Studies on graft unions

Summary De novo formation of cytoplasmic cell connections are studied at the graft interface of 5 day old in vitro heterografts ofVicia faba onHelianthus annuus. Continuous and half plasmodesmata, both branched and unbranched, are described at various stages of development in non-division walls between unlike and like dedifferentiated callus cells. In apical portions of protruding callus cells and in the contact zone between opposing cells extremely thin wall parts with a striking ER/plasmalemma contact are observed. During subsequent thickening of the modified wall parts cytoplasmic strands enclosing constricted ER cisternae are entrapped within the newly deposited wall material. These cytoplasmic strands represent half plasmodesmata which—in case of fusion with corresponding structures of adjoining cells across the loosened wall matrix — form continuous cell connections. Golgi vesicles secreting wall material are involved in the process of forming half and continuous plasmodesmata, thus following the same mechanism of plasmodesmata development as described for isolated protoplasts in cell cultures. The findings suggest the existence of a unifying mechanism of secondary formation of plasmodesmata showing far-reaching similarities with the establishment of primary cell connections.     

Studies on graft unions. I. Plasmodesmata between cells of plants belonging to different unrelated taxa

Summary In order to answer the question whether plasmodesmata exist between the cells of stock and scion in a graft union of higher plants, a heteroplastic graft has been selected with species-specific cell markers.Vicia faba was used as scion andHelianthus annuus as stock. In the mixed callus of the graft union, individual cells of the two partners differ in the structure of the nuclei, plastids and microbodies. In the fused cell walls betweenVicia andHelianthus cells, plasmodesmata interconnect the protoplasts of the unrelated cells. Two types of plasmodesma occur: single strands and branched connections. The fine structure of the interspecific cell bridges, which have been secondarily formed in non-division walls, is similar to that of normal plasmodesmata in division walls. Some questions concerning compatibility/incompatibility in the heterograft are discussed.     

Directional cell-to-cell communication in theArabidopsis root apical meristem II. Dynamics of plasmodesmatal formation

Summary Cell development in the root apical meristem is thought to be regulated by position-dependent information, but as yet, the underlying mechanism for this remains unknown. In order to examine the potential involvement of the symplasmic transmission of positional signals, plasmodesmatal frequency and distribution was quantitatively analyzed in root apical meristem cell walls ofArabidopsis thaliana during root development. A consistent distribution pattern of plasmodesmata was observed in the root apex over four weeks. While cells within initial tiers were uniformly interconnected, more symplasmic connections between the initial tiers and their immature-cell (primary-meristem) derivatives were observed than within the initial tiers. Immature cells were connected across transverse walls by primary plasmodesmata according to a tissue-specific pattern. Cells of the immature vascular tissue and cortex had the highest plasmodesmatal frequencies, followed by the immature epidermis and root cap. Although the numbers of plasmodesmata in transverse walls (primary plasmodesmata) was reduced in all tissues as the root aged, the tissue-specific distribution remained constant. The extent of symplasmic coupling across the boundaries of each tissue appeared to be limited by fewer secondary plasmodesmata in longitudinal walls. The frequency of all plasmodesmata decreased as the root aged. The primary plasmodesmata within each tissue increased at one week and then dramatically decreased with root age; the frequency of secondary plasmodesmata in longitudinal walls also decreased, but more gradually. These findings are discussed with respect to the roles likely played by plasmodesmata in facilitating transport of position-dependent information during root development.     

A Study of the graft union in in vitro micrografted apple

Light microscopy was used to study graft union formation in in vitro micrografts of tissue cultured apple (Malus domestica. Borkh). Micrografts were constructed using horizontal incisions to form the grafting surface, and placing the cut ends of rootstock and scion into sterile silicon tubing to permit graft formation to occur.The outer morphological and histological development was similar for different stock-scion micrograft combinations but graft union formation was slower in heterografts than in autografts. Initial leaf expansion at the scion shoot apex occurred in all micrografted plantlets within 1–4 days and was not indicative of graft success. Progressive scion growth and development could be used as an indication of graft success by ten to fourteen days after grafting and probably was related to establisment of cell to cell contact at the graft interface. Microscopy showed initiation of callus proliferation in the vascular cumbium and the pith ten days after grafting. Differentiation was observed subsequently and this was reflected in scion development. Longitudinally orientated cambial cells began to differentiate between twenty and forty days after grafting, and formed a bridge between the vascular cylinders of scion and rootstock. The scions at this stage had as many as eight newly expanded leaves and micrografts were strong enough to permit silicon sleeve removal without damage. Continuity of new vascular elements in rootstock and scion was established around forty days. New vascular elements curved slightly in towards the pith to form a c shaped bridge across the graft union. Vascular development continued until it reached completion after six months.     

