Abstract
The anatomic structure of roots and culms of two Juncus species with different degrees of salt tolerance was analysed in plants grown for two months under salt stress (NaCl treatments) and in control, non-treated plants. The aim of the study was not only to compare the anatomical structures of a halophyte (J. acutus) and a related glycophyte (J. articulatus), but mostly to assess whether salt stress induced anatomical modifications, by identifying differences between control and treated plants. Several slight differences have been indeed detected, in terms of endodermis type, development of aerenchyma and extent of sclerenchyma in perivascular sheaths. The role of Casparian endodermis was here discussed in relation to its complex implications in controlling salt influx at the root level that is an efficient mechanism involved in halophytes. Aerenchyma is a common feature found in marshy halophytes, allowing them to survive naturally under flooding conditions; however, when occurring in non-waterlogged plants, as is the case of this study, it should be regarded as a genetically, constitutive adaptation rather than an inducible one. Nevertheless, such anatomic modifications should be regarded as mere alterations due to stress – that is, as stress responses – and not as truly adaptations to salinity. In this context, the nature of these modifications – either considered as adaptations or damage indicators of salt stress – should be further reconsidered.
Highlights
Nowadays, the study of plant responses to salt stress and salt tolerance mechanisms is one of the most active research fields in plant biology, since salinity – together with drought – is the main constraint for agricultural production worldwide (Marcum, 2002; Munns, 2002, 2005; Ashraf, 2004; Bartels and Sunkar, 2005; Mittler, 2006)
Plant material and experimental design Seeds of J. acutus were collected from a salt marsh located in the Natural Park of La Albufera (Province of Valencia, Spain) and those of J. articulatus from a non-saline area in the Natural Park
In J. acutus a well-developed aerenchyma was noticed in the root, while in J. articulatus it was absent
Summary
The study of plant responses to salt stress and salt tolerance mechanisms is one of the most active research fields in plant biology, since salinity – together with drought – is the main constraint for agricultural production worldwide (Marcum, 2002; Munns, 2002, 2005; Ashraf, 2004; Bartels and Sunkar, 2005; Mittler, 2006). Anatomical (structural) responses to salinity of salt-tolerant plants (halophytes) have been much less studied. 2010; Grigore et al, 2014 and reference therein), but data on possible structural modifications of halophytes in response to controlled salt stress treatments are very scarce. A controversial issue regarding possible changes in structural features under salt stress refers to the way in which these modifications can be interpreted. Salinity is known to induce changes in plant anatomy and morphology These changes are often considered to be adaptations which increase the chance of the plant to endure stress imposed by salinity, but they may be regarded as signs of damage and disruption of the normal equilibrium of life processes (Poljakoff-Mayber, 1975; Larcher, 1995; Schulze et al, 2005).
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