The OKRA leaf shape mutation in cotton is active in all cell layers of the leaf

Okra (L2O) is a semidominant mutation of cotton (Gossypium barbadense) that alters leaf shape by increasing the length of lobes and decreasing lamina expansion. Chimeras containing L2O and wild-type tissue were generated using Semigamy (Se), a mutation that blocks syngamy during fertilization and produces haploid maternal/paternal chimeral progeny at low frequency. In sectorial chimeras, changes in leaf morphology coincide with the boundary between mutant and wild-type tissues, suggesting that L2O does not regulate a laterally diffusible factor within the leaf. However, in mericlinal or periclinal chimeras, the presence of L2O in tissue derived from any of the three histogenic layers (L1, L2, or L3) of the shoot apical meristem produced leaves with a partial mutant phenotype. The presence of L2O in the epidermis (an L1 derivative), or in the subepidermal mesophyll of the leaf (L2 derivatives) reduced the growth of the lamina and thus increased the depth of leaf lobes. The presence of L2O in the middle mesophyll of the lamina and the vasculature of major lateral veins (L3 derivatives) had no local effect on the expansion of the lamina, but significantly increased lobe length. These results demonstrate that L2O is active in every tissue layer of the leaf.     

Increased nuclear DNA content in developing cotton fiber cells

The nuclear DNA content of developing cotton fiber cells (Gossypium hirsutum, cv. MD51ne) increases ∼24% after 2 d postanthesis (dpa). The amount of nuclear DNA at 2 dpa is 5.4 ± 0.27 pg. At 3–4 dpa it increases to 6.7 ± 0.24 pg and by 5 dpa it is 6.8 ± 0.70 pg. These values were obtained by nuclear fluorescence after staining with Hoechst 33258. Human oral squamous cell nuclei were used as a DNA standard. Nuclear DNA content increases in fibers growing on either fertilized or unfertilized ovules. The increase also is detectable in Feulgen stained nuclei using two-wavelength cytospectrophotometry. All measurements were made on isolated fiber cell nuclei using a newly developed method tailored to cotton fiber cells. The results imply that during the early stages of development fiber cell nuclei either selectively amplify certain sequences or enter S-phase replicating a portion of their genome.     

Clonal analysis of leaf development in cotton

Clonal analysis has been used to describe the cellular parameters of leaf development in American Pima cotton (Gossypium barbadense). Sectors (clones) induced before leaf initiation indicate that the leaf primordium arises from ~100 cells on the flank of the shoot meristem. An analysis of sector frequency during the period of leaf expansion suggests that the rate of cell division is fairly uniform throughout the length of the leaf, but is lower at the margin of the lamina than in intercalary regions. The shapes of marginal sectors indicate that the orientation of cell division (as defined by the orientation of the new cell wall) in this region is more often parallel to the margin than perpendicular to it, although the degree of polarization varies along the length of the margin. There is a slight gradient in the duration of cell division along the length of of the lamina late in development, with cell division ceasing progressively from the lamina tip to the base over two cell cycles. The parameters of cell division in cotton are therefore similar to those described for tobacco with the notable exception of the behavior of cells at the leaf margin.     

Stomatal conductance and transpirational responses of field-grown cotton to ozone

Abstract Stomatal conductance and transpiration were measured on normally-irrigated (NI) and water-stressed (WS) field-grown cotton (Gossypium hirsutum L.) exposed throughout the growing season to a gradient of ozone (O₃) concentrations. Environmental conditions during the growing season strongly affected stomatal responses and yield reductions due to O₃ exposure. Maximum stomatal conductance and transpiration decreased with increased O₃ concentration both in NI and WS treatments. Maximum conductance in severely O₃-stressed plants averaged 30% lower than charcoal-filtered (control) plants, but maximum transpiration was only 17% lower. Conductance in WS plots averaged 22% lower than in NI plots but transpiration rates were the same in both treatments. Yield reductions induced by O₃ were highly correlated (r²= 0.84) with daily transpiration. Stomata of O₃-stressed plants opened and closed at the same rate as control plants in response to changes in light intensity, suggesting that the mechanism of stomatal movement had not been impaired by exposure to O₃. Reductions in conductance and transpiration in O₃-stressed plants were attributed to inhibition of photosynthesis by O₃, leading to accumulation of CO₂ in intercellular spaces.     

Diurnal water relations of expanding and full-sized cotton fruits and subtending leaves

Water relations of cotton (Gossypium hirsutum L.) fruits have received less attention than those of leaves, although crop water status has an important influence on fruit physiology. This study was conducted to describe diurnal changes in the water relations of cotton fruits and subtending leaves. Young, expanding fruits and full-sized fruits were compared because of previously reported changes in xylem maturity with ontogeny. Diurnal changes in relative water content were greater in leaves than in the capsule walls of fruits. The capsule walls of young fruits had a higher relative water content than subtending leaves, and water content was lower in full-sized (87%) than in expanding (92%) fruits. Water potentials of subtending leaves were always approximately 0-3 MPa lower than those of capsule walls. Water potential gradients favoured passive water flow from young fruits to branches, but water potentials of branches and the capsule walls of full-sized fruits were similar (?0.7 MPa). Water potential gradients were consistent throughout the day. These results indicate that xylem transport to young fruits is unlikely, but may occur in older fruits.     

