Overexpression of Rubisco Activase Decreases the Photosynthetic CO2 Assimilation Rate by Reducing Rubisco Content in Rice Leaves

Abstract

The effects of overexpression of Rubisco activase on photosynthesis were studied in transgenic rice expressing barley or maize Rubisco activase. Immunoblot and SDS-PAGE analyses showed that transgenic lines from both gene constructs expressed the foreign Rubisco activase at high levels. The activation state of Rubisco in transgenic lines was slightly higher than that in non-transgenic plants (NT). In addition, light activation of Rubisco was significantly more rapid in transgenic lines compared with NT. These findings indicate that the overexpression of Rubisco activase can enhance Rubisco activation. However, despite enhanced activation of Rubisco in these transgenic plants, the CO(2) assimilation rate at ambient CO(2) conditions was decreased. This decrease in CO(2) assimilation rate was observed in both young developing and mature leaves independent of nitrogen nutrition. The contents of nitrogen and Chl did not differ significantly between transformants and NT; however, Rubisco content was substantially decreased in transgenic lines. There was no evidence for reduced transcription of RbcS or RbcL in these transgenic lines; in fact, transcript levels were marginally increased compared with NT. These results indicate that the overexpression of Rubisco activase leads to a decrease in Rubisco content, possibly due to post-transcriptional mechanisms.

The Regulatory Properties of Rubisco Activase Differ among Species and Affect Photosynthetic Induction during Light Transitions

“…Certain plant species like Arabidopsis, camelina, and spinach express equal amounts of a-Rca and b-Rca, while others like rice (Oryza sativa) and wheat (Triticum aestivum) accumulate much more b-Rca than a-Rca Fukayama et al, 2012). In still others like maize, only b-Rca has been detected at the protein level under nonstress conditions Vargas-Suárez et al, 2004), even though the genome contains an open reading frame that encodes for an a-Rca (accession no.…”

Unusual Small Subunit That Is Not Expressed in Photosynthetic Cells Alters the Catalytic Properties of Rubisco in Rice

“…Rice (Oryza sativa 'Nipponbare') plants were grown in soil under natural sunlight conditions in a temperature-controlled greenhouse at day and night temperatures of 30°C and 23°C, respectively, and relative humidity of 70%, as described previously (Fukayama et al, 2012). All samples for molecular and biochemical analyses were collected at 11 AM to 1 PM on sunny days, immediately frozen in liquid nitrogen, and stored at -80°C until required.…”

“…Chlorophyll was determined spectrophotometrically as described in Porra et al (1989). Total nitrogen was determined by indophenol colorimetric assay after the Kjeldahl digestion of leaf tissue as described previously (Fukayama et al, 2012).…”

Análisis de crecimiento de árboles de guayaba (<i>Psidium guajava</i> L.) var. ICA Palmira II sometidos a deficiencia de N, P, K, Mg, Ca y B en fase de vivero

“…(O FRPSRUWDPLHQWR GH OD 75& GH ODV SODQWDV VRmetidas a deficiencia de nitrógeno, se debe a que este macronutriente está ligado a la constitución propia de la planta, es decir, a los componentes estructurales funcionales que proporcionan energía metabólica a esta, mientras que una porción más pequeña se incorpora en componentes celulares (De Groot et al, 2003); al presentar deficiencia de este, se produce material vegetal nuevo (hojas) pero en menor magnitud (figura 2); por tal motivo se podría decir que, ante el posible estrés en la nutrición mineral, la actividad respiratoria de la planta podría ser afectada como consecuencia a una eventual disminución en el proceso de la fotosíntesis debido a la interrupción de forma GUiVWLFD OD UHJHQHUDFLyQ \ DFWLYLGDG GH OD 5XELVFR (Fukayama et al, 2012).…”