Abstract
This review focuses on recently characterized traits of the aquatic floating plant Lemna with an emphasis on its capacity to combine rapid growth with the accumulation of high levels of the essential human micronutrient zeaxanthin due to an unusual pigment composition not seen in other fast-growing plants. In addition, Lemna’s response to elevated CO2 was evaluated in the context of the source–sink balance between plant sugar production and consumption. These and other traits of Lemnaceae are compared with those of other floating aquatic plants as well as terrestrial plants adapted to different environments. It was concluded that the unique features of aquatic plants reflect adaptations to the freshwater environment, including rapid growth, high productivity, and exceptionally strong accumulation of high-quality vegetative storage protein and human antioxidant micronutrients. It was further concluded that the insensitivity of growth rate to environmental conditions and plant source–sink imbalance may allow duckweeds to take advantage of elevated atmospheric CO2 levels via particularly strong stimulation of biomass production and only minor declines in the growth of new tissue. It is proposed that declines in nutritional quality under elevated CO2 (due to regulatory adjustments in photosynthetic metabolism) may be mitigated by plant–microbe interaction, for which duckweeds have a high propensity.
Highlights
The smallest known flowering plants are found in the Lemnaceae family and are recognized for their attractive combination of extremely high growth rates [2,3] with high nutritional quality, including a high protein content, with all essential amino acids for humans, as well as a high content of essential human micronutrients [4]
Chloroplast-containing plant organs emit chlorophyll fluorescence, a signal that proorgans emit chlorophyll fluorescence, a signal that providesChloroplast-containing information about the plant fraction of absorbed light utilized in photosynthesis versus vides information about the fraction of absorbed light utilized in photosynthesis versus the the fraction dissipated alternatively in the form of thermal energy
We examine the possibility that duckweed may be less sensitive to the possible adverse effects of elevated CO2 on plant productivity than many other species
Summary
The smallest known flowering plants are found in the Lemnaceae family and are recognized (see recent comprehensive review by Acosta et al [1]) for their attractive combination of extremely high growth rates [2,3] with high nutritional quality, including a high protein content, with all essential amino acids for humans, as well as a high content of essential human micronutrients [4]. Additional traits of interest include duckweed’s ability to accumulate high levels of starch as well as their relatively low susceptibility to the undesirable effects of elevated atmospheric carbon dioxide levels (for details, see sections dedicated to these topics below). The pronounced tolerance of a wide range of growth light intensities and a remarkable capacity to accumulate high levels of antioxidant micronutrients, such as the essential carotenoid zeaxanthin, due to an unusual pigment composition not seen in fastgrowing land plants. The response to elevated CO2 as evaluated in the context of plant metabolic regulation of the source–sink balance (balance between the plant’s sugar production and consumption), carbon-to-nitrogen ratio, and redox homeostasis (balance of oxidants and antioxidants)
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