Will Casuarina glauca Stress Resilience Be Maintained in the Face of Climate Change?

Abstract

Actinorhizal plants have been regarded as promising species in the current climate change context due to their high tolerance to a multitude of abiotic stresses. While combined salt-heat stress effects have been studied in crop species, their impact on the model actinorhizal plant, Casuarina glauca, has not yet been fully addressed. The effect of single salt (400 mM NaCl) and heat (control at 26/22 °C, supra optimal temperatures at 35/22 °C and 45/22 °C day/night) conditions on C. glauca branchlets was characterised at the physiological level, and stress-induced metabolite changes were characterised by mass spectrometry-based metabolomics. C. glauca could withstand single salt and heat conditions. However, the harshest stress condition (400 mM NaCl, 45 °C) revealed photosynthetic impairments due to mesophyll and membrane permeability limitations as well as major stress-specific differential responses in C and N metabolism. The increased activity of enzymatic ROS scavengers was, however, revealed to be sufficient to control the plant oxidative status. Although C. glauca could tolerate single salt and heat stresses, their negative interaction enhanced the effects of salt stress. Results demonstrated that C. glauca responses to combined salt-heat stress could be explained as a sum of the responses from each single applied stress.

Mechanisms of salt stress tolerance in Casuarina: a review of recent research

“…This highlights the importance of both enzymatic and non-enzymatic scavenging components in the control of oxidative stress and, thereby, their key role in stress tolerance enhancement. However, it should be noted that the concomitant presence of heat stress (45°C) might jeopardize C. glauca acclimation to salinity (400 mM NaCl), due to a negative heat and salt interaction that aggravated stress severity (Jorge et al 2021). The analysis of the proteome of C. glauca branchlets corroborated the previous studies, highlighting the robustness of tolerance to single salt stress exposure in this species (Graça et al 2020).…”

“…On the other hand, membrane permeability and the unsaturation degree of membrane lipids remained mostly unchanged (Scotti-Campos et al 2016). Complementary, metabolomics of salt stress revealed the importance of the secondary metabolome, namely of the flavonoid-based antioxidant system (Jorge et al 2019) in complementing the increased activity of enzymatic scavengers of reactive oxygen species (ROS) associated with the ascorbate-glutathione cycle (Scotti-Campos et al 2016;Jorge et al 2017aJorge et al , 2021. This highlights the importance of both enzymatic and non-enzymatic scavenging components in the control of oxidative stress and, thereby, their key role in stress tolerance enhancement.…”

“…Similarly, C. glauca seedlings from an Egyptian ecotype nodulated by Frankia CcI156 and CgIM4 were able to withstand up to 200 mM NaCl, with a more prominent contribution of CgIM4 (Mansour et al 2016), while young plants (seeds from www.nzseeds.co.nz) tolerated up to 600 mM NaCl. On the other hand, Frankia casuarinae strain Thr (Hurst et al 2014) did not enhance salt tolerance of young C. glauca plants (seeds from www.nzseeds.co.nz), likely associated with an intrinsic plant ability to cope with stress (Batista-Santos et al 2015;Jorge et al 2021). However, this might be due to the fact that F. casuarinae strain Thr showed low salt tolerance in planta (Duro et al 2016;Ribeiro-Barros et al 2016).…”

“…In C. glauca an integrated analysis of salt tolerance (including the contribution of Frankia symbiosis) has been performed by our team. This was mainly centered in the branchlets and included, ecophysiological studies (Batista-Santos et al 2015;Duro et al 2016), evaluation of membrane lipid remodeling (Scotti-Campos et al 2016), metabolomics (Jorge et al 2017a(Jorge et al , 2017b(Jorge et al , 2019(Jorge et al , 2021, and proteomics (Graça et al 2020). According to Batista-Santos et al (2015), despite the decrease in plant growth and the accumulation of Na + and Cl − ions in branchlets of C. glauca exposed to increasing levels of NaCl up to 600 mM, the RWC decreased only ca.…”