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|Title:||The Effect of Chilling Temperatures on Photosynthetic Electron Transport and Electron Transport Components in Tomato Plants|
|Department / Program:||Plant Biology|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Subject(s):||Biology, Plant Physiology|
|Abstract:||The effects of chilling tomato (Lycopersicon esculentum hybrid Floramerica) plants in the dark and under strong illumination, and the effects of leaf detachment and dark storage (at room temperature), were investigated using isolated chloroplasts capable of transporting electrons at rates higher than needed to account for the observed maximal CO(,2)-fixation rate in untreated intact plants. (1) Placing intact plants and detached leaves under darkened conditions at room temperature (dark storage) caused a slight loss in both photosystem I and II photosynthetic electron transfer capability when storage was longer than 10 hours. (2) Chilling intact plants (1(DEGREES)C) and detached leaves (0(DEGREES)C) in the dark (dark chilling) resulted in decreased photosystem II activity. This loss was abated by feeding electrons from catechol into the electron transport chain at a site between the water-oxidation step and P(,680). Dark chilling thus has an adverse effect on water-oxidation. Dark chilling also increased the photosystem I quinol oxidation activity of the cytochrome b(,6)/f complex. This was true for both the endogenous quinol, plastiquinone, and the exogenous quinol, durohydroquinone. (3) Leaf detachment accelerated the onset of injury symptoms by about a factor of two. (4) Dark storage led to a small decline in the chlorophyll content of the leaves. This loss in chlorophyll was suppressed by dark chilling. Decreased electron transport rates is therefore not correlated with chlorophyll loss in the leaves. (5) Intact plants chilled (4 to 7(DEGREES)C) under intense light (1000 (mu)E (.) m('-2) (.) s('-1)), in addition to exhibiting the damages seen in dark-chilled plants, showed decreased photosystem I activity which was reflected in a loss of active photosystem I centers. Loss of electron transfer activity was accompanied by a decrease in the chlorophyll a to chlorophyll b ratio and a reduction in leaf chlorophyll content.
Parallel studies by Dr. B. Martin in our laboratory indicated that the loss of CO(,2)-fixation rates--in dark chilled attached and detached leaves and in attached leaves chilled under strong illumination--occurred too early into the treatment to be accounted for by the decline in photosynthetic electron transport activity. And since the CO(,2)-fixation measurements were conducted under saturating CO(,2) levels, thereby eliminating stomatal influences, the early damage to photosynthesis by chilling temperatures must be a site(s) in the chloroplast beyond the electron transport reactions.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1984.
|Date Available in IDEALS:||2014-12-16|