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     

Distribution of Lateral Root Primordia in Root Tips of Musa

The distribution of lateral root primordia in the root tipsof four Musa landraces (Grande Naine, Pisang Berlin, Ngok Egomeand Yangambi Km5) grown in the field has been investigated toevaluate the range of genetic variation of lateral root initiation.In banana (Musa sp.), lateral roots are initiated in the roottip, 0.6–4 mm behind the root/cap junction and arise inseveral protoxylem-based longitudinal rows or ‘ranks’.Significant differences were observed among landraces for theposition of the most distal primordium, however the longitudinalspacing between successive primordia along the ranks was similarfor all landraces. All ranks were involved in lateral root initiation.The number of ranks also showed significant variations amonglandraces and was proportional to the stelar diameter. Hencethe density of lateral roots (roots cm^-1) was affected by stelardiameter variations. Finally, root elongation in the root tipwas landrace-specific and not necessarily exponential, unlikesuggested in previous studies. It is concluded that lateralroot initiation in Musa is not involved in the genetic variationsof root architecture in the field. A dissection of root architectureinto components which may account for these variations is proposedin relation to the improvement of root system architecture.Copyright 1999 Annals of Botany Company Lateral root initiation, root architecture, Musa, banana.     

Lateral Root Development in Attached and Excised Roots of Zea mays L. Cultivated in the Presence or Absence of Indol-3-yl Acetic Acid

The initiation of lateral root primordia and their subsequentemergence as secondary roots have been examined in attachedand excised roots of Zea mays grown in the presence or absenceof indol-3-yl acetic acid (IAA). Exposure to IAA enhanced anlageinception in both batches of roots. In the attached roots, theIAA-induced stimulation of primordium initiation was followedby a similar increase in lateral emergence. IAA treatment, however,had no effect on the number of laterals produced, per centimetreof root, in the excised primaries. Thus, exposure to IAA didnot directly enhance lateral emergence in the attached rootsnor did it stimulate such emergence in the excised ones. Nocorrelation was found between proliferative activity in themeristem at the apex of the primary or the rate of root elongationon the one hand, and either the number of primordia initiated,or the number of laterals produced, per centimetre of primary,on the other. Zea mays, maize, root, primordium, lateral, indol-3-yl acetic acid, meristematic activity     

Shoot and Root Growth of Lettuce Seedlings Following Root Pruning

Hydroponically-grown lettuce seedlings with 13 to 18 primarylateral roots were root pruned in one of four ways; the rootapices were removed from the main root only (1) or from allthe root membranes (2), or half the total root system was removedwith the remaining apices left intact (3) or removed (4). Duringthe following 8 d the rate of lateral root production on prunedplants increased, decreased, and then increased again relativeto the unpruned control. Conversely, the rate of increase intotal root length decreased, then increased, and if all theroot apices were removed, declined again, prior to increasingon day 8. These changes in the rates of lateral root productionand growth resulted in similar, but less pronounced, patternsof change in the total root length and the total number of lateralroots with time. The changes in total lateral root productionwere related to differences in the rates of primary, secondaryand tertiary root emergence. The shoot d. wt of the most severely root pruned seedlings (treatment4) fell below that of the control 4 d after pruning and remainedlower than the control on day 14, whereas the root d. wt hadrecovered to the control level by day 6. The root: shoot d.wt ratio, which was reduced by root pruning, rose above thatof the control on days 6 and 8. Lactuca sativa L., lettuce, root pruning, root growth, lateral root, nutrient solution     

Pattern Formation in Cluster Roots: Some Developmental and Evolutionary Considerations

