Callose Plugs Research Articles

POLLEN‐PISTIL INTERACTIONS IN TRISTYLOUS PONTEDERIA SAGITTATA (PONTEDERIACEAE). II. PATTERNS OF POLLEN TUBE GROWTH

Pollen tube behavior was compared after legitimate and illegitimate pollinations of tristylous Pontederia sagittata. All pollinations resulted in substantially fewer pollen tubes in the style than pollen grains on the stigma surface. Number of pollen tubes showed a characteristic attrition, particularly by the midpoint of the style in all pollination types. Two classes of illegitimate pollination could be identified. In pollinations with pollen smaller than the legitimate size class for a given morph, pollen tubes ceased growth in characteristic regions of the style. In pollinations with pollen larger than the legitimate size class, pollen tubes entered the ovary. In the latter class of pollination, pollen tube behavior in the M morph was similar to that of legitimate pollinations. In the S morph illegitimate pollen tube behavior was distinctive. Pollen tubes entered the ovary but rarely contacted the obturator most often growing down the funiculus of the ovule and terminating growth at its base. The associations between pollen size, pollen tube length and width, and callose plug length regardless of pollination type suggest that incompatibility in P. sagittata is governed by the interaction of heteromorphic characters rather than by an active rejection mechanism mediated by molecular specificities. The distinctive features of incompatibility in P. sagittata are discussed in relation to structural features of the pollen tube pathway, incongruity mechanisms, and gametophytic incompatibility in monocotyledonous families.

Pollen-Pistil Interactions in Tristylous Pontederia sagittata (Pontederiaceae). II. Patterns of Pollen Tube Growth

Pollen tube behavior was compared after legitimate and illegitimate pollinations of tristylous Pontederia sagittata. All pollinations resulted in substantially fewer pollen tubes in the style than pollen grains on the stigma surface. Number of pollen tubes showed a characteristic attrition, particularly by the midpoint of the style in all pollination types. Two classes of illegitimate pollination could be identified. In pollinations with pollen smaller than the legitimate size class for a given morph, pollen tubes ceased growth in characteristic regions of the style. In pollinations with pollen larger than the legitimate size class, pollen tubes entered the ovary. In the latter class of pollination, pollen tube behavior in the M morph was similar to that of legitimate pollinations. In the S morph illegitimate pollen tube behavior was distinctive. Pollen tubes entered the ovary but rarely contacted the obturator most often growing down the funiculus of the ovule and terminating growth at its base. The associations between pollen size, pollen tube length and width, and callose plug length regardless of pollination type suggest that incompatibility in P. sagittata is governed by the interaction of heteromorphic characters rather than by an active rejection mechanism mediated by molecular specificities. The distinctive features of incompatibility in P. sagittata are discussed in relation to structural features of the pollen tube pathway, incongruity mechanisms, and gametophytic incompatibility in monocotyledonous families.

DIFFERENTIAL POLLEN‐TUBE GROWTH RATES AND NONRANDOM FERTILIZATION IN HIBISCUS MOSCHEUTOS (MALVACEAE)

The prevalence of nonrandom fertilization due to postpollination events has rarely been studied in natural populations, despite important implications for outcrossing rates, mate choice, and plant fitness. Nonrandom paternity within fruits can be caused by both unequal fertilization and unequal embryo abortion. Using self‐compatible Hibiscus moscheutos, we studied the potential for nonrandom fertilization by comparing growth rates of pollen‐tubes from different donors. The branched style of Hibiscus allowed within‐flower comparisons between pollen donors. Relative pollen‐tube growth rates were determined by applying pollen from pairs of donors to different stigmas on adjacent stylar branches. We then measured the number of callose plugs per tube in cross‐sectional transects across the style after 3 hr. We demonstrate that rates of callose plug formation can be used as a sensitive indicator of relative pollen‐tube growth rate. Differences between pollen donors were common and repeatable. Self‐pollen‐tubes grew slower than outcross pollen‐tubes in some crosses and faster in others. Allozyme variation in glucose phosphate isomerase was used to show that individuals with fast‐growing pollen‐tubes sired a disproportionate number of seeds following mixed pollinations (up to 72%). Since seed abortion was negligible, we conclude that variation in pollen‐tube growth rates leads to nonrandom paternity within fruits.

