Silicon deposition in roots minimizes the cadmium accumulation and oxidative stress in leaves of cowpea plants

Abstract

Silicon (Si) frequently accumulates in plants tissues, mainly in roots of dicotyledons, such as cowpea. By contrast, Cadmium (Cd) is a metal that is extremely toxic to plant metabolism. This research aims to investigate if the deposition of Si in root can reduce Cd contents and minimize its negative effects on leaves, measuring gas exchange, chlorophyll fluorescence, antioxidant metabolism, photosynthetic pigments and growth, which may explain the possible role of Si in the attenuation of Cd toxicity in cowpea. This study had a factorial design, with all factors completely randomized and two Cd concentrations (0 and 500 µM Cd, termed as - Cd and + Cd, respectively) and three Si concentrations (0, 1.25 and 2.50 mM Si). Si reduced Cd contents in the roots and in other plant organs, such as stems and leaves. The Si contents were highest in roots, followed by stems and leaves, which was explained by the passive absorption of Si. The application of Si promoted increase in both the macro- and micronutrient contents in all tissues, suggesting that Si mitigates the effect of Cd on nutrient uptake. Si attenuated Cd-mediated effects on light absorption of photosystem II (PSII), increasing the effective quantum yield of PSII photochemistry and the electron transport rate. Additionally, toxic effects induced by Cd on gas exchange were mitigated by the action of Si. Plants treated with Cd + Si showed increase in the activities of antioxidant enzymes and reductions in oxidant compounds; these modifications were promoted by Si via detoxification mechanisms. Increases in the photosynthetic pigments and growth of plants treated with Si and exposed to Cd stress were detected and were due to the reduced deterioration of cell membranes and maintenance of chloroplasts, which had positive repercussions on growth and development. This study validated the hypothesis that the accumulation of Si in roots induces benefits on metabolism and alleviates the toxic effects caused by Cd in leaves of cowpea.

Aluminum stress tolerance in potato genotypes grown with silicon

“…1 and 2). This beneficial effect of Si on plant growth was reported by several studies in the literature (Shi et al 2010;Gu et al 2012;Pereira et al 2018b). This increase in the growth of shoot may be related to the Si effect on mineral absorption, resulting in increased availability of some nutrients to plants and hence increasing biomass production (Pavlovic et al 2013).…”

The effect of silicon (Si) on the growth and nutritional status of Schizolobium amazonicum seedlings subjected to zinc toxicity

“…It also enabled increased availability and assimilation of these minerals, as well as increased plant growth. The action of Si as mitigator of nutrient content decrease in plants subjected to metal toxicity was also observed in O. sativa (Mehrabanjoubani et al, 2015, Wang et al, 2015, E. urophylla (Pinto et al, 2009) and V. unguiculata (Pereira et al, 2018).…”

“…The addition of 1.5 mM of Si to the nutrient solution mitigated the macro and micronutrient content decrease in S. amazonicum plants; the reduction rate in Ca, P, Mg, Fe, Mn and Cu concentrations decreased to 14%, 20%, 21%, 18%, 34% and 35% in the shoot and to 9%, 33%, 23%, 25%, 26% and 42% in the roots, respectively. The low nutrient accumulation caused by the excess of Zn is a toxicity feature of metals that can delay the vegetative growth of plants (Pereira et al, 2018, Santos et al, 2018, Rizwan et al, 2019. Marques and Nascimento (2014) observed decreased K, Mg, P, N, Ca, Cu, B, Fe, Mo and Mn accumulation in R. communis plants subjected to toxic Zn levels.…”

“…The adopted Zn concentrations were: 1 (control), 150, 300 and 600 μM in the form of ZnSO 4 .7H 2 O, whereas Si concentrations were: 0 and 1.5 mM in the form of Na 2 SiO 3 •5H 2 O. Zinc levels used in the current study were based on Zn concentrations that caused toxicity symptoms in Psidium guajava guajava (Natale et al, 2005), Eucalyptus maculata and Eucalyptus urophylla (Pinto et al, 2009) and Thlaspi caerulescens (Brown et al, 1995). The herein adopted silicon concentration was based on the ones that reduced the toxicity caused by metals in Vigna unguiculata (Pereira et al, 2018), E. urophylla (Pinto et al, 2009) and Zea mays (Šimková et al, 2018). Seedlings were subjected to the treatments for 30 days (from the 41 st to the 70 th experimental day).…”

“…Plant roots can absorb it in silicic acid [Si(OH) 4 ] form and translocate it to the shoot through the xylem (Yang and Zhang, 2018). Although Si is not seen as an essential element, its beneficial effects on biotic and abiotic stress, such as the one caused by heavy metal toxicity, were found in different species (Haddad et al, 2018, Pereira et al, 2018. This beneficial nature can result from metal immobilization in the soil, antioxidant enzyme activity stimulation, and from the co-precipitation, complexation and compartmentalization of silicon/metal ions in plant tissues (Liang et al, 2015, Garg andSingh, 2018).…”