八角莲组织培养的器官发生途径研究

为探究小檗科植物八角莲组织培养的器官发生方式,该研究以八角莲离体叶片、叶柄在MS培养基上诱导产生的愈伤组织、不定芽、不定根为对象,用连续石蜡切片技术分析八角莲组织培养的器官发生途径。结果表明:八角莲愈伤组织形成的解剖学特征是靠近表皮的薄壁细胞经激素刺激恢复分裂能力,继续培养形成拟分生组织。拟分生组织可形成许多分化中心。通过对八角莲组织培养产生的不定芽细胞组织学观察发现芽原基起源于愈伤组织外侧的几层薄壁细胞,芽原基背离愈伤组织中央生长形成不定芽,故八角莲脱分化形成的芽起源方式为外起源。而八角莲的根原基起源于组织深处髓部薄壁细胞和部分维管形成层细胞,进而形成类似球形或楔形并朝韧皮部突起的根原基轮廓,根原基继续发育会突破表皮生成不定根,起源方式为内起源。八角莲离体再生途径为器官发生型,在组培苗生长过程中先诱导形成不定芽,再诱导形成不定根,在愈伤组织上形成维管组织将不定芽和不定根连接成完整植株。     

The formation of symplasmic domains by plugging of plasmodesmata: a general event in plant morphogenesis?

Summary The plasmodesmal network was examined in multicellular protoplast-derived calluses of the dicotyledonSolanum nigrum which had not yet formed any visible adventitious organs and in globular proembryogenic structures developed from scutellar calluses of the monocotyledonMolinia caerulea. Electron microscopical analyses revealed that both calluses and proembryos consisted of small, undifferentiated cells. The interconnecting plasmodesmata at many cell interfaces were structurally inconspicuous in both systems; in particular cell walls, however, all plasmodesmata were occluded with an osmiophilic, dense material. As the blocking material was obviously located in the microchannels of the plasmodesmal cytoplasmic sleeves, the plugged plasmodesmata can be assumed to be nonfunctional. Thus, selective occlusion of all the plasmodesmata in specific cell walls resulted in the symplasmic disconnection of particular adjacent cells. Complex patterns of symplasmic continuity and discontinuity were established within the developing tissues. Some cells or groups of cells were entirely symplasmically disconnected from the surrounding cells by plugged plasmodesmata and might function as independent domains. However, blockage of plasmodesmata was achieved by the surrounding cells rather than by those cells belonging to the isolated domains. The demarcation of symplasmic domains might be a general prerequisite for differential morphogenesis, since they were found to be established very early in the course of morphogenetic processes.     

Distribution and structure of the plasmodesmata in mesophyll and bundle-sheath cells of Zea mays L.

In leaf blades of Zea mays L. plasmodesmata between mesophyll cells are aggregated in numerous thickened portions of the walls. The plasmodesmata are unbranched and all are characterized by the presence of electron-dense structures, called sphincters by us, near both ends of the plasmodesmatal canal. The sphincters surround the desmotubule and occlude the cytoplasmic annulus where they occur. Plasmodesmata between mesophyll and bundle-sheath cells are aggregated in primary pit-fields and are constricted by a wide suberin lamella on the sheath-cell side of the wall. Each plasmodesma contains a sphincter on the mesophyll-cell side of the wall. The outer tangential and radial walls of the sheath cells exhibit a continuous suberin lamella. However, on the inner tangential wall only the sites of plasmodesmatal aggregates are consistently suberized. Apparently the movement of photosynthetic intermediates between mesophyll and sheath cells is restricted largely or entirely to the plasmodesmata (symplastic pathway) and transpirational water movement to the cell walls (apoplastic pathway).Abbreviation ER endoplasmic reticulum     