Differential Pollen-Tube Growth Rates and Nonrandom Fertilization in Hibiscus moscheutos (Malvaceae)

The prevalence of nonrandom fertilization due to postpollination events has rarely been studied in natural populations, despite important implications for outcrossing rates, mate choice, and plant fitness. Nonrandom paternity within fruits can be caused by both unequal fertilization and unequal embryo abortion. Using self-compatible Hibiscus moscheutos, we studied the potential for nonrandom fertilization by comparing growth rates of pollen-tubes from different donors. The branched style of Hibiscus allowed within-flower comparisons between pollen donors. Relative pollen-tube growth rates were determined by applying pollen from pairs of donors to different stigmas on adjacent stylar branches. We then measured the number of callose plugs per tube in cross-sectional transects across the style after 3 hr. We demonstrate that rates of callose plug formation can be used as a sensitive indicator of relative pollen-tube growth rate. Differences between pollen donors were common and repeatable. Self-pollen-tubes grew slower than outcross pollen-tubes in some crosses and faster in others. Allozyme variation in glucose phosphate isomerase was used to show that individuals with fast-growing pollen-tubes sired a disproportionate number of seeds following mixed pollinations (up to 72%). Since seed abortion was negligible, we conclude that variation in pollen-tube growth rates leads to nonrandom paternity within fruits.

POLLEN TUBE GROWTH AND INBREEDING DEPRESSION IN AMSINCKIA GRANDIFLORA (BORAGINACEAE)

To discriminate between the roles of differential pollen tube growth and inbreeding depression in causing reduced seed production following self‐pollination of distylous Amsinckia grandiflora (Boraginaceae), callose plug and pollen tube production were compared following cross‐ and self‐pollinations of A. grandiflora. Pin (long‐styled morph) × thrum (short‐styled morph) crosses yielded more pollen tubes than pin × pin crosses or pin self‐pollinations; no difference could be detected for the pin × pin or pin self‐pollination categories. Using thrums as the female parent, no significant differences were detected in any pollination category. These results indicate that reduced seed production following self‐fertilization of A. grandiflora is likely to be the result of inbreeding depression rather than inhibition of self pollen tubes.

ナス (<i>Solanum melongena</i> L.) と近縁野生種との交雑和合性について

Pollen tube growth behavior and success of interspecific crosses between eggplant and wild relatives were studied. Solanum gilo, S. insanum and S. integrifolium were found compatible to eggplant. S. indicum, as the male and female parent, produced mostly unfilled seeds with eggplant ‘Senryo 2 gou’. This species as seed parent produced about 50% filled seeds when it was pollinated by eggplant ‘Uttara’. Only pollination by ‘Senryo 2 gou’ produced a few viable seeds on S. surattense and S. xanthocarpum. Pollen tubes of S. mammosum grew normally in the pistils of ′Senryo 2 gou′ resulting 100% parthenocarpic fruit development. The ‘Uttara’ produced no parthenocarpic fruit, while the former cultivar produced parthenocarpic fruit with 8 different species. Failure or poor germination of pollen, retarded growth of pollen tubes, termination of pollen tube growth before reaching the ovary, weak fluorescence of the pollen tubes, irregular deposition and size of callose plugs, swollen and/or branched pollen tube apex alone or in combination were observed in most of the incompatible crosses.

Actomyosin and movement in the angiosperm pollen tube: an interpretation of some recent results

Recent confirmations of the presence of myosin in angiosperm pollen tubes indicate that an energy-transducing actomyosin system is involved in the motility system of the vegetative cells. Myosin has been localised by immunofluorescence on the surfaces of vegetative nuclei and generative cells. It has been shown to be associated with individual amyloplasts in grass pollen, and there are indications that it is present on other particulate bodies in the cytoplasm. The organelles in the leading part of the tube move along separate traffic lanes of acropetal and basipetal polarity, known from electron microscopy and phalloidin labelling to contain numbers of fibrils containing aggregates of actin microfilaments; in older segments the movement can be related to single, uniformly polarised, fibrils. Circulatory flow is maintained at the proximal end by the looping of the fibrils in the grain or at callose plugs. Such loops do not occur at the apex, where entering organelles undergo random movement before becoming associated with basipetal streams. Vegetative nuclei and generative cells interact with several fibrils, and it is suggested that they are held in the leading part of the protoplast in unstable equilibrium between acropetal and basipetal forces. Constantly changing form, especially of the vegetative nucleus, is one consequence of these varying stresses. Possible analogies with the intracellular motility system of the giant cells of the Characeae are noted, and it is suggested that lipid globuli and other nonorganellar bodies may be transported in the pollen tube by association with myosin-bearing membranes similar to those involved in endoplasm movement in the characean cells.

