Submitted to: American Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2003
Publication Date: 9/1/2003
Citation: Logan, B., Monteiro, G., Kornyeyev, D., Payton, P.R., Allen, R., Holaday, S. 2003. Transgenic overexpression of glutathione reductase does not protect cotton gossypium hirsutum (malvaceae) from photoinhibition during growth chilling conditions.. American Journal of Botany. 90(9):1400-1403. Interpretive Summary: The photosynthetic activity of chilling-sensitive plants measured at optimum conditions is severely inhibited after exposures to sub-optimal temperatures and high light conditions. Maintenance of photo-assimilate supply during fruit development is critical in achieving high yields in cotton. Because photosynthesis is the driving force behind plant productivity, although not the only factor that determines yield, plants have developed numerous mechanisms that serve to protect the photosynthetic apparatus during stressful conditions. One such mechanism is the ability to scavenge reactive oxygen intermediates (ROIs). ROIs produced in response to environmental stress are a major source of cellular damage. To investigate their role in stress tolerance, we increased the levels of three key anti-oxidant enzymes in cotton via transgenic over-expression. Initial studies by this group showed that increases in the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR) provided some protection to the photosynthetic apparatus, during short-term, abrupt chilling stress in the light. The findings of this study indicate that the nature of the chilling stress (i.e., short-term vs long-term) has profound effects on the response of transgenic and wild-type plants. During longer-term chilling, plants are able to acclimate to cool temperature stress. Part of this acclimation response includes an increase in native GR activity. Although the wild-type GR activity was significantly less than that in transgenic GR over-expressing plants, the moderate increase in native GR activity was sufficient to meet the demand for enzymatic capacity to scavenge ROIs.
Technical Abstract: In some studies, tissues from plants that have been genetically transformed to overproduce antioxidant enzymes sustain less damage when abruptly exposed to short-term chilling in the laboratory. However, few studies have examined the performance of transgenic plants during longer-term growth under chilling conditions. We compared growth of transgenic cotton that overproduces glutathione reductase (GR+; 40-fold overproduction) to growth of the wild type in a controlled environment chamber as leaf temperature was lowered from 28° to 14°C over 9 d and for a subsequent 9-d period at 14°C. In wild-type and GR+ cotton, chilling temperatures resulted in decreased dark-adapted Fv/Fm (the ratio of variable to maximal fluorescence; a measure of maximum photosystem II quantum yield) and mid-light period photosystem II quantum yield, coupled with increased 1 - qP (a nonlinear estimate of the reduction state of the primary quinone acceptor of photosystem II). The capacity for photosynthetic oxygen evolution decreased during the first portion of the chilling exposure, but recovered slightly during the second half. At no point during the chilling exposure did the performance of GR+ plants differ significantly from that of wild-type plants in any of the above parameters. The absence of an effect of GR overproduction under longer-term chilling may be explained, in part, by the fact that wild-type cotton acclimated to chilling by upregulating native GR activity