In the early C17th, a century before the masons raised the mauve rubblestone walls of St.Edith’s,
a wordsmith merged the Latin Ab (off) with Scindere (to cut), to create
abscindere, or abscissio, and thence today’s abscission.
An action noun meaning a cutting off; a breaking off.
But first, an explanation.
Principally because, for most temperate plants, leaves aren’t capable of surviving frosts. So the first significant frost will kill all leaves, which would fall from the plant, or just collapse in the case of many annuals or herbaceous perennials. For many deciduous woody perennials – shrubs and trees, planned ageing or senescence of the leaves is just a normal precursor to leaf abscission and loss. Or death.
So the plant prepares, annually, for the onset of winter by altering the complex biochemistry inside the leaf. Protein synthesis reduces, protein levels within the leaf are reduced due to enzymic protein breakdown, respiration declines, and the rate of carbohydrate breakdown also increases. RNA is broken down, and finally the photosynthetic green compound chlorophyll is degraded. The breakdown products of all this biochemical change are rapidly transported from the ageing leaf, and into the other permanent parts of the plant (trunk or stem, and roots), for upcycling in due course.
These complex changes are coordinated by plant hormones, in particular ethylene and abscidic acid. To enable abscission to take place, a special layer of cells (the abscissional layer) develops at the base of the leaf’s stem, or petiole. As senescence proceeds, increasing levels of ethylene stimulate these abscissional layer cells to respire faster, and causes the cells nearest the stem to increase in size. At the same time cells in the abscissional layer furthest from the stem begin to break down polysaccharides in the cell walls, again under hormonal influence, thus weakening their strength. The pressure between the enlarging cells closest to the stem, and the weakened cell walls nearer the leaf eventually causes a split to develop, and the leaf falls to the ground. So the combination of senescence and abscission is a great way for deciduous plants to recycle carefully produced nutrients before the chill of winter would rob the plant of this material.
First to Hergest Croft. On the very borders of England and Wales. And with good fortune, timed to perfection, for a clear blue sky, sunny day. Surprisingly the changes here were perhaps 2 weeks ahead of our own plants. Stunning vistas, and on this late October day, fewer than a dozen cars in the car park, around lunch. If you’ve never been, plan a trip for next year – particularly late spring, or autumn. A visual treat, only limited by the shortened days at this time of the year.
Then for the third time in 2 years, a different autumnal trip. I can now predict with some accuracy, the relative timing of leaf colour change and abscission in our own woody plants, and value them all for their beauty, and sequential guiding of seasonal change.
Under more clear, cold, blue skies, another life remembered. The wedding church revisited. Too soon. For such raw emotions.
A Whole Life condensed into 10 memorable short stories. How was that done?
An hour of favourite music, to contemplate amongst the hushed banter with closed eyes, as pews filled and tears welled.
Much time to think.
As our third trip in a long week takes us to the National Botanic Garden of Wales in time to be excitedly ushered towards the pupae cabinet, by the young staff scientist in the tropical house where a butterfly is trying to emerge from its chrysalis, tip superglued, hanging between empty neighbouring shells, from a thin dowel. Willing it on, the three of us are gripped, misted lenses censoring records, as after all the efforts of metamorphosing soups within the crisp pupal cage has transformed rubbered larva into laced butterfly, ultimate success balances. Precariously on life’s snaking line …
Struggle out within a few minutes, more than just those flailing legs, little butterfly, or use up your energy supplies, exhaust yourself, and succumb, before your perhaps deformed wings have ever even inflated.
Click below if you’ve never heard this reflective piece of piano music before.
And if you’ve got the data allowance and know it well, then click anyway! A recently rediscovered and enjoyed musical postscript, courtesy of Stephen Hough, and Stephen Baggaley…