Infiltration of wheat (Triticum aestivum L.) seedling leaves with excess of nitrate, nitrite, or the NO donor sodium nitroprusside leads to increase both in content of hydroperoxide and activity of peroxidase and decrease in superoxide dismutase (SOD) activity in the leaf apoplast. Polymorphism of extracellular peroxidases and the presence of Cu/Zn-SOD have been shown in apoplast. Using an ESR assay, a considerable increase in the level of NO following infiltration of leaf tissues with nitrite has been demonstrated. These data suggest development of both oxidative and nitrosative stresses in leaves exposed to high levels of nitrate or nitrite. A possible interplay of NO and reactive oxygen species in plant cells is discussed.

The effect of exogenous abscisic acid and cAMP on synthesis of soluble proteins in wheat caryopses in drought has been studied. Both compounds affected the formation of the polypeptides whose synthesis was stimulated by dehydration: they increased the incorporation of the label into polypeptides of 13, 15, and 26 kD and decreased the incorporation of the label into polypeptides of 14, 64, and 77 kD. Abscisic acid and cAMP increased the level of the incorporation of [(14)C]leucine into the low-molecular-weight polypeptides of 12, 17, and 19 kD whose synthesis was suppressed by drought. These data suggest that the cyclic adenylate signal system is probably involved in the effect of abscisic acid on protein synthesis in drought.

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All investigated exogenous phytohormones (jasmonic, salicylic, and abscisic acids) induced the appearance of (14)C-label in a polypeptide with molecular mass 29 kD that was not found in the control; these acids also increased [(14)C]leucine incorporation into a 25-kD polypeptide and decreased such incorporation into a 45-kD polypeptide. This can be considered as a nonspecific response of the plants to the action of these hormones. Salicylic and abscisic (but not jasmonic) acids induced the synthesis of a 19-kD polypeptide, and jasmonate induced the synthesis of a 96-kD polypeptide.

The effect of salicylic acid on the content of soluble proteins and individual polypeptides in Tatar buckwheat Fagopyrum tataricum calluses differing in ability for morphogenesis was studied. Changes in the protein composition of the calluses cultivated in the dark and in the light indicated the higher sensitivity of the non-morphogenic callus. Different response of callus cultures to salicylic acid and conditions of cultivation (light, darkness) is suggested to be associated with the antioxidant defense system, which is, in particular, characterized by the hydrogen peroxide content in the calluses. Salicylic acid increased the H2O2 content in non-morphogenic calluses more strongly than in morphogenic calluses, and the difference was more significant for the calluses cultivated in the light.