DSilva, Lorraine I. , Robertson, James , Robison, Mary , Micallef, Barry J. .
Photoperiodic injury in tomato is a circadian phenomenon caused by alterations in the diel coordination between nitrate and nitrite reductase.
Photoperiodic injury (PI) of vegetative tissues occurs under either extended photoperiods or non-24 h light/dark cycles in a number of plants providing evidence that PI is linked to the circadian clock. Tomato is particularly susceptible to PI, and we have identified and characterized genetic variation for susceptibility of tomato to PI. Use of these genetically-distinct lines has shown that PI is linked both to circadian-controlled processes and to N metabolism as evidenced by nitrite accumulation under light/dark cycles that elicit PI. In the present study, the genetic and physiological basis for nitrite accumulation was examined. Genetic analysis of populations segregating for PI indicate that the trait is controlled by two genes through a suppressive-epistatic interaction. Photoperiodic injury symptoms could be induced using the nitrate-analogue chlorate, which is converted to the nitrite-analogue chlorite. Analysis of diel activities of nitrate and nitrate reductase using lines either tolerant or susceptible to PI when grown under either a 12 hour photoperiod or 24 hour light showed that nitrite accumulation occurred when the ratio of nitrate to nitrite reductase activity approached a value of one or more; this only occurred in 24 hour light for lines susceptible to PI. The data also indicate that activity of nitrite reductase but not nitrate reductase showed a circadian rhythm, and that the diel timing of nitrate uptake differed between lines that vary in susceptibility to PI. The effects of elevated nitrite at the cellular level will also be discussed. Collectively, the data provide evidence that the circadian clock is important for regulating N metabolism including the relative activities of nitrate and nitrite reductase.
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1 - University of Guelph, Guelph, Ontario, Canada N1G 2W1, Plant Agriculture
2 - University of Guelph, Plant Agriculture, Guelph, Ontario, N1G 2W1, Canada
Presentation Type: Plant Biology Abstract
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM