Chromium-Induced Ultrastructural Changes and Oxidative Stress in Roots of Arabidopsis thaliana

Abstract

Chromium (Cr) is an abundant heavy metal in nature, toxic to living organisms. As it is widely used in industry and leather tanning, it may accumulate locally at high concentrations, raising concerns for human health hazards. Though Cr effects have extensively been investigated in animals and mammals, in plants they are poorly understood. The present study was then undertaken to determine the ultrastructural malformations induced by hexavalent chromium [Cr(VI)], the most toxic form provided as 100 μM potassium dichromate (K2Cr2O7), in the root tip cells of the model plant Arabidopsis thaliana. A concentration-dependent decrease of root growth and a time-dependent increase of dead cells, callose deposition, hydrogen peroxide (H2O2) production and peroxidase activity were found in Cr(VI)-treated seedlings, mostly at the transition root zone. In the same zone, nuclei remained ultrastructurally unaffected, but in the meristematic zone some nuclei displayed bulbous outgrowths or contained tubular structures. Endoplasmic reticulum (ER) was less affected under Cr(VI) stress, but Golgi bodies appeared severely disintegrated. Moreover, mitochondria and plastids became spherical and displayed translucent stroma with diminished internal membranes, but noteworthy is that their double-membrane envelopes remained structurally intact. Starch grains and electron dense deposits occurred in the plastids. Amorphous material was also deposited in the cell walls, the middle lamella and the vacuoles. Some vacuoles were collapsed, but the tonoplast appeared integral. The plasma membrane was structurally unaffected and the cytoplasm contained opaque lipid droplets and dense electron deposits. All electron dense deposits presumably consisted of Cr that is sequestered from sensitive sites, thus contributing to metal tolerance. It is concluded that the ultrastructural changes are reactive oxygen species (ROS)-correlated and the malformations observed are organelle specific.

Ethylene mediates dichromate‐induced inhibition of primary root growth by altering AUX1 expression and auxin accumulation in Arabidopsis thaliana

“…Cr stress inhibits primary root elongation, in a dose‐dependent manner (Eleftheriou et al, ; Martinez‐Trujillo et al, ; Ortiz‐Castro et al, ). To investigate the effects of Cr(VI) on the inhibition of primary root elongation, 7 days old WT seedlings were exposed to 0, 50, 100, and 200 μM concentrations of Cr(VI) for 24 hr in ½ MS. All of the treated seedlings were transferred to fresh ½ MS for another 4 days, and the increase in the primary root length after treatment was measured and statistically analysed.…”

“…In plants, high Cr(VI) levels cause a decrease in seed germination, root elongation, leaf number, area and biomass, and greatly affect plant morphology as well as physiological, biochemical, and molecular processes (Huda et al, ; Kabir, ; Martinez‐Trujillo et al, ; Ortiz‐Castro, Martínez‐Trujillo, López‐Bucio, & Cervantes, ; Shanker, Cervantes, Loza‐Tavera, & Avudainayagam, ). Cr stress also exerts cytotoxic, genotoxic, and mutagenic effects in plant cells by causing cell cycle seizure, diminishing of cell division dynamics, derangement of the cytoskeleton, chromosomal aberrations, and stimulation of micronuclei formation (Eleftheriou et al, ; Patnaik, Achary, & Panda, ; Truta, Mihai, Gherghel, & Vochita, ). Root is the first plant organ that senses soil Cr(VI), typically responding to Cr‐exposure by inhibiting primary root elongation (Eleftheriou et al, ; Martinez‐Trujillo et al, ).…”

“…Cr stress also exerts cytotoxic, genotoxic, and mutagenic effects in plant cells by causing cell cycle seizure, diminishing of cell division dynamics, derangement of the cytoskeleton, chromosomal aberrations, and stimulation of micronuclei formation (Eleftheriou et al, ; Patnaik, Achary, & Panda, ; Truta, Mihai, Gherghel, & Vochita, ). Root is the first plant organ that senses soil Cr(VI), typically responding to Cr‐exposure by inhibiting primary root elongation (Eleftheriou et al, ; Martinez‐Trujillo et al, ). Furthermore, the adverse effects of Cr(VI) are more pronounced in comparison with other heavy metals such as cadmium (Cd) and lead (Shanker et al, ).…”

Comparative transcriptome profiling of two Brassica napus cultivars under chromium toxicity and its alleviation by reduced glutathione

“…Prominent changes induced by heavy metal are the generation of reactive oxygen species (ROS), that are involved in deterioration of plant physio-molecular attributes by the direct damages of nucleic acid, chloroplast structures and cell membranes [11, 12]. Enhanced level of ROS in different plant parts might be the imbalance between its production and inactivation by antioxidants that known as superoxide dismutase, peroxidase, catalase and ascorbate peroxidase, and also non enzymatic defense machinery called glutathione and carotenoids [13, 14]. …”

Bridging a Gap between Cr(VI)-Induced Oxidative Stress and Genotoxicity in Lettuce Organs after a Long-Term Exposure

“…Besides the direct interaction of Cr with nucleic acids (e.g., promoting DNA-DNA cross-links), it has also been demonstrated that Cr(VI) may increase the generation of reactive oxygen species (ROS), leading to indirect cytotoxic effects [7][8][9][10]. The correlation of the antioxidant status with genotoxic damage remains a matter of debate.…”