Heinz-Dietmar Behnke

Sieve-tube plastids in relation to angiosperm systematics - an attempt towards a classification by ultrastructural analysis

I n t r o d u c t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 S t r u c t u r e o f s ievetube p las t ids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156 L i g h t m i c r o s c o p e inves t iga t ions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156 U l t r a s t r u c t u r a l s tud ie s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 Speci f ic s t r u c t u r e and d i s t r i b u t i o n o f s i evetube p las t ids in se lec ted p lan t t axa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164 P r e l i m i n a r y t a x o n o m i c and p h y l o g e n e t i c c o n s i d e r a t i o n s .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 C o n c l u d i n g r e m a r k s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180 A c k n o w l e d g m e n t s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 Tab les . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 L i t e r a t u r e c i ted . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194

Dilated cisternae inCapparales—an attempt towards the characterization of a specific endoplasmic reticulum

SummaryDilated cisternae (DC) of endoplasmic reticulum were found to be a typical component of stem-, hypocotyledon-, and root vascular parenchyma as well as root cap cells inBrassicaceae (14 species screened) andCapparaceae (7 species). In general, DC are very long, utricular organelles containing proteins and bound by a unit membrane which is studded with ribosomes. In aerial parts of the plants tested the proteins are tubular structures arranged parallel to the DC axis, in roots there ar filamentous proteins. In someBrassicaceae (e.g., Lunaria, Ptilotrichum, Schivereckia) DC are irregularly shaped and contain granular protein material. These forms are discussed to be leading to protein-containing vacuoles as found in companion cells ofTovaria. Since DC do occur in taxa which contain glucosinolates, an EM-cytochemical test for β-thioglucosidases (as first performed byIversen) was applied to some of the species. The results, however, did not prove a specific location of the enzyme inside DC. In addition to questions on the reliability of the method it is discussed whether it is likely that DC are a site of β-thioglucosidases while it is known thate.g., the glucosinolate-containingResedaceae do not contain this organelle. Also,Erythroxylum (Erythroxylaceae) andJacaranda (Bignoniaceae) gave the same precipitations when subjected to the cytochemical test (see “note added in proof”).

Fine structure, pattern of division, and course of wound phloem in Coleus blumei

The wound phloem bridges which have developed six days after interrupting an internodal vascular bundle contain wound sieve-elements, companion cells, and phloem parenchyma cells. An analysis of the meristematic activity responding to the wounding clearly demonstrates that three consecutive divisions are prerequisite to the formation of phloem mother-cells. Companion cells are obligatory sister cells of wound sieve-elements, connected to the latter by specific plasmatic strands and provided with a dense protoplast. Six days after wounding most of the wound sieve-elements are still at a nucleate state of development, but already have characteristic P-protein bodies and plastids containing sieve-element starch. Their cytoplasmic differentiation corresponds to the changes recorded during maturation of ordinary sieve elements. Sieve-plate pores penetrate through preexisting parenchyma cell walls, only, and develop from primary pitfield-plasmodesmata. Wound sieve-elements do not connect to preexisting bundle sieve-elements, they open a new tier of young sieve elements produced by cambial activity.

Ultrastructure of phloem and its development inGnetum gnemon, with some observations onEphedra campylopoda

SummaryAn ultrastructural study of the phloem tissues of the stems of bothGnetum gnemon andEphedra campylopoda has shown that they contain only two types of cells—the sieve cells and the phloem-parenchyma cells.The phloem-parenchyma cells belong to the axial parenchyma of the stem. They are nucleate through all their life, contain starch-storing plastids and a normal set of organelles, and are laterally connected to the sieve cells by specialized plasmatic strands.The development of the sieve cell has been studied in detail inGnetum. During its differentiation most of the cell organelles are lost, the developed sieve cell being lined by plasmalemma and only containing plastids, mitochondria, and agranular ER. The nucleus undergoes a typical pycnotic degeneration, implying decrease of volume associated with increase of stainability. The formerly granular ER changes for the agranular type that during some stages becomes prevailing in the sieve cell and, finally, is aggregating into several complexes, preferentially attached to the pycnotic nuclei and lateral or end-wall sieve areas. Sieve areas as well as lateral connections to the phloem-parenchyma cells uniformly contain median cavities in the region of the middle lamella that combine the sieve pores of a sieve cell with either the pores of another sieve cell or the plasmodesmata of a phloem parenchyma cell.Both the sieve cells and the phloem-parenchyma cells lacked P-protein at every stage of differentiation inGnetum as well as inEphedra.

Sieve-element plastids ofGymnospermae: Their ultrastructure in relation to systematics

The distribution of S-type and P-type plastids in the sieve elements of 30 species from 13 families of theConiferophytina andCycadophytina is recorded, of which 21 species were studied for the first time with respect to their sieve-element plastids. While starch storing S-type plastids are the most commonly occurring type throughout both taxa, all thePinaceae examined (11 species of 7 genera) contain P-type plastids characterized by a peripheral, ring-shaped bundle of protein filaments, an additional protein crystalloid, and several starch grains. Starch grains of sieve-element plastids in theConiferophytina andCycadophytina are commonly club-shaped. Taxonomic implications of these ultrastructural findings on sieve-element plastids are discussed.

Plastids in sieve elements and their companion cells : Investigations on monocotyledons, with special reference to Smilax and Tradescantia.