PH‐DEPENDENCE OF CHLORTETRACYCLINE(CTC)‐INDUCED PLUG FORMATION IN NITELLA FLEXILIS (CHARACEAE)1

ABSTRACTThe formation of chlortetracycline(CTC)‐induced wall appositions (callose plugs) in Nitella flexilis (L.)Ag. was pH‐dependent in the range between 4.3‐8.3. Plug number and plug diameter increased with the pH of the CTC solution. At pH 4.3 plug formation was light‐dependent and occurred below the alkaline regions of the cell surface which form during photo synthetic assimilation of HCO3−. Inhibition of photosynthesis by 3–(3′,4′‐dichlorophenyl)‐1, 1‐dimethylurea prevented plug formation in the light. Dark‐treated cells could be induced to form plugs by raising the pH of the CTC solution. The formation of large but incomplete plugs in the presence of cytochalasin B is explained by the formation of numerous weak alkaline sites. I suggest that CTC enhances locally the Ca2+content at the cytoplasm near the plasmamembrane. The ionophoric character of CTC is probably more pronounced at high pH mainly because of a weaker binding with cations and a closer contact with the membrane.

INCOMPATIBILITY IN AMSINCKIA GRANDIFLORA (BORAGINACEAE): DISTRIBUTION OF CALLOSE PLUGS AND POLLEN TUBES FOLLOWING INTER‐ AND INTRAMORPH CROSSES

The distribution of callose plugs and pollen tubes was investigated following inter‐ and intramorph crosses of Amsinckia grandiflora (Boraginaceae), a distylous species possessing cryptic self‐incompatibility. Callose plug distribution provided a good indication of the distribution of pollen tubes. Compared to intramorph crosses, many more callose plugs and pollen tubes were found in basal stylar regions following intermorph crosses, indicating that differential pollen tube growth is a likely cause of cryptic self‐incompatibility. The incompatibility response differed for the floral morphs: in the pin (long‐styled) morph pollen tubes were most likely to cease growth in the midstylar region, while inhibition was more likely to occur in the upper stylar region of the thrum (short‐styled) morph. There was no evidence of stigmatic inhibition of pollen tubes for either morph, although the incompatibility response in the Boraginaceae is normally located in the stigmatic region.

The effect of cherry leaf roll virus infection on the performance of birch pollen and studies on virus replication in germinating pollen

SUMMARYThe rates of germ tube elongation in vitro of pollen from cherry leaf roll virus (CLRV)‐infected birch (Betula pendula) did not differ significantly from those of pollen from virus‐free trees. Differences in percentage germination of pollen collected from trees at different sites were significant but percentages of germination of pollen from virus‐infected and virus‐free trees did not differ greatly from one another. In vivo, pollen from infected trees germinated on healthy and CLRV‐infected stigmas and callose plugs formed in both types of tissues.However, the extent of callose plug formation was greater in the pollen tubes of virus‐free grains germinating in infected stigmas than in reciprocal crosses. CLRV coat antigen was detected by ELISA in stigmatic tissue, from healthy trees, on which virus‐carrying pollen grains had germinated.Using fluorescein isothiocyanate conjugated to CLRV‐specific γ‐globulin, viral coat antigen was detected throughout germ tubes from virus‐carrying but not virus‐free pollen germinating in vitro. Protoplasts released following Driselase digestion of pollen germ tubes from virus‐infected trees contained CLRV antigen detectable by ELISA. During germination of virus‐infected pollen there was little synthesis of viral coat protein or nucleic acid but, following inoculation with purified virus particles, protoplasts made from healthy germinating pollen produced increasing amounts of CLRV‐specific antigen implying that CLRV replicated in this system.

