Amarjit S. Basra

Development of the Cotton Fiber

Publisher Summary This chapter discusses the various facets of cotton-fiber development and focuses on some currently critical areas of investigation. In addition to its commercial importance, cotton fiber has several attributes that make it an experimental system of choice for the investigation of physiological and biochemical changes accompanying cell elongation and/or maturation. The fiber originates and ends as a single cell, and thus elongation can be studied free of any complications from cell division. The variability in fiber length and secondary wall thickness of fibers among different cotton varieties depends upon the interplay of a complex pattern of metabolic processes and regulating mechanisms that govern fiber growth. The in vitro methodology of cotton ovule culture holds considerable promise for investigating the effects of a number of plant growth substances on cell growth. The developing cotton fibers provide a rich source of homogeneous single cells, which should be preferred for structural and biosynthetic studies of the cell wall.

Diurnal Regulation of Leaf Blade Elongation in Rice by CO2 (Is it Related to Sucrose-Phosphate Synthase Activity?).

The relationship between leaf blade elongation rates (LER) and sucrose-phosphate synthase (SPS) activity was investigated at different times during ontogeny of rice (Oryza sativa L. cv Jarrah) grown in flooded soil at either 350 or 700 [mu]L CO2 L-1. High CO2 concentrations increased LER of expanding blades and in vivo activity (Vlimiting) SPS activity of expanded blades during the early vegetative stage (21 d after planting [DAP]), when tiller number was small and growing blades were strong carbohydrate sinks. Despite a constant light environment, there was a distinct diurnal pattern in LER, Vlimiting SPS activity, and concentration of soluble sugars, with an increase in the early part of the light period and a decrease later in the light period. The strong correlation (r = 0.65) between LER and Vlimiting SPS activity over the diurnal cycle indicated that SPS activity played an important role in controlling blade growth. The higher Vlimiting SPS activity at elevated CO2 at 21 DAP was caused by an increase in the activation state of the enzyme rather than an increase in Vmax. Fructose and glucose accumulated to a greater extent than sucrose at high CO2 and may have been utilized for synthesis of cell-wall components, contributing to higher specific leaf weight. By the mid-tillering stage (42 DAP), CO2 enrichment enhanced Vlimiting and Vmax activities of source blades. Nevertheless, LER was depressed by high CO2, probably because tillers were stronger carbohydrate sinks than growing blades.

Chilling injury in germinating seeds: basic mechanisms and agricultural implications

Germinating seeds of many species, especially those of tropical or subtropical origin, suffer chilling injury when exposed to low but non-freezing temperatures, resulting in poor seedling establishment and reduction in yield. The severity of injury depends upon several factors such as (i) the species or the cultivars involved, (ii) the initial water content of the seed, (iii) the temperature to which seed is exposed, (iv) the duration of chilling exposure and (v) the period during the course of germination when the chilling exposure takes place. The period of imbibition by seeds is the period of sensitivity to the stresses but especially to chilling temperatures. Imbibitional chilling injury is defined as sensitivity to a combination of low seed-water content and imbibition at cold temperature. The mechanism of chilling injury in seeds is different from chilling injury of hydrated tissues and is discussed in relation to the involvement of membranes, respiration, rate of hydration and the concept of discreet moisture levels. Furthermore, the mechanistic and applied aspects of pre-sowing seed treatments for improved germination performance under chilling stress are discussed with an emphasis on hydration-dehydration, osmotic priming and growth regulator treatments.

Involvement of ethylene in the morphological and developmental response of rice to elevated atmospheric CO2 concentrations

We tested the hypothesis that increased carbohydrate flux under elevatedCO2 regulates accelerated development using rice (Oryzasativa L. cv. Jarrah). Plants were grown either in flooded soil orsolution culture at either 360 or 700 μL CO2L−1. Total dry mass, shoot elongation rates (SER),tiller appearance rates (TAR) and ethylene release from intact rice seedlingswere measured from 5 to 42 days after planting (DAP). At maturity, shoot andsheath length, tiller number and grain mass were also measured. ElevatedCO2 had a profound effect on growth, morphology and development andthe effects were more pronounced during the early growth phase. Total aboveground biomass increased at elevated CO2 and this was accounted for by enhanced tiller number. Grain yield was increased by 56% under elevated CO2mainly due to increased tiller number and hence panicle number. TAR and SERwereenhanced at elevated CO2 but SER increased only untill 25 DAP.Elevated CO2 stimulated a 2-3-fold increase in endogenous andACC-mediated ethylene release but the ACC concentration in the leaves waslittleaffected showing that rates of ACC synthesis matched its oxidation. Inhibitionof ethylene action by 1-aminocyclopropane (1-MCP) had a more pronouncedinhibitory effect on ethylene release in plants that were grown at 700 ascompared to 360 μL CO2 L−1. Feedingsucrose to intact plants enhanced ethylene synthesis and these results areconsistent with the hypothesis that increased accumulation of sucrose atelevated CO2 may enhance expression of genes in the ethylenebiosynthetic pathway. We conclude that increase in ethylene release may becentral in promoting accelerated development under elevated CO2 andthis coincides with the release of auxiliary buds and accelerated rates oftiller appearance hence increased grain yield at elevated CO2.

