Comparison of Growth Responses of Barnyard Grass (Echinochloa oryzoides) and Rice (Oryza sativa) to Submergence, Ethylene, Carbon Dioxide and Oxygen Shortage

Unlike germination of wheat (Triticum aestivum), millet (Eleucinecoracana), and sorghum (Sorghum caudatum), that of Echinochloaoryzoides (barnyard grass) and Oryza satwa (rice) was not inhibitedby poorly aerated solutions with 11 k Pa oxygen (equilibriumpartial pressure) or less In the dark, seedling shoots of riceincluded a coleoptile, and in Echinochloa, a mesocotyl alsoGrowth in fresh and dry weight of shoots was strongly depressedby poorly aerated solutions in both rice and Echinochloa butthe effects on extension differed in the two species in rice,coleoptile extension was promoted by solutions partly depletedof oxygen, and also by the absence of oxygen The stimulationin partly de-oxygenated solutions resulted from the combinedpromoting effects of small oxygen partial pressures, carbondioxide, ethylene and buoyant tension in contrast, these treatmentsneither promoted nor inhibited elongation by the Echinochloacoleoptile while severely inhibiting extension of the mesocotyl Overall, poorly aerated solutions lengthened the shoot of riceand shortened it in Echinochloa when compared with those submergedin well-aerated solutions These opposite effects were broughtabout by the same gaseous changes, i e oxygen shortage, elevatedethylene and carbon dioxide The effect on Echinochloa was almostentirely restricted to the mesocotyl, coleoptile extension beingremarkably insensitive to large increases in ethylene and carbondioxide, or to extreme oxygen shortage Seedlings of the twospecies thus have contrasting strategies for survival Stress, submergence, ethylene, oxygen shortage, carbon dioxide, adaptation, anaerobiosis, rice (Oryza sativa L), barnyard grass [Echinochloa oryzoides (Ard) Fritseh]     

Ethylene and carbon dioxide: regulation of oat mesocotyl growth

Either ethylene or carbon dioxide stimulated the growth of oat mesocotyls in darkness, although the effect was much greater for carbon dioxide. Maximum elongation was obtained in the presence of both gases. Ethylene also induced lateral expansion of the mesocotyl: the volume of the mesocotyl was increased more in air with added ethylene than in air depleted of ethylene. Ethylene also stimulated mesocotyl growth under red light. Gibberellin only slightly increased mesocotyl length under red light and acted cooperatively with ethylene in the promotion of growth. The oat mesocotyl is a unique organ in terrestrial plants because ethylene simultaneously stimulates not only longitudinal growth but also lateral expansion. The ecological significance of oat mesocotyl growth in relation to the response to ethylene and carbon dioxide is discussed.     

Changes in cell wall composition of rice mesocotyls in relation to growth and treatment with 4-ethoxy-1-(p-tolyl)-s-triazine-2,6(1H, 3H)-dione

A synthetic substance, 4-ethoxy-l-(p-tolyl)-s-triazine-2,6(1H,3H)-dione [TA] dramatically promoted mesocotyl growth in dark-grownrice (Oryza sativa L. cv. Nato) seedlings, the optimal concentrationbeing 0.1–0.2 mM. Changes in the cell wall compositionof the rice mesocotyls were examined in relation to growth andtreatment with 0.1 mM TA. The amount of the cell wall increasedduring the elongation in control and treated mesocotyls. Particularly,TA caused a large increase in the amount of the cell wall permesocotyl but a decrease per unit length of mesocotyl. Hydrolysisof the cell wall with trifluoroacetic acid liberated xylose,glucose, arabinose, galactose, and trace amounts of rhamnose,fucose and mannose. An increase in the relative amount of xyloseand a decrease in that of glucose in the noncellulosic fractionduring growth were found in control and treated mesocotyl walls.On the 2nd day after planting when the mesocotyl emerged, TAsignificantly affected the cell wall composition; TA decreasedthe relative amount of -cellulose in the wall, and caused anincrease in the relative amount of glucose and decreases inthose of xylose and arabinose in the noncellulosic fraction. ¹This paper is Part 7 in the series "Plant Growth-regulatingActivities of Isourea Derivatives and Related Compounds." (Received March 18, 1980; )     

Auxin and Ethylene Control of Growth in Seedlings of Zea mays L. and Avena sativa L

