The tolerable surface area increment (TSAI_(50)) of protoplasts isolated from nonacclimated leaves of Secale cereale cv. Puma and suspended in sorbitol or NaCl+CaCl_2 solutions was about 1000 μm~2, and was independent of the extent of contraction of the protoplasts. However, when the protoplasts were suspended in proline solution, the TSAI_(50) changed with the contraction. When the protoplasts from isotonic proline solutions expanded in hypotonic solutions, the TSAI_(50) was approximately 1000 μm~2. Howeve...