The peripheral xylem of grapevine (Vitis vinifera). 1. Structural integrity in post-veraison berries

During the development of many fleshy fruits, water flow becomes progressively more phloemic and less xylemic. In grape (Vitis vinifera L.), the current hypothesis to explain this change is that the tracheary elements of the peripheral xylem break as a result of berry growth, rendering the xylem structurally discontinuous and hence non-functional. Recent work, however, has shown via apoplastic dye movement through the xylem of post-veraison berries that the xylem should remain structurally intact throughout berry development. To corroborate this, peripheral xylem structure in developing Chardonnay berries was investigated via maceration and plastic sectioning. Macerations revealed that, contrary to current belief, the xylem was comprised mostly of vessels with few tracheids. In cross-section, the tracheary elements of the vascular bundles formed almost parallel radial files, with later formed elements toward the epidermis and earlier formed elements toward the centre of the berry. Most tracheary elements remained intact throughout berry maturation, consistent with recent reports of vascular dye movement in post-veraison berries.     

Solute Accumulation by Grape Pericarp Cells: IV. PERFUSION OF PERICARP APOPLAST VIA THE PEDICEL AND EVIDENCE FOR XYLEM MALFUNCTION IN RIPENING BERRIES

Findlay, N., Oliver, K. J., Nii, N. and Coombe, B. G. 1987.Solute accumulation by grape pericarp cells. IV. Perfusion ofpericarp apoplast via the pedicel and evidence for xylem malfunctionin ripening berries.—J. exp. Bot. 38: 668–679. ¹⁴C-labelled sucrose was applied to freshly-cut pedicels ofexcised unripe and ripening grape berries and let perfuse fordifferent periods; skin and flesh tissues were then extractedand the radioactivity partitioned and measured. Accumulationof radioactivity in a compartmented fraction was greatest inthe skin of unripe berries at the stage when sugar accumulationin vivo was slow. Total radioactivity of parts of berries showedthat activity spread rapidly throughout when the berry was unripebut slowed once ripening commenced. The perfusion of eosin from pedicels was also rapid in unripeberries but in ripe berries it was blocked beyond the pedicelat the outer edge of the 'brush' where the pericarp is aerenchymatousand tanniniferous. The failure of movement through the vascularbundles beyond the brush could not be associated with the developmentof tyloses in tracheary elements; it appeared to be associatedwith stretched tracheids in the network of dorsal vascular bundlesevidenced by irregularities in the spacing of wall thickeningsand breaks in the bounding membranes. This physical disruptionof the tracheary elements of the vascular bundles occurred whenthe berry expands suddenly, about a week after the inceptionof rapid sugar accumulation. The different rates of perfusion limit the utility of the pedicelroute for studies of compartmentation and metabolism in grapeberries at different developmental stages. Nevertheless, therapid compartmentation of radioactivity after pedicel perfusionof unripe skin with ^l4C-labelled sucrose discounts the hypothesisthat the slow rate in skin in situ is due to an apoplastic inhibitor. Key words: Grape berry, accumulation, xylem malfunction     

Comparison of vegetative anatomy of piperales. I. Juvenile xylem of twigs

Medullary bundles of Piperaceae resemble those of Ranunculaceae. The nature of tracheary elements of primary xylem suggests that Houttuynia cordata (Saururaceae), Piper cubeba (Piperaceae) and Chloranthus officinalis (Chloranthaceae) are of lower evolutionary status than others. Among these three, P. cubeba shows stratification of secondary xylem, a specialized character. Lateral wall of metaxylem tracheary elements and distribution of bundles of Peperomia, suggest their primitive status and distinctness, supporting separation of "Peperomiacea:" (of NOVAK). Piper cubeba, Houttuynia and Chloranthus bear one important Ranunculaceous character: scalariform perforation in primary vessels. Primitive species of Peperomia carry probably another Ranunculaceous character, i.e., many circles of medullary bundles. Shape and pattern of vascular bundles of Piper cubeba, Houttuynia and Chloranthus are similar. Other species of Piper show modifications. Peperomia represents another distinct pattern.     

