Morphological Description of Transgenic Soybean Chimeras Created by the Delivery, Integration and Expression of Foreign DNA Using Electric Discharge Particle Acceleration

Transgenic soybean (Glycine max L.) plants derived from electricdischarge particle acceleration experiments exhibited varyingdegrees of chimerism which was followed by the expression ofthe introduced ß-glucuronidase (gus) gene. Degreesof chimerism in transgenic plants were established by determiningexpression of the gus gene observed as blue spots, streaks orsectors in stem and leaf tissues in in vitro grown plantletsand greenhouse plants. Clonal plants were also obtained. Presenceof the gene was confirmed by Southern blot analysis. These studiespermitted the reconstruction of a partial picture for the developmentof the soybean plant. Glycine max L. cv. Williams 82, soybean, transformation, ß-glucuronidase, chimeric plant phenotypes, development     

Hydrogen Effect on Nitrogenase (C2H2 Reduction) Response to Oxygen in Bradyrhizobium japonicum-Phaseoleae Symbioses

The influence of hydrogenase in Bradyrizobum-Phaseoleae symbioseswas studied ex-planta and in-planra in soybean (Glycine max)and cowpea (Vigna unguiculata). The hydrogenase was activatedby the addition of hydrogen in the incubation gas phase whichmodified the response of nitrogenase activity of Hup⁺ (hydrogenuptake positive) symbiosis to the external oxygen partial pressure.For bacteroids the hydrogenase expression increased nitrogenaseactivity at supraoptimal pO₂, acting possibly as a respiratoryprotection of nitrogenase. However, at suboptimal pO₂, nitrogenaseactivity of Hup⁺ bacteroids decreased with hydrogen, a phenomenonattributed to the lower efficiency of ATP synthesis from hydrogenthan from carbon substrates oxidation. For undisturbed nodules,the hydrogenase expression in soybean increased the optimalpO₂ for ARA (COP), from 35.3 to 40.3 kPa O₂, and the ARA atsupraoptimal pO₂; at suboptimal PO₂ there was a negative effectof hydrogenase on ARA, although this inhibition was less thanon bacteroids and was not detected if plants were grown at 15°C rather than 20 °C root temperature. No H₂ effectwas detected on cowpea nodules. The results on soybean nodulesare consistent with the concept that symbiotic nitrogen fixationis oxygen-limited and that hydrogenase activity has no beneficialeffect on nitrogen fixation in O₂ limitation. Key words: Glycine max, hydrogenase, nitrogenase, nitrogen fixation, nodules, Vigna unguiculata     

Effects of Nitrate Level on Nitrogen Metabolism in Winged Bean and Soya Bean

The effects of high (15 mM) and low (0.75 mM) solution nitratelevels on nitrogen metabolism in three genotypes (IL 7A, IL13 and IL 21) of winged beans [Psophocarpus tetragonolobus (L.)DC.] and one genotype (Williams) of soya bean [Glycine max (L.)Merrill] were investigated. Plants were grown for 42 days ina greenhouse in solution culture prior to sampling. The 15 mM nitrate treatment resulted in greater growth of allplant parts except roots. Growth of soya beans was more responsiveto nitrate level than was growth of winged beans. The high nitratelevel inhibited nodulation in all plants. The IL 13 and IL 21winged bean genotypes had similar nitrogenase activity (acetylenereduction per plant) as the soya bean and IL 7A winged beangenotype had lower activity. However, the IL 13 winged beangenotype had higher nitrogenase activity (acetylene reductionper unit nodule mass) than the other three genotypes which allhad similar activity. The 15 mM solution nitrate level stimulatedleaf and root nitrate reductase (NR) activity for all plants.All winged bean genotypes had higher leaf NR activity and higherpercentage reduced- and nitrate-nitrogen contents of leavesand stems compared with soya beans. However, total protein (reducednitrogen) was greater in soya beans when sampled indicatingthat more nitrate had been metabolized by soya beans than bywinged beans during the 42-day growth period. Psophocarpus tetragonolobus (L.) DC., winged bean, Glycine max (L.) Merrill, Soya bean, nitrate reductase, nitrogen fixation, nitrogenase activity, nodulation     

Partitioning and Utilization of Photosynthate Produced at Different Growth Stages after Anthesis in Soybean (Glycine max L. Merr.): Analysis by Long-term 13C-Labelling Experiments

