Galactoglucomannan oligosaccharides mitigate cadmium toxicity in maize protoplasts by improving viability and cell wall regeneration.

To avoid human health endangerment via the food chain, the investigation of Cd's effects on plant growth and development, and the discovery of various compounds that would mitigate the toxic effects of Cd, are essential. Galactoglucomannan oligosaccharides (GGMOs) are biologically active compounds, which improve the growth and development of plants. Therefore, the impact of GGMOs on the mitigation of Cd toxicity on maize (Zea mays L.) protoplasts was the main objective of this research. Here, protoplast viability, de novo cell wall regeneration on protoplasts' surface and Cd-uptake by protoplasts were studied. To study the influence of different treatments over time, the protoplasts were sampled on various days during the 14-day-long cultivation. The medium containing 2,4-dichlorophenoxyacetic acid, 6-benzylaminopurine, and GGMOs in a 10-9 M concentration with a pH of 3.8 was found to be optimal for protoplast cultivation. The toxic effect of Cd2+, which was evident already on the 2nd day of cultivation, resulted in decreased protoplast viability, the de novo cell wall regeneration, and in increased Cd-uptake. However, the application of GGMOs on Cd-stressed protoplasts increased cell wall regeneration. Fully or partly regenerated cell walls decreased the uptake of Cd2+ through the plasma membrane and improved protoplast viability. This is the first study that confirmed that biologically active oligosaccharides promote cell wall regeneration on the protoplast surface in both non-stress and Cd-stress conditions.

The changes in the maize root cell walls after exogenous application of auxin in the presence of cadmium.

Cadmium (Cd) is a transition metal and hazardous pollutant that has many toxic effects on plants. This heavy metal poses a health risk for both humans and animals. The cell wall is the first structure of a plant cell that is in contact with Cd; therefore, it can change its composition and/or ratio of wall components accordingly. This paper investigates the changes in the anatomy and cell wall architecture of maize (Zea mays L.) roots grown for 10 days in the presence of auxin indole-3-butyric acid (IBA) and Cd. The application of IBA in the concentration 10-9 M delayed the development of apoplastic barriers, decreased the content of lignin in the cell wall, increased the content of Ca2+ and phenols, and influenced the composition of monosaccharides in polysaccharide fractions when compared to the Cd treatment. Application of IBA improved the Cd2+ fixation to the cell wall and increased the endogenous concentration of auxin depleted by Cd treatment. The proposed scheme from obtained results may explain the possible mechanisms of the exogenously applied IBA and its effects on the changes in the binding of Cd2+ within the cell wall, and on the stimulation of growth that resulted in the amelioration of Cd stress.

Galactoglucomannan oligosaccharides alleviate cadmium toxicity by improving physiological processes in maize.

Phosphate fertilisers and past mining activity are significant source of cadmium (Cd) pollution; thus, the concentration of Cd in agricultural soils has been substantially rising. Various substances have been tested for their potential to alleviate the toxicity of Cd and stimulate the accumulation of Cd in plant organs. This study brought new insight of the impact of galactoglucomannan oligosaccharides (GGMOs) on the maize plants grown under/in Cd stress. The application of GGMOs reduced concentration of Cd in the maize leaves and thus GGMOs increased their growth (by 24%), concentration of photosynthetic pigments (up to 39.4%), effective quantum yield of photosystem II (up to 29.6%), and net photosynthetic rate (up to 19.6%). The concentrations of stress markers increased in the Cd and Cd + GGMOs treatment; however, significantly lower concentration was detected in the Cd + GGMOs treatment (malondialdehyde by 21.7%, hydrogen peroxide by 13%). The concentration of auxin increased almost by two-fold in the Cd + GGMOs treatment compared to the Cd treatment. The recovered auxin level and enhanced nutrient uptake are proposed mechanisms of GGMOs' action during stress. GGMOs are molecules with biostimulant potential that could support vitality of maize plants in Cd stress.

Silicon Actuates Poplar Calli Tolerance after Longer Exposure to Antimony.

