Journal of Experimental Botany

This Article Abstract FREE Full Text (PDF) E-letters: Submit a response Alert me when this article is cited Alert me when E-letters are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to My Personal Archive Download to citation manager Request Permissions Disclaimer Google Scholar Articles by Kauder, F. Articles by Heineke, D. Search for Related Content PubMed PubMed Citation Articles by Kauder, F. Articles by Heineke, D. Agricola Articles by Kauder, F. Articles by Heineke, D. Social Bookmarking          What's this?

Journal of Experimental Botany, Vol. 51, No. 90001, pp. 429-437, February 2000
© 2000 Oxford University Press

Ontogenetic changes of potato plants during acclimation to elevated carbon dioxide

F. Kauder¹, F. Ludewig² and D. Heineke^1,3

¹ Albrecht-von-Haller-Institut für Pflanzenwissenschaften, Abteilung Biochemie der Pflanze, Untere Karspüle 2, D-37073 Göttingen, Germany
² Institut für Pflanzengenetik und Kulturpflanzenforschung, Corrensstraße 3, D-06466 Gatersleben, Germany

Received 26 March 1999; Accepted 4 October 1999

	Abstract

Top Abstract Introduction Materials and methods Results Discussion References

 
Transgenic potato plants (Solanum tuberosum cv. Desirée) with an antisense repression of the chloroplastic triosephosphate translocator were compared with wild-type plants. Plants were grown in chambers with either an atmosphere with ambient (400µbar) or elevated (1000 µbar) CO₂. After 7 weeks, the rate of CO₂ assimilation between wild-type and transgenic plants in both CO₂ concentrations was identical, but the tuber yield of both plant lines was increased by about 30%, when grown in elevated CO₂. One explanation is that plants respond to the elevated CO₂ only at a certain growth stage. Therefore, growth of wild-type plants was analysed between the second and the seventh week. Relative growth rate and CO₂ assimilation were stimulated in elevated CO₂ only in the second and the third weeks. During this period, the carbohydrate content of leaves grown with elevated CO₂ was lower than that of leaves grown with ambient CO₂. In plants grown in elevated CO₂, the rate of CO₂ assimilation started to decline after 5 weeks, and accumulation of carbohydrates began after 7 weeks. From this observation it was concluded that acclimation of potato plants to elevated CO₂ is the result of accelerated development rather than of carbohydrate accumulation causing down-regulation of photosynthesis. For a detailed analysis for the cause of the stimulation of growth after 2 weeks, the contents of phosphorylated intermediates of wild-type plants and transgenics were measured. Stimulation of CO₂ assimilation was accompanied by changes in the contents of phosphorylated intermediates, resulting in an increase in the amount of dihydroxyacetone phosphate, the metabolite which is exported from the chloroplast into the cytosol. An increase of dihydroxyacetone phosphate was found in wild-type plants in elevated CO₂ when compared with ambient CO₂ and in triosephosphate translocator antisense plants in ambient CO₂, but not in the transgenic plants when grown in elevated CO₂. These plants were not able to increase dihydroxyacetone phosphate further to cope with the increased CO₂ supply. From these changes in phosphorylated intermediates in wild-type and transgenic plants it was concluded that starch and sucrose synthesis pathways can replace each other only at moderate carbon flux rates.

Key words: Elevated carbon dioxide, Solanum tuberosum L., transgenic plants, potato

