Anatomical Modifications in two Juncus Species under Salt Stress Conditions

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.