“…During grain filling, in heat stressed bread wheat genotypes, Ca assimilation to the shoots and spikes can increase (Dias et al, 2009d), possibly accumulating in the citosol, alleviating heat injury (Biyaseheva et al, 1993;Palta, 1996;Gong et al, 1998;Jiang and Huang, 2001), increasing cellular survival (Bamberg et al, 1998;Gong et al, 1998) and limiting oxidative damage (Larkindale and Knight, 2002), namely Chl photodestruction, as also found by Jiang and Huang (2001), working with heat stressed Festuca arundinacea L. and Poa pratensis L. In bread wheat genotypes, Ca accumulation also seems to be linked with a higher tolerance to heat stress, possibly because this nutrient can shield chlorophylls from photodestruction (Jiang and Huang, 2001;Dias et al, 2009d) and maintain stomata functioning (Webb et al, 1996;Hare et al, 1998), thus attenuating the heat stress effects through transpiration (Palta, 1996). Nevertheless, although Ca bonds the phosphate and carboxylate groups of phospholipids and proteins, at the membranes surface of plant cells (Caldwell and Haug, 1981;Legge et al, 1982), this nutrient accumulation is not coupled with the maintenance of the selectivity of membrane permeability (Dias et al, 2009d), as higher tolerance to heat stress in bread wheat follows a different pattern relatively to the Ca metabolisms in sugar beet and potato (Cooke et al, 1986;Coria et al, 1998). Calcium and Mg might also regulate cellular pH and cationanion stability (Marschner, 1995), yet during plant growth of some plant species, Mg 2+ uptake can be depressed by Ca 2+ (Marschner, 1995), unbalancing photosynthetic carboxylations (Günther, 1981;Bergmann, 1992;Schoefs and Bertrand, 1997) and isoprenoids (Jiang and Huang, 2001) accumulation.…”