STRUCTURAL ORGANIZATION OF PLASTID DNA IN TWO ANOMALOUSLY PIGMENTED DINOFLAGELLATES1

The structural organization of DNA in the plastids of two anomalously pigmented dinoflagellates, Glenodinium foliaceum Stein and Gyrodinium aureolum Hulburt, was determined using the DNA-specific fluorochrome DAPI and correlated with TEM observations. The plastids of G. foliaceum were found to possess both a peripheral DNA ring and isolated point nucleoids. This arrangement was shown to be similar to that of the diatom Asterionella formosa Hass. and may be characteristic of the Bacillariophyceae. G. aureolum exhibited a novel distribution of plastid. DNA as one or two beaded bands, whereas the plastids of the similarly pigmented haptophyte, Emiliania huxleyi (Lohm.) Hay & Mohler, possessed scattered point nucleoids. These findings support the idea that G. foliaceum harbours an endosymbiotic diatom, but suggest that the plastids of G. aureolum and E. huxleyi are unrelated. The use of plastid DNA configuration as a phylogenetic marker is considered.     

Quantitative,three-dimensional analysis of alfalfa egg cells in two genotypes: Implications for biparental plastid inheritance

In alfalfa (Medicago sativa L.), plastids are inherited biparentally. Patterns of plastid transmission vary according to the genotypes involved, but there is a strong bias in favor of male plastid transmission. Previous cytological studies on the male gametophyte of this species have not provided an adequate explanation for the differences in plastid transmission frequencies among genotypes. In the present study, we compared egg cells from genotypes classified as strong or weak plastid transmitters to determine whether plastid transmission strength is correlated with egg cell structure before fertilization. We found that plastids in the mature egg cells of the strong female (genotype 6–4) are significantly larger than in mature eggs of the weak female (genotype CUF-B), and that significantly more plastids are positioned in the apical portion of the mature egg cell of genotype 6–4 than in CUF-B. Immature eggs in the two genotypes show the same pattern as mature eggs with regard to plastid number and polarization. Since only the apical portion of the egg cell/zygote gives rise to the functional embryo, these results indicate that the potential input of female plastids, in terms of plastid size and number, may be an important factor in determining the inheritance patterns of these organelles in alfalfa.Support for this work by the United States Department of Agriculture under grant 88-37234-3876, the National Science Foundation under grant DCB-9103658, the Organized Research Fund of Northern Arizona University, and the Arizona Agricultural Experiment Station is gratefully acknowledged. We are indebted to Dr. Craig Caldwell, Northern Arizona University Computer Visualization Laboratory, for his expert help with the computer graphics.     

CYANOPHYTE AND CYANELLE DNA: A SEARCH FOR THE ORIGINS OF PLASTIDS1

Cyanophyte-like prokaryotes are widely presumed to be the progenitors of eukaryote plastids. A few rare protistan species bearing cyanophyte-like cyanelles may represent intermediate stages in the evolution of true organelles. Cyanophyte DNA disposition in the cell, so far as is known from electron microscopy, seems uniform within the group and distinctly different from the several known arrangements of DNA in plastids. Therefore a survey of representative cyanophytes and protistan cyanelles was undertaken to determine whether forms reminiscent of plastids could be found. DNA-specific fluorochromes were utilized, along with epifluorescent microscopy, to study the DNA arrangement in situ in whole cells. Only the endospore (baeocyte)-forming Cyanophyta contained more than one, centrally located DNA skein per cell, and then only for the period just preceding visible baeocyte formation. Such forms might, with modification, presage the “scattered nucleoid” DNA disposition found in plastids of several groups, including Rhodophytes, Cryptophytes, Chlorophytes and higher plants. The DNA arrangement in cyanelles of two protists, Cyanophora and Glaucocystis, appear different from each other and possibly related to, respectively, the cyanophytes Gloeobacter and Synechococcus. Cyanelles of the third protist, Glaucosphaera, like the cells of the unique prokaryote Prochloron, appear to have multiple sites of DNA, somewhat similar to those of the “scattered nucleoid” line of plastid evolution. No obvious precursor of the “ring nucleoid” or other types of plastid DNA conformation was found.     