菰适应湿地环境的解剖和屏障结构特征研究

菰(Zizania latifolia)是一种多年生挺水植物,为了探讨该植物根、茎和叶的解剖结构、组织化学及其质外体屏障的通透性生理。该文利用光学显微镜和荧光显微镜,对菰的根、茎、叶进行了解剖学和组织化学研究。结果表明:(1)菰不定根解剖结构由外而内分别为表皮、外皮层、单层细胞的厚壁机械组织层、皮层、内皮层和维管柱;茎结构由外而内分别为角质层、表皮、周缘厚壁机械组织层、皮层、具维管束的厚壁组织层和髓腔。叶鞘具有表皮和具维管束皮层,叶片具有表皮,叶肉和维管束。(2)不定根具有位于内侧的内皮层及其邻近栓质化细胞和外侧的外皮层组成的屏障结构;茎具内侧厚壁机械组织层,外侧的角质层和周缘厚壁机械组织层组成的屏障结构,屏障结构的细胞壁具凯氏带、木栓质和木质素沉积的组织化学特点,叶表面具有角质层。(3)菰通气组织包括根中通气组织,茎、叶皮层的通气组织和髓腔。(4)菰的屏障结构和解剖结构是其适应湿地环境的重要特征,但其茎周缘厚壁层和厚壁组织层较薄。由此推测,菰适应湿地环境,但在旱生环境中分布有一定的局限性。     

侧柏扦插不定根发生模式研究

该研究以侧柏一年生硬枝插穗为实验材料,利用连续组织切片技术观察插穗不定根发生发育过程中的组织结构变化,分析插穗外部形态变化、不定根原基起源和不定根的形成过程,探讨侧柏插穗不定根发生模式和不定根的组织学起源。结果显示:侧柏扦插后可由愈伤组织、皮部诱导产生不定根,出现皮部生根、愈伤组织生根、愈伤组织兼具皮部生根3种类型;侧柏插穗中存在少量潜伏根原基,但插穗生根类型以诱导生根为主;不定根原基诱导产生于愈伤组织、木质部、形成层及次生韧皮部等部位。研究认为侧柏扦插生根属于多位点发生模式,不定根原基的组织学起源是愈伤组织、髓射线、射线原始细胞、尚未分化成熟的木质部细胞,通过人工诱导同时激活这些不定根起源位点能够显著提高生根率和生根质量。     

Formation of branched plasmodesmata in regenerating Solanum nigrum-protoplasts

During the early stages of culture, discontinuous branched half-plasmodesmata were found randomly scattered in the newly formed outer cell walls of regenerating Solanum nigrum L. protoplasts. During later culture stages, most of these outer-wall plasmodesmata, which had been exposed to the culture medium, disappeared, except for those near the periphery of division walls between daughter cells and those near non-division walls between secondarily associated unrelated cells. Moreover, in the peripheral parts of older division walls, there were continuous branched plasmodesmata which showed the typical morphological characteristics of secondary cell connections: several cytoplasmic strands joined in the median plane of the cell wall and were often linked by so-called median cavities. Evidence is presented that this type of continuous plasmodesma originates from the fusion of the half-plasmodesmata which persisted in the outer walls adjacent to the division wall. Due to growth of the cells after division, opposite parts of the outer walls of the daughter cells come into close contact and fuse, elongating the original division wall peripherally. Opposite half-plasmodesmata remaining in these parts of the outer wall may thereby also be brought into contact and fuse to form a continuous secondary cell connection in the secondarily coalesced wall part. Our assumption is supported by further experiments: (i) longterm video observations of living cells showed differences in the development of the shapes of regenerating cells and (ii) electron-microscopical investigations showed differences in the frequency of the, presumably secondary, cell connections in the peripheral parts of the division walls — both related to the firmness of the embedding medium. In the central parts of division walls, unbranched primary cell connections were found as well as a second type of continuous branched plasmodesma showing an entirely different branching pattern: the region of the middle lamella was always traversed by straight, unbranched parts of these plasmodesmata and the branches occurred exclusively within the younger wall layers. Evidence is given that these branches are modifications of originally unbranched primary plasmodesmata, developing during subsequent thickening of the division wall.The authors are indebted to Prof. H. Binding, Botanisches Institut, Universität Kiel, for making his cell-culture laboratory available to us and to Dr. F. Grundler, Institut für Phytopathologie, Universität Kiel, for placing the video equipment at our disposal. The work was supported by the Deutsche Forschungsgemeinschaft.     

