Influence of Age and Microclimate on the Photochemistry of Rhododendron Maximum Leaves Ii. Chloroplast Structure and Photosynthetic Light Response

The influence of age on chloroplast structure and photosynthetic light response of Rhododendron maximum L. was studied in three different microhabitats. The three microhabitats constituted a gradient of low, intermediate, and high irradiance levels. The most dramatic change in chloroplast structure with increasing age was the proliferation of the number and size of plastoglobuli. The magnitude and age specific rate of chloroplast occlusion by plastoglobuli increased in habitats with higher irradiance. Photosynthetic responses to light differed among the age categories of leaves. Light saturated photosynthesis and quantum yield decreased as leaves aged. However, in high light environments the rate of reduction of quantum yield or light saturated photosynthetic rate was more rapid than in the low light environment. The quantity of plastoglobuli increased in association with reduced light reaction capacity. The presence and abundance of plastoglobuli in R. maximum chloroplasts and their association with reduced photosynthetic performance indicates that the photosynthetic apparatus of the R. maximum chloroplast is sensitive to photodestruction by high irradiance: commonly a winter phenomenon in these environments.