	Introduction

Top Abstract Introduction Materials and methods Results Discussion References

 
Assimilation of carbon is strongly dependent on the availability of CO₂ and the gradient of CO₂ between the atmosphere and the chloroplast. Although a sudden increase in the partial pressure of CO₂ in the atmosphere, often called elevated CO₂, may lead to closure of stomata, a higher rate of CO₂ assimilation generally occurs (for review see Drake et al., 1997). However, when plants are grown in elevated CO₂ for a long period, this stimulation often disappears and is accompanied by complex changes in leaf metabolism. In some species in elevated CO₂, a lower rate of CO₂ assimilation is found than in those plants kept in ambient CO₂ (Sage et al., 1989; Drake et al., 1997). This phenomenon is described as ‘acclimation’ (Bowes, 1993), but the mechanism is not understood. A possible explanation (Stitt, 1991) is that acclimation could result from an insufficient sink capacity to cope with the increased carbohydrate production of plants grown in elevated CO₂. This would lead to an accumulation of sugars in the leaves and to a reduced capacity of CO₂ assimilation due to ‘sugar sensing’ (Jang and Sheen, 1994). Recently, ontogenetic changes were monitored in the rates of photosynthesis and the content of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) of tobacco plants grown in ambient (350 µl l^-1) and elevated CO₂ (950 µl l^-1) (Miller et al., 1997) and an alternative explanation for the acclimation was offered: development of tobacco plants grown in elevated CO₂ was faster than that of plants in normal CO₂ and there was an earlier onset of natural decline in photosynthetic rates associated with plant senescence. This hypothesis was supported by a study of growth and sink induction of radish plants grown with normal and elevated CO₂ (Usuda and Shimogawara, 1998). Radish plants grown with elevated CO₂ grew faster and induced root formation earlier than plants grown in normal CO₂. In young leaves, the rates of CO₂ assimilation were independent of the CO₂ concentration, and after 45 d the rate in elevated CO₂ became lower than that in ambient CO₂, due to earlier initiation of leaf senescence. This concept was further supported by a study with transgenic potato plants expressing an antisense gene of the B subunit of the ADP-glucose pyrophosphorylase (Ludewig et al., 1998). In wild-type potato plants grown in elevated CO₂, the rate of CO₂ assimilation was higher in an early state of plant development than in plants grown in ambient CO₂ and declined as plants became older. This stimulation of CO₂ assimilation was not observed in the ADP-glucose pyrophosphorylase antisense plants corresponding with a lower capacity of starch accumulation in leaves. This observation implies that a high capacity for starch synthesis is necessary to stimulate growth in elevated CO₂.

View this table: [in this window] [in a new window]   Table 1. Gas exchange data, Rubisco, chlorophyll and protein contents of leaves from wild-type and TPT 1 plants grown in ambient (400 µbar) and elevated (1000 µbar) CO2 for 7 weeks Gas exchange data are measured with a portable infrared gas exchange system in the growth chambers (means±SE n=13, respiration n=2). Activities of Rubisco (n=5), chlorophyll and protein (n=8) were determined from similar leaves of the same plants±SE.

 
A detailed analysis of growth and development of potato plants is reported in this paper. Additionally, the results obtained from wild-type potato plants were compared with those from transgenic plants, which were restricted in their capacity to export triose phosphates from the chloroplast into the cytosol of leaf cells by antisense repression of the triosephosphate translocator (TPT-plants). The amount of TPT protein in these plants was reduced only by about 30% (Riesmeier et al., 1993), which strongly influenced carbon partitioning. It has been shown (Heineke et al., 1994) that in these plants the rate of CO₂ assimilation was identical to wild-type plants, when grown in ambient CO₂. The main difference between wild-type and transformed plants was the partitioning of the products of CO₂ assimilation. In wild-type plants, most of the assimilates were exported from the leaves during the light period and a minor part was transiently stored as starch. In the transgenics, however, 80% of assimilate was stored as starch. This altered carbon partitioning was reflected by changes in the contents and subcellular distribution of phosphorylated intermediates of the sucrose and starch synthesis pathway. The amounts of 3-PGA and Ru-1,5-P₂ in the chloroplasts were higher and the amounts of the cytosolic metabolites were reduced compared to the wild type. The ratio of 3-PGA to P_i, which is known to regulate ADP-glucose pyrophosphorylase, the key enzyme of the starch synthesis pathway (Preiss and Levi, 1980) was dramatically increased in the transgenics. These observations imply that in ambient CO₂ the capacity of starch synthesis is sufficient to cope with the current CO₂ assimilation, but may not be sufficient in elevated CO₂.

