Distribution of Lateral Root Primordia in Root Tips of Musa acuminata Colla

The distribution of lateral root primordia in Musa acuminatashows discrete elements of pattern, a major element of whichis the rather regular spacing of laterals along protoxylem-basedranks. There is some co-ordination of positions of lateralsin different ranks. Laterals are apparently not initiated ina single acropetal sequence within the root tip as a whole althoughthey are initiated in acropetal sequence within each rank. Musa acuminata, banana, roots, lateral roots     

Patterns of Distribution of Lateral Root Primordia

The distribution of lateral root primordia has been examinedin Pistia stratiotes and Potentilla palustris, and re-examinedin Pontederia cordata. The major feature of the distributionpattern is a rather regular spacing along protoxylem-based ranks.There appears to be some correlation of activity between ranks,but simulations of patterns based on the data from Pontederiasuggest that the observed correlation is spurious. Pistia stratiotes, Pontederia cordata, Potentilla palustris, roots, lateral roots, pattern     

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     

Chimeras and the Origin of Lateral Root Primordia in Zea mays

The difficulty of determining the contribution made by the pericycleand endodermis of mother roots to lateral primordia in the Gramineaehas been solved by inducing polyploid chimeras at initiation. The endodermis forms a layer covering the primordium, but thislayer does not form the epidermis of the lateral. It does formthe root cap of the young primordium, but this is replaced ata variable stage of development by the quiescent centre donatinga new set of cap initials of pericyclic origin. Reasons forthe previous diversity of interpretations are presented. chimera, lateral root primordia, Zea mays     

Cell Death in Cells Overlying Lateral Root Primordia Facilitates Organ Growth in Arabidopsis

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The Development of Lateral Root Primordia in Vicia faba L. and Their Response to Colchicine

Lateral root primordia in i are first initiated 2–3 daysfollowing the onset of germination, after which they take 5.17–6.35days to complete their development and emerge as lateral roots.Variation in the amount of time elapsing between primordiuminitiation and emergence as a lateral is probably a reflectionof the cell number attained by any one primordium at the timeof emergence. The number of primordia produced per cm of primaryroot growth (5.35–6.65) was not affected by variationin the rate of root elongation, although the number of primordiaproduced each day increased with increase in the rate of rootgrowth. In colchicine-treated roots, the amount of time between primordiuminitiation in the C-tumour and the subsequent emergence of alateral (5.43–6.43 days) was similar to the value obtainedin control roots. Primordia which were present at the time ofcolchicine treatment responded to treatment in a number of differentways, depending on the stage of development reached. Primordiain the first 2.66 days of their development die following treatment;those between 2.66 and 3.69 days old have their developmentinhibited but stay alive; primordia which have been developingfor 3.69–4.91 days following initiation grow out as straightlaterals, while those between 4.91 and 5.77 days old form C-tumoursand emerge as inhibited laterals.     

Cell Population Studies in Developing Root Primordia

The proliferation of polyploid and diploid cells was followedduring the development of lateral root primordia of Vicia faba.Presumptive primordial cells were treated with weak solutionsof colchicine, 0.003, 0.006, and 0.0125 per cent, for 3 h. Somecells are induced to become polyploid and they form a markedsub-population. The relative frequencies of diploid and polyploidcells were determined from the time small primordia were presenttill lateral roots were fully emerged. These frequencies havebeen found to change in a regular fashion and the changes reflectdifferent levels of mitotic activity in different parts of aprimordia as it develops. Polyploid cells occupy the centralcore of the primordia and they divide actively except for theperiod just before lateral root emergence. Coincident with thistemporary quiescence of the core cells, the peripheral cells,which remain diploid after treatment with the weaker solutionsof colchicine, continue to divide. These changes in mitoticactivity of the central and peripheral cells are shown bothin the changes in the relative frequencies of polyploid anddiploid mitoses as a primordium grows and in changes in mitoticindex. A microspectrophotometric study indicates that the centralcells are held, temporarily in the G₁ phase of the cell cycle.     

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     

Reserve Lipids in Stem Root Primordia of Poplar

Lipids are reserve substances in stem root primordia of poplarand occur as droplets approximately uniformly in all cells ofroot primordia. In ultrathin sections they appear as sphericalelectron-dense particles (0.5–1.4 µm diameter),filling up virtually all the available space in the cytoplasm.The presence of lipids in stem root primordia was demonstratedin several species of the genus Populus from the section Aigeirosand Tacamahaca, as well as in another representative of thefamily Salicaceae, viz. in the genus Salix.     

