Manlio Silvestre Fernandes

Mineral Nitrogen in Plant Physiology and Plant Nutrition

Abstract Nitrogen (N) nutrition enhances metabolic processes that influences the physicochemical environment at the soil-root interface, modifies rhizosphere conditions, interferes with the uptake of cations and anions, and enhances or represses the activity of several enzyme systems. Also, it affects growth patterns, protein content, and protein quality of seeds. Ammonium (NH4)-N nutrition increases anion uptake, free amino-N/protein ratios, and acidity of root free space; it reduces carbohydrate levels in plant tissues. NO3-N nutrition results in higher cation uptake, higher carbohydrate content in tissues, and alkalinization of root free space. N-Assimilation interferes with the allocation of dry matter and energy, which causes different growth rates of plant parts. In this article we review the effects of mineral-N nutrition on uptake of cations and anions, activity of enzymes, growth patterns of roots and shoots, and water use efficiency, protein content, and protein quality of seeds.

Participatory maize breeding for low nitrogen tolerance

The local maize variety Sol da Manhã has a broad genetic background. It was identified in 1985 in a participatory evaluation trial as being suitable for cultivation under low soil fertility conditions in Sol da Manhã, situated in Seropédica, State of Rio de Janeiro, Brazil. The variety was then improved for 6 selection cycles by the formal breeding sector at the experimental station of Embrapa Agrobiologia. There were three cycles of mass selection, one selection cycle between and within half-sib families, one selection cycle within full-sib families, and one selection cycle between and within S1 families. Thereafter, the variety was improved in collaboration with the informal sector, viz. a group of farmers of the agricultural community of Sol da Manhã for 6 cycles of mass selection. The variety was evaluated in 1994 in field trials for grain yield and nitrogen use efficiency. Sol da Manhã can be characterised as efficient in nitrogen use, under both favourable and unfavourable growing conditions.

Nitrogen remobilization during the reproductive period in two Brazilian rice varieties

Abstract Two rice varieties, IAC‐47 (improved) and Piaui (traditional), were grown in a greenhouse with and without foliar nitrogen (N) supplementation at 10 and 20 days after anthesis (DAA). Changes in N content in shoots (leaves+ sheaths+stalks) and grains were monitored at regular intervals from five days before anthesis (5 DBA) to grain maturity (28 DAA). In the controls of both varieties, the decrease of total N in the shoot was proportional to the increase in total N in the grains. At anthesis, variety IAC‐47 exhibited a higher level of total N in the shoot than variety Piaui (9.32 mg N g‐1 versus 7.22 mg N g‐1). At 28 DAA, IAC‐47 exhibited a lower level of grain crude protein than Piaui (66.5 mg N g‐1 versus 74.7 mg N g‐1). In Piaui, the highest level of protein N in the flag leaf occurred at the time‐1 of anthesis and decreased with grain maturity. In IAC‐47, the protein N of the flag leaf increased parallel to grain N up to 10 DAA. The lower level of crude protein in the grains of IAC‐47 was perh...

Isoforms of plasma membrane H+-ATPase in rice root and shoot are differentially induced by starvation and resupply of NO3− or NH4+

The goal of this study was to evaluate the effects of nitrogen starvation and resupply in 10 PM H+-ATPase isoforms and the expression of NO₃⁻ and NH₄+ transporters in rice. The net uptake of both forms of NO₃⁻-N or NH₄+-N was increased with its resupply. Resupply of NO₃⁻ resulted in induction of the following PM H+-ATPase isoforms, OsA1, OsA2, OsA5 and OsA7 in the shoots and OsA2, OsA5, OsA7 and OsA8 in the roots. Resupply of NH₄+ resulted in the induction of the following OsA1, OsA3 and OsA7 isoforms in the roots while OsA1 was induced in the shoots. It was observed that increased PM H+-ATPase activity also resulted in increased net uptake of NO₃⁻ and NH₄+. In the roots, OsNRT2.1 and OsNRT2.2 were induced by NO₃⁻ resupply, while OsAMT1.1 and OsAMT1.2 were induced by NH₄+ deficiency. The results showed that the expression of PM H+-ATPase isoforms is related to NO₃⁻ and NH₄+ transporters as well as in which section of the plant it takes place. PM H+-ATPase isoforms OsA2 and OsA7 displayed the strongest induction in response to N resupply, therefore indicating that these genes could be involved in N uptake in rice.

Compostos nitrogenados e açúcares solúveis em tecidos de alface orgânica, hidropônica e convencional

The distribution of some physiologic metabolites was evaluated in lettuce plants. Crest leaf lettuce plants were grown in the organic, hydroponic, and conventional system. Plants from each systems were split in eight parts (old, medium, and new leaf limbos, old, medium, and new main leaf veins, stem and root). Analyses of nitrate, amino-N, soluble sugars, and dry mass partition were accomplished throughout the parts. In general, considering the aerial part and roots, the contents resemble literature reports. However, when the analyses are accomplished in the different plant parts that compose the shoot, there are significant differences among parts in all analyzed metabolites. This allows a better choice of which part of the plant to analyze, depending on what one wants to observe. During physiologic studies of nitrogen metabolism, the separation of parts may be fundamental in the interpretation of the results. Nitrate, amino-N and free sugars showed great differences between shoot parts and stem. Stems appear to accumulate their maximum contents. The hydroponic lettuce showed nitrate contents greater than any other lettuces, reaching a maximum of 1,000 mg kg-1 of fresh mass in stems. Therefore, this amount is well below the maximum allowed by the European legislation for lettuce nitrate content. The results suggest that the lettuce stem works as the main accumulator of free nitrogen compounds, specially nitrate and amino-N, besides soluble sugars. Further studies are necessary to confirm if lettuce stems would have buffer function in case of large amounts of nitrogen uptake.