Cluster roots, also known as proteoid roots, are one of themajor adaptations for nutrient acquisition in terrestrial vascularsporophytes, occurring in many important plant families, inkey areas of biodiversity, and in significant ecological niches.Their development and function are closely linked and presentan ideal experimental system with which to investigate the basisof pattern and its morphogenetic amplification. Both meristemfunction and root initiation are controlled within a spatialand temporal framework, resulting in predictive phenotypic expression.In this paper, these patterns of development are described withinthe context of our knowledge of lateral root initiation anddevelopment. Recent work is summarized in an attempt to highlightthe issues of most importance for future research. The caseof the genus Lupinus is taken as a means of exploring the phylogeneticrelationships of species with cluster roots. The first evidenceof cluster roots having arisen only once within the Lupinusgenus is presented. Copyright 2000 Annals of Botany Company Cluster root, development, lateral root, lupin evolution, nutrient acquisition, pattern, proteoid root     

Structural Relationship among the Rice Glutelin Polypeptides

When the glutelin protein fraction of rice (Oryza sativa L.) seeds was fractionated by sodium dodecyl sulfate polyacrylamide gel electrophoresis, three size classes of proteins, 51 kilodaltons (kD), 34 to 37 kD, and 21 to 22 kD, as well as a contaminating prolamine polypeptide of 14 kD were detected. Antibodies were raised against these proteins and employed in studies to determine whether a precursor-product relationship existed among the glutelin components. Antibodies of the 34 to 37 kD and 21 to 22 kD polypeptides strongly reacted with the 51 kD protein, and conversely, anti-51 kD protein cross reacted with both of the putative subunits. Immunoprecipitation of in vitro translated products resulted in the synthesis of only the precursor form, indicating that the α and β subunits are proteolytic products of the 51 kD precursor protein. The poly(A)⁺ RNA directed in vitro translated product was about 2000 daltons larger than both the authentic glutelin precursor and the in vitro translated product from polysome run-off synthesis. Western blot analysis of the 34 to 37 kD and 21 to 22 kD polypeptides partially digested with Staphylococcus aureus V8 protease revealed distinct patterns indicating that these proteins are structurally unrelated. As observed for the glutelins, the rice prolamines are also synthesized as a precursor of 16 kD, 2000 daltons larger than the mature polypeptide. Addition of dog pancreatic microsomal membranes to a wheat germ protein translation system resulted in the processing of the prolamine preprotein but not the preproglutelin to the mature form.     

Change in Size and Cell Number during the Development of Lateral Root Primordia in Zea mays L.

Increase in cell number, anlage volume and length have beeninvestigated during the overall period of lateral root primordiumdevelopment in excised primaries and in attached roots of Zeamays L. Each of these aspects of anlage growth was found toincrease more or less exponentially during the interval betweenprimordium initiation and subsequent emergence as a lateralin both batches of roots. Values were then determined for celldoubling time (Td), the size of the proliferative fraction (Pf),and for anlage volume (Tv) and length (Tt) doubling times duringthe overall period of primordium development and at intervalsduring this period in both the excised and attached roots. Thepattern of change which took place in Td, Tv, Tl and Pf duringlateral primordium development was found to be similar in bothbatches of roots. However, the overall period of anlage developmentwas shorter in the excised roots than in the attached ones.Moreover, when laterals grew out of the excised roots they didso with fewer cells than comparable laterals emerging from theattached roots. Zea mays L., maize, root primordia, lateral emergence, cell doubling time     

Endogenous Development of Adventitious Root Primordia in Lettuce Hypocotyls

Rudimentary adventitious root primordia were observed in optically-sectionedFeulgen-stained hypocotyls of 8-d-old lettuce seedlings germinatedin the dark and in a low light intensity environment. It issuggested that formation of these primordia may represent anaspect of normal development in the seedling. Adventitious, root primordia, hypocotyls, lettuce, Lactuca sativa     

Chromosaponin I Stimulates the Elongation of Cortical Cells in Lettuce Roots

Chromosaponin I (CSI) stimulates the growth of lettuce roots(Lactuca sativa L. cv. Grand Rapids), causing accelerated cellelongation. Growth stimulation was detected 6 h after the initiationof treatment with CSI, continuing for 3 days. Elongation ofroot cells in various other plants was also promoted by CSI. (Received January 30, 1995; Accepted April 17, 1995)     

Site, Scale and Time-course for Adjustments in Lateral Root Initiation in Wheat Following Changes in C and N Supply

