The answers are derived from the physiological functions of plant growth regulators mentioned in the context. (a) Auxins help initiate rooting in stem cuttings and are widely used for plant propagation. (b) Ethylene is highly effective in fruit ripening and enhances respiration rate during ripening. (c) Cytokinins promote nutrient mobilisation which helps delay leaf senescence. (d) Cytokinins help overcome apical dominance, thereby promoting growth of lateral/axillary buds. (e) Gibberellins induce bolting in rosette plants. (f) Abscisic acid (stress hormone) induces immediate stomatal closure in leaves under stress conditions.