From little seeds, a fascinating secret is unravelled

ANOTHER LIFE:A DOZEN YEARS ago, in a plant nursery in west Cork, I formed a deep fancy for the golden hop, Humulus lupulus "Aureus", a spectacular twining climber. Taken home and planted beside a woodshed pillar, it duly burst into life each spring, and, reaching the roof, went on vertically a couple of extra feet to crown the yard-light in a wreath of leaves. This golden-green corona, lighting the leaving of party friends, has been a special summer pleasure.

Early this year, however, renovations demanded that the hop be moved round the corner of the woodshed. It survived realignment and later revived on cue, climbing a trellis towards the roof. As the first shoot passed the tin roof, to probe the empty air, I kept a morning eye on it through the loo window. From its new position, the shaft of the yard-light was now some 50cm to its right. How would it reach it? Did it really care? Habitués of this column may remember previous explorations of twining and climbing plants. Darwin and son decided that they cast about with a tip or tendril, like a man swinging a rope around his head, until they touch something vertical. The stem-tip or tendril then curls around it by a differential growth of cells: those touching a twig stop growing, while those on the outside are elongated, pushing the tip around. This search-and-spiral movement the Darwins called “circumnutation”.

Modern biologists still differ on whether circumnutation is solely determined by the plant or is also an effect of external stimuli, such as gravity (the “gravitropic overshoot hypothesis”), though I don’t see how gravity could prompt the hop’s sudden grab for the light fixture.

Did I miss a morning or two of its progress while thinking of other things? I would swear (but that’s not science) that the shoot did no particular waving about. But at sunrise this morning, there it was, suddenly grown and swung over to the right, and making its first firm curl around the metal tube. Within a couple of hours it had grown another 8cm or so, curving to tighten its grip.

My spying on the hop has coincided, as it happens, with reading a book that, if not quite crediting plants with intelligence, grants them almost everything short of it. Unaccountably, I missed Seed to Seed: The Secret Life of Plants on its first publication in 2006 and only now have the chance to rave about it. As a scientist’s book about the natural world, it has been one of the most enjoyable and enlightening reads of my life –­ and that includes skipping technical bits I couldn’t quite get my head around. I shall read it again and try harder, and probably yet again for sheer pleasure.

PROF NICHOLAS HARBERD is one of the world’s leading plant geneticists. He also has two kids, Alice and Jack, likes his pint, cycles around the Norfolk fens and takes his family on holiday to west Cork. Seed to Seed, his first book, is part scientific field-diary through a year of study, part excited fever of speculation, experiment and discovery, part lyrical commentary on the moods and microcosms of the countryside and musings on the wonder and mystery of life. As the not-so-secret life of a scientist, this is intensely engaging.

The diary centres on the growth, death and resurrection of a single wild plant found growing on a grave in a local churchyard. Thale-cress, Arabidopsis thaliana, a nondescript little member of the cabbage family, is the geneticist’s plant equivalent of the fruit-fly, having an accelerated life-span from seed to seed and a relatively small genome. Grown wholesale in laboratories for study of mutation and its genes, it is rarely considered in the wild, where slugs and rabbits can be drastically disruptive. Discovering this the hard way in St Mary’s churchyard, Harberd rescues what’s left of his subject to conjure up flowers and seeds beneath a dome of wire netting.

What makes a plant grow short or tall – or at all? There’s a growth hormone called gibberellin that, to borrow from Dylan Thomas, is “the green fuse that drives the flower”. There are growth shoot-tips called meristems that generate proliferating, expanding cells to build leaves, stems, roots and flowers, their blueprints directed by genes. But all this demands a second force to restrain the drive of gibberellin. Harberd and his research team zero in on a group of proteins called DELLA that, restraining growth, also give the plant a way of tuning itself to local conditions and soils.

Pursuing such checks and balances, Harberd has a whole lot more to teach – too much, it seems, even to try to index. Nothing about circumnutation, Arabidopsis not being that sort of plant, but Seed to Seed has given me even greater engagement, as one bundle of cells to another, with the golden hop now twining up the pole.

EYE ON NATURE

I watched a female mute swan and her five recently hatched cygnets swimming in the Leitrim river in Wicklow town. She began to hiss violently and drove off an otter trying to drag a cygnet under the water. Next day I saw the same swan family with only four cygnets.

Peter Duggan, Wicklow

Parts of the hedge in front of my house were covered with a very fine, dense web. When trimming it I dislodged hundreds of tiny caterpillars, about 1cm in length, which abseiled down on strands of web. They are grey/green in colour with a double row of dark dots. The hedge is now stripped of leaves.

Ciarán Mac Murchaidh, Ard Mhacha

Caterpillars (photo enclosed) have completely stripped the leaves off a local hedge so identification of the host plant is difficult.

Ian McCullagh, Kilkenny

Both of those are the larvae of a sawfly. The second one is that of the dusky birch sawfly, and the first one is probably the same. They will pupate in the ground and may produce another generation this year which should be sprayed with insecticide.

When cycling from Tully to Renvyle House in Connemara on June 9th we heard a magical sound, a corncrake.

Carmel Hourican, Killarney

Michael Viney welcomes observations at Thallabawn, Carrowniskey PO, Westport, Co Mayo. E-mail: viney@anu.ie. Include a postal address