Each spring, the Connecticut River Valley is filled with fresh colors and scents as leaves and flowers sprout from dormant buds on trees and shrubs. Green shoots sprout in the last snow and over last year's brown leaves, covering the ground with new green forms.
Each new flower and leaf is the result of a clear "choice" of the plant's growth point: to bear flowers or leaves. Or! Because once a growing point begins to develop into a flower and eventually a fruit, there is no turning back for that sprout.
Fruits and seeds are essential for plant species to survive, but so are leaves to capture the carbon and energy needed for further growth and seed formation. As you can imagine, flowering time is a critical element in the life history of any plant species.
Not all plants flower. Maybe the day length isn't long enough to start flowering, or the days weren't cool enough. The mechanisms that lead to flowering are quite complex and certainly not the "solutions" we think of in terms of selection and selection. Light sensors in plants that measure the length of day and night and chemical pathways that track the number of cold days since winter bring peace. Many factors combine to determine the fate of growing seedlings.
However, when a particular plant, such as an apple tree, usually flowers, in many cases some seedlings simply will not produce flower buds - usually stubborn juveniles! These plants are still in their infancy, and this condition has been known to gardeners for centuries. Early flowering of the tree can promote reproduction and fruit production, so many botanists have tried different treatments.
For example, Thomas Andrew Knight wrote in 1795: “I took cuttings from some old, ungrafted pear trees, others from trees grown from trunks at ground level, and from all trees planted on the same trunks. The first one grew without thorns. grows like the cultivars and flowers in its second year, the second taking the appearance of shoots fresh from seed, covered with thorns, but without any flowers.
Based on these and other experiments, he concluded that "any cutting from an apple tree (and probably any other) depends on the condition of the mother shoots. If it is too young to bear fruit, it will grow vigorously but not flower; and when very old it bears fruit immediately, but is never a healthy tree.
Two things should be noted here. First, the bud stage remains the same, whether young or mature, even if it grows on a tree at a different stage. Any growth point change is permanent. And it differs not only in the presence of flowers - the shoots are more prickly, sometimes they have leaves of different shapes, colors or density.
Another plant with many different young and mature forms is English ivy. It has a distinct juvenile climbing and spreading phase with glossy, thick, lobed leaves and a tendency to root along the stem. The fruiting stage develops as a bush with clusters of yellow-green flowers that produce blue-black berries.
Both forms grow from the same root. After flowering, you can take cuttings from the vine and plant more vines and get flowers and berries from the cuttings of the upright bushy fruit form. I have read reports of unflowered and flowering clones propagated from cuttings without phase change for 30 years.
Other plant species have distinct young and mature leaves. Many, like some species of acacia, grow in New Zealand and Australia. Another native plant, Boston ivy, also has a young form with three-lobed leaves. Mature Boston ivy blooms and bears fruit and has triangular, unjointed leaves.
So what's going on here? A permanent change in a growth pattern is not a genetic change, but an epigenetic change, that is, a change in the behavior of a gene, but not a change in the gene itself.
Finally, we began to observe what might change in Arabidopsis, a small, fast-growing annual mustard plant. Yearlings change phase from adolescence to adulthood in a short life span. Arabidopsis has a very different shape of young leaves. These plants initially grow as a compressed whorl of short-stemmed rounded leaves for a few days to a few weeks. Then the stem grows, bearing jagged edges and "mature" leaves with an elongated, irregular shape. This shoot tip eventually turns into a seed-producing flower, ending the life of the plant.
With the advent of molecular biology, particularly the ability to identify and modify small RNA molecules, two specific types of small RNAs accumulate and cause widespread changes in cell growth and plant development.
So why do these molecules accumulate at a certain rate only in certain plant species? Maybe some plants, like some people, are late bloomers.
Lawrence J. Winship (o) is Distinguished Professor of Botany at Hampshire College and former Board Member of the Hitchcock Center for the Environment.
Earth Matters is a 14-year project of the Hitchcock Center for the Environment. After more than three years of the COVID-19 pandemic, the center's doors and avenues are now open at 845 West St. in Amherst. is open at For more information, visit hitchcockcenter.org.
