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.
Highlights
The gaseous plant hormone, ethylene (ET), plays an important role in growth, development, and responses of plants to biotic and abiotic stresses (Abeles et al 1992)
Exogenous ACC was converted to ET and elicited a concentration-dependent ET production in the root and an increased ET emanation at higher concentration from the leaf tissues of tomato, which, with the exception of samples treated with 100 μM ACC, proved to be significantly higher in the root than in the leaves (Fig. 1)
Exogenous ACC applied via the root system of tomato was readily converted to ET during long-term experiments
Summary
The gaseous plant hormone, ethylene (ET), plays an important role in growth, development, and responses of plants to biotic and abiotic stresses (Abeles et al 1992). ACS catalyses the rate-limiting step in the ET biosynthetic pathway, the available free ACC pool in the tissues may be regulated by the formation of ACC conjugates (malonyl-, γ-glutamyl-, and jasmonoyl-ACC), which can affect the ACC-induced ET production. While ET can diffuse from cell to cell, long distance ET responses can be Journal of Plant Growth Regulation (2019) 38:1110–1126 accomplished through the transport of ACC from the roots to the shoot or vice versa during stress and developmental processes (Van de Poel and Van Der Straeten 2014). The second, larger peak in stressed plant tissues lasted 30 h in this system (Wi et al 2010) but it may extend for weeks (Rodríguez-Serrano et al 2006), ET may initiate detrimental processes such as senescence, chlorosis and leaf abscission
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