	Materials and methods

Top Abstract Introduction Materials and methods Results Discussion References

 
Transgenic plants containing a fragment of the TPT gene in reverse orientation under the control of the cauliflower mosaic virus 35S promoter have been described in detail (Riesmeier et al., 1993). TPT expression was reduced by about 20–30%. Wild-type and transgenic potato plants (Solanum tuberosum cv. Desirée) were propagated from axenic tissue culture and transferred to soil. They were grown in controlled environment chambers with a light/dark period of 12/12 h with a photon flux of 600 µmol m^-2 s^-1. The partial pressures of CO₂ in the chambers were 400 µbar or 1000 µbar, respectively. After 10 d, the plants were transferred to 2.5 l pots containing a mixture (2:1, by wt) of soil and a complete nutrient substrate (Substrat 2^TM, Klasmann), respectively. Plants were watered daily. For the growth analysis, six plants were planted out every week in both growth conditions. As plants originated from axenic tissue culture and growth conditions were controlled, starting material and plant development were highly reproducible. Measurements started when the youngest plants were 2 weeks old. Gas exchange was measured on leaflets of mature leaves attached to the plants in the growth chambers in ambient CO₂ and light or at a photon flux of 1500 µmol m^-2 s^-1, using a portable infrared gas exchange system (LI-6400, Li-Cor, Inc.). Samples for the determination of sugars, amino acids and enzyme activities were taken from fully mature leaves at the end of the light or dark period. Then the shoot and the tubers were harvested and weighed. For the determination of the tuber composition from each individual tuber one small disc was sampled (according to Heineke et al., 1992). The discs of one plant were pooled. All extraction procedures and determinations were carried out as described (Büssis et al., 1998). All measured data are presented as mean values ±SE. No standard error was calculated, when results are calculated from mean values (Tables 2, 3; Fig. 1).

View this table: [in this window] [in a new window]   Table 2. Contents of carbohydrates and amino acids in leaves of wild-type and TPT 1 plants grown in ambient (400 µbar) and elevated (1000 µbar) CO2 atmosphere for 7 weeks Leaves were harvested at the end of the light (L) and the dark period (D) from those plants of Table 1. C/N ratio is calculated from the mean values of the carbohydrate and amino acid contents at the end of the light period and the protein content of table 1. Results are mean values±SE (n=10).

 

View this table: [in this window] [in a new window]   Table 3. Tuber composition of wild-type and TPT 1 potato plants grown in ambient (400 µbar) and elevated (1000 µbar) CO2 atmosphere for 9 weeks Tubers were from plants of Tables 1 and 2. Results are mean values±SE (n=10 (yield), n=5 other results). C and N are calculated from the mean values of the carbohydrate, amino acid and protein contents.

 

View larger version (11K): [in this window] [in a new window]   Fig. 1. Change with time in the relative growth rate from the fresh weights of the shoot (A) and the tubers (B) of wild-type potato plants grown in an atmosphere with ambient (400 µbar, ) or elevated (1000 µbar, ) CO2. The points are means of six plants.

 

	Results

Top Abstract Introduction Materials and methods Results Discussion References

 
Acclimation of potato plants to elevated atmospheric CO₂
When measured under growth conditions in the growth chambers, the rate of CO₂ assimilation of leaves from wild-type plants grown in elevated CO₂ for 7 weeks was nearly identical with that of plants grown in ambient CO₂, but the intercellular partial pressure of CO₂ was three times higher (Table 1). This observation, and only a slight reduction in leaf conductance, indicated that the lack of stimulation of CO₂ assimilation was not the result of a reduction in stomatal opening and internal CO₂ limiting CO₂ assimilation. Rubisco activity was measured in two conditions reflecting the maximum and the in vivo activity. Rubisco from leaves grown in elevated CO₂ was slightly, but not significantly lower than in 400 µbar CO₂. Therefore, reduction in Rubisco activity is not responsible for the absence of stimulation of CO₂ assimilation in elevated CO₂. However, the contents of chlorophyll and total protein were significantly reduced in elevated CO₂. The differences in the gas exchange, chlorophyll and protein content of wild-type plants grown in ambient and elevated CO₂ were also true for potato plants with antisense repression of the triosephosphate translocator. In Table 1 the data from TPT 1 are listed, similar results were also obtained with other lines.

In leaves of plants grown in elevated CO₂, the content of soluble sugars and of amino acids was slightly and that of starch dramatically increased, both at the end of the light and the dark periods (Table 2). When comparing the amount of carbon fixed during the light period (700 mmol C m^-2) with the carbon in starch (>1300 mmol C m^-2) in leaves of plants grown in elevated CO₂, it is obvious that only a small part of carbon stored as starch was degraded during the night. These observations confirm previous results (Ludewig et al., 1998). Summing up all the carbon and nitrogen using the mean values for carbohydrates and amino acids of Table 2 and the protein from Table 1, showed that the C/N ratio and also the sucrose/amino acid ratio of leaves of wild-type and TPT-plants grown in elevated CO₂ were considerable higher than of leaves of the corresponding plants grown in ambient CO₂. In ambient CO₂, the starch content of TPT 1 plants was higher, and those of soluble carbohydrates and amino acids slightly lower, than in the corresponding leaves of wild-type plants. The comparison of changes between 400 and 1000 µbar CO₂ shows the same trends in TPT 1 and wild-type leaves.

