End Wall Perforation Research Articles

Comparative Studies of Tracheary Element Structure of Some Gymnosperms with Angiosperms

Tissues of the pinna and rachis of Cycas diannaensis and pinna, rachis, and root of Cycas taiwaniana, rachis of Cycas szechuanensis, stem of Metasequoia glyptostroboides (Taxodiaceae), stems of Chamaecyparis obtusa (Sieb.et Zucc.) Endl cv. Tetragona (Cupressaceae), and leaves and stems of Michelia alba and Michelia figo and stems of Amygdalus persica (angiosperms) were compared using the scanning electron microscopy. In all species of these gymnosperms, their many tracheary elemnts have perforations in end walls and lateral walls. These structures are the same as vessels of angiosperms; therefore, these tracheary elements are vessel elements. Many types of vessels were found in cycads: pitted vessels in M. glyptostroboides, spiral and pitted vessels in Chamaecyparis obtusa cv. Tetragona. The development and structural characteristics of vessels of cycads, the two other gymnosperms, and the angiosperms were identical. Some characters such as extent of incline of perforation plate in the end wall showed that vessel characters of some angiosperms were more primitive than the cycads or M. glyptostroboides and C. obtusa cv. Tetragona. Many of the vessel elements of the angiosperms were band shaped, without end walls, and had only two lateral walls and other two margins; the end was acuate or with an arc margin; the end of some vessel elements was acute with no perforations, many perforations located only in lateral wall. Such results are rarely reported in previous work. In all species, perforations were seen only in tracheae, and the walls of parenchyma cells only had a thin primary wall and without perforation. Analysis and discussion to the experimental measures which were observed and research of the structure of vessel or tracheid, pointed out that several measures all could be used and the Jeffrey’ method effects were better. Comparing the vessels of cycads, Taxodiaceae and Cupressaceae helps us to understand the mechanism in which these most primitive or more primitive extant gymnosperms were adapted to harsh environments and to understand these species’ evolutionary extent, and has the significance to the studies of plant anatomy, plant systematics and plant evolution.

EARLYWOOD VESSELS IN RING-POROUS TREES BECOME FUNCTIONAL FOR WATER TRANSPORT AFTER BUD BURST AND BEFORE THE MATURATION OF THE CURRENT-YEAR LEAVES

This paper reviews the development of xylem vessels in ring-porous dicots and the corresponding leaf phenology. Also included are our original observations on the time-course of vessel element growth, secondary wall deposition, and end wall perforation in the deciduous hardwood Kalopanax septemlobus. Different patterns of xylem growth and phenology serve different strategies of the species for adaptation to seasonal climates. Trees with ring-porous xylem form wide earlywood vessels (EWV) in spring and narrow latewood vessels in summer. The wide EWV become embolized or blocked with tyloses by the end of the growing season while the narrow vessels may remain functional for many years. The co-occurrence of wide and narrow vessels provides both efficiency and safety of the water transport as well as a potentially longer growing season. It has for a long time been assumed that EWV in ring-porous hardwoods are formed in early spring before bud burst in order to supply sap to growing leaves and shoots. However, the full time-course of development of EWV elements from initiation of growth until maturation for water transport has not been adequately studied until recently. Our observations clarify a crucial relationship between leaf maturation and the maturation of earlywood vessels for sap transport. Accumulated new evidence shows that EWV in branches and upper stem parts develop earlier than EWV lower in the stem. The first EWV elements are fully expanded with differentiated secondary walls by the time of bud burst. In lower stem parts, perforations in vessel end walls are formed after bud burst and before the new leaves have achieved full size. Therefore, the current-year EWV network becomes functional for water transport only by the time when the first new leaves are mature.

The effect of SEM preparation on pit membrane remnants in vessel element end-walls of primitive angiosperms

Scanning electron microscope (SEM) is necessary to demonstrate presence or absence of pit membranes in possible perforations or the type of pit membrane remnants in perforations in vessel element end-walls of angiosperms, but it was unconfirmed and questionable whether pit membrane absence in pits was affected by the processing and handling before SEM observations. To solve this question, the secondary xylem of four woody species from primitive angiosperms, Illicium henryi Diels. (Illiciaceae), Schisandra rubriflora (Franch.) Rehd. et Wils. (Schisandraceae), Tetracentron sinensis Oliv. and Trochodendron aralioides Sieb. & Zucc. (Trochodendraceae) was chosen and the following techniques were used: (1) fresh materials were examined in low-vacuum with ESEM. (2) Air-dried materials were examined both in low- and high-vacuum with ESEM. (3) Fresh materials fixed in several different fixatives were observed in low-vacuum, respectively. (4) Smooth surface of the material by paraffin section methods was examined in high-vacuum. (5) Materials treated by Jeffrey's Fluid were observed in high-vacuum. Pit membranes and remnants in perforations of fresh material were little different from that of treated materials. Absence of the pit membrane in perforations (pits) in the end-wall was not attributed to the processing and handling. Information of pit membranes and remnants in perforations in end-wall based on the SEM observation might be validly claimed.

