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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