Changes in the Root System of Wheat Seedlings Following Root Anaerobiosis I. Anatomy and Respiration in Triticum aestivum L.

Anatomical changes in roots of wheat seedlings (Triticum aestivumL. cv. Hatri) following oxygen deficiency in the rooting mediumwere investigated. The response of the plant to stress was testedat a very early developmental stage when the first adventitiousroots had just emerged. In order to analyze the adaptation ofdifferent roots, respiration rates of the roots 1–3 and4–n were compared with the respiration rates of the totalroot system. Oxygen deficiency was induced either by flushingnutrient solution with nitrogen or flooding of sand. In contrast to plants grown in well aerated media, both stressvariants led to a significant increase of the intercellularspace of the root cortex in seminal and first adventitious roots.Radial cell enlargement of cortical cells near the root tip,cell wall thickenings in flooded sand cultures and an increasein phloroglucinol-stainable substances were found to be furtherindicators of low oxygen supply. The roots 4–n which were promoted in growth under hypoxiashowed higher respiration rates; hence the total root respirationwas not restricted. Triticum aestivum L. cv. Hatri, wheat, roots, anatomy, anaerobiosis, stress, root respiration, intercellular space     

Effects of Soil Nutrients and Moisture on Root/Shoot Ratios in Lolium perenne L. and Trifolium repens L

The dry weights of foliage and roots (excluding stembases) werecompared in a 3³x2² factorial experiment with Lolium perenneL. and Trifolium repens L. grown in pots with three nitrogen(0–300 ppm N), phosphorus (0–300 ppm P), and soilmoisture (pF 3.2, pF 2.4, and waterlogged) treatments, eachduplicated. Root/shoot ratios were influenced significantly (P < 0.001)by N, P, and W (soil moisture), but these main effects werequalified by highly significant first-order interactions andsecond-order interactions which included N and P. The lowestR/S ratios occurred where N, P, and W were all non-limiting,and the highest where there was an imbalance of these factors. The explanation suggested is that a decrease in the availabilityof N, P, or W causes an increase in the relative weight of roots,but in the presence of N, P, or W deficiency an increase inany one of these factors causes a further increase in the R/Sratio by increasing the relative efficiency of the foliage.     

Changing Kinetic Properties of Barley Alcohol Dehydrogenase during Hypoxic Conditions

The Finnish barley cultivar (Hordeum vulgare L, cv. Hankkija-673)was grown in solution culture for periods of one and two months.The one month old plants had seminal roots, whereas the twomonth old plants grew adventitious roots from the lower nodes.The roots were tested for ADH activity during aeration, during3 d of hypoxic treatment (brought about by passing nitrogenthrough the nutrient solution), and during a 4 d recovery period.The ADH activity, calculated on a protein basis, rose about4-fold during the nitrogen treatment, the greatest increaseoccurring in the adventitious roots. Differences in the kineticproperties of ADH during the hypoxic period were also foundbetween seminal and adventitious roots. The K_m for acetaldehydechanged little in the seminal roots during the hypoxic treatment,but in the adventitious roots it decreased considerably. Thephysiological significance of these changes is discussed. Key words: Hordeum vulgare, alcohol dehydrogenase, hypoxia, enzyme kinetics     

Changes in the Root System of Wheat Seedlings Following Root Anaerobiosis II. Morphology and Anatomy of Evolution Forms

Morphological and anatomical parameters which are variable underroot anaerobiosis in Triticum aestivum were checked on fivetaxa of primitive and modern wheats (and the related genus Aegilops).The plants were grown in nutrient solution which was eitheraerated or flushed with nitrogen. When the plants were flushedwith nitrogen a general retardation in longitudinal root growthoccurred in all of them, but only Triticum aestivum showed aclear promotion of growth of later appearing roots enablingit to maintain the same root/shoot ratio even under stress conditions.There was an increase in the volume of intercellular space inthe root cortex of nearly all the plants investigated. The diameterand the lignin content of the roots and the form of their corticalcells also varied. All these changes were expressed in the primitivewheats to a lesser extent than in the advanced Triticum aestivumindicating that there is a clear increase in the adaptive responsein the latter. Triticum species, Aegilops species, wheat, roots, anatomy, anaerobiosis, stress, intercellular space, selection     

Silicon Deposition in the Roots of Hordeum sativum Jess, Avena sativa L. and Triticum aestivum L.

