Annals of Botany 74: 389-396, 1994
© 1994 Annals of Botany Company
Seasonal Changes in the Pattern of Assimilatory Enzymes and of Proteolytic Activities in Leaves of Juvenile Ivy
Institute of Plant Physiology, University of Bern, Altenbergrain 21, CH-3013 Bern, Switzerland
Ivy growing under natural conditions is an interesting plant to study the influence of external (e.g. temperature, light) and internal (e.g. source/sink relations) factors on leaf metabolism. Leaves of this evergreen plant are subject several times to seasonal changes. The contents of selected assimilatory enzymes were well conserved throughout the winter indicating that ivy leaves are probably able to make use of short periods with higher temperatures and to immediately restart growth in spring. Total proteins and carbohydrates increased considerably between February and May before the emergence of the new leaf generation. The increase in the content of non-structural carbohydrates was due to the accumulation of starch, while soluble sugars peaked in winter and decreased in spring. From May onwards, the assimilates were retranslocated to the emerging young plant parts. Marked seasonal changes in the peptide hydrolase pattern were observed. All exo- and endopeptidases investigated were minimal during summer suggesting that the net protein remobilization from older leaves was not based on an increase in the level of these major peptide hydrolases. Source/sink interactions on a whole plant level seem to be decisive in the regulation of seasonal changes in the pattern of assimilatory enzymes and of proteolytic activities. Since ivy leaves remain active for several years, the changes must be reversible and occur repeatedly during the life-span of a particular leaf.Copyright 1994, 1999 Academic Press
Hedera helix L., ivy, peptide hydrolase, assimilatory enzyme, low temperatures, retranslocation