Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Spinacea oleracea L. cv Savoy was utilized to determine the effects of growth temperature and temperature shifts after leaf expansion on growth, photosynthesis and photoinhibition.;Growth was slowed at 5{dollar}\sp\circ{dollar}C with the second leaves reaching full expansion at 92 days after planting compared to 32 days for 16{dollar}\sp\circ{dollar}C grown plants. Growth at 5{dollar}\sp\circ{dollar}C compared to 16{dollar}\sp\circ{dollar}C resulted in a 2 to 3 fold increases in leaf area, dry weight per area, and leaf thickness of fully expanded leaves. Further, growth at 5{dollar}\sp\circ{dollar}C resulted in an increase from 2 to 3 palisade layers and an increase in the freezing tolerance from {dollar}-2\sp\circ{dollar}C to {dollar}-8\sp\circ{dollar}C. However, growth temperature had no affect on chl content (64 {dollar}\mu{dollar}g chl {dollar}\cdot{dollar} cm{dollar}\sp{lcub}-2{rcub}{dollar}) or quantum efficiencies and light saturated rates of CO{dollar}\sb2{dollar} and O{dollar}\sb2{dollar} exchange.;Imposition of a growth temperature shift for 12 days after leaf expansion resulted in 20% to 40% reductions in the gas exchange parameters. This indicates that sudden changes in growth temperature inhibit photosynthesis and appear to cause a significant stress. However, it is shown that the reduction in photosynthesis observed upon a temperature shift can be accounted for by aging of the leaf. Thus, growth at low temperature should not be considered a stress for cold tolerant herbaceous plants.;It is shown that exposing spinach plants to a combination of high light and low temperature can result in significant reduction in photosynthetic efficiency. More important, growth at low temperature increased the resistance to this low temperature induced photoinhibition. In contrast, exposure of leaves to a temperature shift after full leaf expansion did not induce a resistance to photoinhibition. However, an eight day shift to a lower temperature in conjunction with a photoperiod reduction from 16 to 8 hours resulted in an increased resistance to photoinhibition equivalent to leaves expanded at 5{dollar}\sp\circ{dollar}C. In addition, it is shown that older leaves were more susceptible to photoinhibition than were younger leaves. Thus, developmental age, past history and acclimation protocols are factors affecting the sensitivity to low temperature-induced photoinhibition.



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