The Regulation of Ion Homeostasis, Growth, and Biomass Allocation in Date Palm Ex Vitro Plants Depends on the Level of Water Salinity

Abstract

The date palm, a central plant in the fragile oasis ecosystem, is considered one of the fruit species most tolerant to salt stress. However, the tolerance mechanisms involved are yet to be addressed and their evaluation until now was mainly based on heterogenous plant material such as seedlings or limited to in vitro experiment conditions. For these reasons, we propose to deepen our knowledge of the morphological and physiological responses to salt stress using acclimated ex vitro plants resulting from the propagation of a single genotype. The plants were irrigated with 0, 150, 300, or 450 mM NaCl solutions for four months. Our results showed that the influence of water salinity on growth and ion-homeostasis regulation was very dependent on stress levels. The 150 mM NaCl concentration was found to improve dry biomass by about 35%, but at higher salt concentrations (300 and 450 mM) it decreased by 40–65%. The shoot:root dry mass ratio decreased significantly at the 150 mM NaCl water concentration and then increased with increasing water salt concentration. The leaf:root ratio for Na+ and Cl− decreased significantly with increasing water salinity up to a concentration of 300 mM NaCl, and then stabilized with similar values for 300 mM and 450 mM NaCl. In contrast to Na+ and Cl−, leaf K+ content was significantly higher in the leaf than in the root for all salt treatments. Unlike Na+ and K+, Cl− was expelled to the surface of leaves in response to increased water salinity. Overall, date palm plants appear to be more capable of excluding Cl− than Na+ and of changing biomass allocation according to salt-stress level, and their leaves and roots both appear to play an important role in this tolerance strategy.

Characterization of Salt-Tolerant Cultivars of Date Palm Based on Morphological and Biochemical Responses Under Salinity Stress

“…Salt stress significantly reduced the root length in the cultivars Haleemi, Basrawali, Dhakki, Sanduri, and Gajjar. The results of the present study are in line with the earlier scientific work of Hewitt [36].…”

Differential effect of water salinity levels on gas exchange, chlorophyll fluorescence and antioxidant compounds in ex vitro date palm plants

“…The development of the in vitro multiplication technique has allowed obtaining homogeneous and vigorous plant material, which is very interesting for carrying out reliable scientific studies (Al-Khayri and Al-Bahrany, 2004;Fki et al, 2011). However, this type of material has been little used in physiological and agronomic studies of the date palm until now (Hammami et al, 2022). The little knowledge available about the physiological response of date palm to salinity, such as enzymatic activity, gas exchange and nutrient uptake, was obtained from seedlings, with the inherent doubts and potential interfering factors that such material may generate (Elshibli and Complained, 2009;Sperling et al, 2014;Al Kharusi et al, 2019).…”

“…Another protective mechanism against salt-stress is the overproduction of antioxidant metabolites like phenolic and flavonoid compounds in order to scavenge harmful reactive oxygen species (ROS) (Cohen and Kennedy, 2010;Agati et al, 2012) and compatible osmolytes such as proline with osmoprotectant activity (Szabados and Savouré, 2010;Dar et al, 2015). In the date palm, a new study in ex vitro plants has shown new insights on the key role of exclusion mechanisms of Cland Na + in the roots and the leaf in the tolerance of this species to salinity (Hammami et al, 2022). However, the mechanisms adopted to protect the PSI and PSII in salt stress conditions have not yet been fully elucidated.…”