The most noticeable feature of both wild-type plants and TPT 1 transformants was that the rates of CO₂ assimilation were identical in both CO₂ concentrations, but the tuber yield was increased by about 35%, when plants were grown in elevated CO₂ (Table 3). The yield of TPT 1 was lower than that of wild-type plants in both growth conditions, and tuber composition was not significantly altered. As leaf metabolism of 7-week-old plants of wild-type and TPT 1 plants responded similarly to elevated CO₂, but tuber yield was different, this suggests that plant ontogeny is influenced by the increase in atmospheric CO₂ concentration.

Ontogeny of growth of wild-type plants
To study possible effects in plant ontogeny, a detailed analysis of growth of wild-type potato plants in ambient and elevated CO₂ was carried out starting at 2 weeks after transfer of plants from tissue culture into soil. The fresh weights of shoots and tubers were determined and from these the relative growth rates were calculated (Fig. 1). To verify the fresh weight as a reasonable measure for the growth rate, the developmental changes in the dry weight of leaves were determined. It was twice as high in leaves of plants grown in elevated CO₂ as in in ambient CO₂ (ambient: 42±10 g m^-2, elevated: 90±23 g m^-2) and this difference was independent of the age of the plants. In ambient CO₂, shoots of potato plants showed a constant growth rate between the second and the fifth week and a decline afterwards. In elevated CO₂, shoot growth was accelerated between the second and the fourth week, and more strongly reduced thereafter than in ambient CO₂. Tuber growth of plants was different only in the very early state of development. Growth in elevated CO₂ accelerated tuber induction. After 3 weeks no CO₂-dependent differences in the relative growth rates were found.

The stimulation of plant growth in elevated CO₂ between the second and the fourth week was accompanied by changes in the rate of CO₂ assimilation and in the carbohydrate and amino acid concentrations. CO₂ assimilation per unit leaf area followed the changes in growth when measured at photon fluxes of 600 (growth conditions, Fig. 2A) and 1500 µmol m^-2 s^-1 (saturating light, Fig. 2B). In leaves grown in elevated CO₂, assimilation was stimulated in the third and the fourth week and declined earlier than in leaves of plants grown in ambient CO₂.

View larger version (9K): [in this window] [in a new window]   Fig. 2. Time-course of the rates of CO2 assimilation measured at a photon flux of 600 (A) or 1500 µmol m-2 s-1 (B) of wild-type potato plants grown in an atmosphere with ambient (400 µbar, ) or elevated (1000 µbar, ) CO2. Means (n=3)±SE.

 
In the period of rapid growth, sugar, starch and amino acid contents of leaves were lower in elevated than in ambient CO₂ (Fig. 3A–D). After 7 weeks the contents of soluble compounds were similar for plants from both growth conditions, but starch increased in elevated CO₂ after 5 weeks, when the relative growth rate started to decline (compare Fig. 1A).

View larger version (18K): [in this window] [in a new window]   Fig. 3. Time-course of the contents of hexoses (A), sucrose (B), starch (C), and amino acids (D) of leaves from wild-type plants grown in an atmosphere with ambient (400 µbar, ) or elevated (1000 µbar, ) CO2. Means (n=10)±SE.

 

Changes in the contents of phosphorylated intermediates of carbohydrate metabolism of leaves
In the phase of stimulated growth, phosphorylated metabolites of leaves from young potato plants were analysed (Fig. 4). The stimulation of CO₂ assimilation in elevated CO₂ was accompanied by higher contents of all phosphorylated metabolites measured, but they did not increase to the same extent. The increase in 3-PGA, DHAP and Fru-1,6-BP was more pronounced than that of Ru-1,5-BP and Fru-6-P.

View larger version (26K): [in this window] [in a new window]   Fig. 4. Contents of phosphorylated intermediates in leaves of 4-week-old wild-type plants grown in an atmosphere with ambient (400 µbar, black bars) or elevated (1000 µbar, grey bars) CO2. Means (n=10)±SE.