The presence of antimony (Sb) in high concentrations in the environment is recognized as an emerging problem worldwide. The toxicity of Sb in plant tissues is known; however, new methods of plant tolerance improvement must be addressed. Here, poplar callus (Populus alba L. var. pyramidallis) exposed to Sb(III) in 0.2 mM concentration and/or to silicon (Si) in 5 mM concentration was cultivated in vitro to determine the impact of Sb/Si interaction in the tissue. The Sb and Si uptake, growth, the activity of superoxide dismutase (SOD), catalase (CAT), guaiacol-peroxidase (G-POX), nutrient concentrations, and the concentrations of photosynthetic pigments were investigated. To elucidate the action of Si during the Sb-induced stress, the impact of short and long cultivations was determined. Silicon decreased the accumulation of Sb in the calli, regardless of the length of the cultivation (by approx. 34%). Antimony lowered the callus biomass (by approx. 37%) and decreased the concentrations of photosynthetic pigments (up to 78.5%) and nutrients in the tissue (up to 21.7%). Silicon supported the plant tolerance to Sb via the modification of antioxidant enzyme activity, which resulted in higher biomass production (increased by approx. 35%) and a higher uptake of nutrients from the media (increased by approx. 10%). Silicon aided the development of Sb-tolerance over the longer cultivation period. These results are key in understanding the action of Si-developed tolerance against metalloids.

Effects of Exogenous Application of Indole-3-Butyric Acid on Maize Plants Cultivated in the Presence or Absence of Cadmium.

Auxins are plant hormones that affect plant growth, development, and improve a plant's tolerance to stress. In this study, we found that the application of indole-3-butyric acid (IBA) had diverse effects on the growth of maize (Zea mays L.) roots treated without/with Cd. IBA caused changes in the growth and morphology of the roots under non-stress conditions; hence, we were able to select two concentrations of IBA (10-11 M as stimulatory and 10-7 M as inhibitory). IBA in stimulatory concentration did not affect the concentration of H2O2 or the activity of antioxidant enzymes while IBA in inhibitory concentration increased only the concentration of H2O2 (40.6%). The application of IBA also affected the concentrations of mineral nutrients. IBA in stimulatory concentration increased the concentration of N, K, Ca, S, and Zn (5.8-14.8%) and in inhibitory concentration decreased concentration of P, K, Ca, S, Fe, Mn, Zn, and Cu (5.5-36.6%). Moreover, IBA in the concentration 10-9 M had the most positive effects on the plants cultivated with Cd. It decreased the concentration of H2O2 (34.3%), the activity of antioxidant enzymes (23.7-36.4%), and increased the concentration of all followed elements, except Mg (5.5-34.1%), when compared to the Cd.

The cadmium tolerance development of poplar callus is influenced by silicon.

Cadmium-tolerant plants were studied for their possible usage in phytoremediation techniques. However, their response to cadmium cations at a cellular level has not been properly studied. Silicon is a beneficial element that seems to change the plant's response to the Cd2+ presence. The aim of the present study was to investigate the Cd2+ tolerance patterns of poplar callus cells exposed to Cd+2 and/or Si over short and long cultivation periods. We determined the growth parameters of the callus, the growth dynamics, cell vitality, photosynthetic pigment concentrations and the activity of antioxidant enzymes. The effects were studied over short (21 days) and long (63 days) cultivation periods. The most important result proved that the poplar callus tissue is able to build up a tolerance to Cd2+ after a longer cultivation period. On the 63rd day of the cultivation, Cd2+ stressed calli showed improvement in studied parameters and the callus cells accumulated Cd2+ more efficiently than on the 21st day. Supplementation with Si in higher concentrations (2.5 mM and 5 mM) heightened the Cd-tolerance potential of the tissue. The treatment of Cd2+, and Si in a 2.5 mM concentration was the most efficient variant for Cd2+ removal from medium. The activity of antioxidant enzymes showed that poplar callus cells effectively develop tolerance against Cd2+ after a longer cultivation period.

The modulation of ion homeostasis by silicon in cadmium treated poplar callus cells.

One of the major reasons why cadmium is toxic in plants is because it disturbs their nutrient balance. The aim of this work is to investigate the effects of cadmium (Cd) and/or silicon (Si) on the nutrient status of poplar callus cells after 3 and after 9 weeks of Cd exposure and to study its possible relationship with the changes in the fresh and dry mass, the plasma membrane integrity, and cadmium tolerance patterns. A principal component analysis (PCA) was performed to reveal the associations among the elements, and the variability between both treatments, and between the 3- and 9-week stages. Cadmium reduced the fresh and dry mass, the plasma membrane integrity, and the concentration of all nutrients except for P. After 9 weeks of exposure, the Cd concentration in callus cells had almost doubled, in spite of an improvement in all studied parameters. These changes may be due to the callus acclimatizing to the Cd stress. In the Cd + Si treatment, the fresh and dry mass, the plasma membrane integrity, and the concentration of nutrients, as well as the growth tolerance index, increased in comparison with the Cd treatment. We assumed that the enhancement in the plasma membrane integrity mediated by Si under Cd stress had caused the improvement in the uptake of nutrients and, consequently, the fresh and dry mass of callus cells had increased. The reduction in Cd concentration due to the Si impact also contributed to the increase in fresh and dry mass.

