Because of the large number of shoots (6,000–12,000) and shoot
clusters (up to 200) produced in a typical PIB, the total number of
shoots was not counted directly; rather, the number was estimated
by determining the average shoot weight for 20 clusters (Fig. 1F)
and then calculating the total number of shoots based on total
sample weight. The multiplication rate (MR) over a standard 4-
week period (28 days) was calculated using the following formula:
MR=exp[ln(Nt/No)(28/T)] where Nt is the final number of shoots,
No is the number of shoots inoculated into the bioreactor, and T is
the duration of the experiment in days. The equation is derived
from the standard growth equation Nt=No[exp(k/T)], where k is the
multiplication rate. By reporting MR as a fold-increase for a
standard 4-week period, we can easily compare experiments of
differing duration. The student t-test or chi-square was used for
comparison of means.