The properties and distribution of alpha-tocopherol oxidase in plants.

but also appeared to have a more complex basis than was originally evident (Fig. 1). Additionally, contents of plastochromanol, a closely related compound (Whittle et al., 1965), showed an interesting pattern (Fig. 2). Under vegetative conditions the contents of both y-tocopherol and plastochromanol exhibited clear daily rhythmic changes in concentration. Both compounds accumulated during the dark period and their contents fell rapidly again to a basal value at the beginning of each light period. Under inducing conditions, the vegetative daily rhythm of y-tocopherol was totally upset. During the longer dark period of the first day, y-tocopherol continued to accumulate, but the content did not fall to the basal concentration at the start of the following light period. Through the next two inducing cycles, contents remained high, well above vegetative ones, and the regular fluctuations did not occur. In contrast with this situation, the daily fluctuations in plastochromanol contents were not destroyed on transfer to inducing conditions. Instead, the vegetative pattern of accumulation in the dark, followed by rapid fall in the light, was maintained throughout the three cycles followed. It is clear that, although structurally similar, aand y-tocopherol and plastochromanol behave very differently with respect to photoperiod. a-Tocopherol contents are not significantly affected. The patterns of y-tocopherol and plastochromanol contents are, however, closely synchronized with photoperiod under vegetative conditions. Further, the synchronization of the y-tocopherol pattern is broken in leaves which are placed in inducing photoperiods, as if some ‘switching mechanism’ is operative, suggestive of a role in the mechanism of flower induction in Xanthium.