Electron-probe microanalysis was used to investigate the locationof silicon at the proximal end of the seminal and adventitiousroots, of almost mature field-grown specimens of Hordeum sativumJess., Avena sativa L. and Triticum aestivum L. In the seminal roots silicon was confined to the endodermis,where it was present in the thickened inner tangential and radialwalls. The outer tangential walls also contained silicon inall of the cells in wheat and in occasional cells in barleyand oats. The adventitious roots of the three cereals displayed differencesin silicon deposition. In barley, silicon was present in allthe walls of the endodermal cells, whereas in oats it was onlylocated in the inner tangential and radial walls. Wheat showedcultivar differences, no silicon was detected in Capelle Desprez,but it was present in the thickened endodermis of Little Jossand Hustler. In all the samples studied silicon was absent fromthe sub-epidermal sclerenchyma layer. The results are discussed in relation to the possible functionsof the endodermis and the signficance of silicification. Hordeum sativum Jess, barley, Avena sativa L, oat, Triticum aestivum L, wheat, silicon deposition, electron-probe microanalysis     

2,4-Dichlorophenoxyacetic acid and kinetin in anther culture of cultivated and wild oats and their interspecific crosses: plant regeneration from A. sativa L.

The effect of 2,4-dichlorophenoxyacetic acid (2,4-D) and kinetin was studied in anther culture of oat Avena sativa L., wild oat A. sterilis L. and progeny of crosses between them. A high 2,4-D concentration (5–6 mg l^–1) increased embryo production in genotypes of both species and promoted plant regeneration in anther cultures of A. sterilis and A. sativa×A. sterilis progeny, while kinetin caused severe browning. However, a low concentration of kinetin was essential for initiation of regenerable embryos from anther culture of A. sativa cv. Kolbu: one green and one albino plant were produced. In addition, medium containing W₁₄ salts gave higher regenerant recovery compared with medium containing Murashge and Skoog salts, when cross progeny were tested. Received: 6 March 1998 / Revised: 30 April 1998 / Accepted: 16 November 1998     

Morphogenetic Aspects of a Leafless Mutant in Tomato: III. GROWTH AND PEROXIDASE ACTIVITY OF ROOTS

Using morphological and biochemical criteria, comparisons weremade between intact and excised roots of normal tomato (Lycopersiconesculentum Mill.) and the reduced form of the homozygous lanceolatemutant. Intact normal roots showed greater growth as reflectedin length of the main root axis, number of lateral roots, andprotodermal cell size. Excised normal roots grew more rapidlythan those of the mutant only during the first 24-h intervalof the first week in culture. Intact mutant roots revealed agreater activity of peroxidase, but excised mutant roots showedno increase in enzyme activity. It is concluded that the primarysite of action of the mutant allele is the shoot system, andin particular the leaf marginal meristem. The effects of thelanceolate gene on the root system in tomato are interpretedas being of secondary importance with regard to gene action.     

Properties of Alkaline Phosphatase in Cucumber Roots Induced by Calcium Starvation

Calcium deficiency caused an increase in alkaline phosphataseactivity in cucumber roots [Matsumoto and Yamaya (1981) Plant& Cell Physiol. 22: 1137]. The activities of other hydrolasesincluding acid phosphatase, nucleases and proteases, however,were much less affected by the removal of calcium. Nucleosidedi- and triphosphates and inorganic pyrophosphate were effectivelyhydrolyzed by the induced alkaline phosphatase, whereas nucleosidemonophosphate-hydrolyzing activity was basically equal in theroots grown with either complete medium or a medium lackingcalcium. The alkaline phosphatase in cucumber roots was foundin fractions pelleting at 3,000 x g and in the 100,000 x g supernatant.The calcium-starved roots increased their alkaline phosphataseactivity in both fractions. Four isozyme bands of the alkalinephosphatase in the soluble fraction were separated by polyacrylamidegel electrophoresis. One of the isozyme bands showed a prominentincrease with the calcium deficiency, but not in the presenceof cycloheximide. (Received June 24, 1981; Accepted September 3, 1981)     

Assimilation of Nitrogen in Mutants Lacking Enzymes of the Glutamate Synthase Cycle

