NaCl-induced physiological and biochemical adaptative mechanisms in the ornamental Myrtus communis L. plants

Abstract

Physiological and biochemical changes in Myrtus communis L. plants after being subjected to different solutions of NaCl (44, and 88 mM) for up to 30 days (Phase I) and after recovery from the salinity period (Phase II) were studied. Myrtle plants showed salinity tolerance by displaying a series of adaptative mechanisms to cope with salt-stress, including controlled ion homeostasis, the increase in root/shoot ratio, the reduction of water potentials and stomatal conductance to limit water loss. In addition, they displayed different strategies to protect the photosynthetic machinery, including limiting toxic ion accumulation in leaves, increase in chlorophyll content, and changes in chlorophyll fluorescence parameters, leaf anatomy and increases in catalase activity. Anatomical modifications in leaves, including a decrease in spongy parenchyma and increased intercellular spaces, allow CO2 diffusion in a situation of reduced stomatal aperture. In spite of all these changes, salinity produced oxidative stress in myrtle plants as monitored by increases in oxidative stress parameter values. The post-recovery period is perceived as a new stress situation, as observed through effects on plant growth and alterations in non-photochemical quenching parameters and lipid peroxidation values.

Plant Responses to Salt Stress: Adaptive Mechanisms

“…In this experiment salt stress was accompanied by an increase in mesophyll thickness due to increased intercellular spaces. Such anatomical modifications in the leaves of salt stressed zucchini squash plants agree with previous findings in the ornamental shrubs Myrtus communis and Eugenia myrtifolia [28,29]. However, despite these modifications, zucchini squash plants supplied with NaCl had sharply reduced leaf PN.…”

“…At 30 days of stress, however, the drop in PN paralleled a decline in qP and Y(II) and increases in non-photochemical parameters, as a safe mechanism for dissipating excess light energy [29] (Figure 2). After the post-stress period, the partial recovery in PN observed in myrtle plants previously treated with 4 dS m −1 NaCl correlated with increases in qP and Y(II), whereas in plants previously subjected to 8 dS m −1 NaCl, both qN and Y(NPQ) dropped [28], reflecting a decrease in the safe dissipation of excess energy that could induce photo-oxidative damage in the photosynthetic apparatus [178]. Long-term NaCl treatment (75-150 mM) also decreased Y(II) and Y(NPQ) in Lawsonia inermis L. plants [94].…”

“…Studying the changes produced in leaf anatomy is an appropriate way to study abiotic stress situations, including salt stress [28,29,93,94]. A pioneer assay in this field was carried out by Longstreth and Nobel [95].…”

“…Under saline conditions, a general decrease in photochemical quenching parameters (Fv/Fm, Y(II), qP) and in the electron transport rate (ETR) takes place, but increases in non-photochemical quenching parameters [qN, NPQ, Y(NPQ)] have also been reported [28,29,[179][180][181] (Figure 2). The response to NaCl stress is correlated with decreases in PSII efficiency and increases in non-photochemical quenching parameters as a mechanism to safely dissipate excess energy.…”

“…In the presence of salt stress, the photochemical quenching parameters increased in Eugenia plants, whereas myrtle plants showed increased non-photochemical quenching parameters, as a safe mechanism for dissipating excess light energy and minimising reactive oxygen species (ROS) generation. Partially reproduced from [28,29].…”