The pattern of lateral root initiation in seminal roots of wheat(Triticum aestivumL. cv. Alexandria) and the location, scaleand time-course for adjustments in initiation were studied afterchanges in C and N supply. Macroscopically visible primordiaappeared in a non-acropetal sequence with the frequency (numberper unit length) increasing with distance behind the main rootapex to a maximum at 40–50 mm behind the root tip. Pruningthe root system to a single seminal axis increased the primordiafrequency by 23% within 15 h. After longer periods, the effectof root-pruning was greater. The enhanced primordia frequencywas first observed in tissue located 0–10 mm behind theapex at the start of treatment. Feeding glucose (50 mM) alsoincreased primordia frequency within 15 h, but to a greaterextent, and here additional primordia were initiated in tissuelocated 0–10and10–20 mm behind the apex at the startof treatment. Withdrawing NO₃^-from one part of a split-rootsystem, whilst maintaining the supply to the other, reducedprimordia frequency in the non-fed roots and, in some cases,a compensatory increase in the NO₃^--fed roots was observed.The location and scale of the adjustments were similar to thosefound with root-pruning and glucose-feeding, but were slightlyslower to appear. In spite of some differences in detail, therewas a broad similarity in site, scale and time-course for adjustmentsin lateral root initiation with these treatments, which is consistentwith the operation of a common mechanism. Whenever an increasein primordia frequency was observed, it was associated withan increase in the ethanol-soluble sugar content of the tissue.However, the reduction in frequency in NO₃^--deprived roots wasalso accompanied by an increase in sugar content. There wasno consistent relationship between total N content of the tissueand primordia frequency, but there was between primordia frequencyand the rate of net NO₃^-uptake. The possible mechanisms controllinglateral root initiation are discussed. Compensatory growth; correlative growth; glucose; initiation; lateral root; nitrate; primordium; split-root; Triticum aestivum; wheat     

Effect of sulphate deficiency on the plasma membrane polypeptide composition of Brassica napus

Highly purified oilseed rape (Brassica napus) root plasma membranefractions were prepared and their polypeptide patterns analysedby two-dimensional gel electrophoresis. Sulphur starvation enhancesthe sulphate uptake capacity of B. napus roots. The relativeabundance of several polypeptides increased significantly andspecifically after sulphur starvation. Several of them (37,38, 60, and 65 kDa), found in sulphur-starved plants, were moreabundant in a phase-partitioned membrane fraction treated withTriton X-100/KBr, indicating that they are intrinsic polypeptides.One polypeptide (47 kDa) was identified in the in vitro translationproducts of the roots mRNAs as specific for S-starved plants.It was also present among the intrinsic polypeptides specificfor —S plants. These plasma membrane polypeptides mightbe involved in sulphate uptake. Key words: Sulphate, sulphur-starvation, plasma membrane, polypeptides, root, transport     

The Inhibitory Effect of (2-Chloroethyl)-trimethylammonium Chloride on Chlorophyll and Protein Synthesis in Lettuce Cotyledons, and its Reversal by Potassium

Germinated seeds of Lactuca sativa (L.) were placed in Petri-dishesin (2-chloroethyl)-trimethyl-ammonium chloride (CCC; 0.005–0.05M), KN0₃ (0.01 M), and KC1 (0.01 M) solutions, and incubatedfor 2 or 5 days under continuous light. CCC strikingly arrestedchlorophyll accumulation, and retarded cotyledon growth relativelylittle. The retardant inhibited ¹⁴C-leucine incorporation intobulk proteins of the cotyledons. KN0₃ and KC1 promoted cotyledongrowth and chlorophyll synthesis per cotyledon by about 150per cent, and about doubled protein synthesis. Potassium saltscompletely reversed the inhibitory effects of CCC on chlorophylland protein synthesis. It is suggested that the inhibition ofgreening by CCC is dependent on a prior inhibition of proteinsynthesis.     

