The molecular basis of phytochrome interconversion (Pr ↔ Pfr) is:

**Assertion (A):** Vivipary (precocious germination of seeds while still on the parent plant) is observed in plants with defective ABA signaling. **Reason (R):** ABA normally maintains seed dormancy; in its absence or when its signaling is disrupted, seeds germinate prematurely.

A coleoptile is illuminated from one side. Auxin concentration in the shaded side is 1.8× higher than the lit side. The shaded side elongates. However, if the same coleoptile is placed upside down (inverted) and illuminated from the same side, where will auxin accumulate?

In tobacco pith callus tissue culture, with equal concentrations of auxin and cytokinin, the callus remains undifferentiated. To induce shoot formation, the medium should be modified to:

At which point on the sigmoid growth curve is the absolute growth rate (AGR) maximum?