Mária Luxová

The extent and differences in mitotic activity of the root tip ofVicia faba L.

Mitotic activity does not stop for different meristematic cells of the root apex at the same distance from the initials. The differences are connected with the functional heterogeneity of the apical meristem of the root. The arrangement of vascular bundles,i.e. the alternation of independent xylem and phloem groups, is of major importance. In broad bean roots, the protophloem sieve elements stop dividing first. The centre of the stelei. e. late metaxylem elements stop dividing next. Division in the stele gradually ceases centrifugally, while it ceases centripetally in the peripheral part of the root. The cylindrical region with prolonged cell division includes internal layers of the cortex including endodermis, pericycle and adjoining cells of the stele. Proximally apical meristem is reduced to isolated strands of cells adjacent to the protoxylem poles. Pericycle cells stop dividing last at a distance of approx. 9–10 mm from the initials.The number of the division cycles is limited and is specific for individual cell types. Epidermal and cortical cells divide in broad bean roots transversely approximately seven times, cells of late metaxylem approximately five times.Root apical meristem is an asynchronous cell population with a different duration of the mitotic cycle. We determined local variations in the duration of the mitotic cycle in the apical meristem of broad bean root by means of colchicine-induced polyploidy. The cells of the quiescent centre had the longest mitotic cycle after colchicine treatment. The region of the proper root adjacent to the quiescent centre was mixoploid (2n and 4n). Isolated cells with a long cycle occurred also in the cortex and in the central cylinder. Cells with a division cycle of 18h were found in the root cap, in the epidermis, in the cortex and in the central cylinder. Relatively numerous cells with the shortest division cycle, approx. 12 h, occurred farther of the quiescent centre in the epidermis, in the cortex, in the pericycle, and in adjacent layers of the stele through-out the entire meristematic region.The results derived from the analysis of the apical meristem are discussed in connection with the ontogenesis of different types of cells taking part in the primary structure of the root.

The seminal root primordia in barley and the participation of their non-meristematic cells in root construction

In addition to the primary seminal primordium, the so-called secondary seminal root primordia are also initiated in a barley embryo. The primary root primordium is developmentally most advanced. It is formed by root meristem covered with the root cap, and by a histologically determined region with completed cell division. On germination, the restoration of growth processes begins in this non-meristematic region of root primordium by cell elongation, with the exception of the zone adjacent to the scutellar node, the cells of which do not elongate but continue differentiating. In the root primordia initiated later, the zone with completed cell division is relatively shorter, in the youngest primordia the non-meristematic cells may be lacking. The root meristem is reactivated after the primary root primordium has broken through the sheath-like coleorrhiza and emerges from the caryopsis as the primary root. The character of root meristem indicates a reduced water content at the embryonic development of root primordium. With progressing growth the root apex becomes thinner, the meristematic region becomes longer, and the differences in the extent of cell division between individual cell types increase. — The primary root base is formed of cells pre-existing in the seminal root primordium. Upon desiccation of caryopsis in maturation, and subsequent quiescent period, their development was temporarily broken, proceeding with the onset of germination. The length of this postembryonically non-dividing basal zone is different in individual cell types. The column of central metaxylem characteristic of the smallest number of cell cycles, has, under the given conditions, a mean length of about 22 mm, whereas the pericycle, as the tissue with most prolonged cell division, has a mean length of about 6 mm. In the seminal root primordia initiated later the non-dividing areas are relatively shorter. The basal region of seminal roots thus differs in its ontogenesis from the increase which is formed “de novo” by the action of root meristem upon seed germination.

The effect of polyethylene glycol-induced water stress on the maize root apex

Following a 24-h exposure to a solution of polyethylene glycol 4 000 of a —12.66 bar osmotic potential the roots of maize ceased growing. The inhibition of growth was conditioned by the inhibition of cell elongation and division. The elongation of cells was substituted by their radial enlargement which took place both in the peripheral and central root parts. The cells either did not divide at all, or sporadic mitoses still occurred in the roots. The meristematic cells treated were highly vacuolized, chromatin condensation being observed in their nuclei. In contrast to growth processes, differentiation was stimulated: the formation of the secondary wall in protoxylem elements occurred at a shorter distance,i.e. 1 500–2 400 µm from the apex, in comparison with 4000–5 000 µm in the control, this evidently being caused not only by the inhibition of growth, but also by the capacity of cells to differentiate more rapidly. The changes induced by a 24-h exposure to water stress were of a reversible nature; however, a 48-h treatment brought about irreversible changes.

