INTRA-TISSUE CHARACTERISTICS OF CHLOROPLASTS IN THE LAMINA AND PETIOLE OF MATURE WINTER LEAF OF ARUM-ITALICUM MILLER

Laminae and petioles from mature winter leaves of Arum italicum were s tudied in order to obtain information on the sun-shade intra-tissue pr operties of chloroplasts. This inference was based on the: (1) micro- and submicroscopic characteristics of the chloroplasts, (2) cytochemic al localizations of functional PS I and PS II, (3) pigment patterns an d compositions, (4) immunolocalization of Rubisco, and (5) net photosy nthesis. It was inferred that all the chloroplasts across the lamina h ad adaptations to intermediate shade conditions, without a sun-shade d imorphism between the palisade and the spongy tissues. In the petiole, where normally-structured chloroplasts were surprisingly present in t he entire thickness of the organ, a structural and chemical dimorphism was found between the outer chlorenchyma and the inner aerenchyma whe re intermediate shade-type and extreme shade-type chloroplasts were pr esent, respectively. However, some anomalies in the pigment compositio n were noted chiefly in the inner aerenchyma (low concentrations of p- carotene and lutein, absence of zeaxanthin, presence of unusual pigmen ts, for instance lutein epoxide, lutein cis-isomer, and chlorophyllide a). The Rubisco immunolabelling in the outer chlorenchyma of the peti ole was similar to that in the lamina, while it was very scant in the inner aerenchyma. Net photosynthesis in the petiole was about 75% of t hat recorded in the lamina. These data suggest that the petiole of the mature winter leaf of A. italicum closely co-operates with the lamina for enhancing light capture and utilization.