THE ULTRASTRUCTURE OF CARPOSPOROGENESIS IN CALOGLOSSA LEPRIEURII (DELESSERIACEAE,CERAMIALES)

Carposporogenesis in Caloglossa leprieurii is divided into three cytological stages. At stage I, the young spores have few plastids and little starch. Abundant dictyosomes secrete a gelatinous wall layer in scale-like units. At stage II, dictyosomes produce a second fibrillar wall component in addition to the gelatinous constituent. Large fibrillar vesicles accumulate in the cytoplasm. Production of gelatinous material decreases in this stage. By stage III, starch grains and fully developed plastids are abundant. Rough endoplasmic reticulum occupies much of the peripheral cytoplasm. A dense, granular proteinaceous component appears in the wall in association with the fibrillar layer. Arrays of randomly oriented tubules are scattered in the cytoplasm. The mature carpospore is surrounded by an outer gelatinous wall layer and an inner fibrillar layer. Few dictyosomes persist in the mature spore. Carposporogenesis in Caloglossa is compared with that in other red algae.     

Diversité des formes d'accumulation de la phytoferritine dans les cellules constituant l'épithème des hydathodes de Taraxacum officinale Weber et Saxifraga aizoon Jacq.

Summary In Taraxacum officinale and Saxifraga aizoon particular aggregations found in plastids of epithem are considered to be phytoferritin. The diversity of plant ferritin arrangement within the plastids is studied. High magnification study of these inclusions indicates that they can be classified morphologically into three distinct groups: dense and amorphous aggregate (F₁), crystalline inclusion (F₂) and diffuse paracrystalline arrangement (F₃). The crystalline (F₂) and amorphous (F₁) structures are both present in the plastids of Saxifraga aizoon; similarly, paracrystalline (F₃) and amorphous inclusions (F₁) are both present in the plastids of Taraxacum officinale. Because of their location and the nature of their organization, we think that the phytoferritin complexes under discussion may be important in phytoferritin synthesis or phytoferritin utilization within the living plant.     

THE FINE STRUCTURE OF OOGENESIS IN MARCHANTIA POLYMORPHA

Archegonium development, beginning with the archegonial initial and culminating in the mature egg, was studied with the electron microscope. The ultrastructural features of the beginning stages in development of the archegonium are relatively similar to one another. Plasmodesmata occur between all adjacent cells at this time. After the secondary central cell is formed these protoplasmic connections are lost, and both axial and parietal cell lineages begin to show signs of ultrastructural differentiation. The mature egg is characterized by cytoplasm rich in ribosomes and larger organelles. Mitochondria and simplified plastids commonly display a juxtaposed association. As far as could be ascertained the numerous plastids and mitochondria in the egg of Marchantia arise through division of preexisting organelles and are not formed anew from evaginations of the nucleus. Blebbing of the nucleus produces polymorphic organelles which appear to be pinched off into the cytoplasm. The mature egg also contains vacuoles and lipid bodies toward its periphery, while dictyosomes and extensive endoplasmic reticulum occur throughout. The space between the wall cells and the mature egg appears to contain an amorphous substance. No extra membrane was observed around the mature egg.     

DIFFERENTIATION OF INTRACAPSULAR CELLS IN THE SPOROPHYTE OF SPHAEROCARPOS DONNELLII

Ultrastructural and histochemical changes during intracapsular cell differentiation in the premeiotic sporophyte of the liverwort Sphaerocarpos donnellii Austin were studied. From an initially undifferentiated meristematic tissue, spore mother cells and nutritive cells become differentiated. The first indications of ultrastructural differentiation into two cell types are the accumulation of lipid within spherosomes and the occurrence of plastid tubules in the presumptive spore mother cells. Once differentiated the two cell types are clearly distinguishable on the basis of cytoplasmic vacuolation, stored food reserve, and cell and nuclear size. The mature spore mother cell contains many spherosomes, small vacuoles, starch-containing plastids, and a large central nucleus. The mature nutritive cell, on the other hand, is extremely vacuolate and contains large, starch-filled plastids, a few spherosomes, and a small nucleus. A previously undescribed type of cell was observed in developing sporophyte capsules. This cell is located peripherally in the capsule and degenerates during differentiation of spore mother cells and nutritive cells.     

