Studies on the control of secondary thickening in excised roots of Lycopersicum esculentum Mill

Sinha, Sunita (1968) Studies on the control of secondary thickening in excised roots of Lycopersicum esculentum Mill. PhD thesis, University of Glasgow.

Abstract

1. In the first section of thin thesis the anatomy of excised tomato roots was compared and contrasted with that of cultured seedling roots. The remaining experimental work comprises a study of the effects of various growth substances on the initiation and growth of the cambium in excised tomato roots. Each substance was tested in two ways: (a) The roots were cultured immersed in a liquid medium supplemented with the compound(s). (b) The growth substances were fed via the cut end using a modified Raggio and Raggio technique (page 25). At the end of each experiment the roots were measured and the anatomy of the basal region of the roots was examined. The substances tested included auxins, cytokinins, a gibberellin, meso-inositol and various complex mixtures such as coconut milk, yeast extract and acid hydrolysed casein. The auxins, cytolcinins and meso-inositol were also tested in various combinations. 2. It has been shown that a well developed vascular cambium is initiated in two week old excised roots in the standard medium but that the activity of this cambium was not maintained. In contrast the cambium initiated in seedling roots was active up to six weeks. 3. It has been shown that IAA and NAA, at the concentrations tested, prevented the formation of a cambium and caused some reduction in the number of xylem cells in the stele. However when auxins were supplied via the cut end of the root no marked effect was observed. 4. Kinettn and 6-benaylaminopurine, added to the liquid medium, inhibited the formation of the cambium and greatly reduced the diameter of the stele and the number of xylem cells within the stele. When the cytokinins were supplied via the cut end, they increased the linear growth of the roots but had little effect on the anatomy aft the base. 5. The effects of gibberellic acid were similar to those of the auxins in that it prevented the formation of a cambium and reduced the number of xylem cells in the stele. 6. Although meso-inositol did not have a stimulatory effect on cambial activity after twooweeks it did markedly prolong its activity and roots grown in a meso-inositol supplemented medium for six weeks showed extensive secondary thickening. No effect on cambial activity was observed when the meso-inositol was fed via the cut end. In experiments with intact seedling roots meso-inositol similarly stimulated the activity of the vascular cambium. After one week's growth meso-inositol increased the growth of excised tomato roots by up to 60%. when added to the standard medium containing 2% sucrose. However, it was much-less effective in media containing 1% or 3% sucrose. After two weeks it was most effective in the medium containing 1% sucrose. Sorbitol, another cyc3litol, had little effect on the growth of tomato roots. 7. When the various combinations of IAA or NAA, cytokinins and meso-inositol were tested for effects on cambial growth, no positive interactions were observed. It was found that at the lower concentrations combinations of NAA, kinetin and meso-indsitol produced thick roots, but this reflected an effect on the thickness of the cortex rather than on the stele. 8. At the concentrations tested coconut milk, yeast extract and acid hydrolysed casein had no detectable effect on cambial activity when added to the liquid medium or when fed via the cut end of the root. 9. Excised roots cultured for six weeks in media supplemented with meso-inositol developed a considerable amount of secondary tissues which were derived from a vascular cambium. It is suggested that meso-inositol may be a factor limiting the cambial growth in excised tomato roots in standard medium. However meso-inositol did not produce roots with secondary tissues extensive as in comparable seedling roots and it was considered that other unidentified factors are also involved in cambium growth.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: D N Butcher
• Keywords: Plant sciences
• Date of Award: 1968
• Depositing User: Enlighten Team
• Unique ID: glathesis:1968-72769
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 11 Jun 2019 11:06
• Last Modified: 11 Jun 2019 11:06
• URI: https://theses.gla.ac.uk/id/eprint/72769