The amelioration of aluminium toxicity by silicon in wheat ( Triticum aestivum L.): malate exudation as evidence for an in planta mechanism

Abstract

Two wheat (Triticum aestivum L.) cultivars, one aluminium tolerant (Atlas 66) and one sensitive (Scout 66), were grown in a continuous-¯ow culture system (£pH 5.0) containing aluminium (0±100 lM) and silicon (0±2000 lM) in factorial combination. Treatment with silicon resulted in a highly signi®cant amelioration of aluminium toxicity as assessed by root growth in both cultivars. Amelioration was in¯uenced by wheat cultivar and silicon concentration, as 2000 lM silicon signi®-cantly ameliorated the toxic eects of 100 lM aluminium in Atlas 66, and only 5 lM silicon alleviated the eect of 1.5 lM aluminium on Scout 66. Nutrient medium pH was critical, as an amelioration by silicon was apparent only at pH > 4.2 for Atlas 66, and at pH > 4.6 for Scout 66. Silicon neither reduced levels of toxic aluminium species in the growth solutions, nor the amount of aluminium taken up by roots. In experiments to assess exudation of malate by Atlas 66 roots treated with 100 lM aluminium, the presence of 2000 lM silicon (pH 4.6) was found to have a negligible eect on exudation. In contrast, citrate, a known aluminium chelator, reduced aluminium-induced exudation of malate at 5±40 lM and completely inhibited it at 100 lM citrate. The results indicate that silicon does not reduce aluminium phytotoxicity as a result of aluminium/silicon interactions in the external media, and that the mechanism of amelioration has an in planta component.

Apoplastic Binding of Aluminum Is Involved in Silicon-Induced Amelioration of Aluminum Toxicity in Maize

“…7), but the exudation was not affected by Si. This result is consistent with Cocker et al (1998b). In their experiments to assess exudation of malate by roots of the wheat cv Atlas 66 treated with 100 mM Al, the presence of Si was found to have a negligible effect on exudation after 24 h of Al treatment.…”

“…Both mechanisms would lead to reduce Al concentrations in the apoplast. Cocker et al (1998b) proposed the formation of HAS in the apoplast, so that Al would be transferred into a nonphytotoxic form, without reducing the Al content. This conclusion is supported by the results of Hodson and Sangster (1993).…”

Laser-Induced Breakdown Spectroscopy and Phytolith Analysis: An Approach to Study the Deposition and Distribution Pattern of Silicon in Different Parts of Wheat (Triticum aestivum L.) Plant

“…Silicon reportedly increases crop quality and yield, protects the plants against fungal infection, insects, pest attack and increases disease resistance [5,17,26,27,38]. Silicon can also alleviate imbalance between zinc and phosphorus supply as well as decrease the toxic effect of aluminum in hydroponic culture in several species [3,9,44,56]. Similar applications of silicon have also been found in other cereals and dicotyledonous plants [11,25,41,48,53].…”

“…The role of silicon is reported to reduce the effects of salt stress, drought stress, metal toxicity, nutrient imbalance and radiation damage [4,8,9,13,44,49,50]. Silicon reportedly increases crop quality and yield, protects the plants against fungal infection, insects, pest attack and increases disease resistance [5,17,26,27,38].…”

Effects of silicon on copper toxicity in Erica andevalensis Cabezudo and Rivera: a potential species to remediate contaminated soils

“…5,18,19 It is the only element that does not cause serious injury when present in excess. 4,5 Silicon plays a significant role in minimizing the toxic effects of excess of metals like Al, 7,12,14,20,21 Cd, 15,22,23 Mn, [24][25][26][27] and Zn. 6,8 In these investigations, different mechanisms were proposed to explain the Si-associated alleviation of metal toxicity.…”