Yamagata, M., Kouchi, H. and Yoneyama, T. 1987. Partitioningand utilization of photosynthate produced at different growthstages after anthesis in soybean (Glycine max L. Merr.): Analysisby long term ¹³C-labelling experiments.—J. exp. Bot. 38:1247–1259. Soybean (Glycine max L. Merr. var. Akishirome) plants were allowedto assimilate ¹³CO₂ with a constant specific activity for 10h at different growth stages (a total of seven times at aboutone week intervals) after anthesis. The plants were harvestedperiodically until the time of full maturity and the partitioningof ¹³C into individual plant parts was investigated with anemphasis on the contribution of carbon assimilated at differentgrowth stages to the seed formation. Carbon assimilated at the middle to late seed-filling stagecontributed most to the seed production; one day contributionaccounted for 3–4% in total carbon of the seed at fullmaturity. Integrated contribution of carbon assimilated afteranthesis was estimated as 96% of the final seed carbon. An approximationbased on the temporal data of the incorporation of labelledcarbon into the seeds indicates that 77% of the final seed carboncame from direct transfer of current photosynthate from sourceleaves, which occurred within a few days after the photosyntheticfixation, while the rest originated from remobilization of carbonreserved mainly in leaves and stems plus petioles. In comparison with the total carbon accumulation in the seeds,protein carbon in the seeds was relatively more dependent onphotosynthate produced during the early period of reproductivegrowth stage, whereas lipid carbon was more dependent on photosynthateproduced during the later reproductive stage. Key words: Photosynthate partitioning, soybean (Glycine max L. Merr.), ¹³CO₂ assimilation, seed formation     

Modification of Seed Growth in Soybean by Physical Restraint: Effect on Leaf Senescence

Crafts-Brandner, S. J. and Egli, D. B. 1987. Modification ofseed growth in soybean by physical restraint. Effect on leafsenescence.—J. exp. Bot. 38: 2043–2049. The effect of total plant sink size on leaf senescence in soybean[Glycine max (L.) Merrill] was investigated by using a simple,non-destructive method to decrease seed growth rate and totalplant fruit sink size without altering fruit or seed number.The treatment consisted of placing plastic pod restriction devices(PPRD), which were made from plastic drinking straws (6·35mm diameter), over the fruits so that all of the seeds werecontained within the PPRD's. The treatment did not alter thetime of initiation of leaf senescence for two cultivars (McCalland Maple Amber), but decreased the rate of leaf senescencebased on declines in chlorophyll, ribulose-l,5-hi'sphosphatecarboxylase/oxygenase level and carbon dioxide exchange rate.The treatment also delayed seed maturation. At the time of seedmaturation, the plants still retained green leaves. In a separate experiment, one seed in each fruit (40% of theseeds on the plant) was not restrained by the PPRD's. This treatmentled to an intermediate rate of leaf senescence compared to controland complete seed restriction treatments. The results indicatedthat, for the cultivars examined (1) leaf senescence was initiatedat the same time regardless of sink size (2) the rate of leafsenescence could be modified by altering sink size and (3) seedmaturation could occur without complete leaf yellowing and leafabscission. The effect of the PPRD treatments on leaf senescencewere similar to results obtained when fruits were physicallyremoved, which indicated that physical removal of fruits doesnot lead to artefacts due to wounding of the plants. Key words: Glycine max L, senescence, source-sink     

A STUDY ON VARIETAL DIFFERENCE IN FLOWERING HABITS OF SOYBEAN PLANTS AS FOLLOWED BY GRAFTING EXPERIMENTS

The material basis of varietal differences in flowering habitwas investigated from the standpoint that flowering is determinedby the balance in amounts of flowering promotor and inhibitor.The grafting method was used throughout the experiments. Late variety of Glycine max L. seems to produce flowering inhibitor(or inhibitors) under the conditions under which midseason varietyproduces flower. Early variety seems to produce flowering hormonewhich overcomes the flower-inhibiting action in the late variety. The amounts of flowering hormone produced under short day conditionbymidseason and late varieties were compared. The results showthat, under the short day condition, the midseason variety producesequal or smaller amounts of flowering hormone as compared withthe late variety. On the basis of these results, the mechanismby which the flowering habits are determined in various varietiesof soybean plants was discussed. (Received June 18, 1962; )     

Sulphate Transport into Plants and Excised Roots of Soybean (Glycine max L.)