Fine structure,distribution and frequency of plasmodesmata and pits in the cortex ofLaminaria hyperborea andL. saccharina

Prior to a long-distance transport of photoassimilate in the sieve elements ofLaminaria, a parenchyma transport across the cortex must occur. It is suggested that this transport is a symplastic one. The structural basis for this statement, continuous cytoplasmic interconnections of cells along the transport pathway, is demonstrated here forL. hyperborea andL. saccharina. The distribution, size, and frequency of pit fields in cell walls of all planes were determined. The data suggest that the conductivity for assimilate transport in the cortex is highest in the long axis of the thallus, not radially across the cortex. The fine structure, arrangement and number of plasmodesmata in pit fields were studied. The estimated flux rates and the anatomical findings clearly point to a symplastic parechyma transport of photoassimilate in the cortex ofLaminaria.     

Studies on the leaf of Amaranthus retroflexus (Amaranthaceae): ultrastructure,plasmodesmatal frequency,and solute concentration in relation to phloem loading

Both the mesophyll and bundle-sheath cells associated with the minor veins in the leaf of Amaranthus retroflexus L. contain abundant tubular endoplasmic reticulum, which is continuous between the two cell types via numerous plasmodesmata in their common walls. In bundle-sheath cells, the tubular endoplasmic reticulum forms an extensive network that permeates the cytoplasm, and is closely associated, if not continuous, with the delimiting membranes of the chloroplasts, mitochondria, and microbodies. Both the number and frequency of plasmodesmata between various cell types decrease markedly from the bundle-sheath — vascular-parenchyma cell interface to the sicve-tube member — companion-cell interface. For plants taken directly from lighted growth chambers, a stronger mannitol solution (1.4 M) was required to plasmolyze the companion cells and sieve-tube members than that (0.6 M) necessary to plasmolyze the mesophyll, bundle-sheath, and vascular-parenchyma cells. Placing plants in the dark for 48 h reduced the solute concentration in all cell types. Judging from the frequency of plasmodesmata between the various cell types of the vascular bundles, and from the solute concentrations of the various cell types, it appears that assimilates are actively accumulated by the sieve-tube — companion-cell complex from the apoplast.     

Mechanism of plasmodesmata formation in characean algae in relation to evolution of intercellular communication in higher plants

It is generally accepted that higher plants evolved from ancestral forms of the modern charophytes. For this reason, we chose the characean alga, Chara corallina Klein ex Willd., em. R.D.W. (C. australis R. Br.), to determine whether this transition species produces plasmodesmata in a manner analogous to higher plants. As with higher plants and unlike most green algae, Chara utilizes a phragmoplast for cell division; however, in contrast with the situation in both lower and higher vascular plants, the developing cell plate and newly formed cell wall were found to be completely free of plasmodesmata. Only when the daughter cells had separated completely were plasmodesmata formed across the division wall. Presumably, highly localized activity of wall-degrading (or loosening) enzymes inserted into the plasma membrane play a central role in this process. In general appearance characean plasmodesmata are similar to those of higher plants with the notable exception that they lack an appressed endoplasmic reticulum. Further secondary modifications in plasmodesmal structure were found to occur as a function of cell development, giving rise to highly branched plasmodesmata in mature cell walls. These findings are discussed in terms of the evolution of the mechanism for plasmodesmata formation in algae and higher plants.This work was supported in part by National Foundation grant No. DCB-9016756 (W.J.L.). We thank the Electron Microscopy Center of Washington State University and the Zoology Department, University of California, Davis, for the use of their microscopy facilities.     

Scanning electron microscopy in nematode-induced giant transfer cells.

A study of giant cells induced by the root-knot nematode, Meloidogyne incognita, in roots of Impatiens balsamina was made by scanning electron microscopy. The cytoplasmic contents of giant cells were removed by a procedure based on KOH digestion, to reveal inner wall structure. Wall ingrowths typical of transfer cells are present in giant cells from six days onwards after induction. They develop on walls adjacent to vascular tissues, and their distribution and development was examined. Pit fields contianing plasmodesmata become elaborated in walls between giant cells, but pit fields are lost between giant cells and cells outside them. The distribution of plasmodesmata in pit fields suggests that de novo formation of plasmodesmata occurs in walls between giant cells. Various aspects of giant cell formation and function are discussed and wall ingrowth development is compared in giant cells and normal transfer cells.     

