Presentation on theme: "WHY DO MENDEL’S PEAS WRINKLE?. Pisum sativum P. sativum, the common garden pea, has been cultivated for over 9,000 years. As an experimental model system,"— Presentation transcript:
WHY DO MENDEL’S PEAS WRINKLE?
Pisum sativum P. sativum, the common garden pea, has been cultivated for over 9,000 years. As an experimental model system, it was a fortunate choice for Mendel as it has a straight forward method of sexual reproduction and inheritance that we today refer to as “Mendelian.”
WRINKLED X SMOOTH IS A MONOHYBRID CROSS SMOOTH WRINKLED
Why are peas with impaired early starch producing ability valuable? Photosynthesis in the leaves creates glucose that is converted to sucrose so it can be “shipped” to the peas in the developing pods. Early starch – making enzymes in developing peas convert this sucrose back to glucose, then glucose -6-P for conversion to starch via several enzymes that make starch chains and add side chains to create starch grains as the pea fills out. This activity subsides as the pea matures. In wrinkled pea varieties, several sorts of mutations interfere with normal starch making during the filling out phase leaving excess free sugar which creates osmotic stress by holding more water. When this water leaves as the peas dry, they wrinkle. The excess sugar also induces secondary starch enzymes late in the filling process.
STARCH GRAIN MORPHOLOGY EARLY ALASKA (normal starch grains) Thomas Laxton & Progress (abnormal lobed starch grains).
PERCENT WEIGHT GAIN Calculated as (wet wt of 5 peas) – (dry wt. of 5 peas) / (dry wt. of 5 peas) * 100 This semester’s data were similar with both wrinkled pea types showing the ability to take on more water due to their lower starch but higher free sugar content.
Late starch –synthesizing enzyme activity, this semester’s results A = Early Alaska (smooth) P = Progress (wrinkled) T =Thomas Laxton (wrinkled) Purple spots where seen, were the results of a 30 minute extract spot incubation. The second sector for each was spotted with extract 2 min before rinsing.
Starch enzyme production schematic The sequence on the left shows normal starch metabolism due to normal functioning of constitutive early enzymes, that on the right that resulting in induction of late enzymes (isozymes) that attempt to compensate for the malfunction of the early enzyme (s). Some residual late enzyme activity can be detected when wrinkled peas are re-hydrated and assayed, creating what initially looks like paradoxical results – the starch deficient varieties having more enzyme activity.