Discovery of vessels in Tetracentron (Trochodendraceae) and its systematic significance

Through SEM observation, we found that there are vessels as well as tracheids in the secondary wood of Tetracentron sinense Oliv. The vessel elements are as narrow and as long as or slightly shorter than the tracheids and generally have 1 to 3 very long, or sometimes relatively short and oblique end-wall perforation plates; such perforation plates are also present on the lateralwalls. The perforation plates of the vessels include scalariform and reticulate-scalariform types, with various degrees of membrane remnants present in the end walls.

Vessels in ferns: structural, ecological, and evolutionary significance

We have studied macerated xylem of ferns, supplemented by sections, by means of scanning electron microscopy (SEM) in a series of 20 papers, the results of which are summarized and interpreted here. Studies were based mostly on macerations, but also on some sections; these methods should be supplemented by other methods to confirm or modify the findings presented. Guidelines are cited for our interpretations of features of pit membranes. Fern xylem offers many distinctive features: (1) presence of numerous vessels and various numbers of tracheids in most species; (2) presence of vessels in both roots and rhizomes in virtually all species; (3) presence of specialized end walls in vessels of only a few species; (4) multiple end-wall perforation plates in numerous species; (5) lateral-wall perforation plates in numerous species; (6) porose pit membranes associated with perforation plates in all species; and (7) pit dimorphism, yielding wide membrane-free perforations alternating with extremely narrow pits. Multiple end wall perforation plates and lateral wall perforation plates are associated with the packing of tracheary elements in fascicles in ferns: facets of tips of elements contact numerous facets of adjacent elements; all such contacts are potential sites for conduction by means of perforations. This packing differs from that in primary xylem of dicotyledons and monocotyledons. Porosities in pit membranes represent a way of interconnecting vessel elements within a rhizome or root. In addition, these porosities can interconnect rhizome vessel elements with those of roots, a feature of importance because roots are adventitious in ferns as opposed to those of vascular plants with taproots. Fully-formed or incipient (small-to-medium sized porosities in pit membranes) perforation plates are widespread in ferns. These are believed to represent (1) ease of lysis of pit membranes via pectinase and cellulase; (2) numerous potential sites for perforation plate formation because of fasciculate packing of tracheary elements; (3) evolution of ferns over a long period of time, so that lysis pathways have had time to form; (4) lack of disadvantage in perforation plate presence, regardless of whether habitat moisture fluctuates markedly or little, because ferns likely have maintaining integrity of water columns that override the embolism-confining advantage of tracheids. Although all ferns share some common features, the diversity in xylem anatomy discovered thus far in ferns suggests that much remains to be learned.

SEM Studies on Vessels of the Homophyllous Species of Selaginella

Metaxylem vessel elements from macerated xylem of rhizomes and rhizophores of Selaginella arizonica, Selaginella bigelovii, and Selaginella oregana were examined with scanning electron microscopy (SEM). All species have transverse to somewhat oblique simple perforation plates on end walls of vessels; presence of tracheids could not be determined with SEM. Lateral walls possess scalariform pitting except for S. bigelovii, in which pitting is opposite. Pit membranes are generally intact, but pits on some areas of lateral walls contain remnants of pit membranes; these remnants chiefly take the form of strands or threads that traverse the pit apertures. Areas of pits with such porose pit membranes may be regarded as incipient perforation plates, like lateral perforation plates or incipient perforation plates we have reported in ferns. These lateral perforation plates, as well as the simple end wall perforation plates, may aid in rapid uptake of water during short periods when water is available; studies on water uptake patterns of homophyllous Selaginella species are needed to examine this possibility.

