Assimilate allocation priority as affected by nitrogen compounds in the xylem sap of tomato

Z. Gao, M. Sagi, H. Lips

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26 Scopus citations


Experiments with tomato (Lycopersicon esculentum (L.) Mill. cv. F144) grown in a greenhouse show that salinity (electric conductivity 6-7 dS m-1) and bicarbonate fertilization enhanced the accumulation of total solids in the fruits. Short term experiments with tomato seedlings were carried out simultaneously to study the effect of salinity (NaCl) and NO3/- concentrations on the activities of nitrate reductase (NR, EC, phosphoenolpyruvate carboxylase (PEPc, EC and glutamine synthetase (GS, EC in roots and leaves to study the mechanisms controlling assimilate transport to reproductive organs. The effect of bicarbonate fertilization on fruit quality was more pronounced under saline conditions which increased NO3/- reduction and assimilation in the roots. Salinity (100 mM NaCl) inhibited xylem loading of NO3/- and its subsequent transport to the shoot, shifting the main NO3/- reduction and assimilation in the plant from the shoot to the root. At the same time, addition of bicarbonate increased dark CO2 fixation in the roots, producing oxaloacetate, aspartate and asparagine. The resulting amino acids were transported from the root to the shoot through the xylem. Low NO3/- concentration, salinity and bicarbonate in the medium produced a higher ratio of N(red)/(N(red) + NO3/- ) in the xylem sap. The ratio N(red)/(N(red) + NO3/-) in the xylem sap was related to the determination of assimilate allocation priorities in the tomato plant. A high ratio correlated with increased allocation to reproductive organs while a low ratio, generated by fertilization with high NO3/- concentrations, stimulated the vegetative growth at the expense of fruit quality.

Original languageEnglish
Pages (from-to)807-815
Number of pages9
JournalPlant Physiology and Biochemistry
Issue number6
StatePublished - 1 Dec 1996


  • Assimilate
  • Lycopersicon esculentum
  • bicarbonate
  • fruit quality
  • nitrate assimilation
  • phosphoenolpyruvate carboxylase
  • salinity

ASJC Scopus subject areas

  • Physiology
  • Genetics
  • Plant Science


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