Y. D. Singh

Genotypic variations and influence of diurnal temperature on cotton fibre development

Two commercially important characters of cotton yarn — the fibre length and dry-weight per seed — revealed marked genotypic variations amongst nine cultivars drawn from four Gossypium species. The growth kinetics showed that both rate and duration of fibre elongation contributed significantly to the variation in final fibre length. The variation in fibre dry-weight per seed, on the other hand, showed significant correlation only with rate of dry-matter accumulation (P < 0.01). Influence of diurnal temperature during boll development in the cultivar SRT-1 revealed significant effects of minimum temperature. A decrease in minimum temperature increased the duration of both fibre elongation and dry-matter accumulation, while it lowered the rates of both elongation and dry-matter accumulation. Additionally, the final dry-weight per seed increased with increasing minimum temperature, whereas no such effect was descernible for final fibre length. It is proposed that such analyses may be useful in determining the adaptability of cotton cultivars to environmental conditions, and in breeding programmes.

Role of peroxidase and esterase activities during cotton fiber development

Cytoplasmic and salt-extracted wall peroxidase and nonspecific esterase activities along with growth analysis were investigated during the entire period of cotton fiber development. Both the peroxidase fractions, when assayed with chlorogenic and ferulic acids as substrates, recorded low levels during the fiber elongation phase, and a close relationship between cessation of elongation growth and increase in peroxidase activity was discernible. Nonspecific esterase activity in both cytoplasmic and salt-extracted fractions, on the other hand, showed higher activity during the elongation phase, whereas during the secondary thickening phase it decreased. The role of cytoplasmic peroxidase in IAA oxidation is discussed. It is suggested that esterases and peroxidases associated with wall fractions may well be involved in turnover of phenolic acids that are cross-linked to wall polysaccharides.

Light and nitrate induction of nitrate reductase in kinetin-and gibberellic acid-treated mustard cotyledons

Nitrate reductase activity in gibberellic acid and kinetin treated mustard (Brassica juncea Coss. cv. T-59 ‘Varuna’) seedlings, grown in the presence or absence of light and/or NO3 was investigated. While both light and NO3, alone could induce NR activity, their combination showed additive effects. Kinetin treatment significantly promoted both light- and NO3- induced NR activities, assayed by either in vivo or in vitro techniques, whereas, gibberellic acid was almost ineffective. In the absence of both light and NO3, however, phytohormones alone could not induce NR activity. Both light-induced and NO3 induced NR fractions had a pH optima of 7.5, preferred NADH as an electron donor (NADH: NADPH ratio 2.5) and Km values for NO3 was 0.2 mM. Actinomycin D, cycloheximide and tungstate were equally effective in suppressing the development of NR activity after exposure to light or NO3. These results indicate that two independent NR fractions operate, with apparently identical properties but separate control mechanisms.

Distribution of Indoleacetic Acid Oxidase, Peroxidase, and Esterase Activities in Relation to Elongation Growth in Pearl Millet Internode

Summary The mean cell length along a differentiating internode, and the associated changes in total phenolic content and activities of IAA oxidase, peroxidase, and non-specific esterase were examined in pearl millet. The rate of cell elongation per mm showed an inverse relation with cytoplasmic IAA oxidase activity. Cytoplasmic peroxidase activity when assayed with ferulic acid and caffeic acid as hydrogen donors, showed similar trends to that of IAA oxidase, whereas with chlorogenic acid as hydrogen donor, it revealed an entirely different trend. Ionically bound wall peroxidase activity increased as the distance from the nodal plate increased, showing a peak activity in the 15-20 mm zone, which was much before the cessation of the elongation zone. Total phenolic content exhibited a clear inverse relationship with the rate of cell elongation. Wall-bound non-specific esterases also showed an increasing trend and maximum activity was recorded in the maturation zone. These results are discussed in relation to the proposed function of peroxdases and esterases in the cessation of elongation growth.

Physiological and Biochemical Changes Associated with Cotton Fibre Development. III. Indolyl-3-acetaldehyde Dehydrogenase

Summary Growth parameters and indolyl-3-acetaldehyde dehydrogenase activity were investigated during the entire period of cotton ( Gossypium hirsutum L. cv. SRT-I) fibre development. A significant increase in indolyl-3-acetaldehyde dehydrogenase activity was recorded during the elongation phase while during the secondary thickening phase it decreased suggesting thereby the importance of auxin biosynthesis in elongation growth. The role of auxin turnover in the regulation of cotton fibre development is discussed.

