Effect of CO 2 ‐Concentration on the Accumulation of Starch and Sugar in Tomato Leaves

120

ABSTRACTrable to or lower than those of plants maintained in normal atmospheric CO2. The length of the enhancement period and the rapidity of decline from the maximum rates apparently depend on the ambient CO2 concentration, with higher concentrations leading to more rapid loss of enhancement (4). In crop species, it has been reported (11, 16) that exposure to high CO2 does not result in growth enhancement during all phases of vegetative growth but can increase dry weights significantly during early stages of seedling growth or early fruit development. This suggests that enhanced rates of photosynthesis per unit area may be maintained only during periods of rapid growth when the demand for assimilate is high. During periods of low assimilate demand, rates of photosynthesis per unit leaf area in high-CO2 grown plants fall off in the manner demonstrated by Aoki and Yabuki (4).The purpose of the present experiment was to measure the effects of assimilate demand on rate of whole plant net photosynthetic carbon fixation in soybeans during long-term exposure to high CO2 and to relate these rates to dry matter production under these conditions. MATERIALS AND METHODS Plant Material and Growth Conditions. Fiskeby V, an early maturing, strongly determinate cultivar of soybean (Glycine max. L. Merrill), was grown in controlled environment chambers at the Duke University Phytotron. Seeds were planted in individual 360-ml plastic pots in a mixture of gravel:vermiculite:Turface (1:1:1; v/v/v) and placed on a 12 h/12 h, light/dark cycle (600 ,uE m-2 s-' at plant height, fluorescent and incandescent lamps) and a 26/ 20 C temperature cycle. On day 16, seedlings were transplanted into 12.7-cm plastic pots and axillary branches removed. Pots were placed on an automatic watering system and, thereafter, were watered to the drip point with modified half-strength Hoagland solution three times per day.Treatments were initiated on day 44 when pod growth was rapid but seeds had not yet begun to develop (stage R6 (9)). At this time, vegetative growth was complete with seven to eight mainstem nodes present on all plants. To establish approximately equal leaf area in all plants, trifoliolates at nodes other than 2, 4, and 6 were excised. For low sink treatments the two smallest pods at nodes 2, 4, and 6 were left (total, six pods) and for high sink treatments the three smallest pods at nodes I through 7 were left (total, 21 pods). On the second day after pruning plants from each sink treatment were assigned randomly to high CO2 (1,000 ,ul C02/1 air) or "low" CO2 (350 ,ul

Section: Discussionmentioning

confidence: 99%

Effects of High Atmospheric CO₂ and Sink Size on Rates of Photosynthesis of a Soybean Cultivar

Clough¹,

Peet²,

Kramer³

1981

120

“…Anatomical changes can occur which change internal leaf structure (15). Changes in degree and rate of leaf expansion and in total leaf area production affect photosynthetic rates on an area basis and on a whole-plant basis (13).Long-term exposure to elevated CO2 can also result in excessive accumulation of starch in the leaves (2,16,17,31). …”

mentioning

confidence: 99%

“…Long-term exposure to elevated CO2 can also result in excessive accumulation of starch in the leaves (2,16,17,31).…”

mentioning

confidence: 99%

“…Long-term exposure to elevated CO2 can also result in excessive accumulation of starch in the leaves (2, 16,17,31 This study was designed to determine the effects oflarge starch accumulations in cotton after long-term exposure to elevated CO2 concentrations but before severe, visible damage occurs. We were interested in the reversibility of feedback inhibition due to starch as well as the repair of any damage to the chloroplasts caused by large starch grains.…”

mentioning

confidence: 99%

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Reversibility of Photosynthetic Inhibition in Cotton after Long-Term Exposure to Elevated CO₂ Concentrations

