Relationships between Carbon Dioxide, Malate, and Nitrate Accumulation and Reduction in Corn (Zea mays L.) Seedlings

Abstract

The observation that exposure of the leaf canopy to increasing concentrations of CO2 (100-400 pill) decreases the influx of nitrate to the leaf blades, but not to the roots or stalks (largely leaf sheaths), was reconfirmed using 15N03-. Decreases in leaf nitrate supply were associated with decreases in induction of nitrate reductase, thus supporting the view that the influx of nitrate to a tissue is a major factor in regulation of the level of nitrate reductase. The whole plant 15N distribution data show that the CO2 effects were due to decreased influx of nitrate into the leaf blade rather than C02-enhanced nitrate reduction. The (22) found that the accumulation of nitrate by roots of illuminated intact corn plants was inversely related to their initial levels of malate (malate levels induced by pretreatment with K2CO3). There was no stoichiometry between NO3-accumulation and malate depletion during the uptake period. It was not established whether the malate in the roots was preventing NO3-uptake or stimulating NO3-translocation. They also showed that NO3-accumulation and induction of NRA in corn leaf blades were depressed when illuminated corn seedlings were supplied with NO3-(roots) and exposed (canopy) to increasing concentrations of CO2 in the air. The concentration of malate in the leaf blades increased with the increases in CO2 concentration (i.e. during the 3-hr treatment, malate levels increased 0.5, 2.5, and 3.1 ,tmol g-' fresh weight for the 100-, 300-, and 600-,ul/l CO2 treatments). In other experiments, a significant correlation (r = -0.75) was found between malate and NO3-concentration (sampled at midday) of leaf blades from corn seedlings grown under normal growth chamber conditions. Due to these observations, malate was implicated as the cause of the depressing effect of CO2 on NO3-accumulation in the leaf blade.Although Ben Zioni et al. (2) indicated that the reduction of NO3-in the shoot resulted in the production of malate, Mulder et al. (19)

Nitrate Assimilation and Crassulacean Acid Metabolism in Leaves of Kalanchoë fedtschenkoi Variety Marginata

“…3 and 4) as showing that the Kalanchoe leaf enzyme is similar to the enzyme in other leaves (2,3,17) in being activated during each day period. Light apparently is required to maintain maximum activity, but the daily pattem proceeds independent of light or dark in CAM as well as in other plant leaves.…”

“…In a variety of C3 and C4 leaf tissues it is widely recognized that NO3 assimilation each day via NO3 reductase involves daily changes in enzyme activity with light having a pronounced role in N03 assimilation (2,13,17). During CAM it is known that daily reciprocal cycles of synthesis and breakdown for acid versus starch occur in green tissue (18,(20)(21)(22).…”

“…However, there does not appear to be any direct relationship between nitrate reductase activity and the level of acid, its daily pattern or the amplitude of CAM. Though nitrate reductase is activated maximally each day by light, in Kalwwhoi leaves for six days the activity followed a precise daily pattern independent of continuous light or dark.In a variety of C3 and C4 leaf tissues it is widely recognized that NO3 assimilation each day via NO3 reductase involves daily changes in enzyme activity with light having a pronounced role in N03 assimilation (2,13,17). During CAM it is known that daily reciprocal cycles of synthesis and breakdown for acid versus starch occur in green tissue (18,(20)(21)(22).…”

Relationship between Nitrate Uptake, Flux, and Reduction and the Accumulation of Reduced Nitrogen in Maize (Zea mays L.)

“…NR was extracted from leaf blades as previously described (14). All leaves from the four plants in each pot were deribbed, composited, and chopped into 10-mm2 sections.…”

Effects of Certain Herbicides and Their Combinations on Nitrate and Nitrite Reduction

“…In leaves, these enzymes differ in cellular location, electron donor, and energy generation system. Nitrate reductase is located in the cytoplasm (16), uses NADH as its electron donor (2), and derives its source of NADH primarily from the oxidation of 3-P-glyceraldehyde (11) or malate (15). Nitrite reductase is located in the chloroplast (16), utilizes reduced ferredoxin as its electron donor (14), and derives its reductive energy from photosynthetic electron flow (14).…”