ALUMINUM EFFECTS ON PHOTOSYNTHESIS AND ELEMENTAL UPTAKE IN AN ALUMINUM-TOLERANT AND NONTOLERANT WHEAT CULTIVAR

The effects of aluminum (Al) on photosynthesis and elemental uptake we re studied in two wheat cultivars (Triticum aestivum L. cvs Yecora E, Nestos) differing in their tolerance to Al. Concentrations of calcium (Ca), magnesium (Mg), potassium (K), and iron (Fe) in the plant tissue s of both cultivars grown in nutrient solutions (pH 4.5) decreased at all Al levels (0, 37.1, 74.1, and 148 mu M). The tolerant cultivar Yec ora E retained larger concentrations of all elements measured in roots and above ground parts compared with the non tolerant cultivar Nestos . Concentrations of Ca and Mg in leaves of the cultivar Nestos under h igh Al treatment were within the deficiency range. Changes in the shap e of the chlorophyll fluorescence induction curves showed that Al-stre ss altered thylakoid photofunctioning even in the more tolerant cultiv ar. Aluminum stress resulted in partial inhibition of photosynthetic e lectron transport at photosystem II and closure of photosystem II reac tion centers. Chloroplast elemental loss and concomitant intrathylakoi d acidification are postulated as mediating mechanisms for Al stress-i nduced inhibition of photosynthesis.