The vascular system in the roots of barley and its hydraulic aspects

Comparatively few data are available about the hydraulic architecture of roots compared with the above-ground organs. The results presented in the literature were mostly obtained by an analysis of root secondary xylem. The roots possess the widest vessels; as distinct from stems, the diameter of vessels in the secondary root xylem usually increases in an acropetal direction (Fayle, 1968; Lebedenko, 1962; Riedl, 1937). The present paper deals with proximal-distal changes of the vascular pattern in barley roots and their hydraulic consequences.

The course of root differentiation from root primordia in poplar stems

Upon rooting of poplar stem cuttiags the total inductive stimulation does not take place, but the individual root primordia maintain a relative independence. This becomes evident by various time parameters of their differentiation. Under experimental conditions, in dormant cuttings from one year individuals of the hybrid I 214 the activation of the first root primordia occurs after 24 h, the pre-emergent development of the roots formed was completed after 72 h.The activated root primordium is divided into two regions. In the distal region with the predominating cell division the root apex with histogens is formed by the action of initials. From peripheral cell layers of the distal region the so-called “Wurzeltasche” develops which covers the root cap. Due to cell elongation in the proximal region the root apex is pushed up towards the stem surface. The beginning differentiation of the connective vascular tissue is a preparative step for the connection of the vascular system of the developing root with the secondary vascular system of the maternal stem. Following the penetration of the root through the peripheral stem tissues this connection is realized with progressing development. In the developed root the protoxylem elements differentiate continuously and acropetally in direct continuity with tracheids of the basal connective region.

Growth region of the primary root of maize (Zea mays L.)

The root of maize has been used by many research workers as an object for studies of the structure and morphogenesis, of physiology and biochemistry of its functions as well as of the problems of uptake and transport. This cooperation directed at a single object causes a faster advance and, at the same time, provides a source of mutual confrontation and supplementation of knowledge. This paper presents the results of the growth analyses of the maize root (hybrid CE 380), summarized [3,4] and completed with the aim of characterizing the growth region of the root growing under defined conditions. The seeds were allowed to germinate in darkness at 25 °C on sheets of moist filter paper in a vertical position. Primary roots that had grown 60 ± 5 mm within 72h were used for analysis.

Latent root primordia in poplar stems

Root primordia initiate in poplar stems in the secondary growing parts, that is in the parts where the elongation growth is terminated and the leaves are mature. Their initiation is connected with the occurrence of unusual biseriate, rarely multiseriate rays. A small cell group in the secondary phloem is initiated by cell division of the ray. It gradually enlarges by continuing cell division, by the addition of cells adjacent to the cell group and by cambial activity. Thus, a hemispherical root primordium is formed, for which a permanent occurrence of reserve lipids is characteristic. In stems several years old the intraprimordial mitotic activity is rhythmically renewed together with the cambium function renewal. Latent root primordia slightly enlarge with the passing years, whereas mainly the cells localized in their centre divide. Further organization and root histogenesis was not observed either in older root primordia. Adjacent to root primordia, cambial initials produce the secondary xylem elements increasingly. Xylem protuberances are thus formed under root primordia. Primordia initiation is most frequent within the first year of stem development, though they can also initiate in later years.

Secondary dilatation growth in the root endodermis

Early secondary growth of roots with persisting cortex is the result of two different growth processes: Cambial growth and dilatation growth. Vascular cambium forms the secondary vascular tissues of the thickening vascular cylinder. At the same time, reactivated, peripherally situated cortex is adequately expanding by the dilatation growth. Dilatation growth of the cortex starts in the endodermis, i.e. the youngest innermost cortical layer. In relation with the species specificity concerning the developmental type of endodermis (species with maturation of endodermis in the state 1, II or III), the dilatation growth of endodermis starts in the state I or III. Secondary dilatation activity of the endodermis is manifested by tangential expansion of endodermal cells, by their renewed division, or by the combination of both processes. The additional anticlinal divisions increase the number of circumferential endodermal cells. In some species, the newly-formed radial walls acquire typical endodermal character by the formation of Casparian bands or even by further deposition of suberin lamellae. In other species, additive radial walls remain unmodified. The use of fluorescence staining techniques allows to characterise chemical properties of additional radial endodermal walls, which do not always coincide with the older reports. The density of endodermal network is changed by the dilatation growth: By cell expansion and by the formation of unmodified additional cell walls it is decreased, while the increased number of modified radial cell walls results in the higher density. The described changes of endodermal network, constituting the apoplastic barrier can have a role as a regulating factor.

Fertilization of Barley (Hordeutn distichutn L.)