The rates of sulphate transport into intact and excised rootsof soybean (Glycine max L.) were not significantly differentin the first hour and were maximal at pH 7. However, intactroots accumulated four times as much sulphate as excised rootsin 24 h, because of a marked reduction in the rate of transportby excised roots. The continued high rates of transport intointact roots were observed in plants kept in the light, andobserved in darkened plants growing in 1 per cent sucrose. Similarly,sulphate accumulation by excised roots was stimulated 2-foldby 1 per cent sucrose. The characteristics of sulphate accumulation by roots were notuseful in predicting sulphate translocation to the leaves. Transportto the leaves was maximal at pH 2–3, was almost totallylight-dependent and was not enhanced by growing plants in sucrose. Sulphate transport, Glycine max L., soybean, excised roots     

Durations of the Photoperiod-sensitive and Photoperiod-insensitive Phases of Development to Flowering in Four Cultivars of Soyabean [Glycine max (L.) Merrill]

Four cultivars of soyabean [Glycine max (L.) Merill] of diverseorigin were grown in pots in a plastic-house maintained at day/nighttemperatures of 30/20°C. Plants were transferred at varioustimes after sowing from short (11·5 h d^-1) to long (13·5h d^-1) days and vice versa. The times from sowing to first floweringfor control plants grown continuously in short days varied from38 to 53 d, whereas the flowering of plants grown continuouslyin long days was delayed by about 20 d in each cultivar. Theduration of the initial photoperiod-insensitive phase (oftencalled the juvenile phase) varied three-fold between cultivars,i.e. from 11 to 33 d. As expected, the duration of the photoperiod-sensitivephase was greater in long days, but there was comparativelylittle genetic variation in photoperiod-sensitivity as definedin terms of days delay in time to flowering per hour increasein photoperiod (9-11 d h^-1). Similarly, there was little variationin the photoperiod-insensitive post-inductive phase; it rangedfrom 15 to 20 d. In consequence, the duration of the initialphotoperiod-insensitive phase was a strong determinant of timeto first flowering in these cultivars. The importance of thisso-called juvenile trait is discussed in terms of preventingthe premature flowering of USA-adapted cultivars when grownin short tropical daylengths and thus improving the adaptationof the crop to the lower latitudes.Copyright 1993, 1999 AcademicPress Glycine max (L.) Merill, soyabean, photoperiodism, juvenility, flowering     

Glutamine Synthetase Activity and Foliar Nitrogen Volatilization in Response to Temperature and Inhibitor Chemicals

In soyabeans (Glycine max (L.) Merr.), glutamine synthetase(GS) activity was greater at 28 °C than at 35 °C. Thereverse was true for foliar-N loss. In field-grown plants at29 °C, the GS activity was higher and foliar-N loss waslower in soyabeans than in Amaranthus palmeri (S.) Wats. Methioninesulphoximine, a GS inhibitor, and 6-diazo-5-oxo-L-norleucine,a glutamate synthase inhibitor, significantly increased foliar-Nloss from soyabeans. The data suggest that conditions conduciveto decreased GS or glutamate synthase activity may result inincreased foliar-N loss. Palmer amaranth, Amaranthus palmeri, soyabean, Glycine max, methionine sulphoximine, 6-diazo-5-oxo-L-norleucine     

Effect of nitrate in the rooting medium on carbohydrate composition of soybean nodules

Nodulated soybean plants (Glycine max [L.] Merr) were grown in sand culture. Carbohydrate composition of nodules, roots, and leaf blades was determined and related to the effects of nitrate in nutrient solution on nodule growth and on nitrogenase activity of nodules.     

Flower and Pod Development in Water-Deficient Soybeans (Glycine max L. Merr.)

Water deficits during flowering decrease the number of seed-bearingpods in soybean (Glycine max L. Merr.). Failure to set podsmay indicate an inherent sensitivity to low tissue water potential(     

Aluminium Stress Affects Nitrogen Fixation and Assimilation in Soybean (Glycine max L.)

