Increased root growth in elevated CO2: a biophysical analysis of root cell elongation

A biophysical analysis of root expansion was conducted in fourchalk downland herbs (Sanguisorba minor Scop., Lotus corniculatusL., Anthyllis vul-neraria L. and Plantago media L.) exposedto either ambient or elevated CO₂in controlled environment cabinets.Measurements of fine (F) and extra-fine (EF) root extensionrate (RER), water relations, and cell wall tensiometric extensibilityrevealed differences in the diurnal pattern of root growth betweenspecies. After 35 d of exposure to elevated CO₂, RER of bothF and EF roots increased significantly in darkness and on illuminationfor S. minor, whilst for A. vulneraria (EF roots only) and L.corniculatus a significant increase occurred at night whereasfor P. media a significant increase occurred during the day.Cells measured in the zone of elongation were longer in allspecies exposed to elevated CO₂. Water potential (     

Epidermal Structure in the Ligule of Rice (Oryza sativa L.)

The structure of the abaxial epidermis of the ligule of rice(Oryza sativa L.) as seen in the light and scanning electronmicroscope is described. Long cells, silica cells, cork cells,prickle hairs, microhairs and stomata-like structures were found.Reasons for considering these latter structures to be true stomataare given. Results of an X-ray analysis for silicon are presentedand the distribution of silica discussed in relation to itsfunctional role in the ligule. Oryza sativa L, rice, Gramineae, ligule, epidermis, scanning electron microscopy, X-ray analysis, silica, stomata     

Photosynthesis and Transpiration in Rice as Influenced by Soil Moisture and Air Humidity

The paper describes the effect of soil moisture content andair humidity on CO₂ exchange (P_N), CO₂ diffusion resistance(Cr) and transpiration (E) in four varieties of japonica rice(Oryza sativa L.). A decrease in soil moisture content reducedthe rate of photosynthesis to a varying degree in the varieties.Reduction in photosynthesis was attributed to increase in Cr.The effect of low soil moisture on photosynthesis and CO₂ diffusionwas further intensified by decrease in air humidity. By maintaininga high humidity in the air around the leaves however, the effectof soil moisture deficiency was reduced considerably, exceptin Rikuto Norin 21 which was very sensitive to soil-moisturedeficiency alone. Dryness of the air enhanced the transpirationrate, although the increase was relatively less in the plantsfacing a simultaneous water crisis at the root surface. In plantsgrowing under flooded conditions, a decrease in air humiditycaused a slight depression in P_N despite the simultaneous decreasein Cr. Oryza sativa L., rice, photosynthesis, transpiration, diffusion resistance, soil moisture, air humidity     

Energetics of Plant Growth Under Anoxia: Metabolic Adaptations of Oryza sativa and Echinochloa phyllopogon

Unlike most plant species, Oryza sativa L. cv. S-201 and Echinochloaphyllopogon (Stev.) Koss germinate and grow under anaerobicconditions. In both species, the radicle or shoot emerged byday 3 when the seeds were germinated in air or N₂. Under eithercondition, shoot and/or root dry weight (d. wt) increased linearlyfrom day 3 to day 7, with a corresponding decrease in seed d.wt. In anaerobically grown O. sativa, d. wt accumulation wasreduced to 7% of that in air whereas d. wt lost from the seedwas reduced to only 37%. No root growth occurred during anaerobicgermination and shoot d. wt accumulation accounted for 10% ofthe d. wt lost from the seed. In E. phyllopogon, d. wt accumulationduring anoxia was 25% of that in air, but loss of d. wt fromthe seed was 44% of the aerobic rate. In air, 48% of the d.wt lost from the seed was converted to shoot or root d. wt.Like O. sativa, E. phyllopogon does not produce a root underN₂, but shoot growth accounted for 27% of the d. wt lost fromthe seed. Thus, either in air or N₂, E. phyllopogon was moreefficient at converting seed reserves to shoot/root structuraldry matter than O. sativa . Based on changes in metabolite pools,O. sativa appeared to shift exclusively to fermentation duringanaerobic growth. In E. phyllopogon, however, fermentation alonecannot satisfy the energy requirement for growth without O₂.Rather, fermentation, coupled with limited tricarboxylic acid(TCA) cycle operation could supply sufficient ATP for growthunder anaerobic conditions. An active oxidative pentose phosphatepathway and lipid synthesis were discussed as important mechanismsfor converting NADH to NAD, a necessary cofactor for fermentationand TCA cycle activity.Copyright 1994, 1999 Academic Press Anaerobiosis, Echinochloa phyllopogon, energetics model, fermentation, mitochondrial activity, Oryza sativa, rice, tricarboxylic acid cycle, watergrass     

