AP BIOLOGY

Detailed explanation-1: -Cytokinin positively regulates cell division and also serves a key role in establishing organization within shoot stem cell centers. Both auxin-dependent and auxin-independent mechanisms have been uncovered by which cytokinin stimulates the endocycle in roots.

Detailed explanation-2: -This suggests that cytokinin may delay leaf senescence not only as a result of exogenous treatment, but as part of an endogenous developmental program.

Detailed explanation-3: -Cytokinins promote cell division and increase cell expansion during the proliferation and expansion stages of leaf cell development, respectively. During leaf senescence, cytokinins reduce sugar accumulation, increase chlorophyll synthesis, and prolong the leaf photosynthetic period.

Detailed explanation-4: -Cytokinin promotes nuclear localization of a transcription factor to activate cell division. Organ morphogenesis in plants is largely determined by the rate and patterns of cell division (1) occurring primarily in meristematic tissues such as the shoot and root meristems, and vascular cambium (2).