 

Effect of antisense repression of the triosephosphate translocator on leaf metabolism
The relation between phosphorylated metabolite concentrations in leaves of wild-type plants grown in ambient and elevated CO₂ were compared with those of transgenic potato plants expressing an antisense gene of the chloroplastic triosephosphate translocator (TPT). These plants have increased phosphorylated intermediates even when grown in ambient CO₂ (Heineke et al., 1994). In the TPT plants, no stimulation of the rates of CO₂ assimilation in high CO₂, which was found in 2-week-old wild-type plants, could be detected (Fig. 5A). This difference between wild-type and TPT plants was restricted to the young plants. After 5 weeks, the rates of CO₂ assimilation in elevated CO₂ were slightly lower than in ambient CO₂ in wild-type and TPT 7 and identical in TPT 1 plants (Fig. 5B).

View larger version (26K): [in this window] [in a new window]   Fig. 5. Rates of CO2 assimilation of leaves of 2-week- (A) or 5-week- (B) old wild-type and triosephosphate translocator antisense potato plants grown in an atmosphere with ambient (400 µbar, black bars) or elevated (1000 µbar, grey bars) CO2. Means (n=4)±SE.

 
To establish why CO₂ did not stimulate net photosynthesis in young leaves of TPT plants, activity of Rubisco and the contents of some phosphorylated intermediates of the Calvin-cycle were determined (Fig. 6A–F). Maximum activity of Rubisco was similar between wild-type and transformant plants in both growth conditions (Fig. 6A), but Rubisco was more activated in TPT than in wild-type plants (Fig. 6B). There was a large difference in the contents of phosphorylated intermediates (Fig. 6C–F). In elevated CO₂, Ru-1,5-BP increased in both plant types, but more in the TPT than in wild-type plants (Fig. 6C). 3-PGA contents were also different in wild-type and transformant plants. In ambient CO₂, 3-PGA was clearly higher in the TPT plants than in wild-type, but in elevated CO₂, the 3-PGA concentration increased in wild-type plants and it remained constant in the two TPT lines (Fig. 6D). Figure 6F shows the total of phosphate bound in sugar phosphates. In wild-type plants it increased in elevated CO₂. In TPT plants, the values were high in ambient CO₂ and the increase in elevated CO₂ was small (TPT 7) or not detectable (TPT 1).

View larger version (31K): [in this window] [in a new window]   Fig. 6. Activity (A) and activation state of Rubisco (B) and contents of phosphorylated metabolites (C–F) of 4-week-old wild-type and triosephosphate translocator antisense potato plants grown in an atmosphere with ambient (400 µbar, dark bars) or elevated (1000 µbar, grey bars) CO2. The values of Fig. 6F are calculated from the contents of Glc-6-P, Fru-6-P, Fru-1,6-BP, Ru-1,5-BP, 3-PGA and DHAP. Means of 5 (Rubisco) or 10 replicates±SE (phosphorylated intermediates). Ratios shown in Fig. 6E are calculated from mean values of Fig. 6C and Fig. 6D.

 

	Discussion

Top Abstract Introduction Materials and methods Results Discussion References

 
Growth of wild-type potato plants in elevated partial pressure of CO₂
When potato plants were grown in elevated CO₂ for 7 weeks, leaf metabolism acclimated to the growth conditions. Compared to plants grown in ambient CO₂, the rate of CO₂ assimilation was not stimulated, the activity of Rubisco was slightly reduced and the contents of carbohydrates were dramatically increased. Such changes were described for several plants (for review see Drake et al., 1997). In potato plants, the increase in carbohydrates was mainly due to a 20-times higher starch content; that of soluble sugars only doubled. Additionally, potato plants, when grown in elevated CO₂, produced more tubers. The higher productivity of 7-week-old plants was not achieved by a stimulation of CO₂ assimilation per leaf area, but from an increase in leaf area. Increase in leaf area required accelerated growth of the plant as recently suggested for tobacco plants (Miller et al., 1997) and verified with radish (Usuada and Shimogawara, 1998).