Fine structure of plasmodesmata in mature leaves of sugarcane

The fine structure of plasmodesmata in vascular bundles and contiguous tissues of mature leaf blades of sugarcane (Saccharum interspecific hybrid L62–96) was studied with the transmission electron microscope. Tissues were fixed in glutaraldehyde, with and without the addition of tannic acid, and postfixed in OsO₄. The results indicate that the fine structure of plasmodesmata in sugarcane differs among various cell combinations in a cell-specific manner, but that three basic structural variations can be recognized among plasmodesmata in the mature leaf: 1) Plasmodesmata between mesophyll cells. These plasmodesmata possess amorphous, electron-opaque structures, termed sphincters, that extend from plasma membrane to desmotubule near the orifices of the plasmodesmata. The cytoplasmic sleeve is filled by the sphincters where they occur; elsewhere it is open and entirely free of particulate or spokelike components. The desmotubule is tightly constricted and has no lumen within the sphincters, but between the sphincters it is a convoluted tubule with an open lumen. 2) Plasmodesmata that traverse the walls of chlorenchymatous bundle-sheath cells and mestome-sheath cells. In addition to the presence of sphincters, these plasmodesmata are modified by the presence of suberin lamellae in the walls. Although the plasmodesmata are quite narrow and the lumens of the desmotubules are constricted where they traverse the suberin lamellae, the cytoplasmic sleeves are still discernible and appear to contain substructural components there. 3) Plasmodesmata between parenchymatous cells of the vascular bundles. These plasmodesmata strongly resemble those found in the roots of Azolla, in that their desmotubules are closed for their entire length and their cytoplasmic sleeves appear to contain substructural components for their entire length. The structural variations exhibited by the plasmodesmata of the sugarcane leaf are compared with those proposed for a widely-adopted model of plasmodesmatal structure.Abbreviation ER endoplasmic reticulum This study was supported by National Science Foundation grants DCB 87-01116 and DCB 90-01759 to R.F.E. and a University of Wisconsin-Madison Dean's Fellowship to K. R.-B. We also thank Claudia Lipke and Kandis Elliot for photographic and artistic assistance, respectively.     

A quantitative analysis of the interspecific plasmodesmata in the non-division walls of the plant chimera Laburnocytisus adamii (Poit.) Schneid.

Non-division walls in petals of the chimera Laburnocytisus adamii (Poit.) Schneid, were screened for the occurrence and distribution of symplasmic connections. The secondary plasmodesmata (PD) between epidermal cells of Cytisus purpureus Scop, and subepidermal cells of Laburnum anagyroides Medik. were compared with the PD of corresponding cell walls in petals of the two parental species. The non-division walls in the petals of L. adamii were traversed mainly by continuous PD and a few half-PD, both being grouped in pit fields. The secondary PD were characterized by a high percentage of branching (82%), with more than 40% consisting of a single strand at the Cytisus cell side interconnected by a median cavity with two strands of the Laburnum subepidermal cell. In addition, more than 30% of all PD showed secondary branching in the subepidermal wall portion. As a consequence, the cross-sectional areas of plasmodesmatal strands on each side of the central cavity differed remarkably in size, representing a “bottleneck” in the epidermal wall portion. In contrast, PD in the petals of the parental species were symmetrically branched. The comparison of cross-sectional areas of PD in the cell wall between the epidermis and subepidermis of petals of L. anagyroides showed a well-tuned system. The occurrence of half-PD in the intraspecific wall indicates a secondary origin. We conclude that, in the chimera, both genotypically different cells take part in the formation of the interspecific PD.     

Transport of assimilates in the developing caryopsis of rice (Oryza sativa L.)