Malate synthase from Gossypium hirsutum

Malate synthase was purified 2000-fold from cotyledons of dark-germinated cotton, Gossypium hirsutum. The purified enzyme had a pH optimum of 8.2, and an absolute requirement for a divalent cation. Only glyoxylate and acetyl-CoA served as condensation partners. Results obtained with functional-group directed inhibitors suggest the presence of lysine, tyrosine and histidine residues in the active site. Temperature optimum was 40°, and energy of activation was 3.3 kcal/mol. The MW of cotton malate synthase, determined by rate-zonal density gradient sedimentation, was 750 000. Initial-rate studies indicated Michaelis-Menten kinetics. Inhibition by substrate analogs, plus substrate-interaction kinetics gave results consistent with a sequential bireactant mechanism.     

Improvements in shoot apex regeneration of two fiber crops: cotton and kenaf

Cotton (Gossypium hirsutum L.) and kenaf ( Hibiscus cannabinus L.) belong to the Malvaceae family, and both are used as sources of fibers. Shoot apices from vigorous seedlings aseptically germinated from 3 different cultivars of both cotton and kenaf were used in this study. The cotton and kenaf shoot apex size was between 2–3 mm containing the meristem, unexpanded leaves, and a small portion of the cotyledon. Shoot apices were placed on 18 different media comparing full and 1/2 strength Murashige and Skoog (1962) plus vitamins, and combinations of 0, 0.1, and 1 mg l^-1 of naphthaleneacetic acid and 6-benzyladenine (BA). The shoot apices of both crops developed successfully without intervening callus formation, and no significant differences among cultivars were found. An average of 58% of the cotton shoot apices initiated shoot and rooted in full strength Murashige and Skoog (1962) plus vitamins in 6 weeks. For kenaf, an average of 92% of shoot apices initiated shoot and rooted in full strength Murashige and Skoog plus vitamins and 0.1 mg l^-1 BA in 3 weeks. All regenerated plants of both crops were phenotypically normal and set seeds. This revised version was published online in June 2006 with corrections to the Cover Date.     

Nucleolar size at early stages of cotton fiber development in relation to final fiber dimension

Changes in nucleolar size and nucleolar vacuolation at early stages of fiber development and final fiber dimensions were determined for cotton of different species: Gossypium hirsutum L. cv. B49, Gossypium barbadense L. cv. Menoufi and Gossypium arboreum L. cv. Virnar. Size of the nucleolus in combination with its vacuolation at an early stage of development was found to be clearly associated with the final result of fiber development.     

A comparative study of low-temperature-induced ultrastructural alterations of three species with differing chilling sensitivities

Abstract. The effects of light and water stress upon chilling injury of chloroplasts have been assessed by electron microscopy in seedlings of three species known to differ in their chilling susceptibility. Chilling injury to chloroplasts was first manifested by distortion and swelling of thylakoids, reduction in starch granule size, and the formation of small vesicles of the envelope, called the peripheral reticulum. More prolonged treatment produced accumulations of lipid droplets, increased staining of the stroma, disintegration of the envelope, and mixing with cytoplasmic contents. Cotton, a notably chilling-sensitive plant, and bush bean, a somewhat less sensitive plant, showed damage within 6 h when exposed to both light and water stress at chilling temperatures (5°C). Even collard, a chilling-resistant species, exhibited signs of chilling injury to chloroplasts after 6 h when exposed to both light and water stress but the plastids remained intact throughout the 48 h of treatment. Comparable chilling injury does not occur in cotton until around 72 h if the plants are exposed to water stress or light separately. Bush bean was affected less by separate treatments of light and water stress. The least chilling injury occurred in all three species when they were kept in the dark at a high humidity.     

Polyphenols des feuilles de cotonniers et influence sur leur composition d'un choc hydrique ou nutritionnel

A range of phenolic compounds were found in leaves of three cotton species. Water and nutrient stress (sulfur deficiency) both caused a significant decrease in phenolic content. Possible interpretations of the observed phenomena are given.     

Effects of water stress on oxygen, hydrogen and carbon isotope ratios in two species of cotton plants

Abstract. Two cotton species ( Gossypium hirsutum L. cv. SJ-2 and Gossypium barbadence cv. S-5) were grown under irrigated (wet) and non-irrigated (dry) conditions in the same field. Leaf water was enriched in ¹⁸O and deuterium in the dry treatment relative to the wet treatment for both species. Only in plants of S-5 was a similar enrichment observed in leaf cellulose. In both species, the isotopic composition of leaf cellulose must reflect the isotopic composition of the actual water pool involved in cellulose synthesis. Therefore, our observations indicate that one species (SJ-2) can maintain a relative isolation of this water pool from direct evapotranspirational effects. Such plant species will more faithfully record, in the isotopic composition of organic matter, the isotopic composition of ground water. In contrast, the isotopic composition of organic matter in plants such as S-5 could be used as an integrated signal reflecting humidity conditions during growth. Water use efficiency, based on seed-cotton yield and total water applied, correlated linearly with differences in carbon isotopic ratios between species in both the wet and dry treatments and between treatments in each species.