Structural Changes in Primary Lenticels of olea Europaea and Cercis Siliquastrum During The Year

The structure of primary lenticels of the Mediterranean evergreen Olea europaea and the winter deciduous species Cercis siliquastrum was investigated during the year using scanning electron, conventional brightfield and epi-fluorescence microscopy. It was revealed that lenticels of O. europaea do not undergo significant structural changes over this time period. The filling tissue of O. europaea lenticels consists of fully-suberized cells that form small intercellular spaces. The air-exposed filling cells are replaced during spring and early summer by new early-suberized cells. Further notable structural modifications during the year were not observed. By contrast, lentice1s of C. siliquastrum possess a closing layer of suberized cells delimiting an underlying mass of non-suberized filling cells. During the period of high metabolie activity of the plant, i.e. during spring and early summer, the suberized closing layer is ruptured from the pressure exerted by the newly formed underlying cells. During late summer a new closing layer is formed, delimiting again the non-suberized underlying filling cells during winter. The possible role of lenticels in the gas exchange process is discussed. In both species the shade-adapted parenchyma cells of the cortex beneath lenticels shows bright red auto-fluorescence of chlorophyll, a phenomenon that is not yet fully understood.</jats:p