Elvia Mariam Lis Martinez Stark

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...

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...

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...

Effects of Seasonal Nitrate Flush on Nitrogen Metabolism and Soluble Fractions Accumulation in Two Rice Varieties

ABSTRACT Two rice varieties, ‘Piaui’ (a landrace) and ‘IAC-47’ (an improved variety), were grown in nutrient solution containing 20 mg nitrate (NO3 −)-nitrogen (N) L− 1 up to 32 days after germination (DAG). After this, a group of plants received 200 mg NO3 −NL− 1, while the other was kept at 20 mg NO3 −NL− 1 up to 42 DAG. From 42 until 56 DAG, all plants received 5 mg NO3 −NL− 1. Plants were collected at 42 and 56 DAG, soluble fractions, nitrate reductase (NR) and GS enzymatic activities were determined. The nutritional history of the plants affected significantly the uptake and use of nitrogen (N), and should be taken into consideration in the studies of N-use efficiency. The variety ‘Piaui’ was more efficient than ‘IAC-47’ in N-uptake use, accumulating more NO3 − in its tissues at the initial phases of its cycle for subsequent utilization.

Enzymes of Nitrogen Metabolism and Proteases Activity in Hairy Roots of Clover and Carrots, with and without Arbuscular Mycorrhizal Fungi

ABSTRACT Hairy roots can be used for metabolic studies and also as a substrate for arbuscular mycorrhizal fungi (AMF). However, little is known about the behavior of these roots when infected with AMF. The metabolism of hairy roots grown with or without AMF, on two culture media, was investigated. An increase in protease activity was observed when the roots were cultured on medium with high nitrogen (N)-content. Glutamate synthase (GOGAT) and glutamate dehydrogenase (GDH) activities increased along the development in both carrot and clover hairy roots. With the advancement of root senescence (at 132 d) a greater degradation of root tissue occurred, which was characterized by an increase in catabolic enzymes activity (proteases and GDH deamination). The results indicate that the glutamine synthetase/GOGAT pathway, characteristic of plant tissues, ceases to act in synchronism and is replaced by the GDH/GOGAT system under conditions of stress or senescence when excess ammonium is present.

Efeito da disponibilidade de nitrato em solução nutritiva sobre a absorção de nitrogênio e atividade enzimática de duas cultivares de arroz

Two rice cultivars, Piaui (a landrace) and IAC-47 (an improved variety), were grown in nutrient solution containing 20 mg nitrate (N-NO3-) L-1 up to 32 days after germination (DAG). After this, a group of plants received 200 mg N-NO3- L-1, while the other was kept at 20 mg N-NO3- L-1 up to 42 DAG. From 42 until 56 DAG, all plants received 5 mg N-NO3- L-1 until the end of the cycle. These treatments were applied with the objective to simulate nitrate flush in tropical regions. Plants were collected at 133 DAG and separated in to leaf flag, leaf 2, stem and roots. N contents in amino acids, nitrate and ammonium forms, soluble sugars, nitrate reductase (NR) and glutamine synthetase (GS) enzymatic activities were determined. The evaluated varieties replay in different manner about accumulate and translocation nitrate. The variety Piaui seems to accumulate more NO3- in the tissues at the initial phases of its cycle, allowing subsequent remobilization. Flag leaf and leaf 2 seem to act as preferential sites of N accumulation, being this accumulation more intense in the landrace variety.