Developmental changes in the diurnal water budget of the grape berry exposed to water deficits

The diurnal water budget of developing grape (Vitis vinifera L.) berries was evaluated before and after the onset of fruit ripening (veraison). The diameter of individual berries of potted ‘Zinfandel’ and ‘Cabernet Sauvignon’ grapevines was measured continuously with electronic displacement transducers over 24 h periods under controlled environmental conditions, and leaf water status was determined by the pressure chamber technique. For well-watered vines, daytime contraction was much less during ripening (after veraison) than before ripening. Daytime contraction was reduced by restricting berry or shoot transpiration, with the larger effect being shoot transpiration pre-veraison and berry transpiration post-veraison. The contributions of the pedicel xylem and phloem as well as berry transpiration to the net diurnal water budget of the fruit were estimated by eliminating phloem or phloem and xylem pathways. Berry transpiration was significant and comprised the bulk of water outflow for the berry both before and after veraison. A nearly exclusive role for the xylem in water transport into the berry was evident during pre-veraison development, but the phloem was clearly dominant in the post-veraison water budget. Daytime contraction was very sensitive to plant water status before veraison but was remarkably insensitive to changes in plant water status after veraison. This transition is attributed to an increased phloem inflow and a partial discontinuity in berry xylem during ripening.     

Functional xylem in the post-veraison grape berry

A number of studies have shown a transition from a primarily xylem to a primarily phloem flow of water as fleshy fruits develop, and the current hypothesis to explain this transition, particularly in grape (Vitis vinifera L.) berries, is that the vascular tissue (tracheids) become non-functional as a result of post-veraison berry growth. In most studies, pedicels have been dipped in a vial containing an apoplastic dye, which was taken up into the entire peripheral and axial xylem vasculature of pre-veraison, but not post-veraison berries. The pressure plate/pressure membrane apparatus that is commonly used to study soil moisture characteristics was adapted and the pre- to post-veraison change in xylem functionality in grape berries was re-evaluated by establishing a hydrostatic (tension) gradient between the pedicel and a cut surface at the stylar end of the berry. Under the influence of this applied hydrostatic gradient, movement of the apoplastic tracer dye, basic fuchsin, was found in the pedicel and throughout the axial and peripheral xylem of the berry mesocarp. A similar movement of dye could be obtained by simply adjoining the stylar cut surface to a dry, hydrophilic wicking material. Since both pre- and post-veraison berries hydrate when the pedicel is dipped in water, it is hypothesized that the absence of dye movement into the vasculature of post-veraison berries indicates not a loss of xylem function, but rather the loss of an appropriate driving force (hydrostatic gradient) in the berry apoplast. Based on this hypothesis, and the substantial decrease in xylem flows that occur in intact grape berries at veraison, it is suggested that there may be significant changes in the pattern of solute partitioning between the fruit symplast and apoplast at veraison. It is further suggested that diurnal patterns in symplast/apoplast solute partitioning in grapes and other fleshy fruit, may explain the observed minimal xylem contribution to the water budgets of these fruits.     

罗汉果营养器官的结构

1.罗汉果根、茎、叶的结构与葫芦科其它植物大致相似。不同之处有三方面:(1)叶子主脉中维管束为5个;(2)叶子中有硅质细胞成群分布;(3)块根具异常次生生长。在次生木质部中围绕导管形成形成层,由之分化出多个具韧皮部与木质部的小维管束。2.叶中的硅质细胞分布于表皮、栅栏组织、海绵组织中,多个细胞集合在一起。其细胞壁加厚并硅质化,细胞内容物消失。推测与增加叶子的支持力量有关。3.罗汉果雌株叶子上、下表皮气孔数之比为0.04,雄株为0.03,比值均很低,同时根据叶的解剖结构推测罗汉果为C_3植物。4.雌株叶子下表皮单位面积气孔数比雄株的多26％,差异很显著,值得进一步研究简化观察统计方法,以用于鉴别幼苗的性别。     