A quantitative and structural comparison of Citrus pollen tube development in cross-compatible and self-incompatible gynoecia

Pollen tube development in Orlando tangelo (Citrus paradisi Macf. × C. reticulata Blanco.) was compared within and between cross-compatible pollinations of Orlando pollen on Dancy tangerine (C. reticulata Blanco.) stigmas and self-incompatible pollinations on Orlando tangelo stigmas. Orlando and Dancy gynoecia were morphologically similar but differed slightly in stigma, style, and ovary lengths. Orlando pollen tube development was studied 1, 3, 6, 9, and 12 days after both cross- and self-pollination to record the number of pollen tubes at each of five levels: stigma surface, upper style, lower style, ovary, and entrance into ovules. In the incompatible cross (self-pollinated Orlando), the stigma was the primary region of pollen tube arrest. In the compatible cross (Orlando pollen on Dancy), some pollen tubes penetrated ovules between 9 and 12 days after cross pollination; however, other pollen tubes were arrested in the stigma. Pollen tubes that successfully penetrated ovules in the compatible cross differed morphologically from pollen tubes arrested in both the compatible and incompatible situations. Successful compatible pollen tubes were straight with thin-walled tips and regularly spaced callose plugs behind the growing tips. Many pollen tube abnormalities associated with the self-incompatible pollination of Orlando were also present among arrested pollen tubes from the compatible cross.

Pollen-pistil interactions in interspecific crosses of Populus (sections Aigeiros and Leuce): pollen adhesion, hydration and callose responses.

Intersectional crosses between species of sections Aigeiros (Populus deltoides, P. X euramericana or P. nigra) and Leuce (P. alba or P. tremuloides) are known to be reciprocally incompatible. The site of pollen tube arrest is on the stigma surface in pollinations between pistils of section Leuce and pollen of section Aigeiros; tubes failed to penetrate the stigma surface. In reciprocal matings, pollen of section Leuce germinated and tubes penetrated the stigma and style, where arrest occurred. Rejection may be accompanied by swelling of the tube tips, and callose plug formation. In the cross between P. deltoides and P. alba a callose response was detected in the cell walls of the transmitting tissue, adjacent to the rejected pollen tubes.

The sieve plate of Echium (Boraginaceae): developmental aspects and response of P-protein to protein digestion

The development of the sieve plate, including pore formation, was examined in sieve elements of the primary phloem in leaf midveins of five species of Echium (Boraginaceae). The material was processed without attempts to prevent callose deposition and plugging of pores with P-protein. A pore develops by enlargement of a plasmodesmal canal and removal of plasmodesmal core. Initially, callose is deposited at each end of a plasmodesma, encircling its strand. Callose accumulates and thickens the wall at the pore site, which is covered with the plasmalemma and endoplasmic reticulum (ER) cisternae. Both membranous entities appear to be spatially associated with the plasmodesmal strand. Lysing of the wall in the middle lamella region allows the merging of the two opposite callose masses. Removal of the plasmodesmal strand and most of the callose opens the pore. The plasmalemma lines the pore. P-protein tightly packed in pores was digested by protease.

Amino Acid Uptake and Protein Synthesis in Cultured Tobacco Pollen

Summary The uptake of amino acids and their incorporation into proteins by tobacco pollen tubes in suspension culture was studied as a function of pollen tube growth. Leucine transport over a 0.01–0.5 mM concentration range occurs against the concentration gradient via an energy-dependent saturable system with an apparent K m × 10 -4 M and maximum velocity 1.25 fmol min -1 per pollen tube in a 4 h culture. A part of the absorbed leucine is released into the medium, the efflux being about 6 % of influx in 10 min preloaded pollen tubes. The rate of uptake per pollen tube increases proportionally to the duration of growth up to at least 8 h and decreases after 12 h of culture. In the period between 6 and 12 h, the first callose plug is formed nearly in 90 % of pollen tubes, separating the about 0.9 mm apical part. The uptake is linear for 30 min and in 2 h an equilibrium between the endogenous and exogenous amino acid pools is achieved in 1 mg · ml -1 of casein hydrolysate. The rate of protein synthesis, as estimated from the proportion of incorporated to free amino acids absorbed, does not decrease and the amount of incorporated exogenous amino acids increases continuously for at least 18 h of culture, provided that pollen tube growth is not depressed. A comparison of the results from different periods of labelling with 14 C-leucine suggest that the free leucine pool is compartmentalized. The protein precursor poll appears to be small and rapidly fed from exogenous source.