STRUCTURE AND DEVELOPMENT OF SIEVE ELEMENTS IN THE LEAF OF ISOETES MURICATA

Leaf tissue of Isoetes muricata Dur. was fixed in glutaraldehyde and postfixed in osmium tetroxide for electron microscopy. The very young sieve elements can be distinguished from contiguous parenchyma cells by their distinctive plastids and the presence of crystalline and fibrillar proteinaceous material in dilated cisternae of the rough ER. During differentiation, the portions of ER enclosing this proteinaceous substance become smooth surfaced and migrate to the cell wall. Along the way they apparently form multivesicular bodies which then fuse with the plasmalemma, discharging their contents to the outside. At maturity, the sieve element contains an elongate nucleus, which consists of dense chromatin material, and remnants of the nuclear envelope. In addition, the mature sieve element is lined by a plasmalemma and a parietal, anastomosing network of smooth ER. Both plastids and mitochondria are present. P-protein is lacking at all stages of development. Tonoplasts are. not discernible in mature sieve elements. The end walls of mature sieve elements contain either plasmodesmata or sieve pores or both, but only plasmodesmata occur in the lateral walls.     

ULTRASTRUCTURE OF CHRYSODIDYMUS SYNUROIDEUS (SYNUROPHYCEAE)1

A clonal isolate of Chrysodidymus synuroideus Prowse was derived form a Sphagnum bog in northern Wisconsin and maintained in culture for over 3 years. Cultured colonies consisted almost exclusively of two cells attached at the posterior, each cell bearing two unequal flagella. Correlative light and electron microscopic observations revealed that colonies composed of smaller, ovate cells represented more recent products of cell division, while colonies of elongate cells were more mature. These results support previous taxonomic conclusions, based on light microscopic observations, of field-collected specimens and body scale ultrastructure, that Chrysodidymus is a valid genus, and that two species described by Prowse on the basis of cell size differences, should be merged. In addition, ultrastructural studies of cultured Chrysodidymus demonstrated that this genus is a member of the Synurophyceae on the basis of characters related to flagellar morphology, basal body arrangement, and cytoskeletal ultrastructure. Chrysodidymus synuroideus resembles Synura sphagnicola in body scale structure, the presence of distinctive linear or clavate scales on both flagella, a relatively loose scale case, and acidophilic habital, Unlike S. sphagnicola, Chrysodidymus has no Pyrennoids, Peripheral (rather than axial) plastids, and a single posterior storage vesicle (rather than two peripheral storage vesicles).     

DIVERSITY OF PLASTID DNA CONFIGURATION AMONG CLASSES OF EUKARYOTE ALGAE1

Information is presented concerning the overall arrangement of plastid DNA (ptDNA) in plastids of approximately 100 spp. of eukaryote algae, representing all classes. The three-dimensional arrangement of the ptDNA was assessed by study of both living and fixed material, stained with the DNA fluorochrome 4′,6-diamidino-2-phenylindole (DAPI), using both phase and fluorescence microscopy. The widespread occurrence of two major types of ptDNA configuration known from prior electron microscopy studies was confirmed. These are (1) DNA densities (nucleoids) of variable size and morphology, scattered throughout the plastid, and (2) a ring nucleoid, beaded or unbeaded, lying just within the girdle lamella. Type 1 is characteristic of Rhodophyta, Dinophyta, Chlorophyta, Cryptophyta, Prymnesiophyceae and Eustigmatophyceae (with one exception). Type 2 is characteristic of Phaeophyceae, Bacillariophyceae, Raphidophyceae, Chrysophyceae (except silicoflagellates and organisms such as Synura and Dinobryon), and Xanthophyceae (with the exception of Vaucheria and three genera known to lack girdle lamellae, Bumilleria, Bumilleriopsis, and Pseudobumilleriopsis). Some of these exceptional forms, as well as Euglenophyta, have configurations of ptDNA not previously recognized. In all the configurations observed, the DNA of a single plastid could be interpreted as being in continuity. This character of plastids appears to be stable under varied conditions of growth and at differing stages of the life cycle, where examined, and has confirmed the reclassification made on other grounds of several taxonomic entities. It has also revealed new questionable classifications. Since DAPI staining is far simpler than serial sectioning for electron microscopy in revealing ptDNA architecture, use of the technique may be valuable for future studies of numerous organisms, both to help in their identification and as an aid to unravelling major taxonomic affinities. In light of the endosymbiont hypothesis, plastid characters may require as great attention as those of the remainder of the cell.     

