Effect of xenon on the excited states of phototropic receptor flavin in corn seedlings

The chemically inert, water-soluble heavy atom gas, xenon, at millimolar concentrations specifically quenches the triplet excited state of flavin in solution without quenching the flavin singlet excited state. The preferential quenching of the flavin triplet over the singlet excited state by Xe has been established by showing that the flavin triplet-sensitized photooxidation of NADH is inhibited while the fluorescence intensity and lifetime of flavin are not affected by Xe. The phototropic response of corn seedlings in an atmosphere of 90% Xe and 10% O2 was compared with that in the 90% N2 plus 10% O2 mixture. No significant inhibition of phototropism and geotropism by Xe was observed, suggesting that a flavin singlet state is more likely involved than the triplet state in the primary photoprocess of phototropism in corn.