This study comprehensively assessed the physiological adaptations of Cymbopogon nardus (citronella) exposed to varying concentrations (25-100 mg.kg(-1)) of cadmium (Cd) and chromium (Cr). The phytoremediation potential was also evaluated over a 60d greenhouse experiment with triplicate replication, where Cd and Cr were introduced as cadmium chloride (CdCl2) and potassium dichromate (K2Cr2O7), respectively. While elevated metal concentrations adversely affected plant growth and chlorophyll content, C. nardus exhibited remarkable tolerance. This was evidenced by the upregulation of antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidise (APX), alongside increases in reduced glutathione (GSH) and proline, effectively mitigating oxidative stress. However, high-intensity metal exposure eventually overwhelmed these systems, leading to reactive oxygen species (ROS) accumulation and oxidative damage. Notably, Western blot analysis revealed that Cr distinctly induced a greater reduction in ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity compared to Cd, highlighting nuanced physiological responses to different metals. The plant demonstrated substantial phytoremediation capacity, achieving bio-concentration factors (BCF) of 0.25 for Cd and 0.28 for Cr at 100 mg.kg(-1), and effectively removing 75.1% of Cd and 72.1% of Cr from contaminated soil. The novelty of this study lies in its comprehensive analysis of physiological adaptations and phytoremediation capabilities of C. nardus under both Cd and Cr stress, revealing its potential as a robust phytoremediator. The observed differential impact on Rubisco activity and efficient metal removal capacity underscore the plant's suitability for remediating soils contaminated with these prevalent heavy metals.

Plants grown under low magnesium (Mg) soils are highly susceptible to encountering light intensities that exceed the capacity of photosynthesis (A), leading to a depression of photosynthetic efficiency and eventually to photooxidation (i.e., leaf chlorosis). Yet, it remains unclear which processes play a key role in limiting the photosynthetic energy utilization of Mg-deficient leaves, and whether the plasticity of A in acclimation to irradiance could have cross-talk with Mg, hence accelerating or mitigating the photodamage. We investigated the light acclimation responses of rapeseed (Brassica napus) grown under low- and adequate-Mg conditions. Magnesium deficiency considerably decreased rapeseed growth and leaf A, to a greater extent under high than under low light, which is associated with higher level of superoxide anion radical and more severe leaf chlorosis. This difference was mainly attributable to a greater depression in dark reaction under high light, with a higher Rubisco fallover and a more limited mesophyll conductance to CO2 (gm). Plants grown under high irradiance enhanced the content and activity of Rubisco and gm to optimally utilize more light energy absorbed. However, Mg deficiency could not fulfill the need to activate the higher level of Rubisco and Rubisco activase in leaves of high-light-grown plants, leading to lower Rubisco activation and carboxylation rate. Additionally, Mg-deficient leaves under high light invested more carbon per leaf area to construct a compact leaf structure with smaller intercellular airspaces, lower surface area of chloroplast exposed to intercellular airspaces, and CO2 diffusion conductance through cytosol. These caused a more severe decrease in within-leaf CO2 diffusion rate and substrate availability. Taken together, plant plasticity helps to improve photosynthetic energy utilization under high light but aggravates the photooxidative damage once the Mg nutrition becomes insufficient.

Heliotropium thermophilum (Boraginaceae) plants have strong antioxidant properties. This study investigated the effectiveness of the antioxidant system in protecting the photosynthetic machinery of H. thermophilum. Plants were obtained from K & imath;z & imath;ldere geothermal area in Buharkent district, Ayd & imath;n, Turkey. Plants in the geothermal area that grew at 25-35 degrees C were regarded as the low temperature group, while those that grew at 55-65 degrees C were regarded as the high temperature group. We analysed the physiological changes of these plants at the two temperature conditions at stage pre-flowering and flowering. We meaured the effect of high soil temperature on water potential, malondialdehyde, cell membrane stability, and hydrogen peroxide analysis to determine stress levels on leaves and roots. Changes in antioxidant enzyme activities, ascorbate and chlorophyll content, chlorophyll fluorescence, photosynthetic gas exchange parameters, and photosynthetic enzymes (Rubisco and invertase) activities were also determined. Our results showed minimal changes to stress levels, indicating that plants were tolerant to high soil temperatures. In general, an increase in antioxidant enzyme activities, ascorbat levels, and all chlorophyll fluorescence parameters except for non-photochemical quenching (NPQ) and F-v/F-m were observed. The pre-flowering and flowering stages were both characterised by decreased NPQ, despite F-v/F-m not changing. Additionally, there was a rise in the levels of photosynthetic gas exchange parameters, Rubisco, and invertase activities. High temperature did not affect photosynthetic yield because H. thermophilum was found to stimulate antioxidant capacity, which reduces oxidative damage and maintains its photosynthetic machinery in high temperature conditions and therefore, it is tolerant to high soil temperature.