HISTOLOGICAL STUDIES ON THE COLEOPTILE. II. COMPARATIVE VASCULAR ANATOMY OF COLEOPTILES OF AVENA AND TRITICUM

The vascular bundles in the uppermost 1-4 mm of the coleoptiles of 9 varieties of Avena sativa, and also of Avena fatua L., all terminate essentially vertically with a small “cap” of tracheary elements. In Triticum vulgare Vill., by contrast, they terminate with a horizontal or downward-pointing section. This brings the two bundles more or less together and may result in their complete fusion, usually with a short vascular extension. In both genera the bundles contain one or more series of apparently active, undifferentiated cells. In the mature embryos the bundles are entirely procambial in nature, but xylem differentiation begins rapidly upon germination and proceeds towards the tip, which is reached by the time the coleoptile is 1.5 mm long; thereafter it proceeds basipetally and it may continue at the base after elongation has ceased there. The differentiation of stomata also appears to proceed basipetally. It may be deduced that the coleoptile cannot form lignin while in the embryo but begins to do so upon germination. Parallels are brought out between auxin production first by the endosperm and then by the tip, on the one hand, and lignification in the xylem and in the stomata, on the other.     

Vessel development and the importance of lateral flow in water transport within developing bundles of current-year shoots of grapevine (<Emphasis Type="Italic">Vitis vinifera</Emphasis> L.)

In the developing xylem bundles of young stems, the presence of immature living vessel elements can strongly restrict or even block axial hydraulic conductance, especially in newly matured vessels. Lateral connections between vessels may provide an alternative pathway for water movement to bypass these closed, living elements. Using the grapevine as a model system, the present study aimed to demonstrate the effects of living vessel elements on water movement patterns, and the importance of lateral flow for effective water conductivity in the developing bundles. Living vessel elements were detected using dye staining and the pattern of vessel development and maturation was then monitored. The importance of lateral flow was confirmed using several approaches: (1) capacity for lateral flow, (2) effect of increasing the distance of water transport, and (3) effect of ion concentrations. Living vessel elements were found along the developing bundles, they occupied a significant proportion of the distal and peripheral parts of the flow path, forming a substantial barrier to apoplastic water flow. Water in the developing xylem bundles could move easily from vessel to vessel and between secondary and primary xylem. Furthermore, data from increasing the transport length and altering the ion concentrations supported the critical contribution of the lateral flow to the total hydraulic conductance within the developing bundles. The hydraulic architecture of the developing xylem bundles is described. The results are discussed in terms of reliability and efficiency of water transport during shoot growth and development.     

Xylem changes in the correlative inhibition of lateral bud growth in flax (Linum usitatissimum L.)

Xylem or tracheary changes at the base of the cotyledonary buds of flax seedlings (Linum usitatissimum L.), released from inhibition by decapitation of the main apex were studied. The differentiation of xylem strands and/or tracheary elements was correlated with the growth in length of the lateral buds, especially 48–72 hr after the removal of the main apex. The xylem strands, connected to the hypocotylary stele or not, and the tracheary elements increased with age within and outside the strands of both non-decapitated and decapitated seedlings. In the latter, the differentiation of these structures, however, occurred much earlier and in greater abundance in the same regions. The early growth in length of lateral buds, 1 or 2 hr after decapitation, was correlated with the early development of tracheary perforations in the xylem strands. The xylary strands with perforated elements are known to be more efficient than those without them. Therefore, it is suggested that the inhibition of lateral-bud growth was due, in fact, to a lack of appropriate tracheary perforations in the bud xylem strands that were connected with the hypocotylary stele of flax seedlings.     

Ultrastructure of graniferous tracheary elements in the haustorium of Exocarpus bidwillii, a root hemi-parasite of the Santalaceae.

