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Title: GROWTH AND PHOTOSYNTHESIS UNDER HIGH AND LOW IRRADIANCE OF ARABIDOPSIS THALIANA ANTISENSE MUTANTS WITH REDUCED RUBISCO ACTIVASE CONTENT

Author
item ECKARDT, NANCY - PLANT BIO UOFI URBANA
item SNYDER, GORDON - PHOTOSYNTHESIS UNIT URB
item PORTIS JR, ARCHIE
item OGREN, WILLIAM - PHOTOSYNTHESIS UNIT URB

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/16/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: The activity of Rubisco, the enzyme that captures carbon dioxide, often limits photosynthesis, the process by which plants use light energy from the sun to make carbohydrates for growth from carbon dioxide and water. The activity of Rubisco is determined and hence regulated by another enzyme known as Rubisco activase, which is normally present at fairly high levels. In this comparative study of transgenic plants expressing reduced amounts of Rubisco activase, we found that wildtype Arabidopsis plants do not contain a great excess of the amount required for optimal growth, in contrast to the indications from previous studies. This information will benefit scientists attempting to modify the properties and regulation of Rubisco in ways beneficial for increased photosynthesis by crop plants.

Technical Abstract: Photosynthesis and growth to maturity of antisense Rubisco activase Arabidopsis thaliana with reduced concentrations of activase relative to wild type (Wt) plants were measured under low (200 umol m**-2 s**-1) and high (600 umol m**-2 s**-1) PPFD growing conditions. Both growth and photosynthesis were significantly reduced in an Arabidopsis clone (R100) with 30-40 percent Wt activase, an effect which was more pronounced in high light. Above-ground biomass of antisense clone R100 reached 80 percent of Wt under low light and 65 percent of Wt under high light. Decreased growth in the antisense plants was attributed to reduced relative rates of growth (RGR) and leaf area expansion (RLE) early in development; all plants attained similar values of RGR and RLE by 21 days after planting. Reductions in photosynthesis were attributed to decreased Rubisco activation in the antisense plants. Rubisco activation state was significantly lower in clone R100 relative to Wt on five out of six sampling days in high light, and three out of six days in low light. Rubisco constituted about 40 percent of total soluble protein in both Wt and clone R100 under both light regimes. Activase content was 5 percent and 1.4 percent of total soluble protein in Wt and clone R100, respectively, and also was unaffected by growth irradiance. The stoichiometry of Rubisco to activase was estimated at 20 Rubisco active sites per activase tetramer in Wt Arabidopsis and 60-80 in transgenic clone R100.