Abstract
In their natural habitats, different mechanisms may contribute to the tolerance of halophytes to high soil salinity and other abiotic stresses, but their relative contribution and ecological relevance, for a given species, remain largely unknown. We studied the responses to changing environmental conditions of five halophytes (Sarcocornia fruticosa, Inula crithmoides, Plantago crassifolia, Juncus maritimus and J. acutus) in a Mediterranean salt marsh, from summer 2009 to autumn 2010. A principal component analysis was used to correlate soil and climatic data with changes in the plants' contents of chemical markers associated with stress responses: ions, osmolytes, malondialdehyde (MDA, a marker of oxidative stress) and antioxidant systems. Stress tolerance in S. fruticosa, I. crithmoides and P. crassifolia (all succulent dicots) seemed to depend mostly on the transport of ions to aerial parts and the biosynthesis of specific osmolytes, whereas both Juncus species (monocots) were able to avoid accumulation of toxic ions, maintaining relatively high K(+)/Na(+) ratios. For the most salt-tolerant taxa (S. fruticosa and I. crithmoides), seasonal variations of Na(+), Cl(-), K(+) and glycine betaine, their major osmolyte, did not correlate with environmental parameters associated with salt or water stress, suggesting that their tolerance mechanisms are constitutive and relatively independent of external conditions, although they could be mediated by changes in the subcellular compartmentalization of ions and compatible osmolytes. Proline levels were too low in all the species to possibly have any effect on osmotic adjustment. However-except for P. crassifolia-proline may play a role in stress tolerance based on its 'osmoprotectant' functions. No correlation was observed between the degree of environmental stress and the levels of MDA or enzymatic and non-enzymatic antioxidants, indicating that the investigated halophytes are not subjected to oxidative stress under natural conditions and do not, therefore, need to activate antioxidant defence mechanisms.
Highlights
Soil salinity is, together with drought, one of the most important environmental conditions that reduce crop yields worldwide and determine the distribution of wild plants in nature (Boyer 1982; Bartels and Sunkar 2005; Watson and Byrne 2009)
The dry summer of 2009 was followed by an extremely wet autumn, in contrast to the dry, but significantly cooler, autumn of year 2. It is characteristic of the Mediterranean climate that, in summer, ETP is considerably greater than precipitation and water deficit is pronounced
The present study confirms some previously published results, and provides novel information contributing to our knowledge on the general mechanisms of abiotic stress tolerance in plants
Summary
Together with drought, one of the most important environmental conditions that reduce crop yields worldwide and determine the distribution of wild plants in nature (Boyer 1982; Bartels and Sunkar 2005; Watson and Byrne 2009). There is substantial evidence that all plants react against adverse environmental conditions by activating a series of conserved responses which are common to different abiotic stresses One of these basic stress responses involves ion homoeostasis and the maintenance of osmotic balance to counteract cellular dehydration caused by, for example, high soil salinity, drought, cold or high temperatures: limitation of water losses, sequestration of toxic ions in the vacuole (according to the so-called ion compartmentalization hypothesis; Flowers et al 1977; Wyn Jones et al 1977; Glenn et al 1999) and synthesis and accumulation of compatible solutes or osmolytes in the cytoplasm (Munns and Termaat 1986; Zhu 2001; Munns and Tester 2008; Kronzucker and Britto 2011). Not surprising that very few studies have been published dealing with the stress responses of halophytes under varying environmental conditions in their natural ecosystems (e.g. Doddema et al 1986; Murakeozy et al 2002, 2003; Walker et al 2008; Mouri et al 2012; Boscaiu et al 2013)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
