Environmental stress of higher plants monitored by the formation of monodehydroascorbate radicals with continuous-wave EPR

By electron paramagnetic resonance (EPR) inspection of leaves of spinach, maize, peas, wheat and conifer needles as well at room temperature with X-band spectrometer in theg = 2 region the photosignals I and II were observed. Plants exposed to unfavorable living conditions either in a green house or in the open country show in addition the typical hyperfine structure of monode-hydroascorbate (MDA). Careful inspection of these signals, for example, by studying the rise and decay kinetics, the exchange of the surrounding atmosphere or the impact of different chemical or physical stress reveals the mechanism responsible for the MDA production. Under all conditions applied the first reaction of green plants in stress situation was an enhanced concentration of MDA radicals which was built up by the reaction of reactive oxygen species either directly or by the action of enzymes. EPR inspection of the leaves of green plants can be directly performed without any time-consuming sample preparation. Therefore this method can be used for an early diagnosis of environmental stress.