The quick adjustments of leaf traits are critical for keeping the survival of plants under dehydration. In this study, we examined the hypotheses that plants would adapt to dehydration by shrinking its mesophyll cells to offset the water loss, or triggering water regulation mechanism caused by enzymes. Leaf structure, elastic modulus (E-m), leaf tensity (LT) and leaf density (LD) were determined with detached leaves of Broussonetia papyrifera (L.) Vent. and Morus alba L. at each water loss moment (0, 1, 2, 3, 4 and 5 h). The coupling model between gripping force and LT was established using the Gibbs free energy equation, and the initial LT was determined. The intracellular water availability of M. alba decreased at 4 h, which was earlier than that of B. papyrifera. The intracellular water availability of M. alba was more sensitive than B. papyrifera. Broussonetia papyrifera adapted to dehydration by shrinking its mesophyll cells to offset the water loss, or triggering water regulation mechanism caused by enzymes, i.e., carbonic anhydrase. The sponge parenchyma of B. papyrifera at 3 h decreased by 25.73% of that at control. Morus alba maintained intracellular water availability just by changing the leaf structure. The offset effects through shrinking cells differed between B. papyrifera and M. alba, because the elastic-plastic behavior of their leaves and cells were different. The E-m of M. alba was over five-fold higher than that of B. papyrifera. The investigations of water status were more accurate in terms of leaf physical traits instead of water content.