High temperature during grain filling stage is the single most important factor that limits the productivity of wheat. Therefore, studies on enzymes that are implicated on thermotolerance during grain development stages are important. Nine homozygous genotypes of wheat (Triticum aestivum L. em. Thell)—PBW 343, WH 283, WH 542, PBW 435, UP 2,565, UP 2,425, EIGN1, EIGN8 and Raj 3,765—and six F1 crosses—PBW 343 x WH 283, PBW 343 x WH 542, PBW 343 x PBW 435, UP 2,565 x UP 2,425, EIGN 1 x Raj 3,765 and EIGN 8 x UP 2,425—were grown in the experimental areas of CCSHAU, Hisar, under normal- and late-sown environments. Changes in protein profiles, based on the banding pattern of isozymes for Superoxide Dismutase (SOD) and Malate Dehydrogenase (MDH), were studied. Based on the banding pattern of SOD isozyme, three isomers of different Rf values, 0.49, 0.75 and 0.85 in normal-sown and 0.84 and 0.87 in late-sown (high temperature condition during grain filling stages), were observed. The band of Rf value 0.75 was found only in the case of EIGN 1 of very dark intensity and light dark intensities in Raj 3,765 and EIGN 8, while in the case of F1s, very dark intensity band in PBW 343 x WH 542 and light dark intensities in PBW 343 x PBW 435 and UP 2,565 x UP 2,425, were observed. Based on the banding pattern of MDH, 4 bands of Rf values, 0.55, 0.67, 0.69 and 0.75 in normal-sown and three bands of Rf values 0.55, 0.75 and 0.82 for late-sown conditions, were observed. The Rf value of 0.82 band was observed only in the case of late-sown among the genotypes PBW 435 (light intensity), UP 2,425, EIGN 1 and EIGN 8 (all three with dark intensity) and F1 crosses PBW 343 x WH 283 (very light intensity, PBW 343 x WH 542 dark intensity), PBW 343 x PBW 435 (dark intensity) and UP 2,565 x UP 2,425 (light intensity). The implications of the results are discussed in the light of the role of enzymes in terminal heat stress in wheat.

Modern cultivars, although well adapted to optimum conditions, are not usually tolerant to sporadic environment fluctuation and temperature extreme. The terminal heat stress can be a problem for up to 40% of the irrigated wheat growing areas in the developing world. High temperature (> 28 °C) during grain filling stage is the single most important factor that limits the productivity of wheat. Starch and protein are the major constituents of mature wheat grain. Environmental stress is the major limiting factor in plant productivity. The antioxidant defence mechanism is a part of heat stress adaptation. Much of the injury to plants is caused by the stress exposure which is associated with oxidative damage at the cellular level. In plants, the highly energetic reactions of photosynthesis and abundant oxygen supply make the chloroplast particularly a rich source of ROIs. Efficient removal of ROIs from chloroplasts is critical, since H₂O₂ concentration as low as 10 mm can inhibit photosynthesis by 50% (Kaiser, 1979). Antioxidant systems of plant chloroplasts include enzymes, such as Superoxide Dismutase (SOD) and Ascorbate peroxidase (APX), and nonenzymatic components, such as ascorbic acid and glutathione. Lei et al. (2005) have reported possible involvement of antioxidant enzymes in the cross tolerance of the germination/growth of wheat seeds to salinity and heat stress. Likewise, Malate Dehydrogenase (MDH) participate in the process of production of ATP and play a direct and key role in the synthesis of starch and hence grain development.

Nine genetically diverse homozygous genotypes of wheat (Triticum aestivum L. em. Thell), viz., PBW 343, WH 283, WH 542, PBW 435, UP 2,565, UP 2,425, EIGN1, EIGN8 and Raj 3,765, along with six F1 crosses, viz., PBW 343 x WH 283, PBW 343 x WH 542, PBW 343 x PBW 435, UP 2,565 x UP 2,425, EIGN 1 x Raj 3,765 and EIGN 8 x UP 2,425, were grown in the experimental area of CCSHAU, Hisar, during 2007-08 under two dates of sowing—normal-sown (E₁-November 24, 2007) and late-sown environments (E₂-December 26, 2007). Changes in the protein profiles having isozymic activity based on the banding pattern for SOD as per Goldberg (1963), Davis (1964) and Ornstein (1964) and for MDH as per Laemmli (1970) and Rucinska et al. (1999) were recorded at 28 days post-anthesis stages in parents and in F1s.

Genetics & Evolution Journal, Superoxide Dismutase, Malate Dehydrogenase, Homozygous Genotypes, Environmental Stress, Grain Development, Electrophoresis, Banding Patterns, Thermoprotection Mechanisms, Noncyclic Photophosphorylation, Antioxidant Systems.