I. Heat stress in Triticum: kinetics of Ca and Mg accumulation

Abstract

In heat stressed genotypes of Triticum aestivum L. (Sever and Golia) and Triticum turgidum subsp. durum (Acalou and TE 9306), chosen according to its genetic background diversity, Ca and Mg accumulations were correlated with its photosynthetic performance. It was found that with high temperatures the concentrations of Ca increased in the shoots, whereas the accumulation of Mg augmented only in bread wheat genotypes. Under heat stress, the pattern of electrolytes release in Golia and Acalou remained similar, but the extrusion rates became higher in Sever. During grain filling, the levels of total chlorophylls decreased in the heat stressed genotypes (excepting in Sever). In all the Triticum genotypes, stomatal conductance and the net carboxilation rate displayed similar trends. After anthesis, the net carboxilation rates did not vary in Acalou and TE 9306 but changed significantly in the heat stressed bread wheat, being found antagonistic patterns in both genotypes. During grain filling, the mean internal CO 2 concentration only increased significantly in the heat stressed Golia. In Golia and TE 9306, the transpiration rates didn't vary between the control and heat stress treatments, but in Sever and Acalou, significant increases were found. Our data identified synergistic patterns among Ca, Mg, chlorophylls accumulation, and stomatal conductance, whose implications on photosynthesis are discussed.

Improving Yield Components and Desirable Eating Quality of Two Wheat Genotypes Using Si and NanoSi Particles under Heat Stress

“…This may be attributed to the influence of heat stress induced by late sowing on Ca 2+ mobilisation during grain filling. In this respect, [ 113 ] reported that Ca 2+ assimilation to the shoots and spikes increased in heat-stressed wheat, alleviating heat injury [ 114 ] and limiting oxidative damage [ 115 ].…”

“…In addition, changing the sowing date influenced the mineral contents of wheat straw ( Table 10 ). The level of Ca 2+ content significantly increased in late-sown wheat straw as a mechanism of heat tolerance in wheat, which is associated with the maintenance of net carbon assimilation rates [ 113 ]. On the other hand, the K + level increased in late-sown wheat straw ( Table 10 ).…”

Bread and durum wheat tolerance under heat stress: A synoptical overview

“…In this context, Mg 2+ strongly interacts with nucleophilic ligands (i.e., phosphoryl groups) through ionic bonding (Günther, 1981), but under heat stress, although might stabilize the covalent bonds of chlorophylls, its depression might limit the synthesis of this molecule (Marschner, 1995). Nevertheless, it has been reported (Dias et al, 2009d) that, in the particular case of the life wheat cycle of most genotypes, Mg uptake is not significantly depressed by Ca and, therefore, an antagonistic interaction between these nutrients accumulations in the shoots is not expected to develop. Moreover, shoot Mg accumulation might display a synergistic pattern with chlorophylls accumulation during grain filling (Bergmann, 1992;Schoefs and Bertrand, 1997;Dias et al, 2009d), but at maturity, as the rate of Mg translocation from the roots tends to decrease (Dias et al, 2009d), the inhibition of chlorophylls accumulation might occur (Dias et al, 2009d).…”

“…Nevertheless, it has been reported (Dias et al, 2009d) that, in the particular case of the life wheat cycle of most genotypes, Mg uptake is not significantly depressed by Ca and, therefore, an antagonistic interaction between these nutrients accumulations in the shoots is not expected to develop. Moreover, shoot Mg accumulation might display a synergistic pattern with chlorophylls accumulation during grain filling (Bergmann, 1992;Schoefs and Bertrand, 1997;Dias et al, 2009d), but at maturity, as the rate of Mg translocation from the roots tends to decrease (Dias et al, 2009d), the inhibition of chlorophylls accumulation might occur (Dias et al, 2009d). In durum wheat, further supporting a different extent of tolerance (Al-khatib and Paulsen, 1989;Maçãs et al, 1999Maçãs et al, , 2000Dias et al, 2009d;, at maturity Ca and Mg shoot accumulation in sensitive genotypes to heat stress might parallel with a diminishing chlorophyll content and a decreased net carbon assimilation rate (Dias et al, 2009d).…”

“…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.…”