A Cellular Timetable of Autumn Senescence

Abstract

We have studied autumn leaf senescence in a free-growing aspen (Populus tremula) by following changes in pigment, metabolite and nutrient content, photosynthesis, and cell and organelle integrity. The senescence process started on September 11, 2003, apparently initiated solely by the photoperiod, and progressed steadily without any obvious influence of other environmental signals. For example, after this date, senescing leaves accumulated anthocyanins in response to conditions inducing photooxidative stress, but at the beginning of September the leaves did not. Degradation of leaf constituents took place over an 18-d period, and, although the cells in each leaf did not all senesce in parallel, senescence in the tree as a whole was synchronous. Lutein and b-carotene were degraded in parallel with chlorophyll, whereas neoxanthin and the xanthophyll cycle pigments were retained longer. Chloroplasts in each cell were rapidly converted to gerontoplasts and many, although not all, cells died. From September 19, when chlorophyll levels had dropped by 50%, mitochondrial respiration provided the energy for nutrient remobilization. Remobilization seemed to stop on September 29, probably due to the cessation of phloem transport, but, up to abscission of the last leaves (over 1 week later), some cells were metabolically active and had chlorophyllcontaining gerontoplasts. About 80% of the nitrogen and phosphorus was remobilized, and on September 29 a sudden change occurred in the d 15 N of the cellular content, indicating that volatile compounds may have been released.

Variation in leaf flushing date influences autumnal senescence and next year’s flushing date in two temperate tree species

“…Our results therefore open the door for new insights in our understanding of the drivers of autumnal leaf senescence in temperate trees. The most widely accepted mechanism underlying the onset of leaf senescence in deciduous trees is represented by the environmental control hypothesis, which proposes that leaf senescence is triggered when the unfavorable autumn season comes, that is, a decrease in day length (45), in temperature (25,(46)(47)(48)(49), or in both day length and temperature (50). However, our study shows that in both oak and beech saplings leaf senescence started significantly later for trees maintained at ambient conditions during the previous winter than trees exposed to winter warming, despite the fact that all saplings experienced identical conditions during the growing season.…”

Metal Homeostasis in Cyanobacteria and Chloroplasts. Balancing Benefits and Risks to the Photosynthetic Apparatus

“…Anthocyanins, which are responsible for the beautiful autumn colors of deciduous trees, provide protection against photooxidative reactions during the latter stages of this process (Keskitalo et al, 2005).…”

The shared and separate roles of aposematic (warning) coloration and the co-evolution hypothesis in defending autumn leaves

“…addition, the fact that there are good physiological measurements of significant volatile release from autumn leaves 47 supports the possibility of the operation of olfactory aposematism by these leaves simultaneously with visual aposematism.…”