The effects of IBA on the composition of maize root cell walls.

Auxin is one of the crucial plant hormones which stimulates and controls cell and plant growth. The effects of auxin IBA (indole-3-butyric acid) during 10-days on maize plants growth in controlled conditions (hydroponic, 16-h photoperiod, 70% humidity, 25/20 °C temperature), depended on its concentration in the substrate. A high concentration (10-7 M) of IBA inhibited root growth, evoked the development of apoplasmic barriers (Casparian bands and suberin lamellae) closer to the root apex, and elevated the amount of lignin in roots. A low concentration (10-11 M) of IBA stimulated root growth but affected neither the development of apoplasmic barriers, nor the amount of lignin. Auxin in a 10-8 M concentration influenced the root growth to a minimal extent compare to the control, and it was the non-effective concentration. Plant cell walls as cell structures ensure cell enlargement and plant growth, and have to react to auxin stimulus by modification of their components. We found the most significant changes in the composition of the PF III fraction (lignocellulosic complex) of the cell wall. The presence of auxin in the substrate affected all three components of this fraction - Klason lignin and both the by acid (2 M TFA) non-hydrolysable and the hydrolysable parts of this complex. The ratio of the non-hydrolysable part to the Klason lignin increased from 1.3 to 3.3 with increasing auxin concentrations in the substrate. This may be related to the deposition of polysaccharides and lignin in the cell wall, which help maintain the specific tensile stress of, and turgor pressure on, the cell walls.

The response of maize protoplasts to cadmium stress mitigated by silicon.

The aim of this article was to evaluate the viability of maize protoplasts, cell wall regeneration, Cd uptake by protoplasts, and the impact of silicon under cadmium cations (Cd) stress in two maize hybrids with contrasting tolerances to Cd toxicity. The differences in protoplast viability between the sensitive (Novania) and tolerant (Almansa) hybrids were noticeable even at the beginning of culture. The percentage of living protoplasts in the presence of Cd was higher in the tolerant hybrid. In both hybrids, Si supplementation significantly increased the viability of protoplasts exposed to Cd. The percentage of protoplasts with regenerated cell walls gradually increased in both hybrids and by the end of the culture it had reached almost identical values. Differences were observed during the first four days, when a lag phase occurred in the protoplasts of the sensitive hybrid accompanied by a rapid decrease in protoplast viability in all the variants tested. The addition of Si increased the cell wall regeneration compared with the Cd variant in both hybrids. The Cd content was higher in the tolerant hybrid than in the sensitive one during the first four days and declined on the seventh day. This may be connected with the increasing intensity of cell wall formation from the fourth up to the seventh day. The addition of Si decreased the Cd uptake into protoplasts of both hybrids. Despite the higher content of Cd, the protoplasts of the tolerant hybrid showed higher viability, obviously indicating unequal mechanisms of Cd processing in studied hybrids. CAPSULE: Protoplasts of two maize hybrids were tested for their viability, regeneration, Cd-uptake and the mitigation of cadmium stress by silicon.

Maize shoot cell walls under cadmium stress.

The composition of shoot cell walls of two maize hybrids (Zea mays L.), the sensitive Novania and the tolerant Almansa, both after cadmium treatment was studied. Previous results showed a smaller effect of cadmium on shoot physiological parameters (e.g., elongation, dry mass, photosynthetic pigments content) in both hybrids compared to their roots. Changes in the composition of shoot cell walls were observed. It was ascertained that the amount of hemicelluloses in shoot cell walls decreased and the amount of lignocellulose complex increased in the sensitive hybrid; the opposite was observed in the tolerant Almansa. Dissimilarities in the cell wall structure of shoots, compared to the roots, in both hybrids were observed mainly in higher quantities of total lignin, in hemicelluloses fractions. The lignocellulose complex remained unchanged in the shoots in comparison to the roots. Nevertheless, in both hybrids, the highest Cd2+ amount was found in hemicelluloses. Such modification of the cell walls might affect the amount of binding sites resulting in lower cell wall permeability and subsequently in a lower pollutant influx into the protoplast.