Assimilates entering the developing rice caryopsis traverse a short-distance pathway between the terminal sieve elements of the pericarp vascular bundle and the aleurone layer. The ultrastructure of this pathway has been studied. Sieve elements in the pericarp vascular bundle are smaller than their companion cells.The sieve elements show few connections with surrounding vascular parenchyma elements but are connected to companion cells by compound plasmodesmata. Companion cells, in turn, are connected to vascular parenchyma elements by numerous compound plasmodesmata present in wall thickenings. Assimilates leaving the sieve element — companion cell complex must laterally traverse cells of the pigment strand before they come into contact with the aleurone layer. The pigment strand cells have modified inner walls made up of a suberin-like material. This material may act as a permeability barrier isolating the apoplast from the symplast of the pigment strand. The walls of the pigment strand cells are traversed by numerous plasmodesmata. Water may be conducted to the endosperm through the isolated cell-wall system of the pigment strand while assimilates possibly move via plasmodesmata. High frequencies of plasmodesmata occur at the junction between the pigment strand and the nucellus and also between adjacent cells of the nucellus. By contrast, plasmodesmata are absent between the nucellus and the aleurone layer and also between the nucellus and the seed coat. A predominantly circumferential and symplastic transport pathway is likely between the pigment strand and nucellus. In view of the total absence of plasmodesmata between the nucellus and the aleurone layer assimilates entering the endosperm may have to cross the plasmalemma of the nucellus. It is possible that constraints to the flow of assimilates may occur in the short-distance pathway between the terminal sieve element — companion cell complexes and the endosperm, and this is discussed.     

Structure and development of cell connections in the phloem ofMetasequoia glyptostroboides needles I. Ultrastructural aspects of modified primary plasmodesmata in Strasburger cells

Summary Symplasmic contacts of Strasburger cells in the mature needle ofMetasequoia glyptostroboides were analysed with special regard to changes of plasmodesmata in fine structure and distribution. In meristematic cells simple primary plasmodesmata are evenly distributed throughout the entire wall, whereas in mature Strasburger cells plasmodesmata are aggregated in defined, dome-shaped wall thickenings. The elongated, often multiple-branched cytoplasmic strands show a distinct neck region besides a considerably dilated sleeve region confluent with cavities, which have formed at branching sites of plasmodesmata in various planes of the wall thickening. Most branches radiating from these cavities connect the protoplasts of the adjacent cells; occasionally some strands are discontinuous. The desmotubules of both, continuous and discontinuous plasmodesmal branches exhibit great variability in structure and number: they may be partially dilated, multiple-stranded and branched within single plasmodesmal branches. Fine structurally, plasmodesmata of Strasburger cells show great resemblance with developing sieve pores of conifers. This characteristic fine structure implicates a special role of the endomembrane system for phloem loading in theMetasequoia leaf.Dedicated to Prof. Dr. Dr. h.c. Eberhard Schnepf on the occasion of his retirement     

Plasmodesmatal distribution and frequency in vascular bundles and contiguous tissues of the leaf ofThemeda triandra

Small and intermediate vascular bundles and contiguous tissues of the leaf blade ofThemeda triandra var.imberbis (Retz.) A. Camus were examined with transmission and scanning electron microscopes to determine the distribution and frequency of plasmodesmata between various cell types. Plasmodesmata are most abundant at the mesophyll/bundle-sheath cell and bundle-sheath/vascular parenchyma cell interfaces, and their numbers decrease with increasing proximity to both thick- and thin-walled sieve tubes. Among cells of the vascular bundles, the greatest frequency of plasmodesmata occurs between vascular parenchyma cells, followed by that of plasmodesmata between vascular parenchyma cells and companion cells, and then by the pore-plasmodesmata connections between companion cells and thin-walled sieve tubes (sieve tube-companion cell complexes). The sieve tube-companion cell complexes of theT. triandra leaf are not isolated symplastically from the rest of the leaf and, in this respect, differ from their counterparts in theZea mays leaf. However, the thick-walled sieve tubes, like their counterparts inZea mays, lack companion cells and are symplastically connected with vascular parenchyma cells that about the xylem.Abbreviations SEM scanning electron microscope - TEM transmission electron microscope     

Chromatin changes related to dedifferentiation and differentiation in tobacco tissue culture (Nicotiana tabacum L.)

Non-histone chromosomal proteins (NHP) were isolated from different stages of Nicotiana tabacum L. pith dedifferentiation to callus and callus redifferentiation. The NHP were separated by sodium dodecylsulfate-polyacrylamide gel electrophoresis on slab gels and analyzed by densitometry. Simultaneous histological changes are reported. In both processes, some high molecular weight protein (HMWP) bands increase drastically in an induction period, previous to cell proliferation, and decrease when cell division declines. Some low molecular weight protein bands, intense in pith tissue, decrease early when callus is forming and increase when cells differentiate. chromatin template activity is high when cells proliferate, coinciding with maximum HMWP-bands intensity.Abbreviations HMWP high molecular weight proteins - IAA indole-3-acetic acid - LMWP low molecular weight proteins - NHP non-histone proteins - TA template activity