¹⁵N labelling was used to investigate the pathway of nitrogenassimilation in photorespiratory mutants of barley (Hordeumvulgare cv. Maris Mink), in which the leaves have low levelsof glutamine synthetase (GS) or glutamate synthase, key enzymesof ammonia assimilation. These plants grew normally when maintainedin high CO₂, but the deletions were lethal when photorespirationwas initiated by transfer to air. Enzyme levels in roots weremuch less affected, compared to leaves, and assimilation oflabelled nitrate into amino acids of the root showed very littledifference between wild type and mutants. Organic nitrogen wasexported from roots in the xylem sap mainly as glutamine, levelsof which were somewhat reduced in the GS-deficient mutant andenhanced in the glutamate synthase deficient mutant. In theleaf, the major effect was seen in the glutamatesynthase mutant,which had an extremely limited capacity to utilize the importedglutamine and amino acid synthesis was greatlyrestricted. Thiswas confirmed by the supply of [¹⁵N]-glutamine directly to leaves.Leaves of the GS-deficient mutant assimilatedammonia at about75% the rate found for the wild type, and this was almost completelyeliminated by addition of the inhibitormethionine sulphoximine.Root enzymes, together with residual levels of the deleted enzymesin the leaves, have sufficient capacityfor ammonia assimilation,through the glutamate synthase cycle, to provide adequate inputof nitrogen for normal growth of themutants, if photorespiratoryammonia production is suppressed. Key words: Hordeum vulgare, ¹⁵N, glutamine synthetase, glutamate synthase, ammonia assimilation     

Some Constituents of Xylem Sap and their Possible Relationship to Xylem Differentiation

Bleeding sap of Actinidia chinensis and Betula populifolia andguttation fluidof Avena sativa were analysed for sugars, amino-acids,auxin, and certain enzymes. A wide range of amino-acids wasfound in all three. Auxin was not detected in the bleeding sap,but was present in Avena guttation fluid (5.1 µg IAA equivalent/l).‘IAA oxidase’, acid phosphatase, ribonuclease, deoxyribonuclease,and protease were detected in the bleeding sap and guttationfluid. The possibility that some of the substances found insap and guttation fluid are products of autolysing, differentiatingxylem cells in the roots is discussed.     

Effectiveness of Lotus Root Nodules: III. EFFECT OF COMBINED NITROGEN ON NODULE EFFECTIVENESS AND FLAVOLAN SYNTHESIS IN PLANT ROOTS

When grown in a nutrient solution containing combined nitrogen(NH₄NO₃), Lotus pedunculatus and L. tenuis seedlings inoculatedwith a fast-growing strain of Rhizoblum (NZP2037) did neitherdevelop root nodules nor develop flavolans in their roots. Incontrast, the roots of nodulated seedlings growing in a nitrogen-freenutrient solution contained flavolans. Flavolan synthesis coincidedwith root nodule development on these plants. When added as a single dose, high concentrations of NH₄NO₃ (5and 10 mg N per plant) stimulated the growth of L. pedunculatusplants but suppressed nodulation and nitrogen fixation. In contrastthe continued supply of a low concentration of NH₄NO₃ (1?0 mgN d^–1 per plant) stimulated nitrogen fixation by up to500%. This large increase in nitrogen fixation was associatedwith a large increase in nodule fresh weight per plant, a doublingof nodule nitrogenase activity, and a lowering of the flavolancontent of the plant roots. The close relationship between nitrogendeficiency, nodule development, and flavolan synthesis in L.pedunculatus meant that it was not possible (by nitrogen pretreatmentof plants) to alter the ineffective nodule response of a Rhizobiumstrain (NZP2213) sensitive to the flavolan present in the rootsof this plant.     

The Effect of Nitrogen Fertilization and Irrigation Frequency on Photosynthesis of Potatoes (Solanum tuberosum)

Gas exchange parameters for the potato (Solanum tuberosum L.,cv. ‘Desiree’) crop were measured under field conditions.Nitrogen nutrition was found to have a positive effect on photosynthesisthroughout the growing season. The gas exchange data and thechlorophyll content in the leaves indicated that this effectwas essentially in the mesophyll. Stomatal resistance increasedas photosynthetic rate decreased, but substomatal CO₂ concentration(Ci) was not affected by nitrogen treatments. Long term effects of water deficit on photosynthetic capacitywere also mostly mesophyllic in origin. A reduction in photosyntheticrate was observed after a period of moisture stress and alsoafter relief of drought by irrigation, indicating a limitedcapacity for recovery. A short term afternoon increase in stomatalresistance, associated with lower Ci values, occurred afterlong periods without irrigation. Leaf water potential was affectedby irrigation frequency, but less strongly than the gas exchangeparameters. Mesophyll activity and stomatal behaviour were bothaffected by water stress and by nitrogen deficiency, whereasCi values were not affected in most cases. Solanum tuberosum L, photosynthesis, mesophyll, stomata, irrigation frequency, nitrogen deficiency, chlorophyll, leaf water potential     

Comparison of growth characteristics of New Zealand isolates of the prymnesiophytes Chrysochromulina quadrikonta and C.camella with those of the ichthyotoxic species C.polylepis