Assembly of the barley light-harvesting chlorophyll a/b proteins in barley etiochloroplasts involves processing of the precursor on thylakoids

A barley gene encoding the major light-harvesting chlorophyll a/b-binding protein (LHCP) has been sequenced and then expressed in vitro to produce a labelled LHCP precursor (pLHCP). When barley etiochloroplasts are incubated with this pLHCP, both labelled pLHCP and LHCP are found as integral thylakoid membrane proteins, incorporated into the major pigment-protein complex of the thylakoids. The presence of pLHCP in thylakoids and its proportion with respect to labelled LHCP depends on the developmental stage of the plastids used to study the import of pLHCP. The reduced amounts of chlorophyll in a chlorophyll b-less mutant of barley does not affect the proportion of pLHCP to LHCP found in the thylakoids when import of pLHCP into plastids isolated from the mutant plants is examined. Therefore, insufficient chlorophyll during early stages of plastid development does not seem to be responsible for their relative inefficiency in assembling pLHCP. A chase of labelled pLHCP that has been incorporated into the thylakoids of intact plastids, by further incubation of the plastids with unlabelled pLHCP, reveals that the pLHCP incorporated into the thylakoids can be processed to its mature size. Our observations strongly support the hypothesis that after import into plastids, pLHCP is inserted into thylakoids and then processed to its mature size under in vivo conditions.     

ULTRASTRUCTURE OF THE DEVELOPING MEGASPORE MOTHER CELL OF GINKGO BILOBA

The immature megaspore mother cell of Ginkgo biloba is essentially spherical and is surrounded by a thick, complex wall. A large nucleus occupies the central region of the cell, and the organelles appear to be randomly arranged in the cytoplasm. With approaching maturity and the onset of meiosis, the cell elongates in the direction of the ovular axis. An extensive system of ER develops at the micropylar pole of the cell during elongation, and the plastids and mitochondria migrate to the opposite or chalazal pole. The micropylar end of the mature megaspore mother cell is usually devoid of plastids and mitochondria, but these organelles are densely packed in the chalazal end of the cell below the nucleus. The dictyosomes and dense spherosome-like bodies do not show such polarity in their distribution. At meiosis I plastids and mitochondria are, as a rule, restricted to the chalazal dyad cell that is destined to produce the functional megaspore. The wall of the megaspore mother cell consists of a middle lamella which is irregularly thickened, an outer wall layer resembling the walls of the surrounding nutritive cells, and an inner layer resembling the middle lamella in appearance.     

CHROMOPLASTS OF TOMATO FRUITS. I. ULTRASTRUCTURE OF LOW-PIGMENT AND HIGH-BETA MUTANTS. CAROTENE ANALYSES

Three pigment lines of the tomato cultivar ‘Pearson’ with isogenic backgrounds were studied to determine the relationship between certain carotenoids and the development of chromoplasts during fruit ripening. The lines were normal red (r⁺/r⁺), in which about 90% of the carotenoids in the ripe fruit is lycopene; high-beta (B/B) mutant, in which beta-carotene is the major pigment and the mature fruit color is deep orange ; and low-pigment (r/r) mutant, in which carotenoids are drastically reduced and the mature fruit is pale yellow-orange. This paper reports pigment analyses for the three lines and the ultrastructural changes in plastids of the two mutant lines. Very young, pale green fruits contain proplastids with limited lamellar structure. As the fruits reach the mature green stage, the plastids in all three lines develop into typical chloroplasts. Differences in pigment content and in ultrastructure among the lines are not apparent until ripening commences. In the low-pigment mutant carotenoids are reduced as ripening progresses and no carotenoid crystalloids are formed. As chlorophyll decreases the fruits become pale yellow. The grana become disorganized and the thylakoids appear to separate at the partitions and tend to be arrayed in lines, some still with their ends overlapping. Globules increase slightly in number. In the high-beta mutant the grana break down during ripening and globules increase greatly in size and number. Beta-carotene, presumed to be largely in the globules, crystallizes into elongated or druse type forms which may distort the globules. The crystals may affect the shape of the chromoplasts; long crystals may extend the length of the plastid to over 15 μ. Thylakoid plexes with a regular lattice structure sometimes occur in the chromoplasts of the high-beta mutant. Granules resembling aggregations of phytoferritin particles occur in the chromoplasts of both of these mutants.     