The xylem in the body of the haustorium of E. bidwillii has the shape of an inverted conical flask with the expanded portion being known as the vascular core. The tracheary elements of the vascular core are notable for the occurrence of numerous granules within their lumina and the presence of mostly imperforate walls. Elsewhere in the haustorium graniferous tracheary elements are absent and the cells are usually ordinary vessel elements. Thin sections for transmission electron microscopy, post-stained in potassium permanganate, show that the secondary wall thickenings of the graniferous tracheary elements consist of eccentric layers in which the microfibrils of each successive layer run alternately longitudinally and transversely. The granules of the tracheary elements average 2 micrometer in diameter and consist of a homogeneous matrix which shows a fine fibrillar structure on high resolution. The granules are naked and mostly remain as separate structures within the lumen of the cell, but occasionally they fuse into small groups or irregular masses. In some cells the granules become transformed into fibrillar material that disperses throughout the lumen. This dispersed material may accumulate in vessels of the interrupted zone proximal to the vascular core. Occasionally, the granules also change into compacted amorphous masses that adhere to the walls of the cell. Ultrastructural cytochemistry confirms that the granules are protein and not starch as was originally believed for the Santalaceae. The function of the vascular core and its graniferous tracheary elements is discussed and we suggest that it might help regulate the pressure and flow of xylem sap entering the parasite from the host. Graniferous tracheary elements in the Santalaceae and in root parasites of the Serophulariaceae are compared and it is concluded that they represent examples of convergent evolution.     

The Vascular System of Maize Stems Revisited: Implications for Water Transport and Xylem Safety

The plexus of vascular bundles in the nodes of grasses is notoriouslycomplex, where long axial bundles pass through a network oftransverse bundles. The xylem pathways for water in maize stemshave been investigated anatomically and with dye and particulatetracers, revealing some of the details of this complexity. Onlyapprox. 3% of axial vessels pass through nodes without beinginterrupted by end walls. Axial bundles at nodes differ fromthose in internodes in having the metaxylem and protoxylem vesselsconnected by small tracheary elements. So it is only at nodesthat exchange of sap occurs between the large vessels withina bundle. End walls, acting as filters for particles and gasbubbles, always separate axial vessels from vessels in transversebundles. The high redundancy of bundle connections in the nodalplexus is interpreted as providing alternative water pathwaysto bypass embolisms and damaged or diseased sections of thexylem. The pores in the filters at the base of nodes and betweenaxial and transverse vessels within nodes are <20 nm in diameter.Where axial vessels connect to transverse vessels, a varietyof unusual shapes of vessel elements mediate two- and three-wayconnections within the plexus.Copyright 2000 Annals of BotanyCompany Zea mays, cryoSEM, maize, node, pits, pit membranes, vessel ends, vessels, xylem embolism, xylem pathogens     

A fasciclin-domain containing gene, ZeFLA11, is expressed exclusively in xylem elements that have reticulate wall thickenings in the stem vascular system of Zinnia elegans cv Envy

The vascular cylinder of the mature stem of Zinnia elegans cv Envy contains two anatomically distinct sets of vascular bundles, stem bundles and leaf-trace bundles. We isolated a full-length cDNA of ZeFLA11, a fasciclin-domain-containing gene, from a zinnia cDNA library derived from in vitro cultures of mesophyll cells induced to form tracheary elements. Using RNA in situ hybridization, we show that ZeFLA11 is expressed in the differentiating xylem vessels with reticulate type wall thickenings and adjacent parenchyma cells of zinnia stem bundles, but not in the leaf-trace bundles that deposit spiral thickenings. Our results suggest a function for this cell-surface GPI-anchored glycoprotein in secondary wall deposition during differentiation of metaxylem tissue with reticulate vessels.     