Chrysochromulina quadrikonta (Prymnesiophyceae), a quadriflagellatespecies previously unrecorded in New Zealand, was isolated fromNelson Harbour, New Zealand, in autumn 1991. It bears unmineralizedplate and spine scales, which morphologically are most likethose of Chrysochromulina ericina. Chrysochromulina quadrikonta,Chrysochromulina camella (isolated from the Marlborough Sounds,New Zealand) and Chrysochromulina polylepis (an ichthyotoxicspecies originally isolated from Scandinavia) grew most rapidly(growth rates, or divisions per day, of 1.41, 1.49 and 1.43,respectively) when cultured in a seawater-based general-purposenutrient medium at a salinity of 24% and pH 7.9, with only C.camellastill growing at 42% Chrysochromulina quadrikonta and C.camellagrew optimally at 25°C. and C.polylepis between 15 and 20°C;only C.polylepis grew at 10°C. Chrysochromulina quadrikontagrew optimally with potassium nitrate and ammonium chlorideas nitrogen source, whereas C.camella and C.polylepis grew equallywell with urea as nitrogen source. Only C.quadrikonta and C.polylepishad a selenium requirement. Unlike C.polylepis, neither of theNew Zealand isolates was phagotrophic nor ichthyotoxic.     

The Influence of Pine on the Form of Sitka Spruce Fine Roots

The form of fine roots of Sitka spruce (Picea sitchensis Bong.Carr.) when grown in immediate proximity to roots of Scots pine(Pinus sylvestris L.) and when grown separately was comparedusing split-root systems. When spruce roots were intimatelymixed with pine roots the mean length of individual spruce lateralswas significantly greater, while the length: weight ratio andnumber of root tips: weight ratio were smaller than when grownalone. A similar alteration in growth strategy was achievedby direct addition of mineral nitrogen. Key words: Fine root form, pine-spruce interactions     

The Physiology and Nitrogen-fixing Capability of Aquatically and Terrestrially Grown Neptunia plena: The Importance of Nodule Oxygen Supply

The aquatic legume Neptunia plena (L.) Benth. was grown in non-aeratedwater culture or vermiculite. Growth, nodulation, nitrogen fixationand nodule physiology were investigated. Over an 80-d period,plants grew and fixed nitrogen and carbon equally well in bothrooting media, although distribution of growth between plantparts varied. Total nodule dry weights and volumes were similarbut vermiculite-grown plants had three times as many (smaller)nodules than those grown in water. Oxygen diffusion resistanceof nodules exposed to 21% oxygen and 10% acetylene did not differsignificantly. Both treatments showed similar declines in rootrespiration and acetylene reduction activity (approx. 10%) whenroot systems were exposed to stepped decreases and increasesin rhizosphere oxygen concentration. However, nitrogenase activityof aquatically grown plants was irreversibly inhibited by rapidexposure of nodules to ambient air, whereas vermiculite-grownplants were unaffected. Aeration of water-cultured N. plenareduced stem length (but not mass) and number of nodules perplant. The concentration of nitrogen fixation by 163%. PossibleO₂ transport pathways from the shoot atmosphere to roots andnodules are discussed. Aquatic legume, diffusion resistance, Neptunia plena, nitrogen fixation, oxygen, root nodules     

Photoregulation of Germination in Freshly-harvested and Dried Seeds of Bromus sterilis L.

Freshly-harvested and dried seeds of Bromus sterilis L. withrespectively 52-54% and less than 10% moisture contents, differedmarkedly in their rates of germination and in their responsesto light. Dried seeds attained full germination in darknessat 15 ?C by 4 d from sowing and were inhibited by the formationof Pfr. In contrast, freshly-harvested seeds required 3-4 weeksto attain maximum germination and were promoted by Pfr. Themodified photoresponse of the seeds was induced only when theseeds were dried in an alternating temperature regime. The resultsare discussed in relation to the importance of desiccation asthe trigger for the transition from the developmental to thegerminative and growth phases of seed maturation of Bromus steriliswhich is well-documented in seeds of other species. Key words: Bromus sterilis, desiccation, light     

The Effect of Root Formation on Photosynthesis of Detached Leaves

The CO₂ exchange of fully expanded detached primary leaves ofdwarf bean (Phaseolus vulgaris) with roots on the petioles hasbeen measured. Rates of apparent photosynthesis and respirationincreased as roots grew, decreased when roots were removed,and increased again as root regenerated. Rates of photosynthesisof different leaves were highly correlated with the dry weightof root on their petioles. Photosynthesis and respiration weredecreased when root growth was restricted by kinetin, and wereincreased when root growth was stimulated by IAA. Photosynthesisof an attached leaf declined with time while that of a comparabledetached leaf increased. The results suggest that photosynthesisis correlated with the size of the roots that are a sink forphotosynthates.     

