Abstract
BackgroundPlants often suffer from hypoxic stress during waterlogging and hydroponic culturing. This study investigated the response of cucumber (Cucumis sativus L.) plant growth parameters, leaf photosynthesis, chlorophyll fluorescence, fast chlorophyll a fluorescence transient (OJIP), and fruit quality parameters to hypoxic stress alleviated by exogenous calcium. During the fruiting period, cucumber plants were exposed to hypoxia and hypoxia + Ca2+ treatment (4 mM Ca2+) for 9 d.ResultExogenous calcium application enhanced the biomass and fruit quality of hypoxic stressed cucumber and also increased the net photosynthesis rate, stomatal conductance, intercellular CO2 concentration, maximum quantum efficiency of photosystem II photochemistry, actual photochemical efficiency of PSII, photochemical quenching coefficient, and non-photochemical quenching coefficient. Additionally, measurement of chlorophyll a fluorescence transients showed the positive K- and L-bands were more pronounced in leaves treated with hypoxia compared with those with hypoxia + Ca2+, indicating that hypoxic treatment induced uncoupling of the oxygen-evolving complex and inhibited electron transport beyond plastoquinone pool (Qa, Qb) including possible constraints on the reduction of end electron acceptors of photosystem I. Exogenous calcium can reduce these stress-induced damages in cucumber.ConclusionThis research focused the effect of exogenous calcium on cucumber photosynthesis during the fruiting period under hypoxic stress. Hypoxic stress might impair the photosynthetic electron-transport chain from the donor side of PSII up to the reduction of end acceptors of PSI, and exogenous calcium enhanced electron transport capacity and reduced hypoxic damage of cucumber leaves.
Highlights
Plants often suffer from hypoxic stress during waterlogging and hydroponic culturing
Land plants are often subjected to low oxygen concentrations in specific tissues during their development and in response to decreased environmental oxygen availability caused by waterlogging, flooding, and hydroponic culturing [1]
This hypoxia-mediated elevation of Ca2+ is fundamental for the activation of genes and synthesis of proteins required for acclimation responses at the cellular, tissue, and organismal levels [6, 12]
Summary
Plants often suffer from hypoxic stress during waterlogging and hydroponic culturing. This study investigated the response of cucumber (Cucumis sativus L.) plant growth parameters, leaf photosynthesis, chlorophyll fluorescence, fast chlorophyll a fluorescence transient (OJIP), and fruit quality parameters to hypoxic stress alleviated by exogenous calcium. Land plants are often subjected to low oxygen concentrations in specific tissues during their development and in response to decreased environmental oxygen availability caused by waterlogging, flooding, and hydroponic culturing [1]. The involvement of calcium in hypoxia responses has been observed in many plants such as rice, wheat, and cucumber [10, 11] This hypoxia-mediated elevation of Ca2+ is fundamental for the activation of genes and synthesis of proteins required for acclimation responses at the cellular, tissue, and organismal levels [6, 12]. Green plants need PSII to absorb energy from sunlight to support fruit development and ripening, but harnessing this tremendous light energy during photosynthesis carries great risk [15], especially when plants suffered from environmental stresses such as salinity [16] and heat stress [17]
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