Zinc-induced Vacuolation in Root Meristematic Cells of Cereals

In the absence of Zn, vacuolar volume fractions of root meristematiccells of Secale cereale L. cv. K2, Triticum aestivum L. cv.Chinese Spring and Oryza sativa L. cv. IR34 were 5.64 x 10^–2,2.17 x 10^–2 and 1.63 x 10^–2 µm³ vacuole µm^–3tissue, respectively. A 4-d exposure to a subtoxic concentrationof zine (0.2 µg Zn cm^–3) induced a 2.93-fold anda 6.78-fold increase in the total vacuolar volume fraction inOryza and Triticum, respectively, whereas no significant increasewas observed for Secale. It is proposed that this Zn-inducedvacuolation represents a compartmentalization mechanism. Theinitial total vacuolar volume fraction in Secale was greaterthan that for Oryza and Triticum and this may enable compartmentalizationof the metal soon after the onset of treatment so reducing itscytotoxic effects. These findings are similar to those observedin contrasting cultivars of Festuca rubra L. Triticum aestivum L, Secale cereale L, Oryza sativa L, zinc, root meristem, vacuolation     

Structural Differentiation of the Nucellar Epidermis in the Caryopsis of Rice (Oryza sativa)

In the developing caryopsis of rice (Oryza sativa L.) the nucellarepidermis forms a uniseriate layer through which assimilatesare transported to the endosperm. An anatomical study demonstratedthat the nucellar epidermal cells are fusiform in shape andare hexagonally packed. The anticlinal walls of the nucellarepidermis are characterized by ribs of wall-thickening whichare orientated radially with respect to the caryopsis. The wall-thickeningsappear to be cellulosic primary walls, as indicated by theirstaining with Calcofluor and periodic acid-Schiff's reagent.It is proposed that the geometry of the nucellar cells and theribs of wall-thickening are structural adaptations to resistthe compressional force which is placed on the nucellar epidermisduring the latter stages of grain filling. Oryza sativa, rice, caryopsis, grain filling, nucellar epidermis, wall-thickening     

Germination and Early Growth of Plants Studied Using Neutron Radiography

Seed swelling, germination, root extension, lateral root initiationand shoot growth were studied in soils of different water contents,using non-destructive, serial neutron radiography. Seeds fromthree varieties of soya beans (Glycine max L.) and one varietyeach of maize (Zea mays L.) and vetch (Vicia sativa L.) wereused. The seeds germinated when they had increased in size bya certain amount, if germination is taken as the time when theradicle first appears. The rate at which roots and shoots extendalso depend on soil water content. Glycine max L., Vicia sativa L., Zea mays L., Soya bean vetch, maize, seed germination, root extension, lateral root initiation, neutron radiography     

Modulation of Sucrose Content by Fructose 2,6-bisphosphate during Photosynthesis in Rice Leaves Growing at Different Light Intensities

Reddy, A. R. and Das, V. S. R. 1987. Modulation of sucrose contentby fructose 2,6-bisphosphate during photosynthesis in rice leavesgrowing at different light intensities.—J. exp. Bot. 38:828–833. The relationship between the rate of CO₂ fixation and sucroseconcentration in the leaves of rice (Oryza sativa L.) grownat different light intensities was investigated. Maximum sucrosecontent coincided with maximum rates of CO₂ fixation, achievedat a photon flux density of 1600 µmol m^–2 s^–1.The levels of sucrose and fructose 2,6-bisphosphate were alsocompared in the leaves under different light intensities. Fructose2,6-Msphosphate accumulated during growth at low light. Theactivity of fructose-6-phosphate 2-kinase was high in the leavesgrown at low light while that of fructose-2,6-bisphosphatasewas low. The activities of phosphoglucose isomerase and phospho-glucomutasewere slightly increased by growth at low light The activitiesof UDP glucose pyrophosphorylase were adversely affected invitro with increased concentrations of fructose 2,6-bisphosphatewhile those of sucrose phosphate synthase were moderately affected.Phosphoglucose isomerase and phosphoglucomutase were activatedby fructose 2,6-bisphosphate (8-0 mmol m^–3) by 12-15%.The results suggested that low light intensities during growthresult in an accumulation of fructose 2,6-bisphosphate whichmodulates the key enzymes of sucrose biosynthesis thus regulatingcarbon flow under conditions of limited photosynthesis. Key words: Oryza sativa, photosynthesis, sucrose synthesis, fructose 2,6-bisphosphate, light     

