Final answer:
Before receiving ethylene, an acacia tree produces oxygen through photosynthesis and tannins for protection and defence. Ethylene, a plant hormone, influences processes like fruit ripening, flower wilting, and leaf fall, particularly affecting the abscission layer in leaves.
Step-by-step explanation:
The acacia tree, like other plants, produces a variety of compounds during its life cycle but does not produce ethylene until it is necessary. Ethylene is a plant hormone associated with various aspects of plant growth and development, including fruit ripening, flower wilting, and leaf fall. Before the tree starts releasing ethylene, it is already producing oxygen through the process of photosynthesis, as well as a range of secondary metabolites like tannins, which can serve functions such as deterring herbivory and providing protection from harmful ultraviolet radiation.
Regarding the question, though the tree does not produce ethylene until it receives a signal (which might be developmental change, stress-related factors among others), it is involved in producing oxygen and tannins. When the acacia tree does start producing ethylene in response to certain stimuli, it can lead to significant changes in its physiology. The ethylene production in plants can be stimulated by internal signals or external factors such as mechanical stress, environmental stresses, or even chemical cues.
Interestingly, ethylene's role was historically noted when gas street lamps, which volatilized ethylene, caused adjacent trees to exhibit twisted trunks and premature leaf fall. When ethylene promotes leaf fall, it does so by triggering the death of cells in a specific leaf region known as the abscission layer, which is where the leaf detaches from the stem.