Sasek¹,

DeLucia²,

Strain³

1985

163

Recovery was correlated to a rapid depletion of the starch pool, indicating that the inhibition of photosynthesis is primarily a result of feedback inhibition. However, complete recovery may involve the repair of damage to the chloroplasts caused by excessive starch accumulation. The rapid and complete reversal of photosynthetic inhibition suggests that the appearance of large, strong sinks at certain developmental stages could result in reduction of the large starch accumulations and that photosynthetic rates could recover to near the theoretical capacity during periods of high photosynthate demand.Studies of short-term exposure to elevated CO2 concentration have shown that increased starch levels are closely correlated with inhibition of photosynthesis (21,26). Although the specific mechanisms of inhibition are not well understood (22), photosynthesis can be affected by factors such as enzyme regulation and activity (26, 28), insufficient pools of metabolites, such as Pi (I 1, 24), or changes in physiological processes which reduce quantum yield (1, 27).Long-term exposure to elevated CO2 concentrations often introduces effects that would not be predicted from short-term exposure studies. Some of these effects influence photosynthetic rates either directly or indirectly. Anatomical changes can occur which change internal leaf structure (15). Changes in degree and rate of leaf expansion and in total leaf area production affect photosynthetic rates on an area basis and on a whole-plant basis (13).Long-term exposure to elevated CO2 can also result in excessive accumulation of starch in the leaves (2,16,17,31).

“…The present study was conducted to obtain more information on the interactions between CO2 enrichment and plant water stress, both of which are known to affect carbohydrate concentrations in leaves (1,4,5,17,18). Specific objectives were to determine the long-term effects of CO2 enrichment on (a) CER and photosynthate partitioning and (b) SPS activity in leaves of nonstressed versus water-stressed plants.…”

mentioning

confidence: 99%

Effects of Water Stress on Photosynthesis and Carbon Partitioning in Soybean (Glycine max [L.] Merr.) Plants Grown in the Field at Different CO₂ Levels

Rogers¹,

Mowry²

1984

124

The effects of water stress and CO2 enrichment on photosynthesis, assimilate export, and sucrose-P synthase activity were examined in field grown soybean plants. In general, leaves of plants grown in C02-enriched atmospheres (300 microliters per liter above unenriched control, which was 349 ± 12 microliters per liter between 0500 and 1900 hours EST over the entire season) had higher carbon exchange rates (CER) weight accumulation of leaves during the light period (28), provides an estimate of the rate of photosynthetic sucrose formation in situ. When CER is restricted (e.g. low irradiance), export rate can be maintained by mobilization of reserves (9-11). One of the principal determinants of export rate is leaf sucrose concentration (7,9,23), which is a function of both CER and the partitioning of carbon among end products.The enzyme SPS may be involved in the regulation of carbon partitioning in leaves in two different ways (14). SPS is activated by glucose-6-P and inhibited by Pi (6), and the concentration of these metabolites changes as a function of CER (26). Thus, metabolic regulation of SPS may coordinate the rate of sucrose formation in the cytosol with the rate of C-assimilation in the chloroplast when CERs are low. However, when CER is high (light-saturated), sucrose formation may be limited by the maximum activity of SPS (12,13,24,25). Consequently, short-term CO2 enrichment of soybean plants did not result in increased rates of export even though CER was increased (14).In addition to using CO2 enrichment as a system to study carbon partitioning (14) and the interaction between C and N metabolism (8), the long-term effects of CO2 supply are also of interest because global CO2 is increasing (16). In particular, plant growth is often enhanced by CO2 enrichment, but the effects are not necessarily related to sustained increases in CER (20). Rather, increased water use efficiency may also be involved (16,20).The present study was conducted to obtain more information on the interactions between CO2 enrichment and plant water stress, both of which are known to affect carbohydrate concentrations in leaves (1,4,5,17,18). Specific objectives were to determine the long-term effects of CO2 enrichment on (a) CER and photosynthate partitioning and (b) SPS activity in leaves of nonstressed versus water-stressed plants. The study was conducted over a 2-week period when plants were in early podfill. The plants were grown in the field from emergence at ambient CO2 or with CO2 enrichment (300 ppm above ambient). The stressed plants had been subjected continuously to cycles ofstress, and measurements were conducted during two drying cycles. MATERIALS AND METHODSSeeds of soybean (Glycine max [L.] Merr. cv 'Bragg') were planted on June 6, 1983 on an Appling-Cecil3 association soil.