NITRATE UPTAKE KINETICS AND METABOLIC PARAMETERS IN TWO RICE VARIETIES GROWN IN HIGH AND LOW NITRATE

A study was conducted on the effect of nitrate (NO3) levels on nitrate uptake kinetics and nitrogen (N) metabolism in two rice varieties, Piaui (landrace) and IAC-47 (improved). At 27 days after germination (DAG) N supply was suspended for 72 h, and then restored as 0.2 or 2 mM nitrate. The nitrate uptake kinetics was determined by the depletion method. Plants were harvested at 0, 6, and 24 h. Plants of the Piaui variety under 0.2 mM nitrate showed higher Vmax and lower KM, indicating higher efficiency of nitrate uptake at low supply. In the sheaths of both varieties, there was a greater accumulation of nitrate and lower activities of nitrate reductase and glutamine synthetase. The V-H+-ATPase activity increased between 0 and 6 h accompanying the nitrate influx, suggesting that the activity of this proton pump is necessary for the antiport activity (H+/2NO− 3) involved in the accumulation of nitrate into vacuoles.

Foliar spraying of rice with nitrogen: Effect on protein levels, protein fractions, and grain weight

Abstract Grain yield and grain protein levels are usually negatively correlated. However, when the appropriate timing for nitrogen (N) supplementation is used, a significant increase in rice grain protein can be obtained without a corresponding decrease in grain yield. Increased N doses, equivalent to 40, 80, and 120 kg N ha‐1, applied at 10 and 20 days after anthesis (DAA), led to 13, 27, and 18% increases in grain crude protein, respectively, compared to the control. The shoot weight of plants receiving foliar spray of N, did not differ significantly from that of untreated check plants, indicating that the extra N was utilized for other processes. The highest crude protein level (86.2 mg g‐1) was obtained at 40+40 kg N ha‐1, whereas the crude protein content, resulting from the highest N dose (60+60 kg ha‐1), was only 80.0 mg g‐1. Glutelin was the fraction that most contributed to the increase in grain protein content. A positive correlation between crude protein and glutelin level (r=+0.92**) indicated...

Effects of supplemental‐nitrogen on the quality of rice proteins

Abstract A study was conducted on the effect of supplemental nitrogen (N) (20 hg/ha) applied as a foliar spray or to the soil on seed production, protein percentage, and protein fractions of rice. Plants were grown in a greenhouse over two different periods of time, i.e., August 1988 to January 1989 (Period I), and December 1988 to April 1989 (Period II). Nitrogen was applied to the leaves 10 and 20 days after anthesis (DAA), and to the soil at anthesis and at 15 DAA. Average temperature was 28.7°C during Period I and 32°C during Period II, corresponding to 18.7 and 22.0 growing degree‐day/day (GDD/day), respectively. The difference in GDD/day reduced the plant cycle from 130 days during Period I to 109 days during Period II. Plants grown during Period II had larger numbers of spikelets, a higher percentage of “full grown grains”;, and higher grain weight. Although percentage crude protein was about the same for the two periods, prolamin content was increased and the albumin+globulin fraction was decrease...

Nitrogen Metabolism in Rice Cultivated Under Seasonal Flush of Nitrate

Abstract Two rice varieties, a land race (Piaui) and an improved variety (IAC-47), were cultivated in pots in a system that simulates the seasonal nitrate flushes in tropical soils. Piaui plants did accumulate more in the shoots than IAC-47, especially in the sheaths. Piaui plants have also shown a low nitrate reductase activity (NRA) at the early stages of growth, what may be and advantage for the accumulation of . Piaui plants showed a higher content and a lower NRA in the flag leaves at anthesis, while IAC-47 on the contrary showed lower content and higher NRA at anthesis. The data indicated that Piaui plants have apparently a higher N-use efficiency than IAC-47 plants do. This ability results in higher content of grain protein, even when growing in poor soils. These results suggest this to be related to a superior capacity of Piaui plants to take up from low nutrient soils, and store it in the reserve pools during the early stages of growth and development.

Effects of supplemental nitrogen on nitrogen‐assimilation enzymes, free amino nitrogen, soluble sugars, and crude protein of rice

Abstract An upland rice variety IAC‐47 was grown in a greenhouse to determine the effect of foliar nitrogen (N) supplementation during grain development on the activity of the N assimilation enzymes, nitrate reductase (NR) and glutamine synthetase (GS), on free amino‐N content and leaf soluble sugars, and on grain crude protein content. At 10 and 20 days after anthesis (DAA), the leaves were fertilized with a liquid fertilizer containing 32% N as 12.8% urea, 9.6% ammonium (NH4), and 9.6% nitrate (NO3) in increasing rates corresponding to 0,20+20, 40+40, and 60+60 kg N ha‐1. Leaves were collected twice (at 12 DAA and 14 DAA for GS activity, sugar and amino‐N content, and at 11 and 13 DAA for NRA) after each application of leaf N. The late foliar application of N increased significantly grain crude protein without a corresponding decrease in grain weight. The NR activity (NRA) increased after the foliar application of N. In the flag leaf, 60+60 kg N ha‐1 (21 DAA) resulted in higher NRA (20x over the control...