Flower senescence

Extract

[...] A lipoxygenase- independent senescence mechanism has been described in Alstroemeria peruviana, somewhat similar to the observations made in orchids where increases in lipoxygenase activity were absent following pollination. However, in this species lipoxygenase activity declined significantly throughout petal development and did not increase leading up to senescence. This is in contrast to some other ethylene-sensitive and -insensitive species where lipoxygenase activity peaks at early to midsenescent stages of development. In Alstroemeria, an ethylene-insensitive species, lipoxygenase activity could not be correlated with the loss of membrane semipermeability indicating that it falls into a new class of flower senescence. [...]

[...] Molecular changes Very little attention has been given to molecular changes from anthesis through senescence with the exception of one recent study. Most genes isolated from petals or corollas of ethylene-sensitive and insensitive species have been cloned from early to mid-senescent plant materials. Therefore, most of the transcripts of these genes are found to accumulate during senescence and not in the events leading up to senescence. A few of these genes have shown developmental regulation independent of senescence in both ethylene-sensitive and insensitive species, even though their highest transcript levels are observed during senescence. [...]

[...] These observations also suggest that they may play an important role in triggering flower senescence in both ethylene-sensitive and -insensitive petals and corollas. Flower senescence may therefore be due to the release of signaling molecules and/or changes in the lipid environment of a number of membranes residing enzymes. SUMMARY Cells maintain the ability to biosynthesize lipids well into senescence. In order to maintain floral structures for considerable amounts of time a lot of resources have to be expended by the plant. [...]

[...] Decreases in fluidity in turn are thought to lead to membrane malfunctions and ion leakage and ultimately senescence and death of the tissue. Other mechanisms responsible for the rigidification or decrease in fluidity of the membranes during petal development such as increased saturation of lipids, possibly due to lipid peroxidation, have been suggested. Indeed increasing levels of lipoxygenase activity and peroxidized lipids are observed from anthesis until early senescence in daylily. Lipoxygenases have been correlated to decreases in membrane fluidity and inhibitors of lipoxygenase activity prevent these membrane-fluidity changes indicating that they may play an important role in events leading up to senescence. [...]

[...] obvious external factor to affect flower longevity and as such this type of flower senescence is one of the most widely studied. Pollination leads to dramatic accelerated flower senescence in a number of commercially important plants. In some plants, however, pollination does not lead to flower senescence or may even prolong the life of the flower. The effect of pollination is most pronounced in long-lived flowers and seems absent from ephemeral flowers such as daylily and morning glory. Ethylene sensitive versus ethylene insensitive Flower senescence can be categorized as ethylene sensitive or ethylene insensitive based on the exogenous application of ethylene. [...]