Light‐induced systemic signalling down‐regulates photosynthetic performance of soybean leaves with different directional effects

• When plants are exposed to a heterogeneous environment, photosynthesis of leaves is not only determined by their local condition, but also by certain signals from other parts of the same plant, termed systemic regulation. Our present study was conducted to investigate the effects of light‐dependent systemic regulation on the photosynthetic performance of soybean (Glycine max L. Merr.) under heterogeneous light conditions.
• Soybean plants were treated with heterogeneous light. Then gas exchange characteristics were measured to evaluate the photosynthetic performance of leaves. Parameters related to photosynthetic pigments, chlorophyll fluorescence, Rubisco and photosynthates were examined to study the mechanisms of light‐dependent systemic regulation on photosynthesis.
• Light‐induced systemic signalling by illuminated leaves reduced the P_n of both upper and lower non‐illuminated leaves on the same soybean plant. The decrease in g_s and increase in C_i in these non‐illuminated leaves indicated restriction of carbon assimilation, which was further verified by the decline in content and activity of Rubisco. However, the activation state of Rubisco decreased only in upper non‐illuminated leaves. Quantum efficiency of PSII (ΦPSII) and ETR also decreased only in upper non‐illuminated leaves. Moreover, the effects of light‐induced systemic signalling on carbohydrate content were also detectable only in upper non‐illuminated leaves.
• Light‐induced systemic signalling by illuminated leaves restricts carbon assimilation and down‐regulates photosynthetic performance of non‐illuminated leaves within a soybean plant. However, effects of such systemic regulation differed when regulated in upward or downward direction.

     

Biochemical responses of glyphosate resistant and susceptible soybean plants exposed to glyphosate

Glyphosate is a wide spectrum, non-selective, post-emergence herbicide. It acts on the shikimic acid pathway inhibiting 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), thus obstructing the synthesis of tryptophan, phenylalanine, tyrosine and other secondary products, leading to plant death. Transgenic glyphosate-resistant (GR) soybean [Glycine max (L.)] expressing an glyphosate-insensitive EPSPS enzyme has provided new opportunities for weed control in soybean production. The effect of glyphosate application on chlorophyll level, lipid peroxidation, catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GOPX) and superoxide dismutase (SOD) activities, soluble amino acid levels and protein profile, in leaves and roots, was examined in two conventional (non-GR) and two transgenic (GR) soybean. Glyphosate treatment had no significant impact on lipid peroxidation, whilst the chlorophyll content decreased in only one non-GR cultivar. However, there was a significant increase in the levels of soluble amino acid in roots and leaves, more so in non-GR than in GR soybean cultivars. Root CAT activity increased in non-GR cultivars and was not altered in GR cultivars. In leaves, CAT activity was inhibited in one non-GR and one GR cultivar. GOPX activity increased in one GR cultivar and in both non-GR cultivars. Root APX activity increased in one GR cultivar. The soluble protein profiles as assessed by 1-D gel electrophoresis of selected non-GR and GR soybean lines were unaffected by glyphosate treatment. Neither was formation of new isoenzymes of SOD and CAT observed when these lines were treated by glyphosate. The slight oxidative stress generated by glyphosate has no relevance to plant mortality. The potential antioxidant action of soluble amino acids may be responsible for the lack of lipid peroxidation observed. CAT activity in the roots and soluble amino acids in the leaves can be used as indicators of glyphosate resistance.     

Alginate Production by Plant-Pathogenic Pseudomonads

Eighteen plant-pathogenic and three non-plant-pathogenic pseudomonads were tested for the ability to produce alginic acid as an exopolysaccharide in vitro. Alginate production was demonstrated for 10 of 13 fluorescent plant-pathogenic pseudomonads tested with glucose or gluconate as the carbon source, but not for all 5 nonfluorescent plant pathogens and all 3 non-plant pathogens tested. With sucrose as the carbon source, some strains produced alginate while others produced both polyfructan (levan) and alginate. Alginates ranged from <1 to 28% guluronic acid, were acetylated, and had number-average molecular weights of 11.3 × 10³ to 47.1 × 10³. Polyfructans and alginates were not elicitors of the soybean phytoalexin glyceollin when applied to wounded cotyledon surfaces and did not induce prolonged water soaking of soybean leaf tissues. All or most pseudomonads in rRNA-DNA homology group I may be capable of synthesizing alginate as an exopolysaccharide.     