ON THE PLASTIDS, MITOCHONDRIA, AND OTHER CELL CONSTITUENTS DURING OÖGENESIS OF A PLANT

In the liverwort Sphaerocarpus donnellii Aust., the behavior of the cell constituents, especially of mitochondria and plastids, was studied by electron microscopy during the development of the egg and its preceding cells. A degeneration and elimination of mitochondria and plastids was not found in any of the developmental stages. In all growth phases of the archegonium, the plastids may deposit starch which becomes especially frequent in the maturing egg cell. No indications have been observed that new mitochondria or plastids generate from the nuclear evaginations, which often penetrate deeply into the cytoplasm of the maturing and fully developed eggs. A quantitative investigation based on general micrographs elucidates the numerical aspects of the cell constituents during oögenesis. With the increase of cell volume, the numbers of dictyosomes, mitochondria, plastids, and lipid bodies increase. From the stages of the mother cell of the axial row up to that of the mature egg, the cell volume enlarges about 8 times and the nucleus volume about 15 times. Simultaneously, the numbers of mitochondria and plastids increase up to 8 to 15 times. On the basis of these findings, mitochondria and plastids with three-dimensional narrow constrictions are interpreted as divisional stages.     

Plastids in sieve elements and companion cells of Tilia americana

Summary Contrary to an earlier report, the sieve elements and companion cells of Tilia americana contain plastids. In young sieve elements and companion cells the plastids contain a moderately electronopaque matrix and internal membranes; the latter are very numerous in the plastids of the sieve elements. Plastids of mature sieve elements contain an electron-transparent matrix, apparently fewer internal membranes than the plastids of young elements, and a single starch grain each. The plastids of companion cells undergo little or no structural modification during cellular differentiation, and apparently contain no starch.This research has been supported by the National Science Foundation, grants GB-5950 and GB-8330.     

Multiple fates of non‐mature lumenal proteins in thylakoids

Most proteins found in the thylakoid lumen are synthesized in the cytosol with an N–terminal extension consisting of transient signals for chloroplast import and thylakoid transfer in tandem. The thylakoid‐transfer signal is required for protein sorting from the stroma to thylakoids, mainly via the cpSEC or cpTAT pathway, and is removed by the thylakoidal processing peptidase in the lumen. An Arabidopsis mutant lacking one of the thylakoidal processing peptidase homologs, Plsp1, contains plastids with anomalous thylakoids and is seedling‐lethal. Furthermore, the mutant plastids accumulate two cpSEC substrates (PsbO and PetE) and one cpTAT substrate (PsbP) as intermediate forms. These properties of plsp1‐null plastids suggest that complete maturation of lumenal proteins is a critical step for proper thylakoid assembly. Here we tested the effects of inhibition of thylakoid‐transfer signal removal on protein targeting and accumulation by examining the localization of non‐mature lumenal proteins in the Arabidopsis plsp1‐null mutant and performing a protein import assay using pea chloroplasts. In plsp1‐null plastids, the two cpSEC substrates were shown to be tightly associated with the membrane, while non‐mature PsbP was found in the stroma. The import assay revealed that inhibition of thylakoid‐transfer signal removal did not disrupt cpSEC‐ and cpTAT‐dependent translocation, but prevented release of proteins from the membrane. Interestingly, non‐mature PetE2 was quickly degraded under light, and unprocessed PsbO1 and PsbP1 were found in a 440‐kDa complex and as a monomer, respectively. These results indicate that the cpTAT pathway may be disrupted in the plsp1‐null mutant, and that there are multiple mechanisms to control unprocessed lumenal proteins in thylakoids.     

Regreening of senescent Nicotiana leaves. II. Redifferentiation of plastids

Single senescent leaves attached to decapitated shoots of Nicotiana rustica L. regreened, especially when treated with cytokinin. Regreening caused an increase in leaf thickness, due to cell expansion. Senescent leaf plastids (gerontoplasts) were smaller than green chloroplasts, with degenerated membrane systems and stroma, and larger plastoglobuli. At advanced senescence, micrographs showed disintegrating gerontoplasts, reduced numbers of plastids were counted, and regreening became variable. The redevelopment of grana and stroma in regreening plastids was accelerated by cytokinin. All plastids in regreening leaves were identifiable as redifferentiating gerontoplasts because of their content of plastoglobuli and starch. Immunogold labelling showed significant association of POR with etioplasts in cotyledons, but with mature plastids in regreening leaves. No proplastids or dividing chloroplasts were observed in regreening leaves. Plastids numbers declined during senescence and did not increase again during regreening. It is concluded that the chloroplasts of regreening leaves arose by redifferentiation of gerontoplasts.Keywords: Chloroplasts, cytokinin, Nicotiana, senescence, regreening.      

