Proline and glycine betaine accumulation in two succulent halophytes under natural and experimental conditions

[EN] Proline (Pro) and glycine betaine (GB) contents were determined in two Mediterranean halophytes, Plantago crassifolia and Inula crithmoides, to assess their possible role in salt tolerance of both taxa. Plant material was collected in a littoral salt marsh under different environmental conditions, and from plants subjected to salt treatments in a growth chamber. Relative growth inhibition by NaCl indicated that I. crithmoides is more salt-tolerant than P. crassifolia, in agreement with the distribution of the two species in nature. Field and laboratory data confirmed GB as the major osmolyte responsible for osmotic adjustment in I. crithmoides, but with only a minor role if any as osmoprotectant in the salt tolerance of P. crassifolia. Under natural conditions, Pro contents were very low in both taxa, but increased to levels high enough to contribute significantly to osmotic balance when plants were artificially treated with 450 600mM NaCl higher salt concentrations than those they would normally encounter in their natural habitats. These data suggest that halophytes possess built-in mechanisms, such as accumulation of additional osmolytes, to rapidly adapt to increasing salinity levels in their natural ecosystems; for example, those expected to be caused by climate change in salt marshes in the Mediterranean region.This work was funded by a grant to O.V. from the Spanish Ministry of Science and Innovation (Project CGL2008-00438/BOS), with contribution from the European Regional Development Fund. COST Action FA0901: "Putting Halophytes to work - From Genes to Ecosystems" supported M. N. Grigore for his stay in Valencia within the frame of a Short-Term Scientific Mission. A. Tifrea was funded by the Erasmus fellowship programme for her stay in Valencia to carry out her Master Thesis.Pardo-Domenech, L.; Tifrea, A.; Grigore, M.; Boscaiu, M.; Vicente, O. (2016). Proline and glycine betaine accumulation in two succulent halophytes under natural and experimental conditions. Plant Biosystems - An International Journal Dealing with all Aspects of Plant Biology. 150(5):904-915. https://doi.org/10.1080/11263504.2014.990943S904915150

Effects of Salt Stress on Three Ecologically Distinct Plantago Species

Comparative studies on the responses to salt stress of taxonomically related taxa should help to elucidate relevant mechanisms of stress tolerance in plants. We have applied this strategy to three Plantago species adapted to different natural habitats, P. crassifolia and P. coronopus both halophytes and P. major, considered as salt-sensitive since it is never found in natural saline habitats. Growth inhibition measurements in controlled salt treatments indicated, however, that P. major is quite resistant to salt stress, although less than its halophytic congeners. The contents of monovalent ions and specific osmolytes were determined in plant leaves after four-week salt treatments. Salt-treated plants of the three taxa accumulated Na+ and Cl- in response to increasing external NaCl concentrations, to a lesser extent in P. major than in the halophytes; the latter species also showed higher ion contents in the non-stressed plants. In the halophytes, K+ concentration decreased at moderate salinity levels, to increase again under high salt conditions, whereas in P. major K+ contents were reduced only above 400 mM NaCl. Sorbitol contents augmented in all plants, roughly in parallel with increasing salinity, but the relative increments and the absolute values reached did not differ much in the three taxa. On the contrary, a strong (relative) accumulation of proline in response to high salt concentrations (600 800 mM NaCl) was observed in the halophytes, but not in P. major. These results indicate that the responses to salt stress triggered specifically in the halophytes, and therefore the most relevant for tolerance in the genus Plantago are: a higher efficiency in the transport of toxic ions to the leaves, the capacity to use inorganic ions as osmotica, even under low salinity conditions, and the activation, in response to very high salt concentrations, of proline accumulation and K+ transport to the leaves of the plants.MAH was a recipient of an Erasmus Mundus pre-doctoral scholarship financed by the European Commission (Welcome Consortium). AP acknowledges the Erasmus mobility programme for funding her stay in Valencia to carry out her Master Thesis.Al Hassan, M.; Pacurar, AM.; López Gresa, MP.; Donat Torres, MDP.; Llinares Palacios, JV.; Boscaiu Neagu, MT.; Vicente Meana, Ó. (2016). Effects of Salt Stress on Three Ecologically Distinct Plantago Species. PLoS ONE. 11(8):1-21. doi:10.1371/journal.pone.0160236S12111