Analysis of the photosynthetic response induced by variation potential in geranium.
Electrical signals (action and variation potentials) caused by environmental stimuli induce a number of physiological responses in plants including changes in photosynthesis; however, mechanisms of these changes remain unclear. We investigated the influence of the variation potential on photosynthesis in geranium (Pelargonium zonale) under different conditions (control, low external CO₂ concentration, and actinic light absence). The variation potential caused by lamina burning induced a reduction in photosynthesis (decreases in effective quantum yields of photosystem I and II, CO₂ assimilation rate, and stomatal conductance) in unstimulated leaves under control conditions. Changes in the majority of light-stage parameters (photosystem I and II quantum yields, coefficients of photochemical and non-photochemical quenching, quantum yield of non-photochemical energy dissipation in photosystem I due to donor-side limitation) were correlated with a decrease in CO₂ assimilation rate. The changes were similar to those caused by lowering [CO₂]; their magnitudes decreased both under low external CO₂ concentration and without actinic light. These results support the hypothesis that Calvin cycle inactivation plays a key role in photosynthetic response induced by electrical signals. However, a decrease in electron transport through the PSI acceptor side also induced by variation potential was not correlated with a decrease in the CO₂ assimilation rate and did not depend on the external CO₂ concentration or actinic light intensity. Thus, we suggest that there are two different mechanisms of light-stage inactivation induced by the variation potential in geranium: one strongly dependent on dark-stage inactivation and one weakly dependent on dark-stage inactivation.
Department of Biophysics, N.I. Lobachevsky State University of Nizhny Novgorod, Gagarin Avenue 23, Nizhny Novgorod 603950, Russia. kbf@bio.unn.ru
Vladimir
V
Sukhov
Lyubov
L
Orlova
Sergey
S
Mysyagin
Julia
J
Sinitsina
Vladimir
V
Vodeneev
D000222:Adaptation, Physiological; D055724:Electrophysiological Phenomena; D004777:Environment; D008027:Light; D031316:Pelargonium / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology; D018515:Plant Leaves / Q000378:metabolism; D013312:Stress, Physiological