Leaf Senescence; Pondering Mid-Life as Autumn Approaches

Senescence is the orderly, age-induced breakdown of cells and their components that lead to the decline and ultimate death of a plant or plant part. The timing of senescence is species-specific. For deciduous trees (non-evergreen) it is typically fall. Leaves last through the growing season before senescing prior to winter.*

People talk about getting old and how they’re going to do it differently. They won’t be grumpy old men, or cantankerous old women. They won’t get fat, or soft. They’ll stay active and eat right and travel the world and have new adventures. In other words, they will use those final years (that last 1/3 of life) rather like a plant’s senescence.

Senescence is a metabolic process and so, it requires energy. It isn’tt just the ending of growth.

Take leaves. They move the products of photosynthesis out of leaf tissue into stem and root tissue during senescence and before leaf drop, The bright green color of chlorophyll fades during this process and the yellow/orange colors of the carotenoids become prominent and combine with the red/blue anthocyanins to produce vibrant colors–quite the display in my neck of the woods right now.

All this talk of activity and world travel from my peers will require energy too.

Around me, my friends are discussing how they will use the products of their own photosynthesis (energy conversion) to fuel other activities or organisms as priorities shift and time moves forward. Energy will be expended prior to the their death, or the death of some part of life they’ve always counted on, like work or health. Perhaps running through neighborhood streets or yoga in converted warehouses will replace subway dashes and five o’clock traffic.

I passed the mid-way mark (is it still 40?) over a decade ago, yet I am only now beginning to think to myself, so how will I grow old? What will be my energy conversion and when will I begin it? Leaves, it is thought, but not known, have a senescence hormone. I suppose that would be a hormone that triggers the process of aging, and death. Soybeans are thought to have what is referred to as the senescence factor, but all plants may not have it. .

I’m not sure all people have it. I fear I do not, and am behind on the senescence, not the physical changes, but the mental processing of it. But then again, I am nothing, if not forever behind.

When my boys were growing up. I was always playing catch up. I thought they were 4 years-old, when really, they were 5, and on their way down the kindergarten hallway. When the heck did that happen? So, I’d scramble to figure out all the nuances and protocols of kindergarten, and just when I nailed that, I looked up, and bless me, they were in the 3rd grade, with a science project due the week before Thanksgiving. Guess who’s buying a turkey while shopping for craft supplies? Is it just me? I’m all like, isn’t this great, we have 3rd graders doing a school play tonight, only if I look closely, it’s my granddaughter, and she’s headed out the door to dance class. How do I miss the change in time that others seem so cognizant of, but to me is as subtle as the light shifting through the slates of my bedroom blinds as autumn approaches?

The role of hormones in senescence is not clear, but the role of hormones in my own senescence is rather apparent. I am at least conscious of it, and I wonder if the plant is. I am unable to name all my particular hormones, and what their roles are in this stage of life, but I see the evidence. Much like the leaves changing colors, there are things changing physically for me. I tire more easily. I am hot now when I used to always be cold. My knees and feet hurt after running or walking a ways. i have little tolerance for lack of sleep, but I wake early no matter what. And while, I hope to make my own list of possibilities for these last years, I find I am still winding down on the previous ones. I wonder if I will miss my opportunity.

Presently, I am having a good dose of reality about aging gracefully, or not.

Growing older must be scarier than we yoga loving, adventure hounds care to admit, or why else would the words mid-life and crisis so often couple? While I see no reason to be all gloom and doom about passing the mid-way mark (more than passing it actually), I do think some of old age’s accouterments make it, well, harder to process than a trip to Europe will soften. I am a realist and must process the facts before considering the possibilities. Still, I am hoping for my own vibrant decline, depressing as that may sound.

As I observe the changing of summer into fall, and am awed by the glorious sight of it, I think how odd that death holds such beauty. Perhaps, hormones and senescence aside, death is speaking to us. Could it be that this bared beauty, that holds nothing back, is telling us, this is just the beginning?

The leaf senescence allows the perennial plant to continue living by providing for the roots and stems what it stored in its leaves. One must die for the other to live. I do not claim to understand the mysteries of death and life, or even plants–who frankly shroud their mysteries well–but I am finally watching the signs.