The effects of applied ethylene on the growth of coleoptilesand mesocotyls of etiolated monocot seedlings (oat and maize)have been compared with those on the epicotyl of a dicot seedling(the etiolated pea). Significant inhibition of elongation by ethylene (10 µll^–1for 24 h) was found in intact seedlings of all three species,but lateral expansion growth was observed only in the pea internodeand oat mesocotyl tissue. The sensitivity of the growth of seedlingparts to ethylene is in the decreasing order pea internode,oat coleoptile and oat mesocotyl, with maize exhibiting theleast growth response. Although excised segments of mesocotyland coleoptile or pea internode all exhibit enhanced elongationgrowth in IAA solutions (10^–6–2 ? 10^–5 moll^–1), no consistent effects were found in ethylene. Ethyleneproduction in segments was significantly enhanced by applicationof auxin (IAA, 10^–5 mol l^–6 or less) in all tissuesexcept those of the eat mesocotyl. Segments of maize show a slow rate of metabolism of applied[2-¹⁴C]IAA (30 per cent converted to other metabolites within9 h) and a high capacity for polar auxin transport. Ethylene(10 µl l^–1 for 24 h) has little effect on eitherof these processes. The oat has a smaller capacity for polartransport than maize and the rate ef metabolism of auxin isas fast as in the pea (90 per cent metabolized in 6 h). Althoughethylene pretreatment does not change the rate of auxin metabolismin oat, there is a marked reduction in auxin transport. It is proposed that the insensitivity of maize seedlings toethylene is related to the supply and persistence of auxin whichcould protect the seedling against the effects of applied orendogenously produced ethylene. Although the mesocotyl of oatis sensitive to applied ethylene it may be in part protectedagainst ethylene in vivo by the absence of an auxin-enhancedethylene production system. The results are discussed in relationto a model for the auxin and ethylene control of cell growthin the pea.     

The Effects of Oxygen, Carbon Dioxide and Ethylene on Ethylene Biosynthesis in Relation to Shoot Extension in Seedlings of Rice (Oryza sativa) and Barnyard Grass (Echinochloa oryzoides)

Exposing dark-grown seedlings for 3 d to oxygen deficiency (0or 5 kPa) or to additions of carbon dioxide (10 kPa) or ethylene(0·1 Pa) slowed shoot extension in Echinochloa oryzoides,while in rice it was promoted by these treatments, except that5 kPa oxygen was without effect. In E. oryzoides this was dueto reduced growth of the mesocotyl, and in rice to enhancedgrowth of the coleoptile. These responses to carbon dioxideand oxygen deficiency were not consequences of increased ethyleneproduction, since this remained unchanged by carbon dioxideand depressed by oxygen shortage in both species. Furthermore,exogenous ethylene and the ethylene action inhibitor 2,5-norbornadieneeach failed to influence extension in anoxic seedlings, indicatingno regulatory role for ethylene in the absence of oxygen. However,concentrations of the ethylene precursor 1 -aminocyclopropane-1-carboxylic acid (ACC) were increased by carbon dioxide and0 kPa or 5 kPa oxygen, although after 72 h without oxygen totalACC production (i.e. changes in ethylene + ACC + MACC) was suppressedin both species. There was little effect on bound ACC [putativemalonyl-ACC (MACC)] formation. Transferring anaerobic (0 kPa)seedlings to oxygenated conditions (21 kPa) resulted in abnormallyfast rates of ethylene formation, possibly due to the accumulationof ACC under anoxia. This post-anoxic ethylene may have contributedto the faster extension by rice coleoptiles and slower extensionby mesocotyls of E. oryzoides compared with those of seedlingsmaintained continuously in air. Echinochloa oryzoides [Ard.] Fritsch, barnyard grass, Oryza sativa L, rice, oxygen shortage, carbon dioxide, ethylene biosynthesis, shoot extension, 1-aminocyclopropane-1-carboxylic acid (ACC), malonyl-ACC, GC-MS     

A Note on the Relevance of the Mesocotyl in the Systematics of the Gramineae

Seedlings of most of the Gramineae possess a mesocotyl, buta few tribes are characterized by its absence. Seedlings ofBromus resemble the Triticeae in having no mesocotyl and thisis further evidence for separating the Bromeae both from theFestuceae and from the Brachypodiae.     

