7 days old	18 days old

Each stage of development in the rosette-dwarf stock is slightly delayed compared to the standard stock. Rather than the hypocotyl lifting the cotyledons above the soil 1-2 days after the seed is sown, rosette-dwarf seedlings push their way out, emerging up to 4 days after planting. True leaf development and flowering are also slightly delayed, all due to a deficiency in the plant growth hormone gibberellin (also known as gibberellic acid or "GA"). Rosette-dwarf plants are believed to produce 4-10 times less GA than standard Fast Plants (Rood et al., 1990).

The plant's stem does not elongate following seedling emergence, so the dark green, lobate true leaves come to rest at an angle close to flat, forming the "rosette" that gives the stock its name.

Flower morphology is normal in comparison to standard Fast Plants, but the flowers themselves are densely clustered on the plant's shortened stems. Flowers can be pollinated. The resulting seed pods are short and stubby as carpel elongation is abnormal in this stock. Seed set is normal with careful pollination.

Tips for the Grower
See Growing Instructions. Moderate experience with growing Fast Plants is recommended prior to using this stock.

Germination in freshly harvested rosette-dwarf seed is inhibited due to an interplay between levels of GA and abscissic acid. This inhibition can be overcome by storing the seed in a cool dry place for 6 months or by soaking newly harvested and dried seed for 10-30 minutes in a 100 ppm solution of GA (seed purchased from Carolina Biological Supply Company has already been stored to overcome the dormancy period). Stem elongation can be stimulated by placing 1 drop of a 100 ppm solution on the first true leaf at Day 7 and again at Day 10.

Notes on Genetics
The stock originated from a mutation discovered early in the history of Fast Plants. The genetics behind the plant's appearance and developmental schedule appear to involve a single recessive gene. When in the homozygous condition, the gene is expressed as a reduced production of GA. The rosette-dwarf trait is genotypically expressed as ros/ros.

Ideas for Investigations
Physiology - Experiment with the application of GA at various stages of development or in varying dosages at a single developmental stage. Investigate hormone chemistry, dosage, dormancy. Can students create a "normal" plant by dosing the rosette-dwarf with GA?

Noninheritance of acquired characteristics - Treat rosette-dwarf plants with GA to stimulate stem elongation, then cross-pollinate two treated plants and raise the offspring. Were the parent's acquired characteristics inherited?

Comparative morphology - Compare the appearance of rosette-dwarf and standard plants at various stages in the life cycle. Rosette-dwarf plants can also be compared to elongated internode plants, a stock that overproduces GA.

S. B. Rood et al., "A gibberellin-deficient Brassica mutant-rosette," Plant Physiol. 89:482-487 (1989).