Utilization of capsaicin and vanillylamine as growth substrates by Capsicum (hot pepper)-associated bacteria

Capsaicin contributes to the organoleptic attributes of hot peppers. Here, we show that capsaicin is utilized as a growth nutrient by certain bacteria. Enrichment cultures utilizing capsaicin were successfully initiated using Capsicum-derived plant material or leaves of tomato (a related Solanaceae) as inocula. No other sources of inoculum examined yielded positive enrichments. Of 25 isolates obtained from enrichments: all utilized 8-methylnonanoic acid; nine were found capable of degrading capsaicin as sole carbon and energy source; 11 were found capable of utilizing vanillylamine; but only two strains could use either of these latter two compounds as sole nitrogen source. Phylogenetic analysis of capsaicin degraders revealed them to be strains of Variovorax and Ralstonia, whereas the vanillylamine degraders were strains of Pseudomonas and Variovorax. Neither of the two strains isolated from one enrichment culture originally inoculated with dried pepper fruit was capable of using capsaicin as sole carbon and nitrogen source. However, good growth was achieved under such conditions when the two isolates, a strain of Variovorax paradoxusThat degraded capsaicin when provided with ammonium, and a vanillylamine degrading strain of Pseudomonas putida, were cultured together. A cross-feeding of capsaicin-derived carbon and nitrogen between members of pepper-associated consortia is proposed.     

Brassinolide alleviated the adverse effect of water deficits on photosynthesis and the antioxidant of soybean (<Emphasis Type="Italic">Glycine max</Emphasis> L.)

Brassinolide (BR) is a relatively new plant growth regulator. To test whether BR could be used to increase tolerance to water deficits in soybean, the effects of BR application on photosynthesis, assimilate distribution, antioxidant enzymes and seed yield were studied. BR at 0.1 mg l⁻¹ was foliar applied at the beginning of bloom. Two levels of soil moisture (80% field capacity for well-watered control and 35% for drought-stressed treatment) were applied at pod initiation. BR treatment increased biomass accumulation and seed yield for both treatments. Drought stress inhibited translocation of assimilated ¹⁴C from the labeled leaf, but BR increased the translocation for both treatments. Drought stress depressed chlorophyll content and assimilation rate (A), while chlorophyll content and A of BR-treated plants were greater than that of drought-stressed plants. BR treatment increased maximum quantum yield of PS II, the activity of ribulose-1,5-bisphosphate carboxylase, and the leaf water potential of drought-stressed plants. Treatment with BR also increased the concentration of soluble sugars and proline, and the activities of peroxidase and superoxide dismutase of soybean leaves when drought-stressed. However, it decreased the malondialdehyde concentration and electrical conductivity of leaves under drought stress. This study show that BR can be used as a plant growth regulator to enhance drought tolerance and minimize the yield loss of soybean caused by water deficits.     