A Critical Study of the Auxin Theory of Growth Regulation in the Mesocotyl of Avena sativa

A method of growing Avena seedlings is described, which allowsthem to be handled individually in darkness. Mesocotyls of seedlinge from which the tip of the coleoptileis repeatedly removed are as long as those of control plantsnot so decapitated. Mesocotyls of seedlings which are deseeded on the 3rd day ofgrowth, followed by decapitation of the cleoptile tip on the4th day, are, at 7 days old, as long as those of controls notso decapitated. When deseeded plants are decapitated, regeneration of auxinproduction occurs at the tip of the coleoptile stump. Where a reduction in the length of the mesocotyl results fromdecapitation, a wound reaction is probably concerned in additionto any auxin changes. Removal of the coleoptilar node causes a sharp decrease in thefinal length of the mesocotyl. Heating intact seedlings at 40° C. for 3 hours causes areduction in the length of the mesocotyl but not of the coleoptile.The effect of heating is not reversed by subsequent treatmentat low temperature, which instead appears to augment these effects. When seedlings are exposed to the action of KCN, iodoacetate,or anaerobic conditions, and illuminated while so exposed, perceptionof light takes place, resulting in a reduction in the lengthof the mesocotyl. Perception of light takes place in seedlings germinated at normaltemperatures, but maintained at low temprature during illuminationand also in seedlings grown for 6 weeks at 2° C. withoutany previous growth at normal temperature. Light perception takes place in embryos excised from dry grainand grown on a culture medium. No difference in free amino-acid content is apparent betweendark grown and illuminated seedlings. The effects of illumination survive a period of drying downand become apparent upon subsequent germination of the grainin darkness. The drying process itself causes an additionalreduction in mesocotyl length. It is concluded that auxin itself is not the primary reactantin the perception process, and that the growth of the mesocotylis probably controlled by the coleoptilar node and plumulargrowing point, rather than by auxin diffusing downward fromthe tip of the coleoptile.     

MESOCOTYL ROOT FORMATION IN ECHINOCHLOA PHYLLOPOGON (POACEAE) IN RELATION TO ROOT ZONE AERATION

Echinochloa phyllopogon was grown hydroponically under four root zone gassing treatments to determine aeration effects on the growth and development of the plant root system. Although mesocotyl growth and the number of nodal roots were unaffected by the treatments, other aspects of plant growth were altered. Shoot growth was reduced by hypoxic (5 kPa partial pressure O₂ in nitrogen gas) and anoxic conditions (O₂ free nitrogen gas), but not by ethylene (0.1 ppm in air). Seminal root growth was unaffected by hypoxia or ethylene treatments, but was reduced under anoxia. Hypoxic environments stimulated the emergence of roots along the length of the mesocotyl when compared to aerobic controls; anoxic and ethylene treatments had no significant effects. Mesocotyl roots elongated from primordia that were produced de novo in response to the hypoxic treatment. Under hypoxic conditions, aerenchyma was present in the cortex of nodal roots and to a lesser extent in seminal roots, but mesocotyl roots were devoid of aerenchyma under these conditions. The results are compared with the literature concerning flooding and aeration effects on growth and development in other species.     

An Examination of the Factors affecting Variability in the Growth of the Mesocotyl and Coleoptile of Etiolated Avena Seedlings

Experiments were carried out on the effect of rate of air-flowand of humidity on the growth of Avena seedlings. The experimentalmethods used are described in some detail. The effect of air-flow on mesocoryl growth was considerablewhen unsaturated air was used, but with saturated air growthwas independent of air-flow. The effect must therefore be dueto variation in transpiration rate. A 10 per cent, variationin relative humidity, at a constant rate of flow, caused a 30per cent, variation in mesocotyl length. The coleoptiles showedless pronounced effects, but even in saturated air variabilitywas not eliminated. Under the conditions used a difference of 2·3 mm. inmesocotyl length (per 50 plants), i.e. 8 per cent., was significantat P = 0·05; for the coleoptiles a difference of 1 mm.(8 per cent.) was significant at this level.     

Some Growth Promotive Effects of Abscisic Acid

Abscisic acid promoted increase in frond number and fresh weightin Lemna polyrhiza when applied at low concentrations althoughhigher concentrations inhibited both parameters. Elongationof coleoptile segments of oats and wheat was also promoted bylow ABA concentrations when the coleoptile tip was not excised,although when the tip was removed no significant promotion wasdetected. Elongation of mesocotyl segments of oats and maizewas promoted by ABA and in these cases the maximum promotionoccurred at higher concentrations with maximum elongation ofmaize mesocotyl segments occurring at the highest concentrationtested. The dose-response relationship for ABA appears to be similarto that reported for IAA in some tissues.     

Effect of high temperature pre-treatment on elongation of the mesocotyl of rice seedlings I. Cell multiplication in the mesocotyl

Mesocotyl elongation in paddy rice seedlings of the japonicatype was markedly stimulated by high temperature pre-treatmentof seeds. Examination of the number of parenchyma cells perone cell layer in longitudinal sections of mesocotyl revealedthat stimulation may be mainly caused by cell multiplication. (Received February 24, 1970; )     

A Relationship between Membrane Permeability and Ethylene Production at High Temperature in Leaf Tissue of Phaseolus vulgaris L.