NON-PHOTOSYNTHETIC FIXATION OF CARBON DIOXIDE AND POSSIBLE BIOLOGICAL ROLES IN HIGHER PLANTS

1. Non‐photosynthetic fixation of CO2/HCO3‐ occurs both under light and dark conditions and involve the addition of carbon to substrates which in higher plants are derived originally from carbon reduced to carbohydrates during photosynthesis. Despite the endergonic nature of these carboxylations, the advantages offered seem to be sufficient to outweigh the disadvantages of energy loss.

Studies on the chemical composition and biological activity of essential oil from Cyperus rotundus Linn.

The sesquiterpene caryophyllene in its alcohol form has been identified for the first time from the essential oil of the tubers of Cyperus rotundus Linn. The structure of the alcohol has been identified by spectroscopic and chemical methods. Bioefficacy of the oil and its hydrocarbon, ketonic and alcoholic fractions is reported for maize and mungbean.

Abscisic acid is a potent inhibitor of growth and sporidial formation inneovossia indica cultures: Dual mode of actionvia loss of polyamines and cellular turgidity

The inhibition of polyamine biosynthesis inNeovossia indica (Mitra) Mundkur by D,L— α-difluoromethylornithine (DFMO) caused an effective reduction of mycelial growth and sporidial production underin vitro conditions, which was reversed by ornithine application. Abscisic acid proved to be similarly effective, not only in inhibiting mycelial growth and sporidial formation but also the germination of teliospores, which constitute the primary inoculum of the pathogen. ABA-mediated inhibition resulted in decreased polyamine levels and loss of cellular turgidity of mycelial cultures. Scanning electron microscopy of ABA-treated cultures revealed extremely shrunken hyphae, in marked contrast to the turgid controls. It is suggested that the manipulation of ABA levels and/or tissue sensitivity in wheat could be a strategy to combat ‘Karnal’ bunt, the disease caused byN. indica.

Hormonal regulation of cotton fibre elongation in Gossypium arboreum L. in vitro and in vivo

Summary Changes in endogenous levels of IAA, GA3 and ABA during in vivo fibre growth of Gossypium arboreum L. cv. LD 230 revealed an overriding influence of ABA in restricting the rate of fibre elongation. No relationship between IAA levels and extent of fibre elongation was discernible. The fibre growth of unfertilized cotton ovules cultured in vitro was promoted by the application of fluridone, an inhibitor of ABA biosynthesis. Fluridone resulted in a marked reduction of ABA concomitant with an increase in IAA and GA3 levels of cultured cotton ovules. The relationship of ABA with IAA and gibberellin is shown to have regulatory influence in determining the extent of cotton fibre elongation.

Hormonal effects on tube elongation, 14CO2 fixation and phosphoenolpyruvate carboxylase activity in Amaryllis pollen: Promotion by abscisic acid

Abscisic acid promoted tube elongation, 14CO2 fixation and phosphoenolpyruvate carboxylase activity during in vitro germination of Amaryllis vittata Ait. pollen. Other growth regulators tested viz. indol-3yl-acetic acid, gibberellic acid, N6-benzyladenine and ethephon did not affect pollen tube elongation at 1 μg/ml concentration but inhibited it at 10 μg/ml. The case for abscisic acid as a growth promoter is argued.

Differential response of carbon and nitrogen metabolism to fluoride application in fruiting structures of chickpea (Cicer arietinum)

The effect of sodium fluoride (10 and 50 mol·m−3) on the activities of sucrose metabolizing enzymes, transaminases and glutamine synthetase in relation to the transformation of free sugars to starch and protein in the fruiting structures (pod wall, seed coat, cotyledons) of chickpea was studied by culturing detached reproductive shoots in a liquid medium. Addition of fluoride to the culture medium drastically reduced starch content of the cotyledons and caused a marked build-up of total free sugars comprised mainly of reducing sugars in the pod wall and seed coat, and sucrose in the cotyledons. Concomitantly, the activity of soluble invertase was stimulated in the pod wall but reduced in the cotyledons. However, soluble protein content of both the pod wall and the cotyledons increased in conjunction with an increase in the activities of glutamate-oxaloacetate transaminase, glutamate-pyruvate transaminase and glutamine synthetase. Disruption of starch biosynthesis under the influence of fluoride and the resulting accumulation of free sugars possibly resulted in their favoured utilization in nitrogen metabolism. Labelling studies with [U-14C]-sucrose showed that the 14C incorporation into total free sugars was enhanced by fluoride in the pod wall but reduced in the seed coat and cotyledons, possibly due to an inhibitory effect on their translocation to the developing seeds.