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1

Growth rate of duckweeds (Lemnaceae) in relation to the internal and ambient nutrient concentrations - testing the Droop and Monod models

100%
Kufel L., Strzalek M., Wysokinska U., Biardzka E., Okninska S., Rys K.
Polish Journal of Ecology
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2012
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tom 60
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nr 2
The Monod model describes the relationship between growth rate and ambient nutrient concentration, the Droop model focuses on internal nutrient resources as the driving factor. Both were applied mainly to explain phytoplankton dynamics in lakes or in experimental cultures. Our test plants were two species of duckweeds – Lemna minor L. and Spirodela polyrhiza (L.) Schleiden sampled from 18 natural stands situated in 6 different water bodies. Plants were grown outdoor in original lake water or in mineral media of varying N and P concentrations (0–21 mg N-NO3 L-1 and 0–1853 μg P-PO4 L-1 for L.minor and 0–4.2 mg N-NO3 L-1 and 0–371 μg P-PO4 L-1 for S. polyrhiza). Moreover, we analysed concentrations of mineral forms of N and P in lake water and tissue nutrient concentrations in plants. Tissue N of both plants was significantly correlated with ambient inorganic nitrogen sources, no such relationship was observed for tissue P. The growth rate of both plants measured under experimental outdoor conditions was better explained by tissue N and P variability (the Droop model) than by the external nutrient availability (the Monod model). The latter also failed to fit the growth rate of both plants in artificial mineral media with a decreasing gradient of N and P concentrations. The plants grew at the expense of internal N and P resources which remarkably declined during 9-day long experiments. Calculated minimum tissue contents (11.19 ± 1.11 mg N g-1 and 0.97 ± 0.07 mg P g-1 in L. minor and 6.10 ± 1.85 mg N and 1.25 ± 0.37 mg P g-1 in S. polyrhiza) show that the latter species would be a superior competitor under N limiting conditions and the former – under P limitation. We confront obtained results with literature data on N uptake kinetics and postulate that the luxury consumption of nutrients and plant growth dependent mainly on internal N and P resources might be an adaptation of duckweeds to varying habitat conditions typical of astatic water bodies.
2

Starch grain surface and starch degradation in turions of the duckweed Spirodela polyrhiza [Lemnaceae]

100%
Appenroth K. J., Reimann R., Krok F., Szymonska J.
Żywność Nauka Technologia Jakość. Suplement
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2002
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tom 09
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nr 4
Turions are survival organs of aquatic plants such as the great duckweed {Spirodela polyrhiza). They consist of approximately 50% storage starch (per dry weight) used to support the growth of newly formed sprouts following germination. They could be employed as a good model system for investigations of the storage starch degradation in plants. To induce starch degradation in the plant cells turions must be irradiated for a few days with continuous light absorbed by the plant photoreceptor phytochrome. During such treatment changes in the profile of proteins associated with the starch grain surface have been observed. It was shown by in vitro binding studies that several proteins (α-amylase, starch dikinase R1, ß- amylase) are desorbed from the surface or lose the ability to bind to it. This effect was especially obvious when starch grains from turions irradiated for 4 days (irradiated samples) were compared to those from turions kept in darkness (dark control). A hypothesis was presented that unknown changes in the surface properties of starch grains might be very important in the mechanism of starch degradation, by altering the binding of proteins. The aim of the study was to investigate these properties immediately before and after the start of the starch degradation. Precise structural analysis of the starch grain surface was performed using a non- contact atomic force microscopy (nc-AFM). The grain surface revealed increasing roughness and a reduced density of the structural elements in the samples after irradiation. Two different kinds of randomly organized surface elements were detected by nc-AFM: the one type of a globular structure and the other one more oblong. They could be considered as the carbohydrate lamellas situated in the different way at the starch granule surface. Both were observed to become larger after irradiation. This might be a result of binding of water molecules to the carbohydrate lamellas or bending the surface carbohydrate helices into superhelices by new inter-carbohydrate hydrogen bonds. Such a modification of the starch granule surface could be a consequence of events started by the photoreceptor phytochrome involving starch phosphorylation / dephosphorylation, perhaps mediated by the newly discovered starch dikinase.
3

Biochemical changes in an aquatic macrophyte Spirodela polyrhiza [L.] growing in different ecological conditions at Bhagalpur, Bihar [India]

100%
Nayak M. R., Choudhary S. K.
Polskie Archiwum Hydrobiologii
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1997
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tom 44
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nr 3
4

Nitrate reductase inactivator from Spirodela polyrhiza [L.] Schleiden

100%
Jerzykiewicz J., Konieczna M., Klobus G., Buczek J.
Acta Physiologiae Plantarum
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1999
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tom 21
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nr 4
5

Species co-occurrence patterns in pleustonic plant communities [class Lemnetea]: are there assembly rules governing pleustonic community assembly?

61%
Wolek J.
Fragmenta Floristica et Geobotanica. Supplementum
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1997
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tom 05
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