Mechanisms of Induction of Stimulus-Specific Systemic Responses of Photosynthesis in Wheat Plants

Systemic photosynthetic responses induced by local stimuli are essential for the formation of systemic acquired acclimation. However, the stimulus-specific features of these responses and the mechanisms that underlie their specificity are still unknown. The aim of this study was to identify the mechanisms of the specificity of photosynthetic responses induced by local heating, burning, and wounding in wheat plants. Photosynthetic responses were multiphasic and included an initial activation of photosynthesis followed by two phases of inactivation, fast and long. The parameters of these responses depended on the type of local stimulus. It has been shown that the activity of Ca²⁺ channels and H⁺-ATPase plays a key role in responses to all types of stimuli. Upon burning and wounding, the fast phase of photosynthetic inactivation is induced mainly by the hydraulic wave, whereas its contribution to heat-induced responses is smaller. The long phase of photosynthetic inactivation is mediated by a decrease in stomatal conductance. In the case of heating, the highest amplitude of the long phase of photosynthetic inactivation and the most substantial increase in the jasmonate levels were observed compared to other local stimuli. Jasmonates probably contribute to the long phase of photosynthetic inactivation through stomatal closure. An increase in jasmonate levels upon heating is probably induced by autopropagating signals. These findings suggest that specificity of responses is provided by different contributions of components to a complex long-distance signal.