fusicoccin and gibberellic-acid

Cytosine DNA methyltransferases (MTases) were isolated from nuclei of wheat seedlings and germinating embryos. The MTases isolated from both sources were able to perform de novo and maintenance DNA methylations. The most purified MTase fraction showed the presence of one main 67-kDa protein (embryos) and of a 85-kDa protein (in seedlings) in SDS-PAGE. Some plant growth regulators (gibberellic acid A3, 6-benzylaminopurine and fusicoccin) elevate by 30-65% the extent of in vitro DNA methylation by nuclear extracts with a maximal effect at 10(-6) M phytohormone concentration. The same phytohormones do not increase the extent of in vitro DNA methylation by purified wheat MTase; rather they inhibit it at concentrations of 10(-4)-10(-5) M. Thus, DNA methylation in the plant nucleus is controlled by phytohormones. The phytohormone effect may be mediated by other proteins in nuclear extracts.

Topics: Adenine; Benzyl Compounds; Cell Nucleus; DNA-Cytosine Methylases; DNA, Plant; Electrophoresis, Polyacrylamide Gel; Gibberellins; Glycosides; Kinetics; Kinetin; Methylation; Molecular Weight; Plant Growth Regulators; Purines; Seeds; Triticum

Segments can be cut from the peduncular-1 internode of oat (Avena sativa L.) shoots so as to contain the graviresponsive leaf-sheath pulvinus and gibberellin-sensitive internodal tissue. Incorporation of [14C]glucose was used to monitor cell wall synthesis in these two tissues as affected by gravistimulus, indoleacetic acid (IAA), gibberellic acid (GA3), and fusicoccin (FC). Pulvinar cell wall synthesis was promoted by IAA and FC (both within about 1 h), as well as by gravistimulus (starting between 3 and 6 h), whereas GA3 had no effect on nongravistimulated pulvini. In contrast, GA3 and FC promoted internodal cell wall synthesis (initiated between 1 and 2 h), whereas IAA and gravistimulus caused a decrease in internodal uptake. FC preferentially promoted incorporation into the matrix component of the wall in both tissues. Gravistimulus failed to increase responsiveness of pulvinar tissue to IAA, whereas GA3 partially overcame gravistimulus-promoted incorporation into pulvinar cell wall, probably because of preferential movement of label into the rapidly elongating internode. The results demonstrate that these eight stimulus/tissue combinations can be examined easily in an isolated 10-mm stem segment, providing new opportunities for the comparative study of tissue- and stimulus-specific events in gene regulation and signal transduction in agronomically important cereals.

Topics: Avena; Carbon Radioisotopes; Cell Wall; Gibberellins; Glucose; Glycosides; Gravitation; Gravitropism; Indoleacetic Acids; Plant Growth Regulators; Plant Shoots; Pulvinus