Vrinda S. Thaker

Physiological and biochemical changes associated with cotton fiber development: IX. Role of IAA and PAA

Abstract Fibers of three cotton cultivars Gossypium hirsutum hybrid-4 (H-4), hybrid-8 (H-8), and G. arboreum G. Cot-15 were analyzed to study the role of auxin in fiber elongation, in vitro and in vivo. The cultivars exhibited variation in final fiber length. Fibers were analyzed for growth, free and conjugated indole acetic acid (IAA) content and phenyl acetic acid (PAA) content during the entire period of their development. Antibodies against IAA and PAA were raised and endogenous contents of IAA and PAA were estimated by indirect ELISA. Cotton fiber development is divided into four phases viz. (i) initiation (0–3 days post-anthesis (DPA)), (ii) elongation (3–24 DPA), (iii) secondary thickening (18–42 DPA) and (iv) maturation (42 DPA onwards). During the phase of rapid cell elongation, water content increased and then decreased after the fiber entered the secondary thickening phase, in all three cultivars. A positive correlation between final fiber length and free and conjugated IAA and PAA content was observed. In in vitro grown fiber, media supplemented with IAA or napthyl acetic acid (NAA) significantly increased the length of fiber in middle and short staple cultivars, whereas PAA promoted fiber length in the short staple cultivar only. The results of cultured cotton fiber suggest an important role of auxin in cotton fiber development, which may help for the selection of gene(s) for better fiber development.

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.

Potential Role of Abscisic Acid in Cotton Fiber and Ovule Development

Abstract. Fibers and ovules of a cotton cultivar (Gossypium hirsutum L. Trambak-108) were analyzed for growth and free abscisic acid (ABA) content by indirect enzyme immunoassay. An inverse correlation between fiber elongation and ABA content was observed. In the seed, accumulation of ABA was observed during secondary thickening and the maturation phase. The potential role of ABA in fiber and seed development is discussed.

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.

Role of gibberellic acid in cotton fibre development

Fibres of three cotton cultivars ( Gossypium hirsutum H-4, H-8 and G. arboreum G. Cot-15) were analysed for growth in terms of fibre length and dry weight and endogenous gibberellic acid (GA 3 ) content thrice during 1997–2000, at Rajkot. The development of cotton fibre was divided into four distinct growth phases but overlap between elongation and secondary thickening was considerable which suggests that both these phases are independent of each other. During fibre elongation, GA 3 content remained low and increased after a decrease in the rate of fibre elongation in all three genotypes. The long staple cultivar (H-4) showed highest endogenous GA 3 content followed by the middle one (H-8) and the short staple cultivar (G. Cot-15). In in vitro studies when GA 3 , NAA or GA 3 +NAA was supplemented to the media, increase in fibre length of the short staple cultivar was maximum, followed by the middle one and the long staple cultivar. Both in vivo and in vitro findings suggest that GA 3 is one of the important factors that determine fibre length.

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.

Screening of potential antimicrobial compounds against Xanthomonas campestris from 100 essential oils of aromatic plants used in India: an ecofriendly approach

Plants are constantly exposed to and threatened by a variety of pathogenic microorganisms present in their environments. Xanthomonas campestris is a major plant pathogen in the world. It is known to cause significant losses in many crop plants due to leaf spot and leaf blight. In the present study, bacteria isolated from infected Citrus limon fruit and identified by 16S rDNA sequencing was X. campestris. In vitro antimicrobial properties of 100 essential oils were evaluated against X. campestris. The chemical composition of the most active essential oils was investigated by gas chromatography–mass spectral (GC–MS) analysis. The potential of these essential oils as ecofriendly and economical biocontrol in agriculture is discussed.

Physiological and biochemical changes associated with cotton fiber development. VIII. Wall components

Fibers of three cotton cultivars (Gossypium hirsutum L.) H-4, H-8 and (G. arboreum) G. Cot-15, which shows variation in staple length were analyzed for growth in terms of fiber length and fresh and dry mass. From the growth analysis cotton fiber development is divided in four distinct phases i.e. (i) initiation (ii) elongation (iii) secondary thickening and (iv) maturation. Rate of fiber elongation and rate of water content shows close parallelism. Highly esterified and less esterified pectic fraction along with high and low molecular weight xyloglucan fractions were estimated from fiber walls of all the three cotton genotypes. Xyloglucans were fractioned in to high and low molecular weight by alkali treatment, 1 M and 4 M KOH respectively. Xyloglucan content shows inverse correlation with fiber elongation. Role of water content and wall components in determination of staple length in cotton genotypes is discussed.

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.

Systemic Control of Cell Division and Endoreduplication by NAA and BAP by Modulating CDKs in Root Tip Cells of Allium cepa

Molecular mechanism regulated by auxin and cytokinin during endoreduplication, cell division, and elongation process is studied by using Allium cepa roots as a model system. The activity of CDK genes modulated by auxin and cytokinin during cell division, elongation, and endoreduplication process is explained in this research work. To study the significance of auxin and cytokinin in the management of cell division and endoreduplication process in plant meristematic cells at molecular level endoreduplication was developed in root tips of Allium cepa by giving colchicine treatment. There were inhibition of vegetative growth, formation of c-tumor at root tip, and development of endoreduplicated cells after colchicine treatment. This c-tumor was further treated with NAA and BAP to reinitiate vegetative growth in roots. BAP gave positive response in reinitiation of vegetative growth of roots from center of c-tumor. However, NAA gave negative response in reinitiation of vegetative growth of roots from c-tumor. Further, CDKs gene expression analysis from normal, endoreduplicated, and phytohormone (NAA or BAP) treated root tip was done and remarkable changes in transcription level of CDK genes in normal, endoreduplicated, and phytohormones treated cells were observed.