Figure 2.

Photosynthetic data from control and salt-stressed plants. Greenhouse-grown maize plants (B73) were assessed for photosynthetic rate (A), transpiration rate (B), and internal CO₂ concentration (C). Measurements were taken at the initiation of salt treatment (12.5 mm NaCl), with each increase in salt concentration, and after 3, 10, and 22 d on 75 mm NaCl. Photosynthetic rate was lower than expected when NaCl was increased to 75 mm. This was a consequence of cloud cover. On such days, C₄ plants take a long time to become photosynthetically active, despite the external light source provided in the chamber. After plants are in low light for some time, a sudden increase in photon flux (from the Li-Cor apparatus) will not result in an instantaneous increase in photosynthesis. An induction period of up to 60 min is due to a buildup of ribulose 1,5-bisphosphate, activation of Rubisco, and opening of stomata (Sims and Pearcy, 1994). White squares are control plants, and black squares are salt-treated plants. Values are means ± sd (n = 3).