Abstract
Intense and excessive (high) light can cause damage to chloroplasts through the generation of reactive oxygen species.
We examined the effects of high light induced oxidative stress on the chlorophyll biosynthesis pathway in etiolated and green (14 h-illuminated) cucumber cotyledons. When etiolated cotyledons were exposed to high light (1500-1600 µE/m2/s), the chlorophyll biosynthesis was completely stopped whereas in green cotyledons the chlorophyll biosynthesis rate was decreased. At an early stage of this treatment i.e. within first 2 h, we observed the accumulation of small amount of protoporphyrin IX in etiolated cotyledons. ALA synthesizing activities were also decreased in both etiolated and green cotyledons. This inhibitory effect was greater in etiolated than in green cotyledons and increased with duration of treatment. High light can have adverse effects on plant growth during early developing stages; therefore we will discuss whether high light mediated regulation of chlorophyll biosynthesis contributes for this effect.