The response of tomato roots (Lycopersicon esculentum Mill.) to iron deficiency stress: alterations in the pattern of protein synthesis

Dicotyledon plants adapt to iron (Fe) deficiency through a seriesof reactions that increase the ability of the plant to assimilateFe and to increase the efficiency of Fe utilization. In an attemptto gain an insight into these adaptive processes, the specificchanges in protein synthesis associated with the onset of theFe deficiency response in tomato roots (Lycopersicon esculentumMill cv. Rutgers) have been investigated. Roots were grown underFe—sufficient and —deficient conditions, and thepattern of protein synthesis was analysed by in vitro translationof root mRNA and by in vivo labelling of root proteins. Polypeptideswere resolved by two—dimensional polyacrylamide gel elec—trophoresis.Seven polypeptides were identified by in vitro translation,whose synthesis was significantly increased during Fe deficiency.The increase was probably specific to Fe deficiency in thatthe polypep—tide synthesis was not increased during phosphatedeficiency stress, was less prominent following prolonged Fedeficiency and was decreased following re—supply of Feto the hydroponic medium. The pattern of in vitro translation of mRNA isolated from Fe—deficientroots was compared to the results obtainedin vivo followingradiolabelling of proteins. In these analyses, eight polypeptideswere identified, tentatively including the seven polypeptidespreviously identified by in vitro translation. All polypeptideswere characterized with regard to molecular mass and pl andtheir localization in the cell, whether being membrane boundor soluble. It is suggested that members of this group of polypeptidesare involved in the response of the root to Fe deficiency: althoughtheir functions remain to be identified. Key words: In vitro protein synthesis, iron, iron deficiency, root, 2-dimensional PAGE     

Mobilization of nitrogen reserves during regrowth of defoliated Trifolium repens L. and identification of potential vegetative storage proteins

Although it is well established that carbon reserves contributeto shoot regrowth of leguminous forage species, little informationis available on nitrogen reserves except in Medicaqo sativaL. and Trifolium subterraneum L. In this study, reserves werelabelled with ¹⁵N to demonstrate the mobilization of endogenousnitrogen from roots and stolons to regrowing leaves and newstolons during 24 d of regrowth in white clover (Thfolium repensL.). About 55% and 70%, respectively, of the nitrogen contentsof these organs were mobilized to support the regrowth of leaves.During the first 6 d, nitrogen in regrowing leaves came mainlyfrom N reserves of organs remaining after defoliation. Afterthese first 6 d of regrowth, most of the shoot nitrogen wasderived from exogenous nitrogen taken up while the contributionof nitrogen reserves decreased. After defoliation, the buffer-solubleprotein content of roots and stolons decreased by 32% duringthe first 6 d of regrowth. To identify putative vegetative storageproteins, soluble proteins were separated using SDS-PAGE ortwo-dimensional electrophoresis. One protein of 17.3 kDa instolons and two proteins of 15 kDa in roots seemed to behaveas vegetative storage proteins. These three polypeptides, initiallyfound at high concentrations, decreased in relative abundanceto a large extent during early regrowth and then were accumulatedagain in roots and stolons once normal growth was re-established. Key words: White clover, regrowth, ¹⁵N-labelled, vegetative storage proteins, electrophoresis     

Prehydration and Priming Treatments that Advance Germination also Increase the Rate of Deterioration of Lettuce Seeds

The influence of prehydration in water or priming in –1.5 MPa polyethylene glycol 8000 solution for various periods,followed by redrying, on germination rate and longevity of lettuce(Lactuca sativa L.) seeds (achenes) was determined during controlleddeterioration at 10% moisture content (fresh weight basis) and40°C. Short prehydration treatments (up to 1 h) had littleeffect on either germination rate or longevity, but significantlyimproved root growth rates. Increasing durations of prehydrationor priming reduced the mean time to germination by up to 61%relative to untreated seeds, but also reduced mean seed longevityby as much as 84% Prehydration and priming altered the relationshipsbetween germination rate and viability and between normal andabnormal seedlings during ageing. Prehydration in abscisic acidor at a temperature inhibitory to germination did not preventthe reduction in longevity under controlled deterioration conditions.While prehydration or priming treatments effectively acceleratesubsequent germination rates of lettuce seeds, the redried seedsare nonetheless highly susceptible to deterioration in storage. Key words: Lettuce, Lactuca sativa L., seed priming, seed deterioration, germination rate     