Vessels in Roots and Rhizomes of Dryopteris crassirhizoma (Dryopteridaceae) from Heilongjiang Province, China

In the present study, tracheary elements in roots and rhizomes of Dryopteris crassi- rhizoma were observed with scanning electron microscopy (SEM). SEM observation revealed that all tracheary elements in both organs were vessels. These vessel elements have end-wall perfo- ration plates and lateral-wall perforation plates. End-wall perforation plates in roots are more specialized than in rhizomes; they are all scalariform and obliquely positioned in end walls. Most end-wall perforations, especially in the center portion of end-wall perforation plates, lack pit membrane remnants, but pit membrane remnants are relatively abundant in some end-wall per- forations of roots and rhizomes. It is noteworthy that several larger perforations on lateral walls usually are grouped together and form local lateral-wall perforation plates. Wide perforations alternating with narrow perforations characterize vessels of roots and rhizomes. In addition, the majority of perforations in lateral-walls have porose pit membranes or pit membrane remnants, range from intact pit membrane to nearly devoid of pit membrane remnants. Some vessels in rhizomes have several facets in which long scalariform pits have various degrees of porose mem- branes. These vessels contact several other tracheary elements for transferring materials.

SEM Studies on Vessels in Ferns. 5. Woodsia scopulina

SEM Studies on Vessels in Ferns. 5. Woodsia scopulina

SEM studies on vessels in ferns. 2. Pteridium

Xylem from roots and rhizomes of two infraspecific taxa of Pteridium aquilinum was studied by means of scanning electron microscopy (SEM). All tracheary elements proved to be vessels. End wall perforation plates were all scalariform, lacked pit membrane remnants in at least the central part of the perforation plate, and varied with respect to width of bars, from wide to tenuous, and with respect to presence of pit membrane remnants. In addition, porose pit membranes on walls that are likely all lateral vessel-to-vessel walls must be considered to be perforations also, although different from those on end walls. Lateral wall perforation plates, hypothesized by one worker on the basis of tylosis presence but denied by another on the basis of light microscopy, were confirmed by demonstration of pores with SEM. In addition, lateral walls of Pteridium vessels bear some grooves interconnecting pit apertures; this feature is newly figured by SEM for ferns. Lateral wall pitting that is not porose may either have striate thickenings of the primary wall or be smooth. Vessel presence and degree of specialization in Pteridium vessels may bear a relationship to the wide ecological tolerances of the genus.

Sem Studies on Vessels in Ferns. III. Phlebodium and Polystichum

Scanning electron microscope (SEM) studies of xylem of roots and rhizomes of one species each of Phlebodium and Polystichum revealed the presence of vessels in both. Vessels in both, like those in Pteridium, have lateral perforation plates and end-wall perforation plates. Perforation plates on lateral walls feature smaller porosities than do the perforations on end walls. In Phlebodium, end-wall perforation plates retain pit membranes with porosities; end walls in Polystichum lack pit membrane remnants in most perforations. End-wall perforation plates are not uniform in either genus but vary with respect to differentiation from lateral-wall pitting, narrowness of bars, and presence of pit membrane remnants. Wide perforations alternating with narrow perforations characterize our material of Phlebodium. Rhizome transections show that tracheary elements in both genera tend to occur in large groupings in which each tracheary element tends to contact two to four other tracheary elements; this may correlate wit...

Vessels in Nymphaeaceae: Nuphar, Nymphaea, and Ondinea

Roots of Nuphar, Nymphaea, and Ondinea were studied with SEM in order to determine presence of perforations in end walls of tracheary elements. Nuphar has occasional small perforations and Nymphaea has a scattering of small perforations, but no perforations were observed in Ondinea. In Nuphar and Nymphaea, metaxylem elements have helical-reticulate wall thickenings, but end walls of tracheary elements have at least some scalariform pitting; in Ondinea, end walls are identical to side walls. In all three genera, striations (thickenings) in primary walls of tracheary elements are common, as in Euryale and Victoria.

Vessel origins in Nymphaeaceae: Euryale and Victoria

Metaxylem tracheary elements of roots have differentiation between end walls and lateral walls in both Euryale and Victoria . End walls have narrower, more closely spaced bars and scalariform plates. Primary walls of end walls (and, to a lesser extent, lateral walls) have striations that are thickened primary wall portions orientated in an axial direction. These striations are less common in Victoria than in Euryale . Although secondary wall strands between perforations occur in some dicotyledons, the report of primary wall striations is new; these can be seen with scanning electron microscopy (SEM) but not with light microscopy. Perforations occur irregularly and sometimes sparsely on end walls of tracheary elements of Victoria , but perforations were not observed in Euryale . Thus, Euryale satisfies one criterion for the presence of vessel (end wall different from lateral wall), whereas Barclaya satisfies another (perforations in end walls) and Victoria satisfies both. Vessel origins in Nymphaeaceae are important in illustrating that there may be multiple vessel origins in dicotyledons.