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Nitrate reductase and nitrate accumulation in relation to nitrate toxicity in Boronia megastigma
Author(s) -
Reddy K. S.,
Menary R. C.
Publication year - 1990
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1990.tb09059.x
Subject(s) - nitrate reductase , nitrate , toxicity , biology , horticulture , chemistry , botany , agronomy , ecology , organic chemistry
Moderate levels of N were toxic to the native Australian plant boronia ( Boronia megastigma Nees). As NO ‐ 3 is the major N form available for plants under cultivated conditions, NO ‐ 3 reduction and accumulation patterns in boronia were examined following the supply of various levels of NO ‐ 3 to understand the physiological basis of this toxicity. At a low level of supplied NO ‐ 3 [15 mmol (plant) ‐1 ], NO ‐ 3 was reduced without any detectable accumulation and without nitrate reductase activity (NRA) reaching its maximum capacity. When higher NO ‐ 3 levels [≥25 mmol (plant) ‐1 ] were supplied, both NRA and NO ‐ 3 accumulation increased further. However, NRA increased to a maximum of ca 500 nmol NO ‐ 3 (g fresh weight) ‐1 h ‐1 , both in the roots and leaves, irrespective of a 4‐fold difference in the levels of supplied NO ‐ 3 , whereas NO ‐ 3 continued to accumulate in proportion to the level of supplied NO ‐ 3 . Chlorotic toxicity symptoms appeared on the leaves at an accumulation of ca 32 μmol NO ‐ 3 (g fresh weight) ‐1 . High endogenous NO ‐ 3 concentrations inhibited NRA. The low level of NRA in boronia was not limited by NO ‐ 3 or electron donor availability. It is concluded that the low NR enzyme activity is a genetic adaptation to the low NO ‐ 3 availability in the native soils of boronia. Thus, when NO ‐ 3 supply is high, the plat cannot reduce it at high rates, leading to large and toxic accumulations of the ion in the leaf tissues.