Cluster Roots in Casuarinaceae: Role and Relationship to Soil Nutrient Factors

N₂-fixing actinorhizal trees in the family Casuarinaceae areeconomically of great interest in tropical and sub-tropicalzones because they are used for many purposes including protectionagainst wind, stabilization of sand dunes and the productionof firewood and charcoal. They are usually able to grow in sandysoils with low fertility by virtue of their ability to fix N₂.The objective of this review is to discuss briefly the roleof mycorrhizas and, more extensively, that of cluster (proteoid)roots, developed by a number of species of Casuarinaceae toimprove the absorption of nutrients other than N from soil,especially those needed for N₂fixation and growth. After evaluatingthe actual relationships between mycorrhizas and the Casuarinaceae,we highlight the possible role of cluster roots as an effectivealternative to mycorrhizas, and as a means of improvement ofgrowth of the trees in nutrient-deficient soils. This raisesthe question of what triggers the formation of cluster rootsin the Casuarinaceae. In addition to phosphorus deficiency,iron deficiency seems to be a major factor inducing the formationof cluster roots in Casuarina glauca and C. cunninghamiana.The number of cluster roots and the precocity of their formationare directly related to plant chlorosis due to Fe deficiency,as expressed by the critical concentration of chlorophyll inthe shoot (0.60 mg g ^{- 1}shoot f.wt). The effect of the nitrogensource on cluster root formation is discussed in relation topH values in the plant culture solution. The number of clusterroots formed in nitrate-fed plants increases with pH in therange of 5 to 9. Experiments carried out with alkaline and acidicsoils show that cluster roots are only produced when they areneeded to overcome soil nutrient deficiency due to the immobilizationof nutrient elements (P and Fe) by soil alkalinity. The possibleinvolvement of ethylene in the initiation and/or the morphogenesisof cluster roots is discussed. Copyright 2000 Annals of BotanyCompany Casuarinaceae, Casuarina cunninghamiana, Casuarina glauca, cluster roots, ethylene, iron deficiency, phosphorus deficiency, proteoid roots     

Sagebrush (Artemisia tridentata Nutt.) roots maintain nutrient uptake capacity under water stress

Phosphorus and nitrogen uptake capacities were assessed during36–58 d drying cycles to determine whether the abilityof sagebrush (Artemisia tridentata Nutt.) to absorb these nutrientschanged as the roots were subjected to increasing levels ofwater stress. Water was withheld from mature plants in large(6 I) containers and the uptake capacity of excised roots insolution was determined as soil water potentials decreased from–0.03 MPa to –5.0 MPa. Phosphorus uptake rates of excised roots at given substrateconcentrations increased as preharvest soil water potentialsdecreased to –5.0 MPa. V_max and K_m also increased as soilwater potentials declined. Declining soil water potentials depressednitrogen uptake at set substrate concentrations, but uptakecapacity, calculated as the sum V_max for both NH⁺₄+NO^–₃,did not change significantly with drying. The sum V_max correlatedwith root nitrogen concentration. Root uptake capacity for nitrogen and phosphorus was extremelystable under severe water stress in this aridland shrub. Maintenanceof uptake capacity, coupled with a previously demonstrated abilityto conduct hydraulic lift, may enable A. tridentata better tomaintain nitrogen and phosphorus uptake as soil water availabilitydeclines. These mechanisms may be important in the ability ofA. tridentata to maintain growth, complete reproduction, andgain an advantage against competitors late in the season whenthe soil layers with higher nutrient availability are dry. Key words: Kinetics, nitrogen, phosphorus, roots, water stress     

Effects of Mineral Nutrition on Endogenous Cytokinins in Plants of Sunflower (Helianthus annuus L.)

The effects of inorganic nutrients on the levels of endogenouscytokinins in plants of sunflower (Helianthus annuusL.) grownin sand culture were studied. Low levels of nitrogen resultedin rapid decreases in the levels of cytokinins extracted fromleaves, buds, roots, and root exudates. Similar effects wereobserved with phosphorus deficiency, but the effects of potassiumdeficiency on the cytokinin content of leaves was less marked.The cytokinin content was higher in plants supplied with nitrogenas nitrate than in those supplied with ammonium sulphate orammonium nitrate. The decline in cytokinin levels in derooted shoots and detachedleaves could be reversed by supplying them with nutrient solution.Although leaves on intact plants may normally be dependent uponthe supply of cytokinins from the roots, isolated leaves havethe capacity for cytokinin production when supplied with inorganicnutrients.