Paramagnetic Manganese and Associated Resonances in Isolated Cucumber (Cucumis sativus L. var. long green) Cotyledons in Light and Dark

Electron spin resonance spectra of cucumber cotyledons showthat paramagnetic manganese exists in three different formsin biological systems. Different resonances appear along withthe manganese signal. Resonances due to copper ions appear alongwith the third peak of the manganese signal from the low-fieldside of the spectrum. Some photo-induced signals appear superimposedover the fourth peak of the manganese sextet corresponding tom/2. The first peak, however, remains unaffected by any detectableresonance and line broadening effects. Since signal height istaken as a measure of manganese concentration, the height ofthe fourth peak or averaging the height of all the six peaksmay give false results in biological systems. Manganese feedinghas a general promotive effect on all the six peaks of Mn(II)and the first peak shows most marked changes. The height ofthe first peak, therefore, can safely be taken as a measureof manganese concentration in a tissue. The resonances causingbaseline drift of the sextet disappear with the growth of thecotyledons in light. The loss of their paramagnetic propertymay either be due to complex formation or change in their redoxstate.