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Title: The influence of light regime on growth and differentiation of cultured tomato explants.
Author: Wetten, Andrew C.
ISNI:       0000 0001 3566 3654
Awarding Body: Oxford Polytechnic
Current Institution: Oxford Brookes University
Date of Award: 1992
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Growth of cultured tomato (Lycopersicon esculentum Mill.) leaf explants was assessed in response to quantitative variation in the light regime. Exposure to a range of photon flux densities (PFD) resulted in distinct PFD optima for callus, shoot and root initiation. Incubation of explants under a range of temperatures also resulted in a wide range of growth responses both in terms of tissue type and dry matter production. It was observed that manipulation of PFD by varying the separation between culture and light source was accompanied by a non-uniform temperature regime between PFD treatments. Therefore irradiance-dependent growth responses cannot be accurately interpreted with this arrangement unless additional compensatory heating is employed to maintain a uniform temperature regime throughout PFD treatments. Culture of explants on media shielded from illumination resulted in a distinct organogenesis response from explants exposed to full illumination when the media contained indole-3-acetic acid (IAA). A comparison of the morphogenic response to PFD with that produced under a matrix of exogenous auxin and cytokinin concentration combinations indicated that morphogenesis may be influenced by PFD-dependent depletion of IAA. A high performance liquid chromatography study of auxin depletion from basal medium showed that IAA was rapidly removed when illuminated and that the rate of removal was proportional to the prevailing PFD and the concentration of basal salts. The inclusion of the photosynthetic inhibitors 3-(3,4-dichlorophenyl)I,I-dimethylurea and 3-amino-l,2,4-triazole in the basal medium resulted in inhibition of explant growth and elimination of the sequential change in the culture vessel headspace CO2 concentration apparent during the light/dark cycle in noninhibited controls. This indicates that in vitro photosynthesis made a significant contribution to PFD-dependent explant growth. While culture of explants under a range of photoperiods of uniform PFD produced a range of growth responses, a uniform growth response occurred when explants were exposed to 16 hour and 24 hour photoperiods of uniform photon dose achieved through PFD variation. This demonstrates that growth was enhanced as a function of the increase in total incident radiation rather than through an effect of the photoperiod per se. Dark or low PFD incubation of explants for the first 4 days of culture significantly enhanced growth as a result of reduced photodestruction of IAA during a period of optimal tissue sensitivity to exogenous auxin.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Botany