Desiccation in Conifer Leaves: Anatomical Changes and Determination of the Lethal Level

Abstract

1. The gradual drying of excised leaves of Austrian and white pine (Pinus nigra Arn., var. austriaca Asch. et Gr. and P. strobus L., respectively) is accompanied by marked shrinkage of cells of the chlorenchyma, transfusion tissue, and endodermis. Rehydration of such leaves may result in irreversible pseudoplasmolysis if dehydration is carried too far, even at the slow rate of dehydration and rehydration described. The color change from grass green to light green during desiccation appears to have a physical rather than a chemical cause, although it is usually related to loss of a positive tetrazolium test and reduction to zero of the CO2 released. 2. The rate of CO2 release from recently thawed, excised leaves of Austrian pine declined rapidly at first, leveled off, and then in a few days increased before decreasing to zero if they were dried rapidly. More slowly dried needles did not show this pronounced rise. Illuminating the needles between measurements caused a temporary increase in CO2 released. Mor...