In this examination, the time-dependent development of shoot and tuber growth rates, leaf CO₂ assimilation, carbohydrate and amino acid contents were monitored between the second and the seventh week. The results clearly show that vegetative growth of potato plants and tuber induction were accelerated in elevated CO₂. The maximum rate of growth was between the second and the fourth week. As the relative growth rate of potato plants in ambient CO₂ was constant during the first weeks, it was dramatically reduced after 4 weeks in elevated CO₂. In the period of rapid growth of plants in elevated CO₂, carbohydrates formed by CO₂ assimilation in leaves were exported to sink tissues and used for an accelerated shoot growth and earlier tuber induction. These results are in good accordance with the observation of vegetative growth and root formation of radish plants described previously (Usuda and Shimogawara, 1998). Carbohydrates accumulated in leaves of potato plants grown in elevated CO₂ after 7 weeks, when shoot growth was already negative. This observation excluded the hypothesis that, in potato, acclimation was the result of sink limitation, indicated by an increase of leaf soluble carbohydrate content. Furthermore, these results imply that plant senescence might be one major factor for leaf acclimation.

Changes in the pattern of phosphorylated intermediates in leaves of wild-type plants during the phase of rapid growth
In wild-type plants, stimulation of CO₂ assimilation in elevated CO₂ was accompanied by an increase in the concentrations of phosphorylated intermediates of the sucrose and starch synthesis pathways (Fig. 4). The concentrations of 3-PGA and Fru-1,6-BP increased more than those of the other intermediates. This becomes more obvious, when calculating the ratios of Ru-1,5-BP to 3-PGA (1.7 in 400 µbar, 0.8 in 1000 µbar CO₂) and Fru-1,6-BP to Fru-6-P (0.6 in 400 µbar, 1.2 in 1000 µbar CO₂). Calculations of metabolite ratios are often used to identify limiting steps in a pathway (Büssis et al., 1998). The lower Ru-1,5-BP/3-PGA ratio indicated that the substrate of Rubisco reaction increases to a smaller extent than the product and that Rubisco is not limiting in elevated CO₂. The increase in the Fru-1,6-BP to Fru-6-P ratio showed that one of the fructose-1,6-bisphosphatases is involved in the flux control. As Fru-1,6-BP mainly occurs in the chloroplast (Gerhardt et al., 1987), the chloroplastic isoenzyme might be responsible for the accumulation of Fru-1,6-BP. A down-regulation of chloroplastic FBPase leads to an increase in DHAP and increases the export of triose phosphates out of the chloroplast. Triosephosphates then become available for the sucrose synthesis in the cytosol. Such an increase in DHAP was earlier observed in transgenic potato plants with antisense repression of both ADPglucose pyrophosphorylase and the triosephosphate translocator (Hattenbach et al., 1997) and functioned as a way to increase the carbon supply for the sucrose synthesis.

Effect of antisense repression of the triosephosphate translocator in potato plants on the acclimation to elevated atmospheric carbon dioxide
Potato plants with an antisense repression of the TPT were suitable to study the role of starch accumulation and the participation of the phosphorylated intermediates in the stimulation of CO₂ assimilation in young leaves of wild-type plants. First, it was earlier found that in these transgenic potato plants carbon partitioning was changed, as 80% of the assimilates were stored as starch even in ambient CO₂ (Heineke et al., 1994). In these plants, CO₂ assimilation, Rubisco activity and the contents of soluble compounds were almost unaltered. Second, the change in carbon partitioning led to an increase in phosphorylated intermediates.

