Figure 4.

The Photosynthetic Defect in the lto1 Mutant Is Due to a Limitation in the Electron Flow from PSII.

Fluorescence induction of representative leaves from wild-type (A) and lto1 (B) plants. Fluorescence was measured using a 10-μs pulse of 430-nm light and appropriate filters to transmit red light. Actinic illumination provided by 520-nm LEDs (1.4 mmol photons m⁻² s⁻¹) commenced immediately after taking F₀ and F_M values at time 0. At each time point, fluorescence immediately before (F₀, open circles) and after (F_M, closed circles) a 80-ms saturating pulse was measured during a brief window in which the actinic light was off (see Methods for details). After 2 min, the actinic light was extinguished and the recovery of fluorescence was followed in the same manner. The variable fluorescence at each point (F_V = F_M − F₀) is also shown as gray triangles. All fluorescence values were normalized to F_M; thus, what is shown is actually F_M/F_M (closed circles), F₀/F_M (open circles), and F_V/F_M (gray triangles). Upward and downward arrows indicate when the actinic light was on or off, respectively.