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 Title: Stomatal and nonstomatal responses of photosynthesis to water deficits and chilling Author(s): Ortiz-Lopez, Adriana Doctoral Committee Chair(s): Ort, Donald R. Department / Program: Plant Biology Discipline: Plant Biology Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Agriculture, Agronomy Biology, Ecology Biology, Plant Physiology Abstract: This thesis deals with the nonstomatal and stomatal responses to photosynthesis to water deficits and chilling. Photophosphorylation was studied as a potential limitation since its fragile and highly integrated nature makes it a prime candidate for disruption by unfavorable environmental conditions and because it had been implicated in earlier in vitro results. In situ measurements of photophosphorylation were made using the flash-induced absorbance change at 518 nm, $\Delta$A$\sb{518}$.Low leaf water potentials ($\Psi$), induced by withholding water from the soil, inhibited flash-induced photophosphorylation in vivo in dark-adapted sunflower leaves. ATP formation was completely inhibited at low $\Psi$ when the actinic flashes were distantly spaced (0.03 to 0.1 Hz) but greater than 50% of the photophosphorylation was restored when $\Delta$p was increased to near maximal level by increasing the flash frequency (3.3 Hz). Based on this flash frequency dependence, it was concluded that the inhibition of ATP formation in dark-adapted leaves by low $\Psi$ involves an increase in the energy required to activate the oxidized CF. However, this low $\Psi$-induced inhibition of oxidized CF was largely eliminated when CF was reduced following light adaptation. It was further shown that, low $\Psi$ did not impair the efficiency of coupling factor reduction. Thus, this work reverses a notion held for more than ten years, establishing that photophosphorylation does not play a major role in the inhibition of net photosynthesis at low $\Psi$.Exposure of maize leaves to 4-6$\sp\circ$C at 1000 $\mu$mol m$\sp{-2}$s$\sp{-1}$ decreased in situ photophosphorylation capacity of thylakoid membranes. The effect of the chilling treatment was for the most part due to a diminished ability to energize the thylakoid membrane due to inactivation of some PS II reaction centers.Autoradiographic images showed that low $\Psi$ (-0.8 to -1.8 MPa) induced nonuniform photosynthesis in leaves of growth chamber-grown sunflower leaves. Rewatering of stressed leaves (-1.6 to -1.8 MPa) showed nearly total recovery of $\Psi$ and stomatal conductance within 24 h but 50% inhibition on the rate of photosynthesis persisted. These data indicate that relatively severe dehydration induces inhibition at the chloroplast level in growth chamber sunflower plants opposing the recent claims that low $\Psi$-induced inhibition of photosynthesis is entirely caused by stomatal closure. Issue Date: 1990 Type: Text Language: English URI: http://hdl.handle.net/2142/21137 Rights Information: Copyright 1990 Ortiz-Lopez, Adriana Date Available in IDEALS: 2011-05-07 Identifier in Online Catalog: AAI9114328 OCLC Identifier: (UMI)AAI9114328
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