Difference of apoplastic NH4+ concentration in flue-cured tobacco varieties with different tolerance to nitrogen nutrition and assay of the related physiological parameters.

【Objective】 The objective of this study was to elucidate the relationship between the apoplastic NH4+ concentration and the nitrogen tolerance of flue-cured tobacco varieties and to provide a theoretical basis for selecting tobacco variety with different tolerance to nitrogen nutrition.【Method】 A pot experiment was carried out to study the difference of apoplastic NH4+ concentration in three flue-cured tobacco varieties,ZY90(tolerance to nitrogen),K326(moderate tolerance to nitrogen) and NC89(sensitive to nitrogen).【Result】 Apoplastic NH4+ concentration exhibited a steady increase in the three varieties.ZY90 and NC89 had higher and lower apoplastic NH4+ concentration,respectively.A sharp decrease in glutamine synthetase activity,apoplastic pH and total nitrogen content and a gradual increase glutamate dehydrogenase activity were also found.pH in apoplastic solution was lower than that in mesophyll throughout the experimental period.A significant positive correlation was found between glutamate dehydrogenase activity and apoplastic NH4+ concentration.Both glutamine synthetase activity and total nitrogen had a significant negative correlation with apoplastic NH4+ concentration.【Conclusion】 The tolerance to nitrogen nutrition of flue-cured tobacco variety had correlation with apoplastic NH4+ concentration and the activity of glutamine synthetase and glutamate dehydrogenase at late growth stage.It was deduced that the tobacco variety with high tolerance to nitrogen nutrition has higher apoplastic NH4+ concentration,glutamate dehydrogenase activity and ammonia volatilization and lower glutamine synthetase activity.