Effects of CO₂ Enrichment and Carbohydrate Content on the Dark Respiration of Soybeans

Abstract

During the period of most active leaf expansion, the foliar dark respiration rate of soybeans (Glycine max cv Williams), grown for 2 weeks in 1000 microliters CO2 per liter air, was 1.45 milligrams CO2 evolved per hour leaf density thickness, and this was twice the rate displayed by leaves of control plants (350 microliters CO2 per liter air). There was a higher foliar nonstructural carbohydrate level (eg. sucrose and starch) in the CO2 enriched compared with CO2 normal plants. For leaves. These increases, however, are due to an increase in the volume and water content of the cells, and not an increase in the actual number of cells (15). Recently, attention has been given to the role of carbohydrate status in regulating carbon metabolism (9). It has been suggested that high carbohydrate levels inhibit photosynthesis (3, 25). Azcon-Bieto (3) postulates that above a certain critical level of carbohydrate, CO2 assimilation would decrease due to carbohydrate accumulation impairing the production or consumption of ATP/NADPH in photosynthesis. However, Robinson (22) has reported higher photosynthetic activities associated with high starch and sucrose levels.Carbohydrate status may also have an effect on dark respiration. A high carbohydrate status has been associated with elevated respiration rates in a number of studies (1,2,5,20,26). Dark respiration is thought to have two components, growth and maintenance. Growth respiration occurs in those parts of a plant which are actively dividing or expanding (21). The rate ofgrowth respiration is thought to be related to the rate of photosynthesis. Maintenance respiration occurs throughout the life of the plant and is proportional to the Dw ofthe plant (18, 21). During plant growth both types of respiration occur, but growth respiration would decrease as the leaf matures. Both are thought to involve carbohydrate oxidation through glycolysis, the pentose phosphate pathway and the tricarboxylic acid cycle (2).In this study, long-term CO2 enrichment was used to increase carbohydrate levels in order to investigate the relationship between dark respiration and carbohydrate status. The effect of increased carbohydrate status on dark respiration was studied by monitoring dark CO2 release from whole leaves. Subcellular fractionation of enriched and control leaves was performed to determine if there were increases in the activity or number of mitochondria as a consequence of a high CO2 level. MATERIALS AND METHODSPlant Material. Soybeans (Glycine max cv Williams) were planted in 15-cm pots containing vermiculite and were grown in Environmental Growth Chambers No. M-2 at 25°C, with a 12-h photoperiod. The plants were illuminated with a mixture of fluorescent and incandescent bulbs at 600 uE/m2 at pot height. They were flushed daily with a nutrient solution described previously (22

Changes in Respiratory Mitochondrial Machinery and Cytochrome and Alternative Pathway Activities in Response to Energy Demand Underlie the Acclimation of Respiration to Elevated CO2 in the Invasive Opuntia ficus-indica

“…1) in plants grown at either ambient or elevated CO 2 were correlated with changes in mitochondrial number (Table IV) and maximum activity of cytochrome c oxidase (Table VI). Azcon-Bieto et al (1994), Hrubeck et al (1985), and Tissue et al (2002) also reported a correlation between the maximum activity of cytochrome c oxidase activity and respiration rates in trees, crops, sedges, and C3 and C4 grasses. These results suggest that the capacity of respiration is tightly regulated in plants (as suggested elsewhere; Gonzalez-Meler and Siedow, 1999; Atkin and Tjoelker, 2003) to maintain certain homeostasis between the capacity of respiration (mitochondrial counts, cytochrome c oxidase activity) and tissue-specific respiration rates, ) or elevated CO 2 (E, 600 mg mL 21 ) for 4 months.…”

Relationship between Fructose 2,6-Bisphosphate and Carbohydrate Metabolism in Darkened Barley Primary Leaves

“…In the present study we (2,4,5,11,13). To determine the effect of high soluble carbohydrates on initial dark F2,6-P2 levels, three approaches were used for altering the soluble carbohydrate content of the leaf.…”

“…In the present study this is what was observed. First, treatments that increase carbohydrate levels in photosynthetically active leaves consistently increase initial dark respiration rates (2,4,5,11,13). Initial dark F2,6-P2 and sucrose levels are considerably higher after longer photosynthetic periods, low temperature treatment, and when loss of carbohydrate is restricted by leaf excision (Table I; Fig.…”

“…Based on in vitro enzyme analysis, an increase in F2,6-P2 concentration could simultaneously activate PPi-PFK (7,8,12) and inhibit cytosolic FBPase (10,21,22). Accordingly, in darkened photosynthetic tissue, as in nonphotosynthetic tissues (7,14,20), high F2,6-P2 levels might stimulate glycolysis as well as inhibit sucrose synthesis.In the present study we (2,4,5,11,13). To determine the effect of high soluble carbohydrates on initial dark F2,6-P2 levels, three approaches were used for altering the soluble carbohydrate content of the leaf.…”

“…Barley primary leaves were extracted using buffered methanol-chloroform-water as described previously (17). Leaf starch, Chl, sucrose, glucose, fructose, G6P, and F2,6-P2 were measured as previously described (6,16 (2,4,5,11,13). To determine the effect of high soluble carbohydrates on initial dark F2,6-P2 levels, three approaches were used for altering the soluble carbohydrate content of the leaf.…”