Browsing by Author "Rowland, Ronelle"
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- ItemResponses of sugarcane to aluminium toxicity(Stellenbosch : Stellenbosch University, 2006-03) Rowland, Ronelle; Cramer, M. D.; Botha, F. C.; Watt, D. A.; Stellenbosch University. Faculty of Agriscience. Dept. of Genetics.ENGLISH ABSTRACT: The aims of this study were (1) to determine whether N03- orNH4+ nutrition could influence the effect of Al on N12 and N19 sugarcane plants grown in sand or hydroponic medium and (2) to assess whether the different root environments of sand and hydroponically cultured plants could influence the effect of Al on Nl2 and N19 sugarcane plants supplied with N03- or NH/ nutrition. N12 and N19 sugarcane was grown in sand and hydroponic culture with and without Al and with either N03- or NH4+as N source. Biomass accumulation, tissue N, P and Al and root assimilation of 14C02 supplied to the root system were measured. Both N12 and N19 sugarcane plants were found to be relatively Al tolerant (tolerating up to 1 mM Al). This lack of effect of Al on plant growth might be due to amelioration of Al-toxicity in sugarcane by the adequate supply of carbon skeletons from the C4 photosynthetic pathways of sugarcane. The supply of carbon skeletons may enable both cultivars to exude large amounts of organic acids into the rhizosphere, which confers a dual advantage to these plants. Organic acids can form soluble complexes with Al thus preventing its entry into the roots and can form soluble complexes with nutrients (cations), which makes some nutrients (e.g. P) more available for plant uptake. The availability of carbon in the root system is dependent on the N source. Increased growth of Al treated plants supplied with NH4 +, relative to those grown on N03-, might be due to the capacity of C4 photosynthesis to meet the needs for both the assimilation of NH4 + into amino acids and the synthesis/excretion of organic acids for Al-detoxification. The fact that growth was improved with NNH4 + and Al may indicate that NH4 + and Al cations compete for access to the root tissue resulting in an increase in root activity, organic acid exudation and nutrient uptake. It was postulated that sand-grown plants would be less influenced by Al than hydroponic plants because organic acids can form a protective sheath that shields the root apex from the toxic Al cations in sand due to the relative lack of mobility of the soil solution. However, Al increased the growth of NH4 +-fed hydroponically grown plants more than that of NH4 +-fed sand grown plants. Thus we did not find evidence to support our expectation that the roots of the hydroponically grown plants would be more exposed to Al due to nutrients and organic acids being uniformly distributed in the growth solution compared to sand grown plants.