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Physiology Pgr’s Nitrogen on Crop Growth Rate, Indole Acetic Acid Oxidase Activity Black Gram 19
the significant role of BR in enhancing the NAR in
black gram besides arriving strong correlation with
seed yield. The increase in NAR due to BR could be
assigned to its growth regulating activity, since its
activity is analogous to auxin and gibberellins.
The nitrate reductase is the rate-limiting enzyme in
nitrogen assimilation and is a key point of metabolic
regulation (Eilrich and Hageman, 1973) in crop plants.
Thus, NRase is intimately associated with the plant
growth and development (Sinha and Nicholas, 1981).
While observing the pattern of NRase activity in
groundnut throughout the growth period, Sung and
Sun (1990) reported that NRase activity declined
rapidly during post flowering stages. However in the
preseh foliage. The enzyme activity was further
triggered by combined effect of BR. Similar to this
finding, Sairam (1994) study high NRase activity was
extended up to pod filling stage, which might be due
to the additional dose of Urea applied throug observed
a significant increase in NRase activity due to
brassinolide application in wheat. Jaisingh et al. (1993)
also recorded an increased rate of enzyme activity due
to brassinolide application in Cicer aurietinum.
Besides brassinolide, CCC was also found effective in
triggering this enzyme activity as revealed in the
present study. Wasnik and Bagga (1992) also observed
the significant effect of CCC in enhancing the enzyme
activity in mungbean.
The IAA oxidase activity determines the auxin levels
and thereby apical dominance. It was also reported
that IAA oxidase activity was low in region of high
auxin content and high in region of low auxin content
(Galston and Dalberg, 1954). In the present
investigation, the time trend of IAA oxidase activity
revealed a decreasing trend up to pod filling stage.
Hormonal treatments played their differential role in
altering the auxin level. The treatment combination
with brassinolide effectively suppressed the enzyme
activity and maintained higher level of auxin in leaves.
This finding was in close confirmity with the result of
Han et al. (1988), in which foliar application of
brassinosteroid increased IAA synthesis in tobacco.
Helmy et al. (1997) also had similar finding with the
view that brassinisteroid application at 30 mg/L had
enhanced the auxin content in broad bean. Bindu
Joseph (2000) also revealed the significant influence
of BR on lowering the activity of IAA oxidase in
groundnut up to flowering stage of the crop. Thus
increase in auxin content by BR application would
have contributed to increased reproductive growth.
BR acted synergistically with auxin in stimulating cell
elongation (Katsumi, 1985) and ethylene production
(Arteca et al., 1995) suggesting that effects of BR are
mediated through auxin (Takeno and pharis, 1982) or
that BRs enhance tissue sensitivity to auxin (Mandava,
1988). BR induced increase in fresh weight of squash
cotyledons was accompanied by an increase in auxin
and decrease in ABA levels (Eun et al., 1989).
3 Materials and Methods
The present investigation was undertaken under field
condition to study the effect of nutrients and plant
growth regulators on growth and productivity of black
gram variety CO5. The research experiment was
carried out at Millet Breeding Station, Tamil Nadu
Agricultural University, Coimbatore during July to
October, 2007. Growth regulators like Naphthalene
Acetic Acid (NAA), Salicylic Acid (SA), Cycocel
(CCC), Brassinosteriod (BR), Humic Acid and the
nutrients such as Nitrogen, DAP, Boric Acid, Ferrous
Sulphate, Zinc Sulphate were used. The data were
statistically analyzed with the Design of Randomized
Block Design with three replication and the Plot size
of 4 × 3 m with Spacing of 30 × 10 cm. In this
research study has nine treatments and the details are
T 1: Control; T2: N 25 kg/ha + Urea 2% + NAA 40 ppm,
T 3: N 50 kg/ha + CCC 200 ppm; T4: N 25 kg/ha +
Urea 2% + CCC 200 ppm; T5 : N 25 kg/ha + Urea 2%
+ Humic acid 0.1%; T6: N 25 kg/ha + Urea 2% +
Salicylic acid 100 ppm; T7 : N 25 kg/ha + Urea 2% +
Brassinosteriod 0.1 ppm; T8: N 25 kg/ha + Urea 2% +
ZnSO4 0.5% + FeSO4 0.5% + Borax 0.2%; T9: N 25 kg/ha
+ Water spray. The CGR was calculated by employing
the formula of Watson (1956) and expressed as
g ·m -2·day-1. NAR (Net Assimilation Rate) was
calculated by using the formula of Gregory et al.
(1917) and subsequently modified by Williams (1946)
and expressed as mg·cm-2·day -1. Employing the
formula of Nicholas et al. (1976), the NR’ase enzyme
activity was calculated and expressed as µg
NO2 ·g-1·hr-1. The IAA-oxidase enzyme activity was
Genomics and Applied Biology