do not grow any further but can germinate and
start a new life cycle from the bottom of the
water body or mud when the water temperature
reaches about 15 °C. In addition, resting fronds
of the ivy duckweed (Lemna trisulca) and
Wolffiella gladiata with reduced air spaces can
accumulate starch and still rather slowly grow on
the bottom of the water, forming new but similar
fronds. However, the common duckweed (Lemna
minor), gibbous duckweed (Lemna gibba),
Lemna perpusilla, and some strains of Lemna
japonica produce starch-rich fronds that do not
sink to the bottom of the water but are just
pressed down under the ice cover during freezing
temperatures. Interestingly, formation of turions
as a survival and adaptive capacity of S. polyrhiza strains collected from a wide geographical
range seems to be genetically determined and
highly influenced by the mean annual temperature of habitats (Kuehdorf et al. 2013). Furthermore, the family displays significant inter- and
intraspecies differences of cell physiology (e.g.,
starch, protein, and oil contents) together with
duckweed potential for industrial applications
(Alvarado et al. 2008; Appenroth et al. 2017;
Hou et al. 2007; Mkandawire and Dudel 2005;
Tang et al. 2015; Yan et al. 2013; Zhang et al.
2009).
Due to their small and abbreviated structures,
morphological and physiological classification of
the 37 duckweed species (Spirodela: 2 species;
Landoltia: 1; Lemna: 13; Wolffiella: 10; Wolffia:
11) can be challenging. In the past decade, for
species assignment as well as resolving intraspecies differences, several attempts have been
carried out to employ molecular genotyping
techniques, including random amplified polymorphic DNA (RAPD; Martirosyan et al. 2008),
inter-simple sequence repeats (ISSR; Fu et al.
2017; Xue et al. 2012), simple sequence repeats
(SSR; Feng et al. 2017), amplified fragment
length polymorphism (AFLP; Bog et al. 2010,
2013), and DNA barcoding using plastid
sequences (Borisjuk et al. 2015; Wang et al.
2010) or nuclear ribosomal sequences (Tippery
et al. 2015). Although DNA barcoding using two
plastidic barcodes aids in identifying most
duckweed species (at least 30 among 37 species)
in a quite simple and straight forward manner,
combination of different techniques or using
additional barcodes may help to unambiguously
and economically assign remaining duckweed
species.
The Lemnaceae family was one of the earliest
model plants due to their ease of aseptic cultivation in the laboratory and simple morphology.
The second volume of Landolt and Kandeler’s
1987 monographic study contains 360 pages
dedicated to the physiological research of the
family in particular and plants as a whole (Landolt and Kandeler 1987). The professors who
organized the first duckweed conference summed
up the duckweed research stating that duckweeds
were the main model for plant biology from 1950
to 1990, when Arabidopsis and rice were used
for their sexual reproduction and applicability to
terrestrial crops (Zhao et al. 2012). In that time,
investigations of duckweeds revealed the
tryptophan-independent synthesis of auxin (Baldi
et al. 1991), translational regulation in eukaryotes
(Slovin and Tobin 1982), and seven of the first
stable plant mutants (Posner 1962). Today,
physiological studies continue largely in the
fields of circadian rhythm research, xenobiotic
plant–microbe interactions, and phytoremediation and toxicology. Starting in 2011, a biannual
series of international duckweed conferences in
research and applications has connected and
helped expand this research community and
increased public awareness and recognition of
duckweed economic and environmental importance (Zhao et al. 2012; Lam et al. 2014;
Appenroth et al. 2015). Together with the completion of the Spirodela genome in the year 2014
and rapid advances in sequencing technologies,
this resurgence of interest has resulted in a proliferation of genome and transcriptome sequences for duckweed species and ecotypes discussed
in the remainder of this book.
