Biotic and abiotic stress responses in wheat (Triticum aestivum L.)

Information on physiological and biochemical responses of plants to environmental and biotic stress factors would help in understanding the intrinsic mechanisms of plants. This information would also aid in the selection and improvement of germplasm. This study focuses on the effects of biotic (Russian wheat aphid, Diuraphis noxia (Mordvilko)) and abiotic (jasmonic acid-methyl ester) stress factors on calli cultures and seedlings of wheat (Triticum aestivum L.) genotypes.; Callus culture growth patterns and protein profile modifications in resistant (PI 137739) and susceptible ('Stephens') genotypes of wheat were induced by fractions from D. noxia extracts. Growth of resistant callus was consistently higher than the susceptible callus. Fresh callus weight of PI 137739 was increased 20% in fraction 2 and 45% in fraction 3 treatments compared with 'Stephens'. Exposure of callus cultures to D. noxia extract resulted in alteration of several polypeptides in PI 137739 and 'Stephens' calli. The differences between the protein profiles of resistant and susceptible calli indicated a potential response to D. noxia extract stress.; Changes in the biological processes of D. noxia and resistant and susceptible wheat genotypes were studied. Varying densities of aphids were used in time-course experiments monitoring modifications in biological processes of the insects and plants. Reproductive rates and population development of D. noxia were significantly higher when fed on the susceptible cultivar 'Stephens' compared with resistant genotypes, PI 137739, PI 140207, and PI 262660. Reproductive rates of D. noxia significantly decreased as aphid density and length of aphid feeding increased. However, D. noxia populations increased as aphid density and length of aphid feeding increased. A significant reduction in total chlorophyll content was observed in resistant genotypes after aphid feeding and could have been caused by increased aphid probing on resistant genotypes. Diuraphis noxia feeding caused modifications in protein profiles of both resistant and susceptible genotypes. Increased expression of {dollar}approx{dollar} 32.0, 33.0, and 35.0 kD polypeptides in the resistant genotype might play a role in the plant defense mechanism.; Jasmonic acid-methyl ester (JA-Me) is a plant growth substance that promotes leaf senescence, and induces defense and novel proteins in plants. The effects of JA-Me on chlorophyll content and protein profile modifications of D. noxia resistant and susceptible wheat genotypes were examined. Jasmonic acid-methyl ester treated leaf segments showed yellowing and senescence. There was a greater reduction in chlorophyll content of the JA-Me treated 'Stephens' compared with PI 137739. Expression of {dollar}approx{dollar} 34.5 and 96.0 kD polypeptides were enhanced in JA-Me treated leaf segments of both genotypes. In the resistant genotype, 50 {dollar}mu{dollar}M JA-Me induced the appearance of a {dollar}approx{dollar} 47.0 kD protein. Western blot analysis indicated that the {dollar}approx{dollar} 96.0 kD protein was cross-reactive with antiserum to lipoxygenase. The novel proteins induced by JA-Me treatment may be involved in leaf senescence and the plant defense mechanism.