Ripening grape berries remain hydraulically connected to the shoot

Berry diameter was monitored during dry-down and rewatering cycles and pressurization of the root system of Vitis vinifera (cv. Merlot) and Vitis labruscana (cv. Concord) to test changes in xylem functionality during grape ripening. Prior to veraison (onset of ripening), berries maintained their size under declining soil moisture until the plants had used 80% of the transpirable soil water, began to shrink thereafter, and recovered rapidly after rewatering. By contrast, berry diameter declined slowly but steadily during post-veraison water stress and did not recover after rewatering; irrigation merely prevented further shrinking. Preconditioning vines with a period of water stress after flowering did not influence the berries' reaction to subsequent changes in transpirable soil water. Pressurizing the root system led to concomitant changes in berry diameter only prior to veraison, although some post-veraison Concord, but not Merlot, berries cracked under root pressurization. The xylem-mobile dye basic fuchsin, infused via the shoot base, moved throughout the berry vasculature before veraison, but became gradually confined to the brush area during ripening. When the dye was infused through the stylar end of attached berries, it readily moved back to the plant both before and after veraison. Our work demonstrated that berry-xylem conduits retain their capacity for water and solute transport during ripening. It is proposed here that apoplastic phloem unloading coupled with solute accumulation in the berry apoplast may be responsible for the decline in xylem water influx into ripening grape berries. Instead, the xylem may serve to recycle excess phloem water back to the shoot.     

Naturally Occurring Regenerative Differentiation of Xylem Around Adventitious Roots in Luffa cylindrica Seedlings

Regeneration of xylem induced by adventitious root formationin the hypocotyl of Luffa cylindrica Roem. seedlings is described.This naturally occurring form of xylem regeneration involvesthe formation of a bypass of regenerated tracheary elementsaround a root without external severance of the vascular strands.The regeneration of xylem around an adventitious root is polarand is very similar in its developmental pattern to the well-knownxylem regeneration induced by wounding vascular strands. Adventitious root formation, Luffa cylindrica Roem, regenerated tracheary elements, vascular differentiation, xylem regeneration     

Light enhances differentiation of the vascular system in the fruit of Actinidia deliciosa

Light is recognized as crucial in determining high quality of fleshy fruits, for example, kiwifruit [Actinidia deliciosa var. deliciosa (A. Chev.) C. F. Liang et A. R. Ferguson]. Among the possible mechanisms through which light improves the quality of kiwifruit berry, there may be a direct morphogenic role on the differentiation of the fruit's vascular system, though this has not yet been investigated. The present study's aim was to determine (1) whether light positively affects the differentiation of the vascular system of the fruit and/or the pedicel, and, if so, (2) which component (xylem, phloem, or both) is more affected, and (3) in which period of the berry's development the improvement of the vascular differentiation (if any) occurs. To this end, fruit morphogenesis of kiwifruit was studied in two developmental environments (i.e., in full sunlight and in paper bags that reduced the full sunlight to 10%), and in two phases of fruit development (i.e., 1 and 5 months [harvest] after anthesis). During the growth period, the type of environment did not affect the differentiation pattern of the vascular system in the three types of bundles present in the fruit. However, in comparison with shade, light improved the vasculature in the fruit pericarp and pedicel, inducing a consistently higher extent of the xylary component in the main bundles of the fruit and pedicel, principally due to an increase in the number of xylem elements. The phloic component was also increased by light, but to a much lesser extent than that of the xylary. During the entire period of development, light-grown fruits contained higher concentrations of calcium and magnesium, as compared with shade-grown fruits. In conclusion, in the berry of Actinidia deliciosa, light enhances the differentiation of the vascular system, in particular the xylary component. The hypothesis that fruit quality is improved through a more efficient translocation of specific mineral nutrients (e.g., calcium) via the xylem is presented.     

Direct in situ measurement of cell turgor in grape (Vitis vinifera L.) berries during development and in response to plant water deficits