When TPT antisense plants were grown in 1000 µbar CO₂ for 7 weeks, few differences in the carbohydrate and amino acid concentrations were observed compared to wild-type plants (Tables 1–3). Antisense repression of TPT obviously did not influence the CO₂-dependent acclimation of leaf metabolism. Differences in leaf metabolism became obvious when leaves of young plants were analysed. The observation that, after 2 weeks, stimulation of CO₂ assimilation which occurred in wild-type plants grown in elevated CO₂, but was not detectable in transgenic plants (Fig. 5), is similar with that obtained in potato plants with an antisense repression of the ADP-glucose pyrophosphorylase (Ludewig et al., 1998). In wild-type plants the stimulation of CO₂ assimilation in elevated CO₂ was accompanied by a 3-fold increase in the sum of phosphorylated intermediates and one might speculate that the concentration of P_i was lower (Figs 6F, 4). Higher metabolite concentrations influence metabolism in different ways. First, higher substrate concentrations for the enzymes allow a higher flux rate. Second, some metabolites allosterically influence the activation state of key enzymes: the increased ratio of 3-PGA to P_i is known to stimulate starch synthesis by activating ADP-glucose pyrophosphorylase (Preiss and Levi, 1980) and the cytosolic Fru-1,6-BPase is activated by DHAP (Stitt et al., 1984). In the TPT plants in ambient CO₂ these changes were found to cope with the reduced transport capacity for triosephosphates and allowed an unaltered rate of CO₂ assimilation (Heineke et al., 1994). In contrast to the wild-type plants, in TPT plants during the phase of rapid growth in elevated CO₂, the phosphorylated intermediates cannot further increase, because the concentration of P_i may not drop sufficiently. As the chloroplastic and cytosolic concentrations of P_i cannot be measured directly, indirect evidence has to be taken. A good indication for the restriction for the P_i availability is the ratio of Ru-1,5-BP to 3-PGA, which was lower in wild-type plants grown in elevated CO₂ and increased in the transgenics when compared with the corresponding plants in ambient CO₂ (Fig. 6E). Rubisco is inhibited by low P_i (Heldt et al., 1978). This regulation could obviously not be overcome by an increased activation state of the enzyme (Fig. 6B).

These studies of the development of CO₂ assimilation in potato plants in elevated CO₂ have confirmed the hypothesis that starch and sucrose synthesis pathways replace each other in moderate assimilate fluxes. The compensation was mediated by changes in the pattern of phosphorylated metabolites (Heineke et al., 1994; Leidreiter et al., 1995; Hattenbach et al., 1997). However, this flexibility was not sufficient to compensate at high rates of carbon flux.

	Acknowledgements

 
The authors thank Professor Uwe Sonnewald for suppling growth facilities and for his critical comments and Professor Wolf B Frommer for offering the TPT-plants. We are grateful to Andrea Nickel and Monika Raabe for their excellent technical assistance. This work was supported by the Deutsche Forschungsgemeinschaft (SPP Stoffwechsel und Wachstum der Pflanze unter erhöhter CO₂ Konzentration)

	Footnotes

 
⁴ To whom correspondence should be addressed. Fax: +49 551 395749. E-mail:dheinek{at}gwdg.de.

	Abbreviations

 
AGPase, ADP-glucose pyrophosphorylase; DHAP, dihydroxyacetone phosphate; Fru-1,6-BP, fructose-1,6-bisphosphate; Fru-6-P, fructose-6-phosphate; Glc-6-P, glucose-6-phosphate; 3-PGA, 3-phosphoglycerate; Ru-1,5-BP, ribulose-1,5-bisphosphate; TPT, triosephosphate translocator.

	References

Top Abstract Introduction Materials and methods Results Discussion References

 
Bowes G.1993. Facing the inevitable: plants and increasing atmospheric CO₂.Annual Reviews of Plant Physiology and Plant Molecular Biology 44, 309–332.[Web of Science]

Büssis D, Kauder F, Heineke D.1998. Acclimation of potato plants to polyethylene glycol-induced water deficit. I. Photosynthesis and metabolism. Journal of Experimental Botany 49, 1349–1360.[Abstract/Free Full Text]

Drake BG, Gonzàlez-Meler MA, Long SP.1997. More efficient plants: a consequence of rising atmospheric CO₂? Annual Reviews of Plant Physiology and Plant Molecular Biology 48, 609–639.[Web of Science]

Gerhardt R, Stitt M, Heldt HW.1987. Subcellular metabolite levels in spinach leaves. Plant Physiology 83, 399–407.[Abstract/Free Full Text]

Hattenbach A, Müller-Röber B, Nast G, Heineke D.1997. Antisense-repression of both ADP-glucose pyrophosphorylase and triose phosphate translocator modifies carbon partitioning in potato leaves. Plant Physiology 115, 471–475.[Abstract]

Heineke D, Sonnewald U, Büssis D, Günter G, Leidreiter K, Wilke I, Raschke K, Willmitzer L, Heldt HW.1992. Apoplastic expression of yeast-derived invertase in potato. Plant Physiology 100, 301–308.[Abstract/Free Full Text]

Heineke D, Kruse A, Flügge U-I, Frommer WB, Riesmeier JW, Willmitzer L, Heldt HW.1994. Effect of antisense repression of the chloroplast triose-phosphate translocator on photosynthetic metabolism in transgenic potato plants. Planta 193, 174–180.

