The Role of lAA in the Regulation of Plant Cell Growth

Batch cell suspension cultures of Acer pseudoplatanus L. provide an excellent system for studies of the hormonal regulation of cell growth. By using gas chromatography-mass spectrometry (GC-MS) for identification of the natural auxin, and spectrophotofluorimetry for a highly specific and sensitive assay it was confirmed that the OS strain cultures synthesise indol-3yl-acetic acid (lAA). Despite the presence of high levels of extracellular 2,4 dichlorophenoxyacetic acid (2,4-D), which the cultures require for normal growth, it is suggested that endogenous lAA is a major regulatory factor. The level of endogenous lAA fluctuated throughout the growth cycle and there appeared to be a correlation between lAA levels and cell division in the batch grown cultures. A more detailed investigation of the first highly synchronous division revealed that lAA levels peaked sharply prior to the rise in the mitotic index (M.I.) which was closely followed by cytokinesis. An increase in the cells’ capacity to convert tryptophan to lAA was observed before the rise in lAA levels. A number of methods for induction of cell division synchrony in the cultures were investigated and it was found that several synchronous divisions could be induced by the use of an appropriate temperature regime. Tn such synchronised cultures the relationship between TAA levels, M.I., and cytokinesis described above remains constant for several divisions. The quantities of lAA found in the cells prior to mitosis suggest that a critical trigger level must be achieved before mitosis occurs. Cytokinins are classically known as cell division factors. Investigations of cytokinin-like activity in asynchronous batch cultures revealed that activity increased prior to the first highly synchronous division. Furthermore, in cultures where several synchronous divisions were induced an increase in activity was observed before each division, indicating the involvement of cytokinin in some aspects of cell division. These changes in endogenous hormone levels in synchronous cultures draw attention to the importance of hormone interactions in eliciting a particular growth response. It is suggested that auxin—Cytokinin interactions play an important role in cell division in sycamore cell suspension cultures. The presence of 2,4 D, TAA and cytokinins in the culture medium of both asynchronous and synchronous batch cell suspension cultures draws attention to the possibility that these hormone pools have a regulatory role in growth processes within the cell. However, preliminary studies indicated that extracellular lAA does not play a significant role in the regulation of cell metabolism.

Name dc:type.qualificationname

PhD

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

De Montfort University

Year dc:date.issued

1982

Author dc:creator

• Robinson, Gillian Mary

Licence

• https://dora.dmu.ac.uk/bitstreams/5f07c445-cba6-40da-a32f-8a6ddfa627f9/download