Cadmium spiked soil modulates root organic acids exudation and ionic contents of two differentially Cd tolerant maize (Zea mays L.) cultivars.

Our earlier work described that the roots of two maize cultivars, grown hydroponically, differentially responded to cadmium (Cd) stress by initiating changes in medium pH depending on their Cd tolerance. The current study investigated the root exudation, elemental contents and antioxidant behavior of the same maize cultivars [cv. 3062 (Cd-tolerant) and cv. 31P41 (Cd-sensitive)] under Cd stress. Plants were maintained in a rhizobox-like system carrying soil spiked with Cd concentrations of 0, 10, 20, 30, 40 and 50 µmol/kg soil. The root and shoot Cd contents increased, while Mg, Ca and Fe contents mainly decreased at higher Cd levels, and preferentially in the sensitive cultivar. Interestingly, the K contents increased in roots of cv. 3062 at low Cd treatments. The Cd stress caused acidosis of the maize root exudates predominantly in cv. 3062. The concentration of various organic acids was significantly increased in the root exudates of cv. 3062 with applied Cd levels. This effect was diminished in cv. 31P41 at higher Cd levels. Cd exposure increased the relative membrane permeability, anthocyanin (only in cv. 3062), proline contents and the activities of peroxidases (POD) and superoxide dismutase (SOD). The only exception was the catalase activity, which was diminished in both cultivars. Root Cd contents were positively correlated with the secretion of acetic acid, oxalic acid, glutamic acid, citric acid, and succinic acid. The antioxidants like POD and SOD exhibited a positive correlation with the organic acids under Cd stress. It is likly that a high exudation of dicarboxylic organic acids improves nutrient uptake and activities of antioxidants, which enables the tolerant cultivar to acclimatize in Cd polluted environment.

Cadmium-induced rhizospheric pH dynamics modulated nutrient acquisition and physiological attributes of maize (Zea mays L.).

Cadmium (Cd) is a highly mobile toxic element in soil-plant systems that interferes with plant growth and nutrient acquisition by modulations in the rhizospheric environment. The current study investigated the influence of maize roots on the medium pH, alterations in nutrient uptake, and impact on the plant's physiological attributes under Cd stress. Among the nine maize cultivars, subjected to Cd stress (9.15 mg/kg of sand), one was identified as Cd tolerant (3062-Pioneer) and the second as Cd sensitive (31P41-Pioneer). The selected maize cultivars were grown in nutrient solutions supplemented with 0, 10, 20, 30, 40, or 50 µM CdCl2 under controlled conditions and a starting pH of 6.0. The rhizospheric pH dynamics were monitored each day up to 3 days. Both cultivars caused medium basification; however, the response was different at low (10 and 20 µM) Cd treatments (sensitive cultivar caused medium basification) and at higher (50 µM) Cd treatment (tolerant cultivar caused medium basification). Furthermore, higher Cd was accumulated by the sensitive cultivar which was predominantly found in the roots. Higher Cd levels in the medium resulted in increased uptake and translocation of both Cd and K (in the tolerant cultivar) or only Cd (in the sensitive cultivar). Uptake of other nutrients (Ca, Zn, and Fe) was antagonistically affected by Cd stress in both cultivars. Moreover, Cd stress significantly impaired chlorophyll content, catalase activity, and total protein content; irrespective of the genotype. The malondialdehyde (MDA) content was found to increase, in both cultivars, together with Cd level. However, the extent to which Cd interfered with the studied attributes was more pronounced in the sensitive cultivar as compared to the tolerant one. It is concluded that the maize roots responded to Cd stress by initiating modulations of medium pH which might be dependent on Cd tolerance levels. The study results may help to develop strategies to reduce Cd accumulation in maize and decontamination of metal-polluted soil sediments.

Efficacy of silicon priming and fertigation to modulate seedling's vigor and ion homeostasis of wheat (Triticum aestivum L.) under saline environment.

Seed preconditioning, a short gun approach to modulate the effects of abiotic stresses on crop plants, has recently gained considerable attention of the researchers to induce salinity tolerance in agronomically important crops. The present study was conducted to explore the comparative efficacy of presowing seed priming with silicon (Si) and Si fertigation to modulate the wheat growth and ion dynamics. Seeds of wheat variety, PUNJAB-11, were sown in Petri plates having nutrient solutions with (120 mM) and without NaCl. Six levels of Si (0, 10, 20, 30, 40, or 50 mM), applied as sodium silicate (Na2SiO3), were tested either as a seed priming agent or as a supplement in the nutrient solution. Priming of seeds with Si mitigated the adverse effects of salinity stress on germination percentage, root as well as shoot length, dry and fresh weight. Application of Si either as preconditioning of seeds or addition in the growth medium resulted in reduced accumulation of sodium (Na(+)) in wheat seedlings under saline environment. Seedling's potassium (K(+)) contents either remained unaffected or decreased whereas calcium (Ca(2+)) contents decreased at all Si concentrations except at 30 mM when Si primed seeds were grown under salt stress. Addition of Si, under salt stress, in cultivation medium exerted a positive effect on seedling's K(+) and Ca(2+) contents. Silicon contribution to decontamination strategies was evaluated.