Leaf discs cut from primary leaves of Phaseolus vulgaris L cvMasterpiece were incubated at temperatures higher than the growthtemperature of 25 °C Both basal and wound ethylene productionincreased up to temperatures of 35–37 5 °C, thereafterdeclining rapidly There was no detectable ethylene productionat temperatures above 42 5 °C Exposure of leaf discs tohigh temperature for 60 mm resulted in a large production ofwound ethylene when they were returned to 25 °C The magnitudeof ethylene production was related to the initial incubationtemperature as was the length of the lag period before maximumproduction was achieved The results are discussed in relationto the requirement for continued membrane integrity for ethyleneproduction ethylene, temperature, membrane permeability, Phaseolus vulgaris L, dwarf bean     

Phenylalanine Ammonia Lyase Activity in Pearl Millet Seedlings and its Relation to Downy Mildew Disease Resistance

Phenylalanine ammonia lyase (PAL) activity was studied in differentgenotypes of pearl millet with varying degrees of susceptibilityto downy mildew disease, after inoculating with Pathotype 1of Sclerospora graminicola. In resistant genotypes, the enzymeactivity significantly increased 24 h after fungal inoculationwhile in the susceptible genotypes, the activity decreased.The increase or decrease in enzyme activity was well-correlatedwith the degree of host resistance to the pathogen. A time-courseof change in activity of PAL after inoculation showed a considerabledifference between resistant and susceptible genotypes. Studieson the activity of PAL in different parts of pearl millet seedlingsrevealed that in the resistant genotype, enzyme activity significantlyincreased at 24 h post-inoculation only in the shoot portion,whereas in mesocotyl and root the activity decreased. In susceptibleseedlings, enzyme activity decreased at 24 h post-inoculationin shoot, mesocotyl and root. The activity of PAL was also foundto be pathotype-specific. Histochemical tests for lignin werepositive in infected cells in the resistant genotypes. The roleof PAL in imparting resistance to pearl millet against downymildew disease is discussed. Key words: Sclerospora graminicola, resistance screening, enzyme activity     

Interaction between ethylene,abscisic acid and gibberellic acid in elongation of rice mesocotyl

Summary Combined application of ethylene, abscisic acid and gibberellic acid produced marked partly synergistic stimulation of mesocotyl growth of japonica rice in darkness.     

PHYSIOLOGICAL ACTIVITIES OF HELMINTHOSPOROL AND HELMINTHOSPORIC ACID: II. EFFECTS ON EXCISED PLANT PARTS

Effects of H-ol and H-acid were observed using excised partsof several plant species. Both H-ol and H-acid were active inelongation of oat coleoptile and mesocotyl, expansion of Raphanusleaf disk, but were inactive in elongation of wheat coleoptileand of green stem of pea. They gave also negative results inthe standard Avena curvature test and in the split pea test.In expansion of lettuce cotyledon, H-ol was inactive while H-acidwas active. In excised plant parts, as in intact plants, theactivity of H-ol and H-acid resembles rather gibberellins thanauxins and cytokinins. (Received August 20, 1966; )     

Rapid Production of Auxin-induced Ethylene

The time course of auxin-induced ethylene production was determined in mesocotyl segments of etiolated sorghum (Sorghum bicolor L. Moench) seedlings. The latent period between addition of auxin and a detectable rise in ethylene release was 15 to 20 minutes in four different genotypes. This may indicate that the initial effect of auxin on ethylene production is too rapid to involve synthesis of an ethylene-producing enzyme. The technique devised for these experiments involves placing tissue segments end to end in a glass tube, and it allows simultaneous determination of growth and ethylene production.     

Emergence of temperate pasture grases from different sowing depths: importance of seed weight, coleoptiele plus mesocotyl length and shoot strength