Root Xylem Influence on the Water Relations and Drought Resistance of Rice

In order to determine the importance of root axial resistanceto water flow for drought resistance of rice (Oryza sativa L.)aseries of glasshouse and growth chamber studies was conductedfrom 1985 to 1986. A preliminary study surveyed root distributionand histological characteristics of six cultivars grown in aerobicsoil (20x20x90cm boxes) under well–watered ormoisturedeficit conditions. Subsequently, four experiments were conductedwith plants grown in culture solution. Our results demonstratethat plant breeders can use root thickness as a selection indexfor xylem size for root diameters up to about 1–2 mm.Usingthe Poiseuille–Hagen Law for water movement in capillaries,rice root axial resistance explained differences in leaf waterpotential and transpiration when only one cultivar was used,but did not explain differences among cultivars. Thus, increasingroot xylem vessel radii probably will not directly increasedrought resistance. Key words: Rice (Oryza sativa), roots, xylem characteristics, drought resistance     

Does ethylene induce elongation of the rice coleoptile through auxin?

Ethylene stimulated the elongation of intact rice (Oryza sativaL.) coleoptiles in which endogenous growth had been stoppedcompletely by decapitation and red light. p-Chlorophenoxyisobutyricacid slightly inhibited endogenous growth, but not the ethyleneinduced growth. Thus, ethylene could stimulate the elongationof coleoptiles in which the auxin level was considered to bevery low. ¹ Present address: Institute for Agricultural Research, TohokuUniversity, Katahira, Sendai 980, Japan. (Received February 16, 1979; )     

Effects of Atmospheric Humidity on Abscisic Acid Accumulation and Water Status in Leaves of Rice (Oryza sativa L.)

Rice (Oryza sativa L ) plants were grown in controlled environmentcabinets with either low (c 0 4 kPa) or high (c 1 6 kPa) atmosphericwater vapour pressure deficit (v p d) The capacity of detachedleaves to accumulate ABA in response to rapidly induced waterstress was increased when plants were grown at high v p d Highv p d significantly lowered solute potential (     

Silica and Ash in Seeds of Cultivated Grains and Native Plants

Silica and ash contents and the depositional patterns of opalinesilica have been determined in the seeds of 31 plant species.Included were 13 monocotyledons, eight dicotyledons and theseeds of eight common cereal grains. The cereal grains, exceptfor Oryza sativa L. (3.2%) and Avena sativa L. (1.4%), werequite low in silica. The silica in these cereals was in thelemma. In seeds with high silica content it often makes up morethan 50% of the ash. Silica in seeds occurs largely in the outercoating of the seed. Dicotyledon seeds tend to have less silicathan those of monocotyledons. Energy-dispersive X-ray analysisshows that the distribution of the element silicon is clearlyrelated to certain epidermal structures such as ridges, raisedareas, trichomes and hairs. It also occurs in cell walls. Membersof a specific plant family tend to have very similar silicadepositional patterns in their seeds. Small amounts of K, S,Cl and Ca are also found in seeds. Light-microscopy studiesshow that the silica in the lemma of seeds such as Oryza sativaL. is deposited in cellular sheet-like structures with crenateedges. Silica in seeds also occurs in fibres and in other cellularstructures (silica cells) that become phytoliths. Seeds, epidermis, seed coat, silica and ash content, scanning electron microscopy, energy-dispersive X-ray analysis, silica depositional patterns, trichomes     

Studies on the Physiology of Nodule Formation: With two Figures in the Text: A Reappraisal of the Effect of Preplanting

Nutman (Arm. Bot. 21, 321, 1957) found that preplanting agarslopes with Trifolium pratense L. or Medicago sativa L. advancedthe time when second lots of plants of these species grown onthe same slopes initiated nodules, and depressed the total numberof nodules formed. He attributed these effects to root secretionswhich at low concentration hasten initial nodulation but athigher concentrations inhibit nodule formation. Further workhas now shown that initial nodulation is stimulated becausethe preplant removes traces of nitrate from the medium. Theamount of nitrate in the tap water used to prepare the medium(6?5 p.p.m. N) also increases the number of nodules formed onthe control plants, and this effect explains to a considerableextent the depression of nodule numbers by preplanting. Initial nodulation was delayed by small amounts of nitrate andnitrite but not by other forms of combined nitrogen (ammonium,asparagine, and urea). All forms of combined nitrogen testedincreased the number of nodules formed over a period of 8 weekswhen supplied at an initial concentration of 20 p.p.m. N.     