SummaryPlastids have been identified in the sieve elements and/or companion cells of 14 monocotyledon species. In contrast to earlier reports, plastids are present in the sieve elements of Smilax and the companion cells of Tradescantia. The development and fine structure of the sieve-element plastids in Smilax do not differ from the type found in all of the 230 angiosperm species we have studied so far contain prominent plastids. The companion cells are easily identified by their specialized plasmatic connections with the sieve elements. The leucoplasts in the companion cells of Tradescantia are identical with those reported for many angiosperms.

The contents of the sieve-plate pores in Aristolochia

Protein filaments, tubular endoplasmic reticulum, and sometimes a genuine filamentous component derived from crystalloids of specific plastids extend through the sieve-plate pores in Aristolochia without plugging them. The frequent appearance of ER in sieve-plate pores has not been shown previously for angiosperms. Individual filaments can be followed through the pores; they have diameters of about 100 A and are composed of repeatedly arranged subunits. The question of what kind of substructures reflect the in vivo pore contents of sieve plates is discussed with regard to investigations of Aristolochia and the conflicting information in the literature.

The development of specific sieve-element plastids in wound phloem ofColeus blumei (S-type) andPisum sativum (P-type), regenerated from amyloplast-containing parenchyma cells

SummaryIn experimentally-induced wound phloem, sieve-element plastids express their genetically determined type in depositing amylopectinrich sieve-tube starch (Coleus, S-type) and polygonal protein crystals (Pisum, P-type). Sieve-element plastids budd off from preexisting amyloplasts, pass through a short amoeboid state and develop into spherical plastids with translucent matrix. During early phases of differentiation wound sieve-elements contain two populations of plastids: typical sieve-element plastids and residual parenchyma plastids with large amylose-rich starch grains. The retardation in the break down of the latter is discussed. Sieve-tube and amyloplast starches are likewise digested by α-1,4- and α-1,6-bond cleaving glucosidases.

Strukturänderungen des Endoplasmatischen Reticulums und Auftreten von Proteinfilamenten während der Siebröhrendifferenzierung beiSmilax excelsa

SummaryThe endoplasmic reticulum (ER) ofSmilax sieve tubes is one of the cell organelles that are continuously present during the entire life of the cells specialized in long-distance translocation. But it passes through major structural changes during sieve-tube ontogeny: Extended cisternae of the granular ER present within young sieve tubes change for convoluted membrane complexes of agranular ER within differentiated cells. The structural changes are initiated by a local swelling of some of the cisternae. The transformation of straight cisternae into slightly swollen and twisted tubuli-like compartments is completed prior to the final degeneration of nucleus and tonoplast and the opening of the sieve-plate pores. Aggregations of protein filaments (P-protein bodies) first are visualized at this stage of ER differentiation. The synthesis of the first protein filaments with the aid of free or membrane bound ribosomes in the initial phase of ER transformation is discussed. Further changes in the ER system, as formation of aggregates of convoluted elements, seem to be of minor importance to the function of the organelle.ZusammenfassungIm Verlauf der Siebröhrendifferenzierung beiSmilax findet eine kontinuierliche Transformation des Endoplasmatischen Reticulums (ER) von über das Plasma gleichmäßig verteilten Zisternen des rauhen zu wandständigen Membrankomplexen des glatten Typs statt. Die Strukturänderungen beginnen in sehr jungen Siebröhren mit dem lokalen Schwellen einiger ER-Zisternen, die allmählich auf alle Zisternen übergreifen und sie zunächst in ein ausgedehntes System gewundener Tubuli überführen, das zunehmend ärmer an Ribosomen wird. Dieser Zustand ist noch deutlich vor der endgültigen Kern- und Tonoplastendegeneration und der Öffnung der Siebporen erreicht. Gleichzeitig treten auch die ersten Ansammlungen von Proteinfilamenten auf. — Für die Synthese der einzelnen Proteinfilamente wird eine Beteiligung freier oder membrangebundener Ribosomen zum Zeitpunkt des Beginns der Strukturänderungen am ER diskutiert. — Spätere Aggregationen des veränderten ER-Systems sind vermutlich nicht mehr funktionsbedigt: Durch Drehungen der ER-Tubuli wird auf möglichst kleinem Raum ein Maximum and Membranen gespeichert, die an den weiteren strukturellen Veränderungen innerhalb des Siebelementplasmas nicht mehr teilnehmen.

Comparative ultrastructural investigations of angiosperm sieve elements: Aspects of the origin and early development of P-protein

Summary The origin of P-protein in young sieve elements of 20 different angiosperms is closely linked to the presence of helical free polysomes. First P-protein is present in small assemblies, individual protein filaments are subsequently formed within them. Still in the nucleate condition of the sieve elements protein filaments aggregate to small groups that enlarge to form prominent P-protein bodies. Coincident with the synthesis of P-protein the organisation of the endoplasmatic reticulum (ER) changes from cisternal rER to tubular sER. This process is initiated by a local swelling of ER cisternae that is purported to be caused after the deprivation of the ribosomes. These ribosomes could be involved in P-protein synthesis. Following the synthesis of P-protein and during the formation of protein filaments ribosomes are no longer in contact to P-protein, they rapidly disappear from the sieve element. — P-protein synthesis as the possibly last operation of free polysomes in sieve elements and the decomposition of the ribosomes in or after this process is discussed.