Heldt HW, Chon CJ, Lorimer GH.1978. Phosphate requirement for the light activation of ribulose-1,5-bisphosphate carboxylase in intact spinach chloroplasts. FEBS Letters 92, 234–240.

Jang JC, Sheen J.1997. Sugar sensing in higher plants. Trends in Plant Science 2, 208–214.

Leidreiter K, Heineke D, Heldt HW, Müller-Röber B, Sonnewald U, Willmitzer L.1995. Leaf-specific antisense inhibition of starch biosynthesis in transgenic potato plants leads to an increase in photoassimilate export from source leaves during the light period. Plant and Cell Physiology 36, 615–624.[Abstract/Free Full Text]

Ludewig F, Sonnewald U, Kauder F, Heineke D, Geiger M, Stitt M, Müller-Röber BT, Gillissen B, Kühn C, Frommer WB.1998. The role of transient starch in acclimation to elevated atmospheric CO₂. FEBS Letters 429, 147–151.[Web of Science][Medline]

Miller A, Tsai C-H, Hemphill D, Endres M, Rodermel S, Spalding M.1997. Elevated CO₂ effects during leaf ontogeny. Plant Physiology 115, 1195–1200.[Abstract]

Preiss J, Levi C.1980. Starch biosynthesis and degradation. In: Stumpf PK, Conn EE, eds. The biochemistry of plants, Vol. 3. New York: Academic Press, 371–423.

Riesmeier JW, Flügge U-I, Schulz B, Heineke D, Heldt H-W, Willmitzer L, Frommer WB.1993. Antisense repression of the triose phosphate translocator affects carbon partitioning in transgenic potato plants. Proceedings of the National Academy of Sciences, USA 90, 6160–6164.[Abstract/Free Full Text]

Sage RF, Sharkey TD, Seemann JR.1989. Acclimation of photosynthesis to elevated CO₂ in five C₃ species. Plant Physiology 89, 590–596.[Abstract/Free Full Text]

Stitt M.1991. Rising CO₂ levels and their potential significance for carbon flow in photosynthetic cells. Plant, Cell and Environment 14, 741–762.

Stitt M, Herzog B. Heldt HW.1984. Control of photosynthetic sucrose synthesis by fructose 2,6 bisphosphate. Plant Physiology 75, 548–553.[Abstract/Free Full Text]

Usuda H, Shimogawara K.1998. The effects of increased atmospheric carbon dioxide on growth, carbohydrates, and photosynthesis in radish, Raphanus sativus. Plant and Cell Physiology 39, 1–7.[Abstract/Free Full Text]

CiteULike    Connotea    Del.icio.us    What's this?

This article has been cited by other articles:

				H. Usuda Effects of Elevated CO2 on the Capacity for Photosynthesis of a Single Leaf and a Whole Plant, and on Growth in a Radish Plant Cell Physiol., February 1, 2006; 47(2): 262 - 269. [Abstract] [Full Text] [PDF]

This Article Abstract FREE Full Text (PDF) E-letters: Submit a response Alert me when this article is cited Alert me when E-letters are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to My Personal Archive Download to citation manager Request Permissions Disclaimer Google Scholar Articles by Kauder, F. Articles by Heineke, D. Search for Related Content PubMed PubMed Citation Articles by Kauder, F. Articles by Heineke, D. Agricola Articles by Kauder, F. Articles by Heineke, D. Social Bookmarking          What's this?

Online ISSN 1460-2431 - Print ISSN 0022-0957

Copyright © 2005 Society for Experimental Biology

Oxford Journals Oxford University Press

• Site Map
• Privacy Policy
• Frequently Asked Questions

Other Oxford University Press sites: Oxford University Press Oxford Journals China Oxford Journals Japan American National Biography Booksellers' Information Service Children's Fiction and Poetry Children's Reference Corporate & Special Sales Dictionaries Dictionary of National Biography Digital Reference English Language Teaching Higher Education Textbooks Humanities International Education Unit Law Medicine Music Online Products Oxford English Dictionary Reference Rights and Permissions Science School Books Social Sciences Very Short Introductions World's Classics