CO2浓度倍增对几种植物叶片的叶绿素蛋白质复合物的影响

研究了CO_2浓度倍增对大豆(Glycine max L.,C_3植物)、黄瓜(Cucumis sativus L.,C_3植物)、谷子(Setaria italica (L.) Beauv.,一种不很典型的C_4植物)和玉米(Zea mays L.,C_4植物)叶片的叶绿素蛋白质复合物的影响。实验植物盆栽于聚乙烯薄膜(或玻璃)的开顶式培养室中。播种后对照室的CO_2浓度立即保持在大气浓度(350±10)×10~(-6)中,CO_2浓度倍增处理室则保持在(700±10)×10~(-6)下。研究结果表明,对于大豆、黄瓜和谷子,CO_2浓度倍增均使其PSⅡ捕光叶绿素a/b-蛋白质复合物(LHCⅡ)的聚合体态的量增多,单体态的量减少。但C_4植物玉米对CO_2浓度倍增没有这样的反应。作者认为在大豆等植物中,LHCⅡ的上述状态变化可能是植物的光合机构对长期高CO_2浓度的一种适应效应,这样能提高光合作用中光能的吸收、传递和转换的效率,并支持高效的光合碳素同化作用。     

Effects of Drought Stress on Key Enzymes of Carbon Metabolism,Photosynthetic Characteristics and Agronomic Traits of Soybean at the Flowering Stage under Different Soil Substrates

Soybean is an important legume food crop, and its seeds are rich in nutrients, providing humans and animals with edible oil and protein feed. However, soybean is sensitive to water requirements, and drought is an important factor limiting soybean yield and quality. This study used Heinong 84 (drought resistant variety) and Hefeng 46 (intermediate variety) as tested varieties planted in chernozem, albic, and black soils. The effects of drought stress on the activities of key enzymes in carbon metabolism and photosynthetic characteristics of soybean were studied during the flowering stage, most sensitive to water. (1) The activities of SS-1, 6PGDH, and G6PDH enzymes in soybean leaves first increased and then decreased under drought stress. The enzyme activity was the highest under moderate drought stress and weakest in the blank group. (2) Drought stress increased Phi2, PhiNO, and Fm in soybean leaves and reached the highest value under severe drought; with the increase in drought stress, PhiNPQ and Fv/Fm of soybean leaves gradually decreased, reaching the lowest under severe drought. (3) With the increase in drought stress, F₀ and Fs of soybean leaves showed a single peak curve, and the maximum was at moderate drought. (4) Correlation analysis showed that F₀ was greatly affected by varieties and soil types; Fs, F0, and Fm soil varieties had a great influence, and chlorophyll fluorescence parameters were affected differently under drought stress with different drought degrees. (5) Drought stress changed the agronomic traits and yield of soybean. With the increase of drought degree, plant height, node number of main stem, effective pod number, 100-seed weight and total yield decreased continuously. (6) Drought stress affected the dry matter accumulation of soybean. With the increase of drought degree, the dry matter accumulation gradually decreased. Among them, the leaf was most seriously affected by drought, and SD decreased by about 55% compared with CK. Under the condition of black soil, the dry matter accumulation of soybean was least affected by drought.     

Indirect effects of insect herbivory on leaf gas exchange in soybean

Herbivory can affect plant carbon gain directly by removing photosynthetic leaf tissue and indirectly by inducing the production of costly defensive compounds or disrupting the movement of water and nutrients. The indirect effects of herbivory on carbon and water fluxes of soybean leaves were investigated using gas exchange, chlorophyll fluorescence and thermal imaging. Herbivory by Popillia japonica and Helicoverpa zea (Boddie) caused a 20–90% increase in transpiration from soybean leaflets without affecting carbon assimilation rates or photosynthetic efficiency (Φ_PSII). Mechanical damage to interveinal tissue increased transpiration up to 150%. The spatial pattern of leaf temperature indicated that water loss occurred from injuries to the cuticle as well as from cut edges. A fluorescent tracer (sulforhodamine G) indicated that water evaporated from the apoplast approximately 100 µm away from the cut edges of damaged leaves. The rate of water loss from damaged leaves remained significantly higher than from control leaves for 6 d, during which time they lost 45% more water than control leaves (0.72 mol H₂O per cm of damaged perimeter). Profligate water loss through the perimeter of damaged tissue indicates that herbivory may exacerbate water stress of soybeans under field conditions.     