Nitrogen fixation and assimilation in nodules and roots were studied in soybean (Glycine max L.) exposed to different levels of aluminium (Al) stress (0, 50, 200 and 500 μM). Al at 500 μM induced oxidative stress, which became evident from an increase in lipid peroxidation accompanied by a concomitant decline in antioxidant enzyme activities and leghaemoglobin breakdown. Consequently, there was also a reduction in nitrogenase activity. However, the leghaemoglobin levels and nitrogenase activity were unexpectedly found to be higher in nodules when the plants were treated with 200 μM Al. Of the enzymes involved in nitrogen assimilation, the activity of glutamate dehydrogenase-NADH was reduced in nodules under Al stress, but it was significantly higher in roots at 500 μM Al as compared to that in the control. In nodules, the glutamine synthetase/glutamate synthase-NADH pathway, assayed in terms of activity and expression of both the enzymes, was inhibited at >50 μM Al; but in roots this inhibitory effect was apparent only at 500 μM Al. No significant changes in ammonium and protein contents were recorded in the nodules or roots when the plants were treated with 50 μM Al. However, Al at ≥200 μM significantly increased the ammonium levels and decreased the protein content in the nodules. But these contrasting effects on ammonium and protein contents due to Al stress were observed in the roots only at 500 μM Al. The results suggest that the effect of Al stress on nitrogen assimilation is more conspicuous in nodules than that in the roots of soybean plants.     

Further Errors in the Acetylene Reduction Assay: Effects of Plant Disturbance

A flow-through gas system was used to study the effects of disturbanceon nitrogenase (acetylene reduction) activity of nodulated rootsystems of soyabean (Glycine max) and white clover (Trifoliumrepens). Detopping plus removal of the rooting medium (by shaking)produced a substantial decrease in maximum nitrogenase activity.This response is due to a reduction in oxygen flux to the bacteroidscaused by an increase in the oxygen diffusion resistance ofthe nodule. The decrease in maximum nitrogenase activity wasmuch smaller for roots subjected to detopping only. Thus, theeffect of root shaking is more important than that of shootremoval. The effect of detopping plus root shaking on nitrogenase activityoccurred whether the plants were equilibrated and assayed at25°C or 15°C. However, the effect of disturbance onthe oxygen diffusion resistance of the nodules, and thus onnitrogenase activity, was greater at the higher temperature.At the lower temperature the oxygen diffusion resistance ofthe nodules had already been increased in response to the reducedrequirement for oxygen. These nodules were less susceptibleto the effects of disturbance. Thus, comparisons of the effectsof equilibration temperature on nitrogenase activity produceddifferent results depending on whether intact or disturbed systemswere used. With intact systems activity was lower at the lowertemperature but with detopped/shaken roots the lowest activityoccurred at the higher temperature. It is concluded that the use of detopped/shaken roots can producesubstantial errors in the acetylene reduction assay, which makesthe assay invalid even when used for comparative purposes. However,comparisons with rates of ¹⁵N₂ fixation and H₂ production showthat accurate measurements of nitrogenase activity can be obtainedfrom maximum rates of acetylene reduction by intact plants ina flow-through gas system. The continued use of assay proceduresin which cumulated ethylene production from disturbed systemsis measured in closed vessels must be questioned. Key words: Nodules, acetylene, nitrogenase activity     

Protein Synthesis During Rehydration, Germination and Seedling Growth of Naturally and Precociously Matured Soybean Seeds (Glycine max)

Soybean seeds [Glycine max (L.) Merr.] synthesize de novo andaccumulate several non-storage, soluble polypeptides duringnatural and precocious seed maturation. These polypeptides havepreviously been coined ‘maturation polypeptides’.The objective of this study was to determine the fate of maturationpolypeptides in naturally and precociously matured soybean seedsduring rehydration, germination, and seedling growth. Developingsoybean seeds harvested 35 d after flowering (mid-development)were precociously matured through controlled dehydration, whereasnaturally matured soybean seeds were harvested directly fromthe plant. Seeds were rehydrated with water for various timesbetween 5 and 120 h. Total soluble proteins and proteins radio-labelledin vivo were extracted from the cotyledons and embryonic axesof precociously and naturally matured and rehydrated seed tissuesand analyzed by one-dimensional PAGE and fluorography. The resultsindicated that three of the maturation polypeptides (21, 31and 128 kDa) that had accumulated in the maturing seeds (maturationpolypeptides) continued to be synthesized during early stagesof seed rehydration and germination (5–30 h after imbibition).However, the progression from seed germination into seedlinggrowth (between 30 and 72 h after imbibition) was marked bythe cessation of synthesis of the maturation polypeptides followedby the hydrolysis of storage polypeptides that had been synthesizedand accumulated during seed development. This implied a drasticredirection in seed metabolism for the precociously maturedseeds as these seeds, if not matured early, would have continuedto synthesize storage protein reserves. Glycine max (L.) Merr, soybean, cotyledons, maturation, germination/seedling growth     