Relationship Between Lateral Root Primordia in Different Ranks

Comparisons with theoretical random distributions indicate thatthe longitudinal positional relationships between lateral rootsin different ranks are random in roots of Musa acuminata, Pistiastratiotes and i, species in which lateral root primordia arisein the root tip. In Potentilla palustris, where lateral rootprimordia arise further back in the root, there is a deficiencyof close spacings, which indicates that there is some interactionbetween ranks. Musa acuminata, Pistia stratiotes, Pontederia cordat, Potentilla palustris, roots, lateral roots, pattern     

QTLs for nitrate induced elongation and initiation of lateral roots in rice (Oryza sativa L.)

To investigate the genetic background of nitrate-induced elongation and initiation of lateral roots in rice (Oryza sativa L.), a doubled haploid (DH) population, derived from a cross between IR64 and Azucena, which showed different responses to local supplied NO₃ ^– in lateral root elongation and initiation, was used in an agar culture experiment with three separated layers. The second agar layer was supplied with 3 mM NO₃ ^– or without NO₃ ^– as two treatments. Average lateral root length, lateral root number and surface area of lateral roots in the second agar layers with and without nitrate, respectively, were measured. The ratio of the parameters from the two treatments were calculated as derived parameters. Seven putative Quantitative trait loci (QTLs) for the 6 lateral root traits in nitrate-deficient and nitrate-supplied layers were detected. These QTLs individually explained about 9% to 15% of the total phenotypic variations in the traits. Identical QTLs for root traits from other reports with QTLs detected in this case were found, which suggests that the genetic factors responsive to local supplied NO₃ ^– is involved in root growth and development     

Effects of fluridone and abscisic acid on lateral root initiation and root elongation of excised tomato roots cultured in vitro

Roots of tomato (Lycopersicon esculentum Mill. cv. Bonny Best) were excised and cultured in the presence of the abscisic acid synthesis inhibitor fluridone, and with concentrations of exogenous abscisic acid ranging from 10⁻¹⁰to 10⁻⁴M to determine the effects of abscisic acid and its synthesis inhibition on the development of lateral roots in in vitro cultured tomato roots. Exogenous abscisic acid inhibited lateral root initiation and emergence at concentrations of 10⁻⁶M and greater. Fluridone (10⁻⁶M) enhanced the formation of lateral roots even in the presence of abscisic acid, at all concentrations tested except 10⁻⁴M. Abscisic acid increased apical distance, and fluridone reduced it up to 10⁻⁵M abscisic acid. Both fluridone and abscisic acid reduced lateral and primary root lengths. It was concluded the endogenous abscisic acid is probably involved in the regulation of lateral root initiation and root apical dominance, and that abscisic acid may affect lateral root initiation differently than lateral root emergence. This revised version was published online in June 2006 with corrections to the Cover Date.     

Some Effects of Indol-3-yl Acetic Acid on Lateral Root Development in Attached and Excised Roots of Pisum sativum L.

The effect of continuous exposure to indol-3-yl acetic acid(IAA) on primordium initiation and their subsequent emergenceas lateral roots was determined in excised and attached rootsof Pisum sativum. IAA was found to stimulate the number of primordiainitiated per centimetre of attached or excised primary. Similarly,lateral emergence in terms of the number produced per centimetreof primary was promoted in the presence of IAA. This stimulationof lateral emergence even took place in excised roots whichwere 1 cm in length at the onset of culture and which neverproduced secondary roots over a 6-d culture period when grownin the absence of auxin. These effects of IAA on lateral rootdevelopment have been considered in relation to the concurrentchanges which take place in proliferative activity in the apicalmeristem of the primary root during exposure to auxin. Pisum sativum, garden pea, anlage, primordium, emerged lateral, cell proliferation, indol-3-yl acetic acid