Inter-specific relationships between mean seed weight, coleoptile + mesocotyl (sub-coleoptile internode) length and width, shoot strength and emergence from different sowing depths were examined for timothy (Phleum pratense L., mean seed weight 0.33-0.48 mg depending on seed line), cocksfoot (Dactylis glomerata L., 0.65-0.78 mg), perennial ryegrass (Lolium perenne L., 1.71-2.19 mg), tall fescue (Festuca arundinucea Schreb., 1.73–2.60 mg), annual ryegrass (Lolium multiflorum Lam., 5.10-5.20 mg) and prairie grass (Bromus willdenowü Kunth., 10.5–12.2 mg). Across species at 10,30 and 60 mm sowing depths in the field and 10, 15 and 30 mm sowing depths under controlled environment conditions, there was a significant (P < 0.05) positive correlation between emergence % and mean seed weight. Across species at 10–30 mm sowing depth under controlled environment conditions, emergence % was not significantly correlated with coleoptile + mesocotyl length but there were significant positive correlations between emergence % and coleoptile and mesocotyl width: shoot strength increased with increased coleoptile width across species. For seed lines of timothy of different mean seed weight (0.21-0.81 mg), emergence %, coleoptile + mesocotyl length and coleoptile and mesocotyl width increased with increased seed weight at 10 and 15 mm sowing depth. Shoot strength increased with increased coleoptile width for timothy. For emerged and non-emerged cocksfoot and timothy seedlings regardless of seed weight, mean coleoptile + mesocotyl length was > 10 mm at 10 mm sowing depth. It is concluded that at 10–30 mm sowing depth, increased emergence % with increased seed weight across species is not due to increased coleoptile + mesocotyl length. It is proposed that increased emergence % with increased seed weight across species at 10–30 mm sowing depths and across seed lines of timothy at 10 mm sowing depth is primarily due to increased coleoptile and mesocotyl width resulting in increased shoot strength and hence an increased ability to penetrate the substrate.     

Ethylene and IAA transport in potato

Although elongation growth is reduced by ethylene, swelling responses do not occur. Ethylene reduces neither transport nor metabolism of applied IAA in either mesocotyl or coleoptile. We propose that maintenance of high auxin levels within these tissues sustains polar transport and contributes to the relative insensitivity of maize to applied ethylene.     

Involvement of Abscisic Acid in Mesocotyl Growth in Etiolated Seedlings of a Foxtail Millet Dwarf Mutant

Etiolated seedlings of foxtail millet (Setaria italica Beauv.) dwarf mutant CH84113 were treated with various concentrations of abscisic acid (ABA), mefluidide, mannitol, or polyethylene glycol (PEG) 6000. It was found that these chemicals, at suitable concentrations, could increase mesocotyl length significantly, whereas these chemicals at higher concentrations had an inhibitory effect. Endogenous levels of ABA in mesocotyl were measured by enzyme-linked immunosorbent assay. It was found that endogenous ABA increased progressively in a chemical (ABA, mefluidide, mannitol, or PEG 6000) concentration-dependent manner, indicating that the effects of these chemicals on mesocotyl growth may be mediated by increased endogenous ABA levels. On the other hand, S-3307, an inhibitor of the oxidative reactions in gibberellin (GA) biosynthesis, inhibited the elongation of mesocotyl significantly. When ABA and GA₃ were applied simultaneously, the effect on mesocotyl growth was additive. These results imply that ABA and GA may control different processes in the regulation of mesocotyl growth. Received October 27, 1997; accepted May 11, 1998     

The Uptake of Growth Substances: XIII. DIFFERENTIAL UPTAKE OF INDOL-3YL-ACETIC ACID THROUGH THE EPIDERMAL AND CUT SURFACES OF ETIOLATED STEM SEGMENTS

The patterns of uptake of indol-3yl-acetic acid (IAA-2-¹⁴C)by etiolated stem segments of varying lengths have been examined,employing tissues excised from (a) the first and third internodesof Pisum sativum, (b) the top and base of the hypocotyl of Gossypiumhirsutum, and (c) the mesocotyl of Avena sativa. For all species,concentrations (10^–5–10^–3 M) and times upto 24 h, there is a steady accumulation of radioactivity inthe segments. For equal volumes of tissue uptake is inverselycorrelated with segment length but for extending tissues theinitial enhanced extension growth is independent of length;that is there is no direct linkage between the rate of extensionand auxin content. Comparisons between segments with free andsealed ends established that over 24 h some 57–73 percent of the IAA enters via the cut surfaces. Initially, thepercentage is greater; expressed as a rate per unit of surfacethe differences between cut and epidermal surfaces can reach28-fold. The rate of entry through the epidermal surface islinearly proportional to the external concentration but thisdoes not hold for cut surfaces. The addition of streptomycin,synthalin, cetyltrimethylammoniumbromide (CTAB), and chitosanto the external medium does not promote uptake of IAA by Pisumsegments; indeed synthalin is markedly inhibitory. With Gossypiumsynthalin causes little inhibition. Larger depressive effectswere induced for entry via the cut surfaces. On entry the IAAis rapidly metabolized and the rate of conversion is higherfor segments with sealed ends. These findings are discussedin relation to (a) differences in the mechanisms determiningthe uptake of IAA and other auxins, (b) cell extension and thedistribution of auxin in the tissues.