Light Gradients and the Transverse Distribution of Chlorophyll Fluorescence in Mangrove andCamelliaLeaves

The light gradient and transverse distribution of chlorophyllfluorescence in mangrove andCamellialeaves, which have differentmorphological characteristics, were examined using a micro-fluorescenceimaging system reported previously (Takahashiet al., Plant,Cell and Environment17: 105–110, 1994). Epidermal cellsscattered light strongly, resulting in an increase in the fluencerate in epidermal cells. For theCamellialeaf, a light gradientwas formed by absorption of light by photosynthetic pigmentsassociated with the induction of chlorophyll fluorescence. Forthe mangrove leaf, a light gradient was formed by backward scatteredlight within a thick layer of non-assimilatory cells. Lightwith a low absorption coefficient (515 nm) penetrated deeperthan that with a higher absorption coefficient (477 nm and 488nm) in theCamellialeaf, while light of both wavelengths showedsimilar profiles in the mangrove leaf. In the mangrove leaves,scattered light declined significantly in the non-assimilatorycell layer which is in front of the assimilatory cells. Light,the intensity of which was reduced to approx. 10% of the maximum,was well scattered and induced a considerable amount of chlorophyllfluorescence in the assimilatory cells, which appear to be wellorganized to capture weak light.Copyright 1998 Annals of BotanyCompany fluorescence, intact leaf, light gradient, mangrove (Rhizophora mucronataLamk.),Camellia japonicaL.     

The Use of 14C-Ethane Diol as a Quantitative Tracer for the Transpirational Volume Flow of Water and an Investigation of the Effects of Salinity upon Transpiration, Net Sodium Accumulation and Endogenous ABA in Individual Leaves of Oryza sativa L.

Yeo, A. R., Yeo, M. E., Caporn, S. J. M., Lachno, D. R. andFlowers, T. J. 1985. The use of ¹⁴C-ethane diol as a quantitativetracer for the transpirational volume flow of water and an investigationof the effects of salinity upon transpiration, net sodium accumulationand endogenous ABA in individual leaves of Oryza sativa L.—J.exp. Bot. 36: 1099–1109. Oryza sativa L. (rice) seedlings growing in saline conditionsexhibit pronounced gradients in leaf sodium concentration whichis always higher in the older leaves than the younger ones.Individual leaf transpiration rates have been investigated todiscover whether movement of sodium in the transpiration streamis able to explain these profiles from leaf to leaf. The useof ¹⁴C labelled ethane diol to estimate transpiration was evaluatedby direct comparison with values obtained by gas exchange measurements.Ethane diol uptake was linearly related to the transpirationalvolume flow and accurately predicted leaf to leaf gradientsin transpiration rate in saline and non-saline conditions. ¹⁴C-ethanediol and ²²NaCl were used to compare the fluxes of water andsodium into different leaves. The youngest leaf showed the highesttranspiration rate but the lowest Na accumulation in salineconditions; conversely, the older leaves showed the lower transpirationrates but the greater accumulation of Na. The apparent concentrationof Na in the xylem stream was 44 times lower into the youngerleaf 4 than into the older leaf 1. Exposure to NaCl (50 molm^–3) for 24 h elicited an increase in endogenous ABA inthe oldest leaf only, but no significant changes occurred inthe younger leaves. Key words: —Salinity, rice, Oryza sativa L., transpiration, volume flow, abscisic acid     

Differential Effects of Day and Night Temperature on Development to Flowering in Rice

There are conflicting reports with regard to difference in effectsof day temperature (T_D) and night temperatures (T_N) on plantdevelopment. The objective of this study is to determine whetherthere are different effects ofT_DandT_Non development from sowingto flowering in rice (Oryza sativaL.). Plants of 24 rice cultivars were grown in naturally-lightedgrowth chambers at five diurnally constant (22, 24, 26, 28 and32 °C) and four diurnally fluctuating temperatures (26 /22,30 /22, 22 /26 and 22 /30 °C forT_D/T_Nwith 12hd^-1each) witha constant photoperiod of 12hd^-1. The treatments were selectedto enable the separation of effects ofT_DandT_Non developmentrate (DR). The response of DR to constant temperatures was typically nonlinear.This nonlinearity could not explain the difference in floweringdates between fluctuating temperatures with the same mean dailyvalue but oppositeT_D/T_Ndifferences. Differential effects ofT_DandT_NonDR to flowering were detected in all but one cultivar. In mostcases,T_Dexerted a greater influence thanT_N, in contrast withmany previous reports based on the assumption of a linearitybetween DR and temperature. The data were further analysed bya nonlinear model which separated effects ofT_DandT_N. The estimatedvalue for the optimumT_Nwas generally 25 –29 °C, about2 –4 °C lower than the estimated optimumT_Din mostcultivars. The effects ofT_DandT_Non DR were found to be interactivein some cultivars. These results form a new basis for modellingflowering dates in rice. Oryza sativa; rice; flowering; development; day and night temperature; thermoperiodicity     

