Flower senescence in this context will happen when it becomes more advantageous for the plant to construct a new flower – including renewed odds of getting pollinated – than to maintain an existing one. Flower senescence can therefore be defined as the events that lead to the death of flower parts signaling the end of an open and functional disseminator and/or receptor of pollen. It should be noted here that the most visible and largest flower part to senesce is the corolla or petals and that this organ will receive most attention in this chapter. However, other flower parts such as styles, anthers, and in the case of unpollinated flowers, ovaries, sepals and pedicels, will also in time senesce.
[...] Therefore, recognition of self and non-self pollen, and the rejection of self is essential in pollination-induced senescence. Although the early events, generally a small ethylene peak produced by the style, are the same in either type of pollination, further ethylene production is non-existent in self- incompatible pollinations. This observation indicates that complex recognition and rejection signals beyond ethylene are at play. Hormones All classical hormones, cytokinin, ABA, gibberellins, auxins and ethylene, have at one point or another been implicated in timing of flower senescence and their individual roles and possible interactions have not, by far, been settled. [...]
[...] The overall conclusion of these studies was that flower longevity can be significantly improved through classical breeding efforts often because improvements in flower longevity have not been focused on before. Carbohydrates Significant changes in carbohydrate levels can be observed throughout the development of petals and corollas. In most petals and corollas, starch, sucrose and a number of other sugars decline after anthesis in both cut and uncut. However, relatively high levels of sugars are maintained through senescence in several species. [...]
[...] In many cases the intensity and timing of these external stimuli dictate enhanced or delayed petal or corolla senescence. High temperatures, water stress, low light, UV light exposure, metal halide light exposure during production, high relative humidity, wounding of the stigma and severing from the plant have all been implicated in decreasing flower longevity. On the other hand, brief exposure to high temperatures after harvest, exposure to red light and low relative humidity during production delayed flower senescence. In most cases the exact mechanisms that lead to enhanced or delayed senescence are not known or highly speculative. [...]
[...] The precise time of flower opening followed by a predetermined time span to petal senescence has been established for a number of plant species with ephemeral flowers, suggesting that plants use their internal clock to dictate timing of senescence. However, the effect of light on longevity and ethylene production, or a circadian rhythm in ethylene production, very little is known about the mechanism that may involve the plants' internal clock in flower senescence. Interorgan communication A significant role in timing of senescence of petals and corollas has been attributed to the style and the gynoecium. [...]
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