STRUCTURE AND DEVELOPMENT OF THE SIEVE-ELEMENT PROTOPLAST IN THE HYPOCOTYL OF PINUS RESINOSA

Hypocotyl tissue of Pinus resinosa Ait. was fixed in glutaraldehyde-paraformaldehyde and postfixed in osmium tetroxide for electron microscopy. Although young sieve cells contain all the components characteristic of young, nucleate cells, they can be identified early in their development. Increase in wall thickness occurs early and rapidly. Concurrently, the plastids, which already contain starch granules, form both crystalline and fibrillar inclusions. As the sieve cell approaches maturity, an extensive network of smooth, tubular endoplasmic reticulum (ER), which becomes mostly parietal in distribution, is formed. At maturity, massive aggregates of this ER occur on both sides of sieve areas. These ER aggregates are interconnected with one another longitudinally by the parietal ER. In addition, the mature, plasmalemma-lined sieve cell contains a degenerate nucleus, mitochondria, and intact plastids. Dictyosomes, ribosomes, and vacuolar membranes are lacking. P-protein is not present at any stage of development.     

STUDIES ON CELL METABOLISM AND CELL DIVISION : II. STIMULATION OF CELLULAR OXIDATION AND REVERSIBLE INHIBITION OF CELL DIVISION BY DIHALO AND TRIHALOPHENOLS

The dihalo and trihalophenols, and phenols containing both halo and nitro substituents in the same molecule, produce, in fertilized eggs of Arbacia punctulata, a rise in rate of oxygen consumption and a reversible block to cell division. To define the conditions which affect the degree of this activity, the following factors have been varied: the arrangement of substituents in the molecule, the concentration of reagent, and the time after fertilization at which the reagent is added. The stimulation of oxygen consumption and reversible block to cell division produced by the dihalophenols are qualitatively the same as those previously produced in fertilized Arbacia eggs by certain dinitrophenols. To yield optimum respiratory effect and maximum division block, it usually requires a higher concentration of dihalo than of the corresponding dinitrophenol. For example, with fertilized Arbacia eggs at 20°C. 2,4-dinitrophenol, in optimum concentration of 3 x 10^–5 molar, raises oxygen consumption to 292 per cent of normal (4). The corresponding values for two dihalo analogues are: 2,4-dichlorophenol, 10^–4 molar and 236 per cent; 2,4-dibromophenol, 6 x 10^–5 molar and 282 per cent. The halophenols differ from the nitrophenols in two interesting respects: (a) The monohalophenols produce little or no oxidative stimulation or division block in fertilized Arbacia eggs; p-nitrophenol is very active in both respects. (b) The symmetrical trihalophenols have an appreciable ability to stimulate oxygen consumption and block division; symmetrical trinitrophenol is inactive in both respects (4). The increases in oxygen consumption produced in fertilized Arbacia eggs by 2,4-dichloro and 2,4-dinitrophenol are larger than the percentage increases given by methylene blue and o-cresol indophenol under the same experimental conditions. The dihalo and dinitrophenols produce a reversible block to the cell division of fertilized marine eggs. The oxidation-reduction indicators, in contrast to the dihalo and dinitrophenols, block cell division irreversibly and fertilized eggs of Arbacia do not recover from optimum respiratory stimulating concentrations of these oxidation-reduction dyes. The present experiments with halophenols are in harmony with and lend considerable support to the hypothesis (4) that nitro and similarly substituted phenols derive their biological activity from the presence and properties of the phenolic OH group, as modified by proper substitution in the phenolic benzene ring.     

Cytological evidence for preservation of mitochondrial and plastid DNA in the mature generative cells of Chlorophytum spp. (Liliaceae)

Summary.  Following 4′,6-diamidino-2-phenylindole staining of mature pollen grains of Chlorophytum comosum, fluorescence microscopy confirmed that cytoplasmic nucleoids (DNA aggregates) were present in the generative cells, which indicated the possibility of biparental cytoplasmic inheritance. Electron and immuno-electron microscopy showed that both plastids and mitochondria were present in the generative cells, and both organelles contained DNA. These results indicate that mitochondria and plastids of C. comosum have the potential for biparental inheritance. Similar results were obtained with mature pollen grains of C. chinense. Therefore, we conclude the coincident biparental inheritance for mitochondria and plastids in the members of the genus Chlorophytum. Received June 28, 2002; accepted September 26, 2002; published online April 2, 2003 RID="*" ID="*" Correspondence and reprints: College of Life Science, Peking University, Bejing 100871, People's Republic of China.