Control of Nutrient Solution pH with an Ion Exchange System: Effect on Soybean Nodulation

186

122

Since N03-availability in the rooting medium seriously limits symbiotic N2 fixation by soybean (Glycine max [L.] Merr.), studies were initiated to select nodulation mutants which were more tolerant to N03-and were adapted to the Midwest area of the United States. Three independent mutants were selected in the M2 generation from ethyl methanesulfonate or N-nitroso-N-methylurea mutagenized Williams seed. All three mutants (designated NODI-3, NOD2-4, and NOD3-7) were more extensively nodulated (427 to 770 nodules plant-1) than the Williams parent (187 nodules plant1) under zero-N growth conditions. This Since the nts mutants selected by Gresshofls group were derived from the cultivar Bragg which is a Maturity Group VII line and cannot be grown to maturity under Midwest growing conditions, the current study was initiated to select nodulation mutants from a background which can be field tested in the major Midwest soybean production area. This paper provides the initial characterization of three soybean lines with enhanced nodulation capability which were selected from mutagenized populations of Williams (Maturity Group III). MATERIALS AND METHODS Plant MaterialSoybean (Glycine max [L.] Merr., cv Williams) seeds were mutagenized with EMS or NMU as previously described (17). In brief, the four mutagen-treatments (two chemicals and two postwash intervals) consisted of presoaking all seed for 16 h in vigorously aerated water, then treating separate seed lots for 2 h with 50 mM EMS or 5 h with 2.5 mm NMU, followed by either 5-or 9-h postwashes. The mutagenized seed (designated M,) was planted in the field and, at maturity, the four M2 seed lots were individually bulk harvested. The M2 seed lots were then screened for nodulation mutants either in the field or in greenhouse gravel beds.

“…Nitrate treatments were as noted below with specific experiments. The solution pH was maintained at pH 6.5 ± 0.5 by the use of ion exchange resin columns as previously described (10).…”

Section: Evaluation Of Mutants Plant Culturementioning

confidence: 99%

Selection and Initial Characterization of Partially Nitrate Tolerant Nodulation Mutants of Soybean

Gremaud

Harper²

1989

186

122

“…In most instances, the hydroponic growth medium contained nitrate and/or ammonia and was buffered with 1.0 mm phosphate. Ammonia and nitrate, however, may repress dinitrogen fixation in soybeans (8,21). Hence, to establish the maximum potential rate of dinitrogen fixation in a soybean plant, it is desirable to deprive the plant of ammonia and/or nitrate. '…”

Section: Introductionmentioning

confidence: 99%

“…It has been suggested that excess solid CaCo3 may serve as a suitable buffer (22), but high concentrations of carbonate promote both phosphate uptake and chlorosis (13,16). Thus, Amberlite IRC resins were proposed as buffers (8,13). Unfortunately, Amberlite IRC resins also can bind trace metal ions; hence, a simple solution to the buffering problem has not been reported.…”

mentioning

confidence: 99%

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Hydroponic Growth and the Nondestructive Assay for Dinitrogen Fixation

