Exogenous 1-Aminocyclopropane-1-carboxylic acid Controls Photosynthetic Activity, Accumulation of Reactive Oxygen or Nitrogen Species and Macroelement Content in Tomato in Long-term Experiments

Abstract

Exogenous ethylene (ET) or its precursor, 1-aminocyclopropane-1-carboxylic acid (ACC) may increase stress tolerance of plants in long-term experiments. ACC applied in hydroponic culture of tomato (Solanum lycopersicum L. cv. Rio Fuego) brought about concentration-dependent differences in plant responses. ACC at 0.01 µM changed K+ distribution between shoots and roots but at higher concentrations K+/86Rb+ uptake was inhibited. Surprisingly, excess Na+ and reduced K+ accumulation could be measured in root and leaf tissues, respectively, which at 100 µM ACC led to a decreased K+/Na+ ratio and to a weak ionic stress in these plant organs. ACC at low concentrations increased the net CO2 fixation rate (AN), however, at 100 µM, it triggered a parallel decline in stomatal conductance, AN and in the actual quantum yield of photosystem II. Photosystem I (PSI) was less sensitive to ACC, lower concentrations caused an increasing tendency in the effective quantum yield and changed the non-photochemical quenching profile of PSI from donor-side dominant to acceptor-side-dominant limitation. Photoinhibition was avoided via the dissipation of light energy by regulated non-photochemical quenching and by transiently enhanced cyclic electron flow (CEF) around PSI. The decrease in CEF at 100 µM ACC correlated well with the accumulation of O2•− and H2O2 in the leaf tissues suggesting that molecular oxygen may function as an electron acceptor when natural acceptors of the linear electron transport were over-reduced. Concentration-dependent changes in soluble sugars and sorbitol as osmoprotectants may also contribute to the stress resistance of plants elicited by ET/ACC.