Abstract
Photoautotrophic suspension cultures have been established from various model and crop plants and proved to be valuable and robust experimental system to assess coordinated responses of primary and secondary metabolism to metabolic and stress related signals. The use of suspension cultures combines the ease of handling microalgae in microtiter plates with the advantage of testing physiological responses of higher plants, notably in combination with the assessment of the response of photosynthetic activity by PAM chlorophyll fluorescence imaging as well as monitoring changes in secondary metabolite production and ROS formation by steady state fluorescence of plant fluorophores or introduced fluorescent probes. Photoautotrophic cultures provide various advantages as fast, highly sensitive, robust and high-through-put experimental system for screening and characterization of the impact of toxic compounds on higher plants. This opinion article discusses and critically evaluates the potential of photoautotrophic cultures of higher plants in combination with fluorescence imaging assays in microtiter plates as a complement to existing guidelines for testing the toxicity of chemicals in plants.
Highlights
Being used in basic research for more than 40 years, higher plant photoautotrophic suspension culture cells are so far an unexplored experimental platform in toxicology that combines the advantage of the ease of handling microalgae for high-throughput screening and characterization in microtiter plates with the possibility to assess physiological responses of primary and secondary metabolism of higher plants fast, highly sensitive and with high precision by fluorescence imaging
The successful application of PA suspension cultures in different topics of basic science research has demonstrated that physiological responses and even complex coordinated regulatory mechanisms of PA suspension cultures correspond to those of intact higher plants and in some cases even provided the basis to identify such mechanisms in higher plant-microbe interactions
The in vitro grown PA cultures ensure a supply of cells of constant quality and make the need for special greenhouse infrastructures and personal resources obsolete as well as the medium and long term planning to have plants at a certain developmental stage available that is not influenced by changing environmental conditions throughout the year
Summary
Toxicity tests on plants are mostly based on growth inhibition and routine assay parameters such as seed germination, root or shoot elongation, wet or dry weight, leaf or frond number are determined [1] [2] [3]. An alternative solution to the slow growth inhibition tests, that does not give any insight into the targets, is method that directly or indirectly determines physiological parameters such as chlorophyll fluorescence (ChlF), multicolor fluorescence (MCF), reactive oxygen species (ROS) probes; oxygen evolution, carbon dioxide assimilation, respiration or transpiration. When used in combination with higher plants, these methods are time consuming, greenhouse space and labor demanding for testing and routine maintenance, and introduce uncertainty into the results due to the variability among individual plants and/or plant organs Given these limitations, there is a need for more sensitive, faster and high-throughput screening systems. This miniaturization of plant experimental material down to individual cells of PA culture allows to use the high-throughput approach as these suspension cultures can be handled in a similar way as microalgae (e.g., in microtiter plate assays) while retaining the features of a higher plant experimental system [17]
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