Sonia Regina de Souza

Humic Acid Effect on Catalase Activity and the Generation of Reactive Oxygen Species in Corn (Zea mays)

Humic acids (HAs) have positive effects on plant physiology, but the molecular mechanisms underlying these events are only partially understood. The induction of root growth and emission of lateral roots (LRs) promoted by exogenous auxin is a natural phenomenon. Exogenous auxins are also associated with HA. Gas nitric oxide (NO) is a secondary messenger produced endogenously in plants. It is associated with metabolic events dependent on auxin. With the application of auxin, NO production is significantly increased, resulting in positive effects on plant physiology. Thus it is possible to evaluate the beneficial effects of the application of HA as an effect of auxin. To investigate the effects of HA the parameters of root growth, Zea mays was studied by evaluating the application of 3 mM C L−1 of HA extracted from Oxisol and 100 μM SNP (sodium nitroprusside) and the NO donor, subject to two N–NO3 −, high dose (5.0 mM N–NO3 −) and low dose (5.0 mM N–NO3 −). Treatments with HA and NO were positively increased, regardless of the N–NO3 − taken, as assessed by fresh weight and dry root, issue of LRs. The effects were more pronounced in the treatment with a lower dose of N–NO3 −. Detection of reactive oxygen species (ROS) in vivo and catalase activity were evaluated; these tests were associated with root growth. Under application of the bioactive substances tested, detection of ROS and catalase activity increased, especially in treatments with lower doses of N–NO3 −. The results of this experiment indicate that the effects of HA are dependent on ROS generation, which act as a messenger that induces root growth and the emission of LRs.

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.

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...

OsAMT1.3 expression alters rice ammonium uptake kinetics and root morphology

Abstract High-affinity ammonium transporters (AMT1) are responsible for ammonium (NH4+) acquisition and/or perception in the micromolar range, and their expressions can be differentially regulated by nitrogen (N) availability. The present study characterised the functions of the rice (Oryza sativa) OsAMT1.3 transporter to understand its contribution to NH4+ acquisition and plant adaptation to environments with low N availability. Transgenic rice plants were obtained to study the activity of the OsAMT1.3 promoter (POsAMT1.3:GFP:GUS) and the overexpression of the OsAMT1.3 gene (UBIL:OsAMT1.3:3xHA) in plants. The OsAMT1.3 promoter activity was induced strongly in the absence of N and occurred primarily in the zones of lateral root emission and root tips. Anatomical sections of the segment of root tips and the middle third showed a differential pattern of OsAMT1.3 activity. Analysis of the OsAMT1.1–1.3 transporter expression profiles indicated that overexpression of OsAMT1.3 positively affected OsAMT1.2 expression. When subjected to a low N supply, plants overexpressing OsAMT1.3 showed lower KM and Cmin values. Additionally, these lines showed longer roots with a higher area, volume, and number of tips. The data suggested that OsAMT1.3 is involved in the ability of rice plants to adapt to low NH4+ supplies.

Effects of nitrogen stress on proton-pumping and nitrogen metabolism in rice.

ABSTRACT Three rice (Oryza sativa L.) varieties: Caiapó (bred for upland crop), Piauí (a landrace), and IAC-47 (an improved variety) were used to study the effects of nitrogen (N) suppression in plant metabolism. Nitrogen suppression increased root growth in Caiapó plants. This growth was simultaneous with increases in hydrogen (H+)-pyrophosphatase (H+-PPase) and vacuolar H+-ATPase (V-H+-ATPase) activities in the roots of Piauí plants. The SDS-PAGE shows 73, 67, and 53 kDa fractions proteins accumulating in the tonoplast what agrees with the observed activities of H+-PPases and V-H+-ATPases. Piauí and IAC-47 varieties exhibited different responses from one another at the beginning of N-Stress: there was an increase in P-H+-ATPase activity for Piauí and a decrease for IAC-47. Piauí plants had a higher content of nitrate (NO3 −) in roots and sheaths, notwithstanding it mobilized less of this NO3 −-N during this growth period than did IAC-47. These results suggest that Piauí plants are better adapted to nutrient-poor environments.