Turgor, temperature and the growth of plant cells:: using Chara corallina as a model system

Rapid changes in turgor pressure (P) and temperature (T) are giving new information about the mechanisms of plant growth. In the present work, single internode cells of the large-celled alga Chara corallina were used as a model for plant growth. P was changed without altering the chemical environment of the wall while observing growth without elastic changes, When P was measured before any changes, the original growth rate bore no relationship to the original P, However, if P of growing cells was decreased, growth responded immediately without evidence for rapid changes in wall physical properties, Growth occurred only above a 0.3 MPa threshold, and increasing P caused small increases in growth that became progressively larger as P rose, resulting in a curvilinear response overall. The small changes in growth close to the threshold may explain early failures to detect these responses. When T was lowered, the elastic properties of the cell were unaffected, but growth was immediately inhibited, The lower T caused P to decrease, but returning P to its original value did not return growth to its original rate. The decreased P at low T occurred because of T effects on the osmotic potential of the cell. At above-normal P, growth partially resumed at low T, Therefore, growth required a P-sensitive process that was also T-sensitive, Because elastic properties were little affected by T, but growth was markedly affected, the process is likely to involve metabolism. The rapidity of its response to P and T probably excludes the participation of changes in gene expression.