Effects of environmental parameters on starch and soluble sugars in Lemna minor

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    The Lemnaceae are small aquatic macrophytes, comprising five genera (Spirodela, Landoltia, Lemna, Wolffia, Wolffiella) and 36 species (Bog et al., 2020). They are usually growing in slow flowing watercourses, ponds and lakes (Lahive et al., 2011). Lemna minor is one of the most widely spread duckweed species. It is a small vascular plant that floats on or just beneath the surface of the water, where it can form dense mats (Driever et al., 2005). It is also characterised by a fast reproduction rate, it can double its biomass within two days (Monette et al., 2006). Given its sensitivity towards different types of pollutants and high pollutant uptake capacity, the use of L. minor as toxicity indicator and as a tool in phytoremediation of polluted waters is broadly investigated (Maldonado et al., 2022; Oros and Toma, 2012; Ozyigit et al., 2021).

    When L. minor plants perform photosynthesis, light energy is absorbed by chlorophyll molecules in the thylakoid membranes and converted into ATP and NADPH. Both ATP and NADPH are used in the Calvin cycle in the stroma to produce three carbon sugars, like 3-phosphoglyceric acid, which can be used for the formation of glucose, sucrose, starch and other carbohydrates. Plants use sugars for their general metabolism, growth and development. Excess of sugars can be stored in soluble form in vacuoles or in polymeric form as starch in plastids (Patrick et al., 2013).

    Because of the high levels of sugars, starch and proteins, L. minor and other duckweeds are of interest for production of biofuels, biomaterials, animal feed and even for human food (Devlamynck et al., 2021; Faizal et al., 2021; Liu et al., 2021). The productivity of the duckweeds depends on the species, biomass production and growth conditions. Sree and Appenroth (2022) studied the accumulation of starch in 21 strains of all five genera as function of nutrient deficiency and concluded that starch content varies not only between duckweed species, but also between strains of the same species.

    In an ideal situation, a high amount of biomass is produced with high contents of sugars, starch and proteins. For example, for the production of bioethanol, the alcohol is resulting from the fermentation of sugars. Starch needs to be converted into simple sugars by e.g. enzymes. Increasing the amount of soluble sugars relative to the amount of starch lowers the costs for the industrial production of bioethanol (Patrick et al., 2013). By changing growth conditions, it is also possible to produce duckweed with higher amounts of sugars and starch and manipulating their ratio too (Sree and Appenroth, 2014; Yin et al., 2015).

    The starch content of L. minor varies depending on the growth conditions and it can be influenced by changing environmental parameters (salinity, nutrient deprivation, low or high temperatures, light intensity and photoperiod) or pollutants (e.g. heavy metals) (de Morais et al., 2019; Li et al., 2016; Sree and Appenroth, 2014; Yin et al., 2015; Zhao et al., 2014). Changing the environmental parameters in most cases results in stress conditions leading to growth retardation and accumulation of starch. This either by inhibition of photosynthesis or a stronger/earlier inhibition of growth resulting in lower growth rates and more carbohydrates that are not used for growth but stored as starch (Sree and Appenroth, 2014). Starch accumulation can also occur during daytime with increased light intensities and/or longer photoperiods and therefore provides more substrates for metabolism and growth during night (Yin et al., 2015).

    Sugars are essential compounds for plants to maintain many biochemical (e.g. photosynthesis, respiration) and physical processes (e.g. transpiration). Less information is available concerning the effects of environmental parameters on the sugar content of L. minor, but information is available for other duckweed species or plants. Salinity, low and high temperatures all lead to increased sugar concentrations in plants (Dubey and Singh, 1999; Gill et al., 2001; Strand et al., 1999). The accumulation of sugars is in direct relationship with photosynthesis, where high light intensities or longer photoperiods decrease the amount of sugars as a result of the higher storage of polymeric compounds such as starch and proteins. Pagliuso et al. (2018) found increasing soluble sugars concentrations in L. gibba at a higher light intensity. Nutrient deprivation has different effects on soluble sugars content. An increase in soluble sugars was observed in tomato plants when exposed to nitrogen deprivation, whereas a phosphorous deprivation leads to a decrease in soluble sugars (Khavari-Nejad et al., 2009).

    This study investigated the starch and soluble sugars contents in L. minor plants as function of environmental conditions (temperature, light irradiance and nutrients). The aim was to evaluate the contents of starch and soluble sugars in L. minor grown at different environmental conditions, without compromising decent growth. Our results form a basis for optimising plant cultivation conditions (including within phytoremediation applications) to increase the suitability of L. minor biomass for practical applications (e.g. biofuels, biomaterials, animal feed and even human nutrition).
    Original languageEnglish
    Article number107755
    Number of pages8
    JournalPlant Physiology and Biochemistry
    StatePublished - Jul 2023

    ASJC Scopus subject areas

    • Genetics
    • Physiology
    • Plant Science

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