Alterations in Apoplastic and Total Solute Concentrations in Soybean Nodules Resulting from Treatments Known to Affect Gas Diffusion

Ureide concentration in the cortical apoplast of soybean (Glycinemax(L.) Merr.) nodules increases rapidly in response to noduleexcision. The objective here was to determine if changes inapoplastic ureide may be related to the control of resistanceto gas diffusion which is thought to be localized in the nodulecortex. Following decapitation of shoots, nitrogenase activity(acetylene reduction) and ureide concentration in total noduleextracts declined over a period of several hours. Apoplasticureide concentration relative to total nodule ureide was elevatedunder these conditions, but the treatment effect was small comparedto non-decapitated controls. Decapitation also caused a significantdecline in the concentrations of sucrose, glucose, and D-pinitolin nodules. However, the decline in carbohydrates was similarin the nodule cortex and the nodule as a whole, suggesting thatthe carbohydrate changes are not related to a cortex-localizedmechanism. Non-invasive treatments involving increases or decreasesin oxygen concentration supplied to nodulated roots caused rapiddecreases in respiration of nodulated roots and in ureide concentrationin total nodule extracts, but did not cause major changes inapoplastic ureide concentrations. The combined results indicatethat apoplastic ureide is probably not involved in the regulationof resistance to gas diffusion. The rapid decline in noduleureide concentrations in response to changing oxygen supplydocuments the sensitivity of ureide synthesis and/or transportto alterations in nodule respiration and/or nitrogenase activity Key words: Glycine max, Pisum sativum, ureide, carbohydrates     

Changes in Soybean Raceme and Petiole Anatomy Induced by 6-Benzylaminopurine

An enlargement of the peduncle and rachis of the terminal racemeand the petiole of the uppermost mainstem leaf was observedin soybean plants [Glycine max (L.) Merr.] treated with thecytokinin, 6-benzylaminopurine (BAP). Histological studies wereperformed to determine the timing and extent of anatomical changesaccompanying BAP treatment. Swelling of treated ‘Tracy-M’peduncles, rachises, and petioles was observed within 4–6d after treatment initiation. A significant increase in totalcross-sectional tissue area was observed at lower and intermediateinternodes of treated rachises after 11 d. Rachis enlargementwas due to increases in both cell size and cell number, particularlyof the vascular tissue. In treated petioles of IX93-100, procambialcells of vascular bundles were the first to respond to the BAPtreatment. These cells differentiated into a vascular cambiumwhich formed secondary xylem and phloem. Soybean, Glycine max (L.) Merr., anatomy, rachis, BAP.     

Moisture Loss as a Prerequisite for Seedling Growth in Soybean Seeds (Glycine max L. Merr.)

Rosenberg, L. A. and Rinne, R. W. 1986. Moisture loss as a prerequisitefor seedling growth in soybeanseeds (Glycine max L. Merr.).—J.exp. Bot. 37: 1663–1674. As soybean seeds [Glycine max (L.) Merr.] develop, they undergoa change in seed moisture. When excised prematurely from thepod and planted, seeds do not exhibit seedling growth until63 d after flowering (DAF) when the seed moisture has fallenbelow 60%. In contrast, seed germination (radicle protrusion)can occur when seeds as young as 35 DAF (68–79% moisture)are excised, but this germination docs not lead to comparableseedling growth frequencies unless seeds are first given a moistureloss treatment to artificially reduce their moisture below 60%.A moisture loss treatment applied at 35 DAF thus enables seedto undergo the transition from germination (cell expansion)to seedling growth (cell division and expansion) to the extentthat treated immature seed have a vigour index comparable toseeds matured on the plant (100%). The pattern of protein synthesisin vivo was examined in 35 DAF seed using [³⁵S]-methionine incorporation.When moisture loss treatment was applied for 24 h to 35 DAFseeds, seeds synthesized several new polypeptides when comparedwith untreated seeds at the same developmental stage. The sameseed samples showed 0% seedling growth in the absence of moistureloss treatment and 80% seedling growth when the treatment hadbeen applied. Moisture loss from soybean seeds appears to bea prerequisite for the synthesis of new proteins which may bepart of the metabolic process or processes that allow the soybeanseed to undergo the transition from seed germination to seedlinggrowth. Key words: Moisture loss, germination/growth, soybean     