One of the largest fields of duckweed research
is ecotoxicology, where the widely distributed
Lemna species minor and gibba serve as model
plants to determine the effect of a compound on
an ecosystem. These growth tests have been
standardized in the International Organization for
Standardization’s protocol ISO 20079 which
1 Importance of Duckweeds in Basic Research and Their Industrial …
3
start a new life cycle from the bottom of the
water body or mud when the water temperature
reaches about 15 °C. In addition, resting fronds
of the ivy duckweed (Lemna trisulca) and
Wolffiella gladiata with reduced air spaces can
accumulate starch and still rather slowly grow on
the bottom of the water, forming new but similar
fronds. However, the common duckweed (Lemna
minor), gibbous duckweed (Lemna gibba),
Lemna perpusilla, and some strains of Lemna
japonica produce starch-rich fronds that do not
sink to the bottom of the water but are just
pressed down under the ice cover during freezing
temperatures. Interestingly, formation of turions
as a survival and adaptive capacity of S. polyrhiza strains collected from a wide geographical
range seems to be genetically determined and
highly influenced by the mean annual temperature of habitats (Kuehdorf et al. 2013). Furthermore, the family displays significant inter- and
intraspecies differences of cell physiology (e.g.,
starch, protein, and oil contents) together with
duckweed potential for industrial applications
(Alvarado et al. 2008; Appenroth et al. 2017;
Hou et al. 2007; Mkandawire and Dudel 2005;
Tang et al. 2015; Yan et al. 2013; Zhang et al.
2009).
Due to their small and abbreviated structures,
morphological and physiological classification of
the 37 duckweed species (Spirodela: 2 species;
Landoltia: 1; Lemna: 13; Wolffiella: 10; Wolffia:
11) can be challenging. In the past decade, for
species assignment as well as resolving intraspecies differences, several attempts have been
carried out to employ molecular genotyping
techniques, including random amplified polymorphic DNA (RAPD; Martirosyan et al. 2008),
inter-simple sequence repeats (ISSR; Fu et al.
2017; Xue et al. 2012), simple sequence repeats
(SSR; Feng et al. 2017), amplified fragment
length polymorphism (AFLP; Bog et al. 2010,
2013), and DNA barcoding using plastid
sequences (Borisjuk et al. 2015; Wang et al.
2010) or nuclear ribosomal sequences (Tippery
et al. 2015). Although DNA barcoding using two
plastidic barcodes aids in identifying most
duckweed species (at least 30 among 37 species)
in a quite simple and straight forward manner,
combination of different techniques or using
additional barcodes may help to unambiguously
and economically assign remaining duckweed
species.
The Lemnaceae family was one of the earliest
model plants due to their ease of aseptic cultivation in the laboratory and simple morphology.
The second volume of Landolt and Kandeler’s
1987 monographic study contains 360 pages
dedicated to the physiological research of the
family in particular and plants as a whole (Landolt and Kandeler 1987). The professors who
organized the first duckweed conference summed
up the duckweed research stating that duckweeds
were the main model for plant biology from 1950
to 1990, when Arabidopsis and rice were used
for their sexual reproduction and applicability to
terrestrial crops (Zhao et al. 2012). In that time,
investigations of duckweeds revealed the
tryptophan-independent synthesis of auxin (Baldi
et al. 1991), translational regulation in eukaryotes
(Slovin and Tobin 1982), and seven of the first
stable plant mutants (Posner 1962). Today,
physiological studies continue largely in the
fields of circadian rhythm research, xenobiotic
plant–microbe interactions, and phytoremediation and toxicology. Starting in 2011, a biannual
series of international duckweed conferences in
research and applications has connected and
helped expand this research community and
increased public awareness and recognition of
duckweed economic and environmental importance (Zhao et al. 2012; Lam et al. 2014;
Appenroth et al. 2015). Together with the completion of the Spirodela genome in the year 2014
and rapid advances in sequencing technologies,
this resurgence of interest has resulted in a proliferation of genome and transcriptome sequences for duckweed species and ecotypes discussed
in the remainder of this book.
One of the largest fields of duckweed research
is ecotoxicology, where the widely distributed
Lemna species minor and gibba serve as model
plants to determine the effect of a compound on
an ecosystem. These growth tests have been
standardized in the International Organization for
Standardization’s protocol ISO 20079 which
1 Importance of Duckweeds in Basic Research and Their Industrial …
3