LONG SHOOT-SHORT SHOOT

An easily recognized shoot design is termed long shoot-short shoot organization, wherein the canopy consists or two distinct classes of shoots: (1) major axes that have long internodes, and (2) lateral axes that have no internodes and therefore appear as very short projections. The classic example of long shoot-short shoot organization is the deciduous gymnosperm Ginkgo biloba, the maidenhair tree (Family Ginkgoaceae).

• Long shoots are rapidly growing shoots, produced mainly at the outer edge of the plant's canopy to achieve a taller or broader canopy reaching into the high light environment.
• From the widely spaced axillary buds along the long shoot form lateral branches that are short shoots with crowded leaves, because stem internodes do not form.
• Short shoots may be determinate, i.e., they form a mature structure and then terminate apical vegetative growth, or indeterminate, in which the apical meristem of the short shoot forms leaves year after year.

Some plants have long shoots and spur shoots, on which flowering often occurs. A spur shoot tends to have some internodal elongation, hence its distinction from short shoots, which lack internodal elongation. Some authors describe short shoots or spur shoots as having "fascicled leaves."

The molecular triggers for long shoot-short shoot organization need to be carefully studied to determine what genes are involved. Studies from the previous generation of plant physiologists observed that different treatments of growth substances (plant hormones) can be used to cause a plant to produce long shoots versus short shoots, and internodal growth is apparently suppressed when a lower than normal level of auxin is present.

Long shoot-short shoot organization has not been studied intensively from an ecological and evolutionary perspective. In desert and semiarid, full sun habitats is where many examples of long shoot-short shoot organization can be observed. There are several possible benefits of this design.

1. Especially in deserts, a dormant shrub or tree can produce a crop of photosynthesizing leaves within several days following an effective rainfall event. Growth is more rapid because, basically, no stem tissues need to be formed.
2. Woody plants with long shoot-short shoot organization, because they have fewer branches, tend to permit sunlight to penetrate deeply through the plant, rather than only striking the uppermost canopy and canopy margins.
3. Inflorescences are formed on the short shoots, a short distance from the leaves supplying the nutrients.
4. Leaves tend to have little development of petioles and are clustered so close to the stem that there may be some benefits in avoiding wind shear of the leaves.

To read more about long shoot-short shoot organizations:

• Examples of Long Shoot-Short Shoot Organization
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