7 days old	16 days old

Plants of the Tall stock overproduce the plant growth regulator gibberellic acid, resulting in the elongation of the hypocotyl and stem internodes (lengths between leaf bracts). This phenotype is first apparent 2-3 days after germination when the seedling hypocotyl continues to extend beyond the standard. The excess elongarion continues to be expressed throughout the plant's development, and the adult plants are tall and spindly. Plants of this stock also have a tendency to appear to be lighter green in comparison with the standard.

Considerable variation in height exists within a population of Tall plants, with some at the shorter end being similar in height to the tallest plants from a standard population. The expression of the Tall phenotype is influenced by the environment. The extent of internode elongation is affected by the ambient temperature: higher temperatures accentuate the elongation.

Tips for the Grower
Moderate experience with growing Fast Plants is recommended prior to using this stock. The plants will require staking after about 8 days of growth. As plants get older the height of the light bank may have to be adjusted to keep the plant tips from getting too close to the bulbs.

Notes on Genetics
The stock originated as a naturally-occurring mutant within the base population. The overproduction of gibberellic acid appears to be the result of a single mutation. This mutation is believed to cause the production of as much as 12 times the amount of GA in standard Fast Plants (Rood et al. 1990). The Tall Plant trait is expressed genotypically as ein/ein.

Ideas for Investigations
Genetics - Cross a rosette-dwarf plant to an Tall plant. What will the offspring look like? Will the hypocotyl elongate with a rosette whorl of leaves at the top?

Comparative morphology - Observe and record the physical differences between standard, Tall, rosette-dwarf, and petite plants through the life cycle. Graph the average heights of the plants.

Physiology - Investigate the effects of growth suppressers like Arrest® on the development of Tall plants. Can you create a "normal" plant? What do you get if you treat this stock with additional GA? If you treat a standard plant with GA, can you mimic the Tall plant phenotype?

Rood et al., "A mutant gene that increases gibberellin production level in Brassica," Plant Physiol. 93: 1168-1174 (1990).