The Effect of Bruising on Starch Degradation in Virginia Tobacco Leaves

The effect of bruising Virginia-type tobacco leaves on starch degradation during yellowing has been investigated. Bruising suppressed starch degradation in greenhouse-grown leaves completely and by about half in field-grown leaves. The increase in sugar levels which normally occurs during yellowing was also suppressed by bruising; in the greenhouse-grown leaves this suppression was complete but in the field-grown leaves it was only partial. As the greenhouse-grown plants ripened, the rate of starch degradation in unbruised leaves held in yellowing conditions decreased substantially. Bruising also suppressed the chlorophyll degradation which normally occurs during yellowing. However, in this case bruising produced a greater degree of suppression in the field-grown than in the greenhouse-grown Ieaves. As the greenhouse-grown plants ripened, the rate of chlorophyll degradation in unbruised leaves held in yellowing conditions increased substantially, in marked contrast with the behaviour of starch. Nicotine levels increased in the greenhouse-grown leaves as they ripened, but the levels were not affected consistently by bruising