水杨酸对莴苣初生根侧根原基的形成和根内激素含量的影响

10-6mol·L-1的水杨酸(SA)处理莴苣幼苗初生根36h,可促进侧根原基形成,与生长素配合处理,则有加合效应。     

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     

Development of Lateral Primordia in Decapitated Adventitious Roots of Allium cepa

In decapitated adventitious roots of Allium cepa L. var. French,the time taken for lateral primordia to appear in five sectorshas been studied. This time is approx. 4–5 d after theapex of the adventitious root gave rise to the primordial initialcells. Allium cepa, adventitious root, lateral primordia     

Cytokinin Inhibits Lateral Root Development at the Earliest Stages of Lateral Root Primordium Initiation in Maize Primary Root

Root architecture is basically controlled by auxin and cytokinin, which antagonize in the formation of lateral roots (LRs) along the primary root (PR) axis. Several mechanisms have been proposed to explain the interaction between these two hormones, cytokinin being the hormone that inhibits LR formation. The analysis of the cytokinin effect on LR formation using LRs in several stages of development could indicate which steps of LR formation are more sensitive to cytokinin. The application of cytokinin to maize PRs showed that the inhibitory effect of cytokinin on LR formation was greater in the zones in which the initial events to form new LRs are taking place. In the presence of cytokinin, the PR is not able to produce new LRs in the initiation zone; this inhibitory effect is permanent as this zone did not recover the capability to form LRs after removing cytokinin. However, the LR density in zones with appreciable LR primordia when cytokinin was applied was only slightly inhibited when a high concentration was used. These results showed that LR formation is more sensitive to the inhibitory effect of cytokinin in the earliest stages of LR development. However, the elongation of a LR primordium to emerge and the subsequent elongation of the new LR were only slightly affected by cytokinin.

     

Tritiated-thymidine Labelled Nuclei in Primordia and Newly-emerged Lateral Roots of Vicia faba L.

The utilization of ³H-TdR in DNA synthesis and the distributionof labelled nuclei have been determined in large primordia (LP)and newly emerged lateral roots (JE) of Vicia faba followingdifferent exposure periods. This nucleoside appears to reachLP and the more basal, unemerged parts of JE by way of the vasculartissue of the primary root, while those parts of JE which projectout from the epidermis of the primary obtain ³H-TdR directlyfrom the surrounding medium. The utilization of ³H-TdR in thesynthesis of DNA in basal segments of JE is also complicatedby the temporary quiescence of nuclei in this part of thesemeristems as LP elongate to form lateral roots.     

Development of Lateral Root Primordia in Vicia faba, Pisum sativum, Zea mays andPhaseolus vulgaris: Rates of Primordium Formation and Cell Doubling Times

Lateral root primordium development has been examined in primaryroots of Vicia faba L., Pisum sativum L., Zea mays L. and Phaseolusvulgaris L. Following their initiation from an estimated minimumnumber of 77–162, 20–57, 17 and 12 cells respectivelyin Vicia, Phaseolus, Pisum and Zea, the primordia rapidly increasedin cell number to emerge as secondary roots about 2.8–3.6days later depending on the species being examined. Cell doublingtimes were estimated directly from cell numbers at differenttimes following primordium inception and were found to increasewith increase in primordium size in each of the species investigated. The number of primordia formed per cm of root growth per daywas greatest in Zea and least in Pisum. A comparison of thedata obtained for Vicia with that in the literature led to theconclusion that although the number of primordia produced percm of root growth was independent of the rate of primary elongation,the number produced per day increased in a linear fashion withincrease in the rate at which the primary lengthened. Vicia faba L, Pisum sativum L, Zea mays L, Phaseolus vulgaris L, broad bean, garden pea, maize, dwarf bean, root primordia, cell division, cell doubling time     

Hemoglobin and Hypoxic Acclimation in Maize Root Tips

Class 1 hemoglobins (Hbs) have a wide distribution in the plant kingdom and have been demonstrated in root, seed, stem, and leaf tissues. They are present at low concentrations in aerobic tissue, but their synthesis is rapidly induced by hypoxic stress. The pattern of expression of the maize Hb gene in roots of young maize plants exposed to hypoxia has been examined. Root Hb gene expression increased rapidly to a maximum within first two hours of hypoxia, then declining to prehypoxia levels within 48-h hypoxic exposure. Limiting oxygen supply to the roots by total plant immersion and darkness did not alter the time course of hemoglobin expression. Hb gene expression was about 20-fold higher in the stele than in the cortex of control, aerobically grown roots. Stele Hb expression increased about fourfold under hypoxic conditions, whereas its expression in the cortex increased about 60-fold. In these samples, alcohol dehydrogenase (Adh) gene expression increased about four- and ten fold in the stele and cortex, respectively. The effect of the state of the Hb on anoxic survival of maize root tips was assessed by exposing root tips to a carbon monoxide atmosphere to maximize the proportion of hemoglobin in the carbonmonoxy form. Carbon monoxide had no significant effect on the survival or the ATP levels in anoxic maize roots, regardless of whether they had been acclimated by exposure to a hypoxic pretreatment. This would suggest that the presence of oxyhemoglobin is not essential for the survival of anoxic root tips.