Water translocation inKalanchoë daigremontianaduring periods of drought

Abstract. Kalanchoë daigremontiana strongly reduced daily water loss within 6 d of drought using CAM to restrict transpiration and net CO 2 uptake to the dark period. Water translocation from old to young leaves of the plant was an additional mechanism which reduced the negative effects of drought on the water relations of young leaves. Excision of old leaves after 7–9 d of drought resulted in a decrease in the water content of young leaves. This was observed despite a decrease in transpirational water loss from young leaves. Water content in young leaves increased slightly in plants with all their leaves in place. The dry weight of young leaves clearly increased during the experimental period when old leaves were present, but it remained relatively constant in plants without old leaves. Obviously, in addition to water, solutes were transported from old to young leaves of the plant via the phloem. Xylem tension was higher in young compared to old leaves; thus, water translocation could have occurred via xylem elements. Since transport of organic matter in the phloem is also linked to water flow, phloem transport additionally may contribute effectively to the balance of the water budget in young leaves.