufficient K(+) supply by maintaining high K(+)/Na(+) discrimination, and maintenance of normal Ca(2+) levels in leaves. The three salt treatments had different effects on the accumulation of ions. Findings in bi-saline-treated plants were of particular interest, where most of the physiological parameters studied showed partial alleviation of SO4(2-)-induced toxicity by Cl(-). Thus, discussions on physiological responses to salinity could be further expanded in a way that more closely mimics natural salt environments.
Assuntos
Prosopis/crescimento & desenvolvimento , Cloreto de Sódio/metabolismo , Sulfatos/metabolismo , Íons , Prosopis/metabolismoRESUMO
The success of Prosopis strombulifera in growing under high NaCl concentrations involves a carefully controlled balance among different processes, including compartmentation of Cl(-) and Na(+) in leaf vacuoles, exclusion of Na(+) in roots, osmotic adjustment and low transpiration. In contrast, Na(2) SO(4) causes growth inhibition and toxicity. We propose that protection of the cytoplasm can be achieved through production of high endogenous levels of specific compatible solutes. To test our hypothesis, we examined endogenous levels of compatible solutes in roots and leaves of 29-, 40- and 48-day-old P. strombulifera plants grown in media containing various concentrations of NaCl, Na(2) SO(4) or in mixtures of both, with osmotic potentials of -1.0,-1.9 and -2.6 MPa, as correlated with changes in hydric parameters. At 24 h after the last pulse plants grown in high NaCl concentrations had higher relative water content and relatively higher osmotic potential than plants grown in Na(2) SO(4) (at 49 days). These plants also had increased synthesis of proline, pinitol and mannitol in the cytoplasm, accompanied by normal carbon metabolism. When the sulphate anion is present in the medium, the capacities for ion compartmentalisation and osmotic adjustment are reduced, resulting in water imbalance and symptoms of toxicity due to altered carbon metabolism, e.g. synthesis of sorbitol instead of mannitol, reduced sucrose production and protein content. This inhibition was partially mitigated when both anions were present together in the solution, demonstrating a detrimental effect of the sulphate ion on plant growth.
Assuntos
Carbono/metabolismo , Osmose/efeitos dos fármacos , Prosopis/efeitos dos fármacos , Plantas Tolerantes a Sal/efeitos dos fármacos , Cloreto de Sódio/farmacologia , Sódio/metabolismo , Sulfatos/toxicidade , Inositol/análogos & derivados , Inositol/metabolismo , Íons/metabolismo , Manitol/metabolismo , Folhas de Planta/efeitos dos fármacos , Folhas de Planta/metabolismo , Raízes de Plantas/efeitos dos fármacos , Raízes de Plantas/metabolismo , Transpiração Vegetal/efeitos dos fármacos , Prolina/metabolismo , Prosopis/metabolismo , Prosopis/fisiologia , Tolerância ao Sal/efeitos dos fármacos , Plantas Tolerantes a Sal/metabolismo , Plantas Tolerantes a Sal/fisiologia , Sais/metabolismo , Sais/farmacologia , Cloreto de Sódio/metabolismo , Estresse Fisiológico , Sulfatos/metabolismo , Vacúolos/metabolismo , Água/metabolismoRESUMO
Mycobacterial porins and other beta-barrel outer-membrane proteins are represented by the structure of Mycobacterium smegmatis porin MspA. On the basis of existing knowledge of beta-barrel outer-membrane proteins, several state of the art prediction methods, as well as a new in-house program (PROB) were employed for the systematic exploration of Mycobacterium tuberculosis predicted proteomes for potential beta-barrel structures. PROB allowed parameter optimization while functioning with an adaptive algorithm for the detection of outer-membrane beta-barrel proteins in highly divergent proteomes. As a result of the predictions, 114 proteins in total were predicted to be beta-barrel structures; of these, 40 were PE-PPE proteins, 8 Mce proteins, 24 hypothetical, 11 probable membrane proteins, 10 transporters, 4 lipoproteins, and 14 classified as other. The congruence among three of the predictors, PROB, TMB-Hunt, and BOMP, was low with only three proteins (MT0318, MT0356, and MT2423) predicted by the three. Overall, 79 new proteins for which no previous experimental work has been performed are reported. At least 10 of these have high potential of being not only surface-exposed but also served as putative vaccine candidates as determined by in silico predictions of CD4T cell MHC-II restricted epitopes.