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Title: CHANGES IN GROWTH CO2 RESULT IN RAPID ADJUSTMENTS OF RBCS GENE EXPRESSION IN BOTH EXPANDING AND MATURE LEAVES OF RICE.

Author
item GESCH, RUSS - UNIV OF FLORIDA
item BOOTE, KENNETH - UNIV OF FLORIDA
item Vu, Joseph
item Allen Jr, Leon
item BOWES, GEORGE - UNIV OF FLORIDA

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/29/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Rice is one of the most important agricultural food crops in the world. This study documents that the modification of carbon dioxide [CO2] in the air to which rice is exposed during growth, leads to rapid changes in the genetic expression and synthesis of Rubisco, the primary protein responsible for absorbing atmospheric CO2 in most plants. Modifying the [CO2] of the atmosphere during growth eventually led to alterations of Rubisco protein content and its activity. Both mature and young leaves maintained the ability to increase Rubisco upon decreasing the atmospheric [CO2], whereas exposure to high [CO2] resulted in the decrease of Rubisco. The signal that is sensed by the plant telling it to make more or less Rubisco as a consequence of altered atmospheric [CO2] appears to be detected within 24 hours after modifying CO2. It is hypothesized that the amount of soluble sugars in the plant may be the signal that is sensed and that changes in sugars resulting from altered [CO2] lead to changes in the synthesis of Rubisco. However, changes in the amount of total leaf soluble sugars alone could not explain the rapid change in Rubisco synthesis that scientists at USDA, ARS, in Gainesville, FL detected. Further work is underway to determine the flux of carbon through soluble sugar pools under growth at elevated CO2 in an effort to determine the signal for Rubisco synthesis as a function of atmospheric [CO2].

Technical Abstract: It is hypothesized that accumulation of soluble carbohydrates resulting from growth under elevated CO2 may potentially signal the repression of gene activity for the small subunit of Rubisco (rbcS). To test this hypothesis we grew rice (Oryza sativa L.) under ambient (350 ppm) and high (700 ppm) CO2 in outdoor, sunlit, environment-controlled chambers and performed a cross-switching of growth [CO2] at late vegetative phase. Within 24 h, plants switched to high-CO2 showed a 15 and 23% decrease in rbcSmRNA while those switched to ambient-CO2 increased 27 and 11% in expanding and mature leaves, respectively. Rubisco total activity and protein content eight days after the switch increased up to 27% and 20%, respectively, for plants switched to ambient-CO2, but changed very little in high-CO2 switched plants. Plants maintained at high-CO2 showed greater carbohydrate pool sizes and lower rbcS transcript levels than plants kept at ambient-CO2. However, after switching growth [CO2], there was not a simple correlation between carbohydrate and rbcS transcript levels. We conclude that although carbohydrates may be important in the regulation of rbcS expression, changes in total pool sizes alone could not predict the rapid changes in expression we observed.