Translocation in Saccorhiza dermatodea (Laminariales, Phaeophyceae): anatomy and physiology

An anatomical, ultrastructural, histoautoradiographic, and physiological study was made of the kelp Saccorhiza dermatodea, which possesses an anatomy "atypical" of Laminariales. A freeze-substitution – histoautoradiographic procedure localized 14C-labelled organic matter in highly elongated cells (solenocysts) in the medulla of Saccorhiza. These cells are the major long-distance, symplastic translocation pathway in this alga. Solenocysts are joined to each other via numerous lateral connections involving small intermediary cells called allelocysts. Sieve plates (pore diam: ca. 0.05 μm; pore density: ca. 100 μm−2), pierced by plasmodesmata in which an occasional tubule may be seen, are present at all allelocyst–solenocyst junctions as well as at intercellular connections in the cortex and meristodermal layers. Solenocyst ultrastructure closely resembles that of typical sieve cells of Laminariales. Secondary wall deposition occurs between June and October constricting the numerous lateral sieve plates and nearly occluding the cell lumen; however, no callose plugging was observed in any of the medullary cells. In vivo14C-photoassimilate transport was monitored in S. dermatodea blades using a Geiger–Müller probe. The translocation velocity was estimated at 60–100 mm∙h−1 with a greater translocation rate during the day than at night. Amino acid analyses of the S. dermatodea exudate showed a high alanine and glycine content with maximum concentrations 300 mm above the blade base. Nearly 90% of the 14C activity in both source and sink portions of the blade was in alcohol-soluble matter at the end of 72-h experiments. The unique anatomy of the Saccorhiza blade lends it to experimental exploration of the translocation process in kelp.

Ultrastructure of cell wall and plugs of tobacco pollen tubes after chemical extraction of polysaccharides

Tobacco pollen tubes grown in vitro and from pollinated tobacco styles were treated by chemical solvents to remove one or more of the following polysaccharides from the tube walls: pectin (ethylenediamine tetraacetic acid); hemicellulose (alkali); callose (alkali; potassium hypochlorite); cellulose (cuprammonium); and all polysaccharides with exception of cellulose (H2O2/glacial acetic acid). Both the inner tube wall, which we had regarded as the secondary wall, and the plugs contained, in addition to callose, microfibrils of cellulose and "non-cellulosic" microfibrils that had "pectin-like" properties. When using the expressions callosic or callose layer and callose plugs in reference to pollen tubes, one should realize that they do not imply the exclusive presence of callose in the inner tube wall layer and its localized thickenings.

Secondary Phloem of the Paleozoic Pteridosperm Callistophyton boyssetii (Renault) Rothwell

Callistophyton boyssetii contains a bifacial, nonstoried vascular cambium of fusiform initials and ray initials. The fusiform initials are thin-walled, spindle-shaped cells. Ray initials are also thin walled but much shorter than fusiform initials and vary in shape. The vascular cambium zone is usually two to four cells wide. The secondary phloem has alternating rows of sieve cells and tangential bands of parenchyma and phloem rays. The sieve cells are thin walled and extremely long. Sieve areas are mostly elliptical and crowded and show evidence of what is interpreted as callose plugging. Phloem parenchyma is relatively thin walled and much shorter than sieve cells. These cells occur in axial strands or as ray parenchyma. Phloem rays vary in height, are mostly one to three cells wide, and dilate tangentially toward the phloem periphery. Secretory cavities occur randomly in rays or in place of a sieve cell or parenchyma band. Callistophyton boyssetii is compared with other pteridosperms and extant cycads ...

Cytochemical Analysis of Callose Localization in Lilium longiflorum Pollen Tubes

Callose, a s, 1-3 glucan as a component of plant cells has received