A Transmission and Cryo-Scanning Electron Microscopy Study of the Formation of Aerenchyma (Cortical Gas-Filled Space) in Adventitious Roots of Rice (Oryza sativa)

The initiation and development ofaerenchyma in adventitiousroots of rice (Oryza sativa) was studied in tissuc up to approximately36-h-old using transmission electron microscopy (TEM) and cryoscanningelectron microscopy (cryo-SEM). Aerenchyma resulting from selective cortical cell collapse isa naturally occurring feature of rice roots. Evidence of somecortical cell disruption was noticeable by TEM in cells thatwere approximately 6-h-old; it became more advanced as the cellsaged. At 12 h, early stages of cell wall breakdown and lossof cell turgidity were seen. Complete collapse of columns ofcells had occurred by 24 h. In tissue that was 36-h-old, thesenescent cytoplasm of many remaining cells began to disperse.The visual evidence suggests that cell collapse was the resultof autolysis. This pattern of cortical degeneration in ricewas dissimilar to that reported elsewhere for Zea roots grownin an oxygen depleted environment. Cryo-SEM revealed the occurrence of small structures withinthe cortex with the external appearance of miniature, intactcells which are not preserved during conventional SEM preparativeprocedures. Key words: Rice (Oryza sativa L.), roots, aerenchyma, ultrastructure     

Biochemical Basis of Different Sensitivity to Methotrexate in Daucus carota and Oryza sativa Cell Cultures

The biochemical basis of the different sensitivity to methotrexateof Daucus carota and Oryza sativa cell cultures has been investigated.Carrot cells have a dihydrofolate reductase activity about tentimes higher than rice cells. In addition, they show a loweruptake rate of the inhibitor. No relevant differences have beenfound in the K_m value for the dihydrofolate of the two enzymesand in the degree of inhibition of their activity by methotrexate. Key words: Dihydrofolate reductase, Methotrexate resistance, Plant cell suspension cultures, Oryza sativa, Daucus carota     

Errors in Leaf Area Measurement with an Automatic Area Meter due to Leaf Chlorophyll in Crop Plants

This study revealed that an area meter with a semi-automaticfeeding mechanism underestimated the area of yellowish leavesand wavy leaves in crop plants. It is recommended that areameasurements should be made using photocopied leaves and leafsegments. The degree of underestimation should be checked whenchlorophyll meter (SPAD) values are less than 30.Copyright 1999Annals of Botany Company Glycine max Merr., Hordeum vulgare L., leaf area meter, leaf colour, Oryza sativa L.,Solanum tuberosum L., SPAD, Triticum aestivum L., Zea mays L.     

Etiolated Growth as Measure of Non-structural Biomass in Lucerne Taproots

Enzymatic hydrolysis of starch in lucerne (Medicago sativa L.)taproots is the conventional method used to determine the quantityof carbohydrates allocated to regrowth. Etiolated growth froma taproot could be used to quantify total root biomass allocatedto regrowth. This study compared concentrations of non-structuralcarbohydrates, as measured by -amylase hydrolysis of starchto glucose, to concentrations of non-structural biomass, asmeasured by etiolated growth from lucerne taproots placed inan incubator and plants in situ. The concentration of starchfrom enzymatically assayed taproots was 325 g kg^-1 expressedas glucose equivalents. Etiolated growth and weight loss byrespiration from plants grown in the incubator accounted for524 g of actual biomass per kg of root. There was 46·2g kg^-1 of N, 3·1 of P, and 33·1 of K in the etiolatedgrowth. An 88% increase in etiolated growth dry weight was observedfrom plants in situ compared to taproots placed in the incubator.Accurate quantification on non-structural biomass should notbe limited to sampling just the taproot, but must included theentire root system. Compared to determining non-structural carbohydratesby enzymatic hydrolysis of starch, the procedure used in determiningnon-structural biomass by etiolate growth gave results in unitsrelative to the plant. The use of etiolate growth also providedinformation on mineral nutrient partitioning from root to shoots,was less technically demanding, and could be applied to theentire root system.Copyright 1993, 1999 Academic Press Medicago sativa, root carbohydrates, etiolated growth, taproot