Source-sink Relationships, Seed Sucrose Levels and Seed Growth Rates in Soybean

Field experiments using two soybean (Glycine max L. Merrill)cultivars (‘Elgin 87’ and ‘Essex’) wereconducted for 2 years near Lexington, KY, USA to evaluate theeffect of source-sink alterations on seed carbohydrate statusand growth. Sucrose concentrations in developing cotyledonsof control plants were consistently low (<50 m M) early inseed development, but they increased to 100–150 m M byphysiological maturity. The concentrations increased in bothyears by 47 to 59% when 90% of the pods were removed from ‘Elgin87’, but the increase had no effect on individual seedgrowth rate (SGR). Shading (80%) reduced cotyledon sucrose levelsand SGR in both years. The critical cotyledon sucrose concentration(the concentration providing 80% of the maximum cotyledon growthrate) was estimated fromin vitro cotyledon growth at sucroseconcentrations of 0–200 m M. These critical concentrationsvaried from 72–124 m M;in planta control cotyledon sucroseconcentrations were below this critical level during the firsthalf of seed growth but exceeded it in the later stages of growthin all experiments. The estimated critical concentration wasconsistent with the failure of in planta SGR to respond to anincrease in assimilate supply and with the reduction in SGRassociated with a decrease in assimilate supply. The resultssuggest that soybean SGR is generally sink limited if photosynthesisincreases during seed filling, but source limited if photosynthesisis reduced. Copyright 2001 Annals of Botany Company Glycine max(L.) Merrill, soybean, source-sink ratios, sucrose, starch, depodding, shade, in vitro culture     

Expression of Rhizobial Nitrogenase: Influence of Plant Cell-Conditioned Medium

Conditioned medium was obtained from suspension cultures of soybean (Glycine max L. Merrit) cells after incubating them for 4 to 8 days with rhizobia which were separated from the soybean cells by two dialysis bags, one within another. This conditioned medium from the plant cell side (PCM) of the two membranes was used to elicit and influence nitrogenase activity (acetylene reduction) in rhizobia. When conditions for obtaining PCM from the soybean cell suspension cultures were varied, it could be shown that freshly grown rhizobia were able to induce active compounds in the PCM. These compounds caused acetylene reduction activity in test rhizobia under conditions where control rhizobia, containing various substrates, showed little or no acetylene reduction activity. Rhizobia that were already capable of acetylene reduction could not induce such compounds in the PCM when this was included with test rhizobia. The PCM from soybean cultures was also found to aid the expression of nitrogenase activity in suspension cultures of rhizobia normally associated with either peas, lupins, broad beans, or clovers. This is the first communication indicating nitrogenase activity in freeliving cultures for various species of rhizobia.     

Linear Relations between Carbon Dioxide Concentration and Rate of Development Towards Flowering in Sorghum, Cowpea and Soyabean

Negative linear relations were detected (P < 0·005)between the rate of progress from sowing to panicle initiationand CO₂ concentration (210-720 µmol CO₂ mol^-1 air) fortwo genotypes of sorghum [Sorghum bicolor (L.) Moench]. Relationsbetween CO₂ concentration and the rate of progress from sowingto first flowering were also negative in soyabean [Glycine max(L.) Merrill] (P < 0·025), but positive in cowpea[Vigna unguiculata (L.) Walp.] (P < 0·025), albeitthat in both grain legumes sensitivity was much less than insorghum. Thus CO₂ elevation does not delay flowering in allshort-day species. The considerable effect of CO₂ concentrationon times to panicle initiation resulted in large differencesamong the sorghum plants at this developmental stage; with increasein CO₂ concentration, plants were taller with slightly moreleaves and more pronounced apical extension. At the same timeafter sowing however, sorghum plants were heavier (P < 0·05)at 210 than at 360 µmol CO₂ mol^-1 air. In contrast, relationsbetween the dry masses of the soyabean and cowpea plants andCO₂ concentration were positive and curvilinear (P < 0·05).It is suggested that the impact of global environmental changecould be severe for sorghum production in the semi-arid tropics.Copyright1995, 1999 Academic Press Sorghum bicolor (L.) Moench., sorghum, Glycine max (L.) Merrill, soyabean, Vigna unguiculata (L.) Walp., cowpea, development, flowering, CO₂, dry matter accumulation, environmental change