Nitrogen Accumulation in the Roots of Tulip Plants (Tulipa gesneriana)

Tulip plants were planted in October and grown in culture solution in a glasshouse under natural conditions. One group of plants was cultivated in a medium containing nitrogen, while the other group in a nitrogen-free medium (—N treatment). Plants were first harvested in December, when the roots were developing actively. The total nitrogen content in the roots in the case of N treatment was very high (about 8.5%/dry weight), although that in the case of —N treatment was low (2.2%/dry weight). The absorbed nitrogen in the roots was accumulated mainly in the “80% ethanol soluble fraction” supplemented with the “water soluble but 80% ethanol insoluble fraction,” and glutamine was a major nitrogen constituent. On the other hand, γ-methyleneglutamine (γ-MGln) was a predominant amino acid in the roots in the case of —N treatment. Plants grown in the N medium were subsequently harvested at the flowering stage in April. At this stage the roots were absorbing nitrogen very actively and transporting it to the leaves and bulblets, and γ-MGln was a major amino acid. This finding suggests that γ-MGln was produced in the roots and transported to the other organs at the flowering stage.