Cytokinins, a type of plant hormone, were tested on in vitro apple leaves to see how they affect water and gas exchange. Different types and concentrations of cytokinins were used on two apple varieties. The results showed that cytokinins influenced how much water vapor the leaves released, how much CO2 they took in, and how open their stomata were. The type and amount of cytokinin, as well as the apple variety, all played a role in these effects. The researchers found that measuring stomatal conductance and transpiration rate are good ways to understand how in vitro apple leaves are functioning, rather than just looking at CO2 exchange.