The rare occurrence of plant tissue culture contamination by Methylobacterium mesophilicum

A pink-pigmented, facultative methylotrophic (PPFM) bacterium, Methylobacterium mesophilicum, which is found on the leaf surface of most plants, has been reported to be a covert contaminant of tissue cultures initiated from Glycine max (soybean) leaves and seeds by Holland and Polacco (1992). The bacteria can be detected as pink colonies when leaves are pressed or tissue culture homogenates are plated on a medium with methanol as the sole carbon source. Since the presence of contaminating bacteria can confound any biochemical results obtained with such cultures (Holland and Polacco 1992), we wanted to determine the extent of the contamination of our tissue cultures of soybean and other species. No PPFMs were detected in any soybean culture we have, and previous results describing the biochemical characteristics of ureide utilization by one of our soybean suspension cultures (27C) also indicates that PPFM bacteria were not present. Analysis of about 200 other strains of 11 different species maintained in this lab showed that only three of about 160 callus cultures, recently initiated from Datura innoxia leaves, contained PPFMs. The D. innoxia leaves did have PPFMs on their surface but in most cases they did not survive the surface disinfestation and culture regimes. Thus PPFM bacterial contamination should not be a serious problem in most plant tissue cultures.Abbreviations AMS ammonium mineral salts medium - PPFM pink-pigmented facultative methylotrophic bacteria     

Chloroplast composition and structure differences in a soybean mutant

A nuclear mutation of Glycine max (soybean) segregates 1:2:1 in regard to chlorophyll content. The heterozygous (LG) leaf blade contains about one-half the pigment content of the wild type (DG) per gram fresh weight. A lethal yellow (LY) type contains about 1 to 2% of the DG leaf pigment values. The chlorophyll a/b ratio in the LG is about 5 compared to about 2 in the DG. Protein/leaf values are lower in the LG and LY types when compared to DG. The LG plastid lamellae contain more protein/chlorophyll, cytochromes/chlorophyll, and quinones/chlorophyll than the DG. P₇₀₀/chlorophyll values are similar in the DG and LG types.     

Effect of Doubled CO2 Concentration on Leaf Chlorophyll-protein Complexes in Several Plants

The effect of doubled CO2 on the chlorophyll-protein complexes of the leaves of soybean ( Glycine max L., Ca plants), cucumber ( Cucumis sativus L., C3 plant), millet ( Setaria italica (L.) Beauv., not a very typical C4 plant) and corn (Zea mays L. ,C4 plant) was studied. Experi- mental plants were pot-cultured in polyethylene membrane (or glass) open top cultured chambers. After sowing, C02 was kept immediately either at ambient ( (350 ± 10) x 10-6) concentration for the control or at doubled CO2 ((700 ± 10) x 10-6) concentration for the treatment chambers. The chlorophyll-protein complexes of the thylakoid membrane of the plants were resolved by disk SDS- PAGE. The results showed that after doubled CO2 treatment,either in the soybean and cucmnber,or in the millet, the quantity of polymer state of PS Ⅱ light-harvesting chlorophyll a/b-protein complex (LHC Ⅱ ) had increased as the monomer state of LHC Ⅱ decreased. But such response to doubled CO2 was not found in corn, the C4 plant. The change of the state of LHC Ⅱ in soybean etc. might be an adaptive effect of plant photosynthetic mechanism to the long term elevated CO2. Thus it could increase the efficiency of the absorption, transfer and conversion of light energy in plant photosynthesis, and support the high efficiency of photosynthetic carbon assimilation.     

Effects of EDTA and EDDS on Heavy Metal Activation and Accumulation of Metals by Soybean in Alkaline Soil

The application of chelating agents for phytoextraction has demonstrated that it is an efficient method to activate heavy metals in polluted soil. We conducted pot experiments using soybean, which has been considered an indicator plant, to study the effects of EDTA and EDDS on heavy metals’ activation, and on the soybean. The study results indicated that EDDS decreased the chlorophyll content of the leaves and increased the malondialdehyde (MDA) content of the soybean. EDTA also decreased the chlorophyll content of the leaves. EDDS had a strong influence on activating Cu (2583-8900-fold) and Zn. The addition of 5 mmol kg^?1 of EDDS markedly increased the uptake of metals. Compared with the control, EDDS increased the Cu uptake (100-205-fold). EDTA greatly increased the activation of heavy metals; it also increased Cu uptake in a concentration-dependent manner. EDTA also increased the biological concentration factor (BCF) and the transfer factor (TF) in a concentration-dependent manner. The BCF and the TF reached maximum levels when 5 mmol kg^?1 EDDS was applied to the pots.     