Fertilization of barley has been studied and photographically recorded. The pollen grain germinates almost immediately after attaching itself to the stigma, pollen tube reaches the embryo sac after 20–30 minutes (temperature 26°C). One of the sperms permeates immediately to the oosphere, the other joins polar nuclei migrating from the oosphere to antipodal cells after the discharge of pollen tube content. Fertilization of the polar nucleus occurs in most cases at the antipodal cells which have pronounced haustorial character.In triple fusion polar nuclei do not usually fuse prior to fertilization. However, some exceptions were noted: sometimes the fertilization takes place after the fusion of polar nuclei or during the fusion. Being slower, pre-mitotic fertilization of the egg cell could be studied in greater detail.AbstractPredmetom práce je opis a fotografická dokumentácia oplodnenia u jačmeňa. Pel′ové zrno vykliči temer bezprostredne po uchytení na bliznu, pel′ové vrecúško dosiahne zárodočny miešok po 20–30 minútach (pozorované pri teplote 26 C). Zatial′ čo jedna z uvol′nenýchspermií prenikne ihned do oosféry, druhá nasleduje polárne jadrá, ktoré sa po vypustení obsahu pel′ového vre-cúska presúvajú od oosféry k antipódam. K oplodneniu polárneho jadra dochádza vo väčšine prípadov až pod antipódami, ktoré majú vyrazne haustoriálny charakter. Uvedený jav pósobí dojmom, akoby išlo o sprostredkovanie presumí druhej spermie do blízkosti antipód ako oblasti, vhodnej pre oplodnenie. Pri trojitom splývaní boli pozorované i výnimočné prípady: polárne jadrá pred oplodnením pravidelne nesplývajú; v niektorych. prípadoch došlo výak k oplodneniu až po fúzii polárnych jadier, prípadne sa oplodnenie uskutočnilo pri ich splyvaní. Podrobnosti premitotického oplodnenia bolo možné pozorovat detailnejšie u vajcovej bunky, pretože tu prebiehalo oplodnenie pomalšie.Abstractусловия для оплодотворения. При тройном слиянии ядер наблюдались также необычные случаи: полярные ядра перед оплодотворением обычно не сливаются, но в некоторыє случаяє, однако, оплодотворение произошло после иє слияния или во время иє слияния. Детали премитотического оплодотворения наблюдались лучше на яйцеклетке, так как ее оплодотворение происєодит медленнее.

Specific conductivity of conducting and non-conducting tissues ofZea mays root

The structure of the maize root enables one to determine the experimental specific conductivity of conducting and non-conducting tissues for the longitudinal water transfer. Using the method of Farmer and Berger in Huber and Schmidts modification, successive differences in orders of magnitude were revealed among the experimental specific conductivities of the tissues of pith, cortex, and those of the area with concentrated xylem. The highest values of specific conductivity (cm3 cm−2 h−1 at 400 mbar per 5 mm distance, at 20° C) were determined in the area with concentrated xylem (mean value 10 018 cm3 cm−2 h−1); in the cortex area values by one order of magnitude lower were obtained (mean value 1 206 cm3 cm−2 h−1); in the pith area by two orders of magnitude lower (mean value 167 cm3 cm−2 h−1). The tissues of the area with concentrated xylem participated in the experimental root conductivity by 72 per cent, cortex tissues by 27 and pith tissues by one per cent. In this paper the individual tissues of maize root are characterized in detail from the anatomical viewpoint and the possible causes of the differences are discussed.AbstractKoreň kukurice umožňuje svojou stavbou stanovenie experimentálnej špecifickej vodivosti vodivých a nevodivých pletív pre pozdĺžny tok vody. Huberom a Schmidtom modifikovanou metódou Farmera a Bergera sa zistilo, že medzi experimentálnou špecifickou vodivosťou pletív stržňa, kôry a oblasti s koncentrovaným xylémom existuje postupný rádový rozdieĺ. Najvyššie hodnoty špecifickej vodivosti (cm3 cm−2 h−1 pri 400 mbar na vzdialenosť 5 mm pri 20° C) sa stanovili v oblasti s koncentrovaným xylémom (priemerná hodnota 10 018 cm3 cm−2 h−1); pre oblasť kôry sa stanovili hodnoty rádove jedenkrát nižšie (priemerná hodnota 1 206 cm3 cm−2 h−1); pre oblasť stržňa rádove dvakrát nižšie (priemerná hodnota 167 cm3 cm−2 h−1). Pletivá oblasti s koncentrovaným xylémom participovali na experimentálnej vodivosti koreňa 72, pletivá kôry 27 a pletivá stržňa 1 percentom. V práci sa podrobne charakterizujú jednotlivé pletivá koreňa kukurice z hĺadiska anatomického. Uvažujú sa zistené a predpokladané príčiny rozdielnej experimentálnej špecifickej vodivosti.