Snider, John , Choinski, John S. Jr. .
Differences in chlorophyll fluorescence temperature optima of young and mature leaflets of Smooth Sumac (Rhus glabra L.).
We have previously reported that when measured early in the growing season, young, not fully expanded leaves of R. glabra have higher mid-day leaf temperatures and lower leaf-air temperature differentials than fully expanded leaves. To test whether warmer temperatures of young leaves might promote growth and expansion during cooler spring weather, we measured the temperature sensitivity of PSII fluorescence (as measured by the dark recovery of variable fluorescence (Fv/F0)) in detached leaflets harvested at different times from June-October 2006. Leaflets were collected in the field and kept moist in a dark container until laboratory fluorescence measurements could be taken (~ 1 h later). Leaf segments were then incubated from 10-40ºC in 5ºC intervals and a light intensity of ~300 μmol m-2 s-1 for 40 minutes. Temperatures of leaf segments were confirmed with a handheld infrared thermometer. Fluorescence transients were obtained at 1 minute intervals for 5 minutes using a 0.8 s excitation period and a light intensity of ~15000 μE and then maximum Fv/F0 values were plotted versus incubation temperature to obtain the optimum recovery temperature. Data collected during June showed the apparent optimal temperature range for recovery of Fv/F0 to be higher in young (4.98 + 0.14 cm2) leaflets (28-30ºC) than mature (12.9 + 0.30 cm2) leaflets (24-26ºC). In contrast, although the temperature optimum for young leaflets at the same developmental stage was higher (30-35°C) when measured from July-August, it was not significantly (α > 0.05) different than more mature leaflets. Significant differences in temperature optima were also not observed in similar leaflets harvested from September to October. We conclude that the lower transpiration rates and higher mid-day temperatures observed in young leaflets in cooler spring temperatures may promote growth and expansion through an affect on the temperature sensitive components of PSII.
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1 - University of Central Arkansas, Biology, Conway, AR, 72035, USA
Presentation Type: Poster:Posters for Topics
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM