Effects Of Phenylpropanoid Pathway And Its Intermediate Product Fa On Cotton Fiber Development

Study on the regulation of cotton fiber development not only can help reveal the mechanism of cell elongation growth and cell wall development but also provide theoretical basis for fiber quality improvement. Plant cell wall phenylpropanoid compounds consist of lignin, the polymer of monolignol units, and low molecular weight hydroxycinnamic acids, that cross-linked to various cell wall components. It can influence the growth, mechanical strength and morphogenesis of the cell wall. Recent research indicated that the phenylpropanoid pathway was just inferior to polysaccharide metabolism pathway in developing cotton fibers and its metabolic products existed in mature cotton fibers. Therefore, they might be quite important to cotton fiber development.The relative quantitative expression of genes in phenylpropanoid pathway in different organ and different time of developmental cotton fibers were studied by RT-PCR. Specificity analysis showed that the expression of C4H, COMT and CCoAOMT had higher levels in both root and stem. Along with the initiation of fiber cell wall thickening, most of the genes displayed high expression levels, such as PAL, 4CL, C4H, COMT, CCoAOMT, CCR and CAD. Those results explained that the pathway was active in vascular tissues and fiber cells with secondary wall thickening.To study the functions of such genes, transient expression vector of CAD6 was constructed and detected. GUS staining showed activity on the fibers after been cultured 15 d and 20 d which corresponded with the high expression amount during such period.For further studies about the effects of the phenylpropanoid compounds to cotton fiber development, based on the system of ovule cultured in vitro, ferulic acid (FA) was fed in the media for either fertilized or unfertilized ovules. With the assistance of image digitization technology, the growth condition of the fibers at different period was analyzed. The results revealed that higher concentration of exogenous FA (100μmol/L) inhibited the normal growth of the fibers, while low level of FA (25μmol/L and 50μmol/L) have not showed such inhibited phenomenon, in the opposite, fiber elongation was accelarated. The results showed that FA had the effects to adjust the cotton fiber growth by adjust the FA concentration in the media. The turning point for accelerating and deccelarating growth of cotton fiber was possiblely at the concentration ranged between 50μmol/L and 100μmol/L. TEM observation on fiber transverse section indicated that the cell wall thickness was significantly increased by exogenous FA(P<0.01). At the level of 50μmol/L, the cell wall thickness of unfertilized fibers increased 62%, while for fertilized fibers increased 35%. In addition, acylbromide chemical analysis revealed that the content of phenylpropanoid compound in cotton fiber was increased 5.2% for the fibers fed with 50μmol/L FA.The relationship between phenylpropanoid compounds and cotton fiber devlopment was explored in this research. The higher expression time of key enzyme genes in phenylpropanoid pathway was coincident with the secondary wall development of both the fiber cells and the organs with vascular elements. The investigation of cotton fiber growth, cell wall thickness and chemical analysis revealed that exogenous FA had significant effects on cotton fiber development in ovule culture system. The work improved our understanding of cotton fiber development mechanism and the effect of phenylpropanoid pathway and its products on cotton fiber development.