Effect of 2-Thiouracil on Cell Differentiation and Leaf Morphogenesis in Cannabis sativa

When supplied through the leaf at low dosage levels, the pyrimidineanalogue, 2-thiouracil, progressively arrests apical growthand organogenesis in young plants of Cannabis sativa. Duringthe treatment period, a generation of leaves arises in whichcell differentiation is inhibited without a parallel reductionin laminal expansion. With the withdrawal of treatment, apicalgrowth is resumed, but severe morphogenetic defects later becomeevident in leaves developing from primordia initiated duringthe treatment period or shortly afterwards, and there is simultaneouslya loss of apical dominance and of the control of phyllotaxis.Growth of a more normal pattern is, however, gradually restoredat stem apices, although local anomalies in the anatomy of thelamina recur throughout the life of the plant, and otherwisenormal leaves continue to show sporadic flecks or streakingsof abnormal pigmentation. The latter phenomenon suggests thatthe analogue induces a persistent state of instability in someof the proplastids of meristematic tissues.