Vitis vinifera L. berries are non-climacteric fruits that exhibit a double-sigmoid growth pattern, and at the point known as 'veraison', which is just before the beginning of the second period of rapid fruit growth, these berries undergo several abrupt physiological changes. Cell pressure probe was used to examine the in situ turgor (P) of cells in the mesocarp during berry development and in response to plant water deficits. Initial tests comparing attached and detached berries demonstrated that cell P was stable for up to 48 h after detachment from the vine, provided that water loss from the berry was prevented. Cell P at pre-dawn was on the order of 0.25 MPa pre-veraison (PreV) and was reduced by an order of magnitude to 0.02 MPa post veraison (PostV). Cell P declined slightly but significantly with depth from the berry surface PreV, but not PostV. When water was withheld from potted vines, cell P declined about 0.2 Mpa, as pre-dawn vine water potential declined about 0.6 MPa over 12 d, whereas cell P was completely insensitive to a 1.10 MPa decrease in pre-dawn vine water potential after veraison. Rewatering of stressed plants also resulted in a 24 h recovery of cell P before, but not after veraison. The substantial decline in cell P around veraison is consistent with the decline in berry firmness that is known to occur at this time, and the PostV insensitivity of P to changes in vine water status is consistent with current hypotheses that the PostV berry is hydraulically isolated from the vine. The fact that a measurable P of about 0.02 MPa and typical cell hydraulic/osmotic behaviour were exhibited in PostV berries, however, indicates that cell membranes remain intact after veraison, contrary to many current hypotheses that veraison is associated with a general loss of membrane function and cellular compartmentation in the grape berry. We hypothesize that cell P is low in the PostV berry, and possibly other fleshy fruits, because of the presence of regulated quantities of apoplastic solutes.     

Causes and effects of changes in xylem functionality in apple fruit

BACKGROUND AND AIMS: The xylem in fruit of a number of species becomes dysfunctional as the fruit develops, resulting in a reduction of xylem inflow to the fruit. Such a reduction may have consequential effects on the mineral balance of the fruit. The aim of this study was to elucidate the dynamics and nature of xylem failure in developing apples (Malus domestica) showing differing susceptibilities to bitter pit, a calcium-related disorder. METHODS: Developmental changes in xylem functionality of the fruit were investigated in "Braeburn" and "Granny Smith" apples by using a dye infusion technique, to stain the vasculature along the path of dye movement. The vascular bundles were clearly visible in transverse section when fruit were sectioned equatorially. The intensity of staining of the vascular bundles in the fruit was recorded at regular intervals throughout the season. Tissue containing dysfunctional bundles was fixed and embedded in wax for subsequent sectioning and examination. KEY RESULTS: As the season progressed, an increasing proportion of vascular bundles failed to show any staining, with the most marked change occurring in the primary bundles, and in nearly all bundles with increasing distance from the stalk end of the fruit. Decreased conductance in the primary bundles of "Braeburn" occurred earlier than in "Granny Smith". Microscopy revealed that the xylem in vascular bundles of the fruit suffered substantial damage, indicating that the mode of dysfunction was via the physical disruption of the xylem caused by expansion of the flesh. CONCLUSIONS: Results support the view that the relative calcium deficiency of apple fruit is due to a progressive breakdown of xylem conductance caused by growth-induced damage to the xylem strand in the bundle. The earlier onset of xylem dysfunction in the cultivar more susceptible to bitter pit suggests that the relative growth dynamics of the fruit may control the occurrence of calcium-related disorders.     

Graniferous Tracheary Elements in the Haustorium of Osyris arborea Wall. (Santalaceae)

In the haustorium of Osyris arborea (a non-host specific roothemi-parasite) a distinct interrupted zone is present abovethe vascular core. The majority of the xylem elements in thevascular core are perforated. Graniferous tracheary elementsin this species are recorded for the first time. Cytochemicaltests showed the granules to be proteinaceous. The suggestedfunction of graniferous tracheary elements in the regulationof pressure and flow of sap is discussed. Osyris arborea, root hemi-parasite, Santalaceae, haustorium, graniferous tracheary elements, protein granules     

Naturally Occurring Regenerative Differentiation of Xylem Around Adventitious Roots in Luffa cylindrica Seedlings

Regeneration of xylem induced by adventitious root formationin the hypocotyl of Luff a cylindrica Roem. seedlings is described.This naturally occurring form of xylem regeneration involvesthe formation of a bypass of regenerated tracheary elementsaround a root without external severance of the vascular strands.The regeneration of xylem around an adventitious root is polarand is very similar in its developmental pattern to the well-knownxylem regeneration induced by wounding vascular strands. Adventitious root formation, Luffa cylindrica Roem, regenerated tracheary elements, vascular differentiation, xylem regeneration.