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Effect of NO 3 ‐ supply on N metabolism of potato plants ( Solanum tuberosum L.) with special focus on the tubers
Author(s) -
Mäck G.,
Schjoerring J. K.
Publication year - 2002
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1046/j.1365-3040.2002.00892.x
Subject(s) - shoot , solanum tuberosum , solanaceae , sucrose , starch , rubisco , glutamine , nitrate reductase , biology , horticulture , metabolism , fructose , botany , biochemistry , photosynthesis , amino acid , enzyme , gene
The response of the tubers to NO 3 – was studied in comparison to the other organs of Solanum tuberosum var. Sava, with special focus on: (a) whether tubers are capable of primary N assimilation; (b) whether N assimilation is stimulated by NO 3 – ; and (c) whether primary N assimilation in tubers is important for tuber growth. NO 3 – reduction via nitrate reductase (NR; EC 1.6.6.1) and NH 4 + assimilation via glutamine synthetase (GS; EC 6.3.1.2) occurred predominantly in the shoots, but up to 20% was contributed by the tubers under low‐NO 3 – conditions. NR activation was highest in tubers (up to 90%) and declined in all organs with increasing NO 3 – supply. NR and GS activity responded with a decline in tubers and roots as opposed to an increase in the shoots. This corresponded to relative organ growth: growth of tubers and roots was stimulated relative to that of shoots at a limiting NO 3 – supply. Absolute growth of all organs was stimulated by NO 3 – , whereas tuber number declined. The concentration of N compounds increased with NO 3 – supply in all organs: NO 3 – increased most dramatically in the shoots (81‐fold), free amino acids most markedly in the tubers (three‐fold). The amount of patatin and of the 22 kDa protein complex in the tuber reached a minimum when the amount of Rubisco in the shoot reached maximum as a response to NO 3 – supply. Tuber sucrose and starch increased by 40%, whereas glucose and fructose declined two‐fold as plant N status increased. It is concluded that tubers are potentially N autotroph organs with capacity for de novo synthesis of amino acids. Primary N assimilation in tubers, however, declines with increasing NO 3 – supply and is not of major importance for tuber growth.