Articles
INFLUENCE OF EXOGENOUS SUGARS ON THE EVOLUTION OF SOME SENESCENCE PARAMETERS OF PETALS
A supply of exogenous sugar (under conditions permitting their transfer to the various organs of the floral branch) delays the onset of senescence.
Exogenous glucose delays proteolysis and promotes protein and amide synthesis.
The sugar supply preserves the enzymatic activities involved in the sucrose biosynthesis (glucose-6P-isomerase, sucrose-P-synthetase, sucrose synthetase). The glucose supplied is immediately converted into sucrose (totally for the rose, partly for the carnation), which seems to be the transport form of sugar.
Sucrose synthesis is therefore a significant step in the transfer of sugars to the petals.
The occurrence of the ethylene peak (characteristic of senescence), the massive exudation of solutes (indicating a loss of membrane integrity), and the degradation of phospholipids are delayed by glucose.
But although the provision of energy is a necessary condition for the survival of petals (property used in the preparation of preservatives), it is not sufficient to explain senescence.
At the stage of maximal withering, the petals are still rich in hexoses.
It is not a lack of substrate which induces the onset of senescence.
An hypothesis is put forth to explain the toxicity of sugar accumulation, in relation to the role played by free radicals.