Cadmium‐induced inhibition of photosynthesis and long‐term acclimation to cadmium stress in the hyperaccumulator Thlaspi caerulescens

Abstract

Summary• Acclimation of hyperaccumulators to heavy metal-induced stress is crucial for phytoremediation and was investigated using the hyperaccumulator Thlaspi caerulescens and the nonaccumulators T. fendleri and T. ochroleucum .• Spatially and spectrally resolved kinetics of in vivo absorbance and fluorescence were measured with a novel fluorescence kinetic microscope.• At the beginning of growth on cadmium (Cd), all species suffered from toxicity, but T. caerulescens subsequently recovered completely. During stress, a few mesophyll cells in T. caerulescens became more inhibited and accumulated more Cd than the majority; this heterogeneity disappeared during acclimation. Chlorophyll fluorescence parameters related to photochemistry were more strongly affected by Cd stress than nonphotochemical parameters, and only photochemistry showed acclimation.• Cd acclimation in T. caerulescens shows that part of its Cd tolerance is inducible and involves transient physiological heterogeneity as an emergency defence mechanism. Differential effects of Cd stress on photochemical vs nonphotochemical parameters indicate that Cd inhibits the photosynthetic light reactions more than the Calvin-Benson cycle. Differential spectral distribution of Cd effects on photochemical vs nonphotochemical quenching shows that Cd inhibits at least two different targets in/around photosystem II (PSII). Spectrally homogeneous maximal PSII efficiency ( F v / F m ) suggests that in healthy T. caerulescens all chlorophylls fluorescing at room temperature are PSII-associated.Key words: acclimation, cadmium (Cd), heterogeneity, imaging and spectral measurements of chlorophyll fluorescence kinetics, metal sequestration, photosynthetic performance. as q CN = ( F m -F m ′ )/ F m = 'complete nonphotochemical quenching of Chl fluorescence' (i.e. with normalisation to F m ); OD, optical density; PSII, photosystem II; RC, photosynthetic reaction centre; Φ PSII = Φ e = ( F m ′ − F t ′ )/ F m ′ = effective quantum yield of photochemical energy conversion in actinic light (Genty et al. , 1989). Here, the values of this parameter were calculated also for responses to saturating flashes during the relaxation period after the end of actinic light in order to follow the return of the system to its dark-acclimated state as measured by F v / F m . AbbreviationsNew Phytologist (2007) 175 : [655][656][657][658][659][660][661][662][663][664][665][666][667][668][669][670][671][672][673][674]

Effect of excess iron and copper on physiology of aquatic plant Spirodela polyrrhiza (L.) Schleid

“…The reduced photosynthetic activity is an effect commonly noticed in plants exposed to heavy metal (Frankart et al, 2002;Hanikenne, 2003;Hou et al, 2007;Hu et al, 2007;Küpper et al, 2007;Li et al, 2008). In our experiment, significant correlation was obtained between Fv/Fm and excess iron and copper (r 5 20.9742, r 5 20.9790, P \ 0.05), suggesting ROS caused by excess metal concentration damaged photosynthetic apparatuses severely.…”

Cadmium uptake kinetics and plants factors of shoot Cd concentration

“…Another reason is that in short term studies of a few hours, in contrast to long term studies, no acclimation of the plants to different Cd levels occurs. During exposure to stress, after the initial shock the plants are able to adapt to both internal and external concentration (Küpper et al 2007). To characterize Cd uptake kinetics, as may be expected for soil grown plants, long term uptake studies in nutrient solution supplied with graded Cd concentrations are needed.…”

Soil cadmium toxicity and nitrogen deposition differently affect growth and physiology in Toxicodendron vernicifluum seedlings

“…In China, the Cd content in heavily polluted soil reaches levels of 5-7 mg kg -1 (Wu et al 1989). The presence of Cd in the soil may induce inhibition of photosynthesis (Küpper et al 2007;Chen et al 2011), and also the generation of reactive oxygen species (ROS) and inhibition or sometimes stimulation in the activity of several antioxidative enzymes, e.g. decreases in superoxidase and catalase activities, and increases in guaiacol peroxidase, glutathione reductase and ascorbate peroxidase activities (Wang et al 2008;Chou et al 2012).…”