Imsande¹,

Ralston²

1981

Hydroponic growth medium must be well buffered if it is to support sustained plant growth. Athough 1.0 milar phosphate is commonly used as a buffer for hydroponic growth media, at that concentration It is generally toxic to a soybean plant that derives Its nitrogen solely from dinitrogen fixati On the other hand, we show that 1.0 to 2.0 milllmolar 2-(N-morpbolno)ethanesulfonic acid, pK. 6.1, has excelent buffering capacity, and It neither interferes with nor contributes nutritionally to soybean plant growth. Furthermore, it neither impedes nodulation nor the assay of dien fixatio Hence, soybean plants grown hydroponically on a medium pemented with 1.0 to 2.0 millm r 2-(N-morpho- Under conditions of nitrogen deprivation, however, 1.0 mm phosphate is often toxic to hydroponically grown soybeans (9, 13). This toxicity can be overcome by reducing the concentration of phosphate to 0.1 mM; this, however, essentially abolishes the buffering capacity of the growth medium. It has been suggested that excess solid CaCo3 may serve as a suitable buffer (22), but high concentrations of carbonate promote both phosphate uptake and chlorosis (13,16). Thus, Amberlite IRC resins were proposed as buffers (8, 13). Unfortunately, Amberlite IRC resins also can bind trace metal ions; hence, a simple solution to the buffering problem has not been reported.The most widely used procedure for the assay of dinitrogen fixation by leguminous plants relies upon the reduction of acetylene to ethylene (1,4,7,17,19). It should be recalled, however, that both acetylene and ethylene dissolve readily in water (3). Thus, the acetylene reduction assay procedure should be performed in the absence of aqueous medium or soil moisture.Combining the concept of hydroponic growth and the inexpensive, yet sensitive, acetylene reduction technique, we have devised a simple, rapid, reproducible assay procedure whereby the rate of dinitrogen fixation by individual plants can be measured throughout the lifetime of those plants. We also report that Mes (pKa of 6.1) satisfactorily buffers soybean hydroponic growth medium, permits excellent plant growth, and does not interfere with dinitrogen fixation.One of the major problems in attempting to increase dinitrogen fixation in legumes is the identification of those plants that are genetically endowed for enhanced dinitrogen fixation (1 1). Screen (2,8,13,(20)(21)(22). In most instances, the hydroponic growth medium contained nitrate and/or ammonia and was buffered with 1.0 mm phosphate. Ammonia and nitrate, however, may repress dinitrogen fixation in soybeans (8,21). Hence, to establish the maximum potential rate of dinitrogen fixation in a soybean plant, it is desirable to deprive the plant of ammonia and/or nitrate. '

“…The nts382 line ' Supported in part by the American Soybean Association, Re (18). The 7-L hydroponic rooting medium included ion exchange resin columns for maintenance of pH at 6.5 (6). The …”

mentioning

confidence: 99%

Nitrogen Fixation of Nodulation Mutants of Soybean as Affected by Nitrate

Wu¹,

Harper²

1990

It was previously reported that three soybean (Glycine max [L.] Merr.) nodulation mutants (NOD1-3, NOD2-4, and NOD3-7) were partially tolerant to nitrate when nitrate was supplied simultaneously with inoculation at the time of transplanting. The current study evaluated the effect of short-term nitrate treatment on nitrogenase activity (C2H2 reduction per plant and per nodule weight) and on relative abundance of ureides when nitrate application was delayed until plants were 3 weeks old and nodules were fully developed. Nitrogenase activity of the mutants was similar to that of Williams after an initial 3-week growth period, prior to nitrate treatment. Application of 5 millimolar nitrate resulted in greater inhibition of nitrogenase activity in Williams than in the three mutants. NOD1-3 was most tolerant of nitrate among the mutants tested and showed the highest relative abundance of ureides. Although C2H2 reduction activity per plant for NOD1-3 was higher than for Williams in the presence of nitrate, C2H2 reduction activity per gram of nodules was lower for NOD1-3 than for Williams in the presence and absence of nitrate. Compared to Williams, NOD1-3 had higher nodule ureide concentration and had similar glutamine synthetase activity in nodule tissue, indicating its nodules have normal nitrogen assimilation pathways. Nitrate application resulted in ureide accumulation in nodule tissue as well as in all plant parts assayed. Unexpectedly, nitrate treatment also increased the rate of ureide degradative capacity of leaves in both NOD1-3 and Williams. The data confirmed that nitrogenase activity of the selected nodulation mutants was more, but still only partially, tolerant of nitrate compared with the Williams parent.also had higher ureide concentration in its nodule tissue (13), likely due to limited growth of the mutant which may have impaired ureide utilization.Partially nitrate tolerant mutants of soybean (NOD1-3, NOD2-4, and NOD3-7) have also been selected from mutagenized Williams populations, and initial characterization of these mutants has been reported (4). The data indicated many similar characteristics of our mutants to those reported by Carroll et al. (1, 2). However, it is not known whether the nitrogenase activity of our mutants is tolerant to nitrate per se, since in the previous study (4) the effects of nitrate on infection steps and on subsequent nodule function could not be separated due to simultaneous inoculation and nitrate addition. Using "5N analysis it was determined that NOD 1-3 fixed more '5N2 than Williams, when grown on urea, and that all three nodulation mutants symbiotically fixed more N2 than wild type when the mutants were grown on nitrate (1 1). This confirmed the earlier report based on C2H2 reduction assays (4). In the present report, nitrate treatment was delayed until plant roots were well nodulated and capable of relatively high N2 fixation activity. N2 fixation was then assessed by using the in situ C2H2 reduction assay and determining the relative abundance of ureide...