Spring again


Someone recently sent me pictures of the campus of Harding University in Searcy, Arkansas (my alma mater), showing it practically buried in beautiful spring flowers. Yes, spring is creeping northward, and soon multicolored flowers and rich green grass and leaves will replace our landscape’s current predominant shades of gray, white and brown.

Exactly when seeds will germinate, plants will put out new leaves, and the buds of trees will open can’t be predicted with any accuracy, because all of these activities are dependent on environmental conditions that change from year to year (although a new Australian discovery may someday allow us to control when plants flower–more on that later!).

The study of the relationship between climate or seasons and recurring biological activity such as the flowering of plants is called phenology (not to be confused with phrenology, which is the study of bumps on your head). Many gardeners take careful note of when flowers appear and trees put out new leaves each year. This data is now being tracked around the world to determine if climate change is beginning to alter the life cycles of plants and animals.

Three main factors, whose importance differs from species to species, govern spring activity in plants: length of day, temperature, and moisture. Seeds, for instance, generally germinate when moisture penetrates their seed coat–but moisture alone isn’t enough. If it were, seeds, which are produced in the late summer and fall, would germinate in the autumn–just in time to be killed by frost. Many plants in the temperate zones get around that problem by producing a chemical called abscisic acid in the late summer and early fall that keeps the seeds dormant. Over the winter, enzymes in the seed degrade the abscisic acid so that the seed is ready to sprout in the spring. Even then, however, the seed won’t sprout unless conditions are right: some seeds can remain dormant for years, even (in the case of the lotus plant) for centuries.

Once water penetrates the seed coat of a no-longer-dormant seed, it begins to soften the hard, dry tissues inside, and causes the seed to swell up. This splits open the coat, allowing more water to enter. The water activates chemicals inside the seed which trigger a series of biochemical events culminating in the sprouting of the plant.

Activity which is governed by the length of day is called photoperiodism. Day length is particularly important to flowering plants; plants of the same species all need to flower at the same time if there is to be any cross-pollination. Of course, the plants don’t have little internal stopwatches; instead, they contain chemicals called phytochromes. When a phytochrome molecule is exposed to certain frequencies of light for a sufficient period of time, it converts to a different form of phytochrome, which signals the plant’s cells to change their activity–to start putting out flowers, opening up buds, etc. The days have to be a certain length, which varies from plant to plant, before this process kicks in.

Plants are also sensitive to temperature. All flowering plants require a certain amount of rest–days when they are unable to grow–referred to as chilling units. (There’s seldom a shortage of chilling units in Saskatchewan.) They also require a certain number of heating units, days when the temperature is above about 8 degrees Celsius. Until the heating requirement is met, the plant will remain dormant. The higher the temperature, however, the faster the plant will bloom. So a cold period followed by a sudden extended warm period can result in what seems like a veritable explosion of leaves and flowers.

The flip side of that is that a cold snap at the wrong moment can have serious effects on flowering plants. We may someday be able to avoid that, however, thanks to the recent discovery by Australians scientists of the Flowering Locus C (FLC) gene. This “master gene” suppresses flowering when it is switched on. Once it collects enough signals from within the plant that day length, moisture and especially temperature requirements have all been met, it turns off, allowing flowering to proceed.

Learning to control this gene could provide more control over year-round production of some crops, including wheat and canola; allow ranchers to prevent the flowering of pasture grasses; allow horticulturalists to produce fruit, vegetables and cut flowers all year in response to market demands and grow bigger vegetables by preventing them from going to seed; and could even help hay fever sufferers by allowing us to prevent the flowering of species whose pollen people are most allergic to.

Alas, however, while we may someday be able to force plants to flower, or prevent them from doing so, there’s no discovery on the horizon that will allow us to force spring weather to set in on schedule.

Permanent link to this article: https://edwardwillett.com/2002/04/spring-again/

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