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

Abstract

Gradual drying of excised leaves of Pinus nigra var. austriaca and P. strobus is accompanied by marked shrinkage of cells of the chlorenchyma, transfusion tissue, and endodermis. Rehydration may result in pseudoplasmolysis if drying proceeds too far. The rate of CO2 released from excised P. nigra needles as measured in a constant-recording infrared gas analyzer continued fairly steadily for about 25 days when dried out slowly, then declined to zero in about 10 more days. When dried somewhat more rapidly a rise in the CO2 released was observed be-fore the final decline. This rise was accentuated by illumination. The tetrazolium chloride test became weaker before the CO2 rate began to decline. In healthy leaves the tetrazolium test was positive in all living cells and also in the resin of the resin ducts. The test persisted longest in cells inside the endodermis with slow drying. Allium tissue did not give the test when cooled to -14[degree]C, boiled, or dried and rehydrated slowly. The test itself caused a decrease in the rate of growth of Allium roots but was much easier to use as a test for viability than a fluorochrome dye. The lethal level in conifer leaves was concluded to be a definite zone of deterioration as drying proceeded, but to vary somewhat with treatment.