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Effect of nitrate limitation on the photosynthetically active pools of aspartate and malate in maize, a NADP malic enzyme C 4 plant
Author(s) -
Khamis Saadi,
Lamaze Thierry,
Farineau Jack
Publication year - 1992
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.1399-3054.1992.tb04726.x
Subject(s) - photosynthesis , malic acid , malate dehydrogenase , biology , biochemistry , malic enzyme , enzyme , metabolism , botany , dehydrogenase , citric acid
After two weeks of moderate N restriction, growth of 3‐week‐old Zea mays L. plants was less than half that of the control and aspartate and malate levels in the leaves were severely suppressed (45 and 65% decrease, respectively). Since in NADP malic enzyme type C 4 plants, such as maize, malate and aspartate are intermediates in the C 4 photosynthetic pathway, the operation of the latter was investigated. Moderate nitrogen deficiency had only a small effect on the rate of photosynthesis (20% decrease) measured under 1000 umol m −2 s −1 irradiance. 14 CO 2 pulse‐ 12 CO 2 chase experiments combined with measurements of in vitro photosynthetic enzyme activities demonstrated the operation of a typical C 4 photosynthetic pathway in N‐restricted plants. The turnover rates of malate and aspartate molecules involved in the C 4 cycle were determined by the loss of label in the carbon 4 moiety of these molecules during the chase period. It is shown that N restriction did not alter the turnover of malate but greatly accelerated that of aspartate. The amounts of malate and aspartate moving through photosynthetically active pools were estimated using a kinetic model. For malate, the size of this pool appeared to be only slightly diminished whereas for aspartate the size of the corresponding pool decreased by a factor of 3. It is proposed that under moderate NO 3 − deficiency, despite deviations in malate metabolism leading to a pronounced decrease in the size of its cellular pool, a large amount of malate remained in the operation of the C 4 pathway. By contrast, the participation of aspartate in the operation of the C 4 pathway was greatly reduced.