Intra‐tissue Characteristics of Chloroplasts in the Lamina and Petiole of Mature Winter Leaf of Arum italicum Miller

Abstract

Abstract: Laminae and petioles from mature winter leaves of Arum italicum were studied in order to obtain information on the sun—shade intra‐tissue properties of chloroplasts. This inference was based on the: (1) micro‐ and submicroscopic characteristics of the chloroplasts, (2) cytochemical localizations of functional PS I and PS II, (3) pigment patterns and compositions, (4) immunolocalization of Rubisco, and (5) net photosynthesis. It was inferred that all the chloroplasts across the lamina had adaptations to intermediate shade conditions, without a sun‐shade dimorphism between the palisade and the spongy tissues. In the petiole, where normally‐structured chloroplasts were surprisingly present in the entire thickness of the organ, a structural and chemical dimorphism was found between the outer chlorenchyma and the inner aerenchyma where intermediate shade‐type and extreme shade‐type chloroplasts were present, respectively. However, some anomalies in the pigment composition were noted chiefly in the inner aerenchyma (low concentrations of β‐carotene and lutein, absence of zeaxanthin, presence of unusual pigments, for instance lutein epoxide, lutein cis‐isomer, and chlorophyllide a). The Rubisco immunolabelling in the outer chlorenchyma of the petiole 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 that 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.