A soybean plastid-targeted NADH-malate dehydrogenase: cloning and expression analyses

A typical soybean (Glycine max) plant assimilates nitrogen rapidly both in active root nodules and in developing seeds and pods. Oxaloacetate and 2-ketoglutarate are major acceptors of ammonia during rapid nitrogen assimilation. Oxaloacetate can be derived from the tricarboxylic acid (TCA) cycle, and it also can be synthesized from phosphoenolpyruvate and carbon dioxide by phosphoenolpyruvate carboxylase. An active malate dehydrogenase is required to facilitate carbon flow from phosphoenolpyruvate to oxaloacetate. We report the cloning and sequence analyses of a complete and novel malate dehydrogenase gene in soybean. The derived amino acid sequence was highly similar to the nodule-enhanced malate dehydrogenases from Medicago sativa and Pisum sativum in terms of the transit peptide and the mature subunit (i.e., the functional enzyme). Furthermore, the mature subunit exhibited a very high homology to the plastid-localized NAD-dependent malate dehydrogenase from Arabidopsis thaliana, which has a completely different transit peptide. In addition, the soybean nodule-enhanced malate dehydrogenase was abundant in both immature soybean seeds and pods. Only trace amounts of the enzyme were found in leaves and nonnodulated roots. In vitro synthesized labeled precursor protein was imported into the stroma of spinach chloroplasts and processed to the mature subunit, which has a molecular mass of ～34 kDa. We propose that this new malate dehydrogenase facilitates rapid nitrogen assimilation both in soybean root nodules and in developing soybean seeds, which are rich in protein. In addition, the complete coding region of a geranylgeranyl hydrogenase gene, which is essential for chlorophyll synthesis, was found immediately upstream from the new malate dehydrogenase gene.     

A comparative analysis of fructose 2,6-bisphosphate levels and photosynthate partitioning in the leaves of some agronomically important crop species

Starch, sucrose, and fructose 2,6-bisphosphate (F2, 6BP) levels were measured in pea (Pisum sativum L.), maize (Zea mays L.), onion (Allium cepa L.) and soybean (Glycine max L.) leaves throughout a light/dark cycle. Leaf starch accumulated in pea, maize, and soybean but not in onion. Sucrose was a major leaf storage reserve in pea, maize, and onion but was only found at low levels in soybean. In all species examined, the most dramatic changes in F2,6BP concentration coincided with light/dark transitions. During the light period F2,6BP levels were about 0.1 nanomole/milligram chlorophyll in soybean source leaves and there was a small increase in effector concentration in the dark. Levels of F2,6BP were also low in pea and maize leaves during the light period but then increased 10- or 20-fold in the dark. Dark onion leaf F2,6BP levels were about 1.1 to 1.3 nanomole/milligram chlorophyll and these values decreased by 20 to 30% in the light. Thus, three different patterns were identified that describe diurnal F2,6BP levels in source leaves. These results support the suggestion that F2,6BP is involved in the regulation of sucrose biosynthesis. However, it was not possible to demonstrate that high levels of F2,6BP are essential for starch synthesis in the chloroplast.     