EFFECT OF PLANT GROWTH REGULATORS AND DIFFERENT NITROGEN SOURCES ON NADP-ISOCITRATE DEHYDROGENASE ACTIVITY OF RADISH COTYLEDONS

NADP-isocitrate dehydrogenase (NADP-ICDH) activity of radish (Raphanus sativus L.) seedlings pretreated with various plant growth regulators: KiN, GA, and ABA and different nitrogen sources viz. KNO3, NH4Cl and NH4NO3 in light and dark was investigated. ICDH activity was significantly higher in light than in dark; addition of different nitrogen sources reduced it to a greater extent in NO3 supplementation. Among hormonal treatment only KiN showed slight promotion with KNO3 and NH4NO3. On the other hand in light KNO3 and/or NH4NO3 promoted ICDH activity and among hormones, KiN significantly promoted the activity in KNO3 and NH4NO3 supplemented seedlings while ABA was effective in NH4CL. It is suggested that in non-photosynthetic tissues, NADP-ICDH provides both reductant and carbon skeleton for glutamate synthesis.

Effect of phytohormones and tungsten on light-induced and nitrate-induced nitrate reductase activity of mustard cotyledons

Mustard (Brassica juncea Coss cv. T-59 ‘Varuna’) seedlings pretreated with gibberellic acid (GA) and kinetin (KiN) were grown in light. In vivo nitrate reductase (NR) activity was estimated and effect of tungsten on light-induced and NO3su−-induced NR activity was investigated. Different concentrations of GA did not show any effect on induction of light-induced NR; addition of nitrate promoted in vivo NR activity but no concentration effect of GA was evident. Light-induced NR was promoted by KiN and like in GA treatment, addition of nitrate increased NR activity. Addition of Na-tungstate inhibited NO3− induced NR while light-induced NR was not much affected in both GA and KiN treated seedlings. The two forms of NRs were further characterized by studying the decay kinetics using Na-tungstate. In light-induced NR, tungstate did not affect NR activity up to 11 h, while at later periods, a slight decay was observed. On the other hand, NO3−-induced NR activity increased up to 4 h and subsequently a rapid fall was observed. It was therefore apparent that light-induced NR had a very low turnover rate as compared to NO3−-induced NR. These results further support the earlier conclusion that in mustard seedlings two distinct types of NR enzyme exist and that nitrate requirement for NR induction is not absolute.

Influence of plant growth regulators on some enzymes of nitrogen assimilation in mustard seedlings

Abstract Effect of plant growth regulators (PGR) viz. gibberellic acid (GA), kinetin (KN), and abscissic acid (ABA) were investigated on growth and activities of nitrate reductase (NR) and glutamine synthetase (GS) in mustard (Brassica juncea) seedlings. All the PGRs tested promoted in vivo NR activity in cotyledons, but the magnitude differed with different treatments. Cytosolic GS in root and hypocotyl was promoted by GA treatment and inhibited by ABA and KN treatments although the latter showed slight promotion initially in hypocotyl; the trend was not clear in cotyledons. Determination of Km value of GS extracted from 96‐h‐old cotyledons recorded lower Km value in GA treatment (2.5 mM), while it increased in ABA treatment (4.35 mM), There was little change in Km value in KN (3.03 mM) treatment. The kinetics of GS enzyme in cotyledons of different treatments showed marked variation in Vmax . Both GA and ABA treatments inhibited GS activity while no significant effect by KN treatment was observed. It is...

Effect of plant growth regulators on nitrate uptake and its reduction in radish cotyledons

Abstract Pretreatment of radish (Raphanus sativus L.) seedlings with exogenous hormones in the absence of external nitrate, resulted in a system having enough hormone levels to mediate the responses or activate the metabolic pathways which are necessary for nitrate (NO3) uptake and reduction. Effects of pretreatment of radish seedlings with KN, GA, and ABA on the induction of NO3 transport and corresponding NR activity, upon exposure to NO3 were investigated. A low NO3, uptake rate was observed with hormones when compared to DW‐control, while its induction pattern exhibited a sort of biphasic kinetics. It was observed that each hormone treatment affected NO3 uptake and reduction specifically at different ambient concentrations of NO3. On the basis of this, the operation of different constitutive and inducible (CHATS, LATS, HATS, and IHATS) transport systems was resolved for different hormonal treatments. Further, the hypothesis that nitrate uptake has direct role on nitrate reduction was supported by all ...

Role of phytohormones in nitrate uptake and in vivo nitrate reductase activity of mustard cotyledons

In vivo nitrate reductase activity and nitrate uptake in gibberellic acid (GA)-and kinetin (KN)-treated mustard (Brassica juncea Coss. cv. T-59 Varuna) seedlings grown in the presence of light were investigated. An attempt was also made to determine the metabolic pool size and in vivo apparent K m value of nitrate reductase (NR) for nitrate (NO 3 ). Both NO 3 uptake and in vivo NR activity showed biphasic saturation kinetics, but causal relationship between them was not evident. Kinetin inhibited uptake and promoted in vivo NR activity, while although GA promoted uptake, in vivo NR activity was almost equal to distilled water (DW) control. The hormones affected the K m value differently, GA showed lower K m value while KN showed higher K m value for NO 3 . Metabolic pool size (MPS) was also significantly affected by both the hormone treatments. The results are discussed in relation to the use of in vivo NR activity for calculating the apparent K m and MPS for NO 3 .