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Riccia fluitans utilizes two amino acid transport systems. System I handles neutral amino acids, while System II specifically transports basic amino acids, potentially via proton cotransport.

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Area of Science:

  • Plant Physiology
  • Membrane Transport
  • Biochemistry

Background:

  • Amino acid transport is crucial for plant nutrition and development.
  • The aquatic liverwort Riccia fluitans provides a model system for studying membrane transport mechanisms.

Purpose of the Study:

  • To investigate the transport mechanisms of various amino acids in Riccia fluitans.
  • To characterize the specificity and kinetics of different amino acid transport systems.

Main Methods:

  • Electrophysiological measurements (plasmalemma depolarization, electrical net current).
  • Uptake studies using radiolabeled amino acids ([(14)C]-glutamic acid, [(14)C]-histidine, [(14)C]-basic amino acids).
  • Manipulation of external pH and substrate concentrations.

Main Results:

  • Evidence for two distinct amino acid transport systems (System I for neutral, System II for basic amino acids).
  • System II exhibits stereoselectivity, favoring L-isomers.
  • Proton concentration significantly influences the transport of basic amino acids.
  • Acidic and neutral amino acid uptake shows distinct pH optima.

Conclusions:

  • Riccia fluitans possesses at least two amino acid transport systems with different substrate specificities.
  • System I transports neutral amino acids and neutral forms of acidic amino acids.
  • System II is specific for basic amino acids and may involve proton cotransport.