ALLELOPATHIC MECHANISMS OF VELVETLEAF (ABUTILON THEOPHRASTI MEDIC., MALVACEAE) ON SOYBEAN

Sampling in a soybean field established that presence of velvetleaf (A. theophrasti) weeds interfered with soybean production. Number of soybean pods and number of pods/stem were significantly lower in transect segments adjacent to velvetleaf plants. In bioassays for phytotoxicity of velvetleaf, several dilutions of aqueous extracts from fresh field-collected leaves depressed germination of radish seeds and inhibited growth of soybean seedlings. Seed germination bioassays from eluates of chromatograms developed in one dimension showed that two of three bands containing phenolic compounds were inhibitory to radish seed germination. Soybeans inhibited by aqueous velvetleaf extracts had increased diffusive resistance, suggesting partial stomatal closure. Inhibited plants also gave evidence of water stress, with leaf water potentials often as low as –20 bars and reduced water content, when compared with controls. Quantification of chlorophyll on a leaf area basis showed that chlorophyll of inhibited plants was below controls. These data demonstrate the allelopathic potential of velvetleaf and suggest that interference with water balance and chlorophyll content may be two mechanisms of inhibitory action of toxins present in the leaves of velvetleaf.     

NaCl胁迫对嫁接黄瓜膜脂过氧化、渗透调节物质含量及光合特性的影响

以日本引进的耐盐品种‘帝王新土佐’南瓜为砧木,以‘津研4号’黄瓜品种为接穗,研究了NaCl胁迫对黄瓜嫁接植株和自根植株的膜脂过氧化、渗透调节物质含量及光合特性的影响。结果表明:在NaCl胁迫下,黄瓜嫁接植株叶片超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)和抗坏血酸过氧化物酶(APX)活性均显著高于自根植株,O·2-产生速率及丙二醛(MDA)含量显著低于自根植株,嫁接植株膜脂过氧化轻于自根植株;嫁接植株叶片游离脯氨酸、可溶性糖、可溶性蛋白质等渗透物质含量均显著高于自根植株;嫁接植株的净光合速率(Pn)、气孔导度(Gs)、胞间CO2浓度(Ci)、叶绿素含量均显著高于自根植株;虽然NaCl胁迫抑制光合作用,但嫁接植株仍表现出优势。以上结果证明,嫁接植株耐盐性优于自根植株。     

Grafting helps improve photosynthesis and carbohydrate metabolism in leaves of muskmelon

The most important quality for muskmelon (Cucumis melo L.) is their sweetness which is closely related to the soluble sugars content. Leaves are the main photosynthetic organs in plants and thus the source of sugar accumulation in fruits since sugars are translocated from leaves to fruits. The effects of grafting muskmelon on two different inter-specific (Cucurbita maxima×C. moschata) rootstocks was investigated with respect to photosynthesis and carbohydrate metabolism. Grafting Zhongmi1 muskmelon on RibenStrong (GR) or Shengzhen1 (GS) rootstocks increased chlorophyll a, chlorophyll b and chlorophyll a+b content and the leaf area in middle and late developmental stages of the plant compared to the ungrafted Zhongmi1 check (CK). Grafting enhanced the net photosynthesis rate, the stomatal conductance, concentration of intercellular CO(2) and transpiration rate. Grafting influenced carbohydrates contents by changing carbohydrate metabolic enzymes activities which was observed as an increase in acid invertase and neutral invertase activity in the functional leaves during the early and middle developmental stages compared to CK. Grafting improved sucrose phosphate synthase and stachyose synthase activities in middle and late developmental stages, thus translocation of sugars (such as sucrose, raffinose and stachyose) in GR and GS leaves were significantly enhanced. However, compared with CK, translocation of more sugars in grafted plants did not exert feedback inhibition on photosynthesis. Our results indicate that grafting muskmelon on inter-specific rootstocks enhances photosynthesis and translocation of sugars in muskmelon leaves.     

Phytoplasma distribution in coconut palms affected by lethal yellowing disease

Lethal yellowing (LY), the most devastating disease affecting the coconut palm in America, is caused by phytoplasmas known to be distributed in different parts of infected plants. However, no comprehensive reports exist on the phytoplasma distribution. This study refers to the detection of LY phytoplasma DNA using PCR in different coconut plant parts, throughout the development of the disease. Sample analysis of positive palms taken at different stages of disease development (either symptomatic or symptomless) showed differences in the percentage of LY detection between plant parts. Some parts showed a very high level of LY DNA (stem, young leaves, inflorescences, stem apex and root apex), low levels were found in the intermediate leaves and roots without apex, whereas no LY phytoplasma DNA was detected in mature leaves. The detection percentage of LY phytoplasma DNA was lowest in symptomless‐infected palms for all parts, except the stem, where phytoplasma accumulations were consistently detected. This pattern of detection among parts is consistent with the hypothesis that phytoplasmas move from photosynthate source tissues to sink tissues via the phloem mass flow process. The accumulations in the (lower) stem, prior to the appearance of symptoms, suggest that this part of the palm is where phytoplasmas first move from leaves after foliar feeding by vectors and in which they probably multiply and distribute to other palm parts, including roots. Embryos from infected palms were analysed by nested‐PCR and 28% of 394 embryos were positive. Phytoplasma DNA was detected in embryos from fruit on any of the fruiting bunches regardless the age, but no pattern of quantitative distribution throughout the bunch developmental stages was observed. Germination of seeds from LY‐positive symptomatic palms was 58% and from LY‐negative symptomless palms were 71%. No phytoplasma was detected in seedlings tested from both symptomatic and non‐symptomatic palms. Seedlings tested after 2 years did not develop LY symptoms or eventually died.     

Increased protein carbonylation in leaves of Arabidopsis and soybean in response to elevated [CO2]

While exposure of C3 plants to elevated [CO2] would be expected to reduce production of reactive oxygen species (ROS) in leaves because of reduced photorespiratory metabolism, results obtained in the present study suggest that exposure of plants to elevated [CO2] can result in increased oxidative stress. First, in Arabidopsis and soybean, leaf protein carbonylation, a marker of oxidative stress, was often increased when plants were exposed to elevated [CO2]. In soybean, increased carbonyl content was often associated with loss of leaf chlorophyll and reduced enhancement of leaf photosynthetic rate (Pn) by elevated [CO2]. Second, two-dimensional (2-DE) difference gel electrophoresis (DIGE) analysis of proteins extracted from leaves of soybean plants grown at elevated [CO2] or [O3] revealed that both treatments altered the abundance of a similar subset of proteins, consistent with the idea that both conditions may involve an oxidative stress. The 2-DE analysis of leaf proteins was facilitated by a novel and simple procedure to remove ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) from soluble soybean leaf extracts. Collectively, these findings add a new dimension to our understanding of global change biology and raise the possibility that oxidative signals can be an unexpected component of plant response to elevated [CO2].     

Translocation in Sugar-beet: I. ASSIMILATION OF 14CO2 AND DISTRIBUTION OF MATERIALS FROM LEAVES

¹⁴CO₂ was supplied to leaves, and movement of labelled carbonto other parts of the plant was assessed. Young growing leavesutilized assimilated carbon for their own growth and did notexport carbon to the rest of the plant, while fully expandedleaves exported much of their photosynthate, both to root andto young leaves. Translocation from a particular leaf was tothe two or three younger leaves on the same side of the plant,and to a sector of root below the source leaf. Specific distributionto growing leaves could be modified by partial defoliation.There was no movement of material to leaves which had emergedbefore the source leaf. Part of the carbon entering a leaf by assimilation (and, foryoung leaves, by translocation) was incorporated into insolublematerial, especially in young leaves. Some of the carbon enteringa developing root was permanently stored as sucrose, althoughmuch also entered insoluble material. Loss from the leaf ofcarbon fixed during a short period of photosynthesis was rapidat first but continued at a decreasing rate for several days.Some carbon fixed into the insoluble fraction was translocatedfrom the leaf later, during senescence. Sucrose was the mainmaterial translocated immediately after photosynthesis.