The Mechanism to Suppress Photosynthesis Through End-Product Inhibition in Single-Rooted Soybean Leaves during Acclimation to CO2 Enrichment

Abstract

Single-rooted soybean leaves were used to investigate the suppression of photosynthesis through end-product inhibition during acclimation to CO(2 )enrichment. The photosynthetic activity was greater in leaves cultured at a CO(2) partial pressure of 70 Pa (high-CO(2)) than that in the leaves cultured at 35 Pa CO(2) (control) during the initial exposure to CO(2) enrichment but then decreased rapidly with a large accumulation of starch, to well below the level of the control leaves. The response curve of photosynthesis (A) to the intercellular CO(2) concentration (Ci) in the high-CO(2) leaves cultured long-term exhibited a significantly low initial gradient. However, on exposure to darkness for 48 h, the initial gradient of the A to Ci curve and rate of photosynthesis were completely restored, and almost all of the accumulated starch was expended. The ribulose bisphosphate carboxylase (RuBPcase) content and activation ratio in the high-CO(2) leaves remained high and roughly constant during the experiment, and were unchanged by the exposure, while this enzyme was slightly inactivated or inhibited after long-term exposure to CO(2) enrichment. The lower rate of photosynthesis in the high-CO(2) leaves could be linearly increased to a rate approaching the control level by increasing the external atmospheric [CO(2)], which thereby compensated for a reduced CO(2) transfer diffusion from the intercellular space to the stroma in chloroplasts. It is consequently concluded that, during the acclimation to CO(2 )enrichment, the suppression of photosynthesis through end-product inhibition was mainly caused by a lowering of the carboxylation efficiency of RuBPcase due to hindrance of CO(2) diffusion from the intercellular space to the stroma in chloroplasts brought about by the large accumulation of starch.

Analysis of Reduced Photosynthesis in the Apple Leaf under Sink-limited Conditions Due to Girdling

“…The leaf extract from the frozen leaf discs and the supernatant from the extract were prepared as described by Sawada et al (2001). The supernatants of the soluble sugar and starch were completely dehydrated using a Centrifugal Dehydrator (EYELA, CVE-100D TYPE, Tokyo Science Equipment Corporation, Tokyo, Japan), and then re-dissolved with ultrapure water.…”

“…The supernatants of the soluble sugar and starch were completely dehydrated using a Centrifugal Dehydrator (EYELA, CVE-100D TYPE, Tokyo Science Equipment Corporation, Tokyo, Japan), and then re-dissolved with ultrapure water. HPLC analysis solutions for sucrose, sorbitol, glucose, fructose and starch were prepared by the method of Sawada et al (2001). Starch concentration was expressed in glucose units.…”

“…RuBPcase activity in the supernatant was assayed at 25°C in a medium containing 100 mM Bicine at pH 8.2, 5 mM MgCl 2 , 20 mM NaHCO 3 , 5 mM creatin phosphate, 1 mM ATP-2Na, 0.1 mM NADH, 0.3 mM RuBP, 10 units of phosphocreatine kinase, 10 units of glyceraldehyde 3-phosphate dehydrogenase, and 10 units of phosphoglycerate kinase, as described by Sawada et al (2001). Enzymatic activities were revised for the decrease in absorbance at 340 nm in the control assay medium prepared without ribulose bisphosphate.…”

Crescimento dos frutos de laranjeira 'Salustiana' situados em ramos anelados com diversas relações de folhas/frutos

“…Entretanto, a atividade fotossintética das folhas não é constante, havendo um mecanismo de controle da oferta-demanda de carboidratos, que pode restringir a atividade fotossintética, na ausência de drenos (Fishler, 1983;Azcon-Bieto, 1983;Paul & Foyer, 2001;Sawada et al, 2001).…”

Analysis of the Feed-Forward Effects of Sink Activity on the Photosynthetic Source-Sink Balance in Single-Rooted Sweet Potato Leaves. I. Activation of RuBPcase through the Development of Sinks

“…Carbamylation is followed by the binding of Mg 2+ to form a catalytically active ternary complex (Miziorko and Lorimer 1983). Several other mechanisms of regulation are superimposed upon this basic mechanism of modulating activity, the most important of which are: (1) lightdependent activation by RuBPcase activase; (2) inhibition by nocturnal and day time inhibitors, and (3) modulation by stromal metabolites such as sugar phosphates, inorganic phosphate and starch (Vu et al 1984, Gutteridge et al 1986, Leegood and Furbank 1986, Portis et al 1986, Berry et al 1987, Sawada et al 1990, Nakano et al 1997, Parry et al 1997, Sawada et al 2001.…”