Induction of growth of submerged cotton (Gossypium hirsutum L.) fibers from cultured ovules has been investigated for the first time. Both exogenous plant hormone levels and the age of the ovules at induction play important roles in induction of submerged cotton fiber growth. The diameter of submerged fibers was about same as that of air-grown fibers but was smaller than that of fibers grown in vivo. Submerged fibers were shorter in the fiber length, stronger in the tensile strength, and they had thicker secondary cell walls and smaller crystallite sizes compared with air-grown fibers and fibers in vivo. Helical secondary cell wall thickenings were exclusively found in submerged fibers. Congo Red is a natural dye that has a high affinity for the biopolymer cellulose. The addition of Congo Red to the culture medium had an influence only on submerged cotton fibers and not on air-grown cotton fibers. When Congo Red was applied in the early primary wall stage, fiber cell elongation was inhibited, but amyloplast production was induced. When Congo Red was applied in late primary wall or early secondary wall stage (about 14-16 DPA), the effects were less severe, but a significant increase in birefringence of secondary cell walls was observed. In both conditions of treatment with Congo Red in the primary wall and the secondary wall stages, a "nodulation" occurred on the wall surface. Neither cellobiohydrolase CBH I or CBH II had affinity for the external wall materials, implying that there was no cellulose present or binding sites for CBH had been occupied by Congo Red. X-ray diffraction data showed that Congo Red decreased the crystallite size of cellulose in submerged cotton fibers. The preliminary investigation with auxin (indole-3-acetic acid) depletion in the culture medium was to study whether or not amyloplasts were produced under this condition. No amyloplasts were observed in submerged fibers grown in the auxindepleted medium, but cellulose microfibrils in the secondary cell wall were greatly disorganized. Possibly, indole-3-acetic acid might play an important role in regulating the arrays of microtubules, which, in turn, may help to organize the patterns of cellulose deposition. / text

The development of cottons with improved fiber quality has been a major objective in breeding programs around the world. Breeders have focused their attention on improving fiber strength and length, and have generally not used fiber elongation in the selection process. Although literature has reported a negative correlation between fiber elongation and tenacity, this correlation is weak and should not prevent breeders from simultaneously improving fiber tenacity and fiber elongation. Furthermore, the work of rupture property, important in the spinning process, could be best enhanced by improving both fiber tenacity and fiber elongation. Fifteen populations were developed in 2007 by crossing good quality breeding lines with high elongation measurements to ‘FM 958’; a High Plains standard cultivar with good fiber quality but reduced elongation. Samples in every generation were ginned on a laboratory saw gin, and the lint was tested on HVI (High Volume Instrument). The F2 and F3 generations showed a wide range of variation for elongation (6.9% - 12.8% for the F2 and 4% - 9.20% for the F3) allowing divergent selection for low and high fiber elongation. A correlation (r) of -0.32 between strength and elongation was observed in the F2 individual plant selections. In the F3, the correlation (r) between strength and elongation was -0.36, and in the F4 the correlation (r) was -0.08. Nine lines were selected from the original 15 populations for spinning tests. The correlation between fiber elongation and strength for these lines was positive (r=0.424), indicating that with targeted selection, fiber elongation and strength can be simultaneously improved. Fiber elongation was positively correlated with yarn tensile properties tenacity (r=0.11), work-to-break (r=0.68) and breaking elongation (r=0.87); and was negatively correlated with yarn evenness properties, number of thin places (r=-0.16), number of thick places (r=-0.9), nep count (r=-0.24), hairiness (r=-0.38) and total number of imperfections (r=-0.38). All selections for high elongation were superior for all tensile properties compared to the low selections and the check in the analysis over locations and in each location. Furthermore, selections for high elongation were significantly different from the selections for low elongation and the check. In addition to developing lines for fiber spinning tests with improved, or differentiated, fiber elongation, this project was amended to evaluate and determine the heritability of fiber elongation. Three different methodologies were used to obtain estimates of heritability; variance components, parent off-spring regression, and realized heritability using F3, F4, and F5 generation. No inbreeding was assumed because there was no family structure in the generations within this study. Estimates of heritability by the variance component methods in the F3, F4 and F5 were 69.5%, 56.75% and 47.9% respectively; indicating that 40-50% of the variation was due to non-genetic effects. Parent off-spring regression estimates of heritability were 66.1% for the F3-4 and 62.8% for the F4-5; indicating a high resemblance from parents to off-spring. Estimates of realized heritability were obtained to determine the progress realized from selection for the low and high selection for fiber elongation. Estimates were intermediate (0.44–0.55), indicating moderately good progress from selection. The results from this project demonstrate that it is possible to improve fiber elongation and to break the negative correlation between elongation and strength. Furthermore, it has been demonstrated that improving fiber elongation results in the increase of length uniformity index and decreased short fiber content. Additionally, directed divergent selection was a successful methodology for the improvement of fiber elongation, and was useful to demonstrate that higher fiber elongation has a positive effect on yarn tensile properties, yarn evenness and processing. The development of new cultivars with improved fiber elongation will improve the quality and reputation of U. S.-grown cotton. The ultimate result will be better yarn quality and improved weaving efficiency, and particularly address current weaknesses in U. S. –grown cotton cultivars, especially from the High Plains of Texas, of more short fiber content, lower uniformity ratios, and weaker yarn strength.

Cotton fiber development is a fundamental biological phenomenon. In spite of its economical importance, a large proportion of cotton fiber initiation is unknown. A naked seed mutant (N1N1) was compared with its isogenic lines of cotton (Gossypium hirsutum, TM-1) using a 70-mer oligonucleotide microarray that contained 1,536 features designed from a subset of cotton fiber ESTs. Statistical analysis and quantitative RT-PCR identified 23 "fiber-associated" genes. The annotation suggested that the temporal regulation of genes involved in transcriptional and translational regulation, signal transduction, and cell differentiation during early stages of fiber development. To get a large view of fiber initiation, a new cotton oligonucleotide microarray was developed containing sequences from an ovule EST library from Gossypium hirsutum L. T̲M̲-1 immature o̲vules (GH_TMO), a set from Jonathan Wendel's lab at Iowa State University, and the pilot set of oligos used for previous study. Global gene expression studies were performed with microdissected fiber initials (or epidermis) and inner ovules to investigate fiber preferentially expressed genes. Laser capture microdissection and antisense RNA (aRNA) amplification allowed us to collect fiber initials (0 DPA and 2 DPA) or epidermal layers (-2 DPA) from whole ovule tissues. The gene expression profiles of fiber initials showed up-regulation of fiber proteins, myb transcription factors, and hormonal regulators as well as trichome related factors during fiber initiation. In each developmental stage, different sets of gene categories in molecular function or biological processes were over- or under-represented, suggesting temporal regulation of genes during fiber development. One of the possible "fiber associated genes" found in microarray analyses, RD22 like gene (GhRDL), was highly enriched in the epidermis of cotton ovules during fiber initiation. The function of GhRDL was studied with the Arabidopsis trichome system which shares many similarities with fiber development. Overexpression of 35S::GhRDL into Arabidopsis thaliana Columia-0 induced seed hairs (or seed trichomes) and pRDL:GUS was localized in Arabidopsis seeds. This suggests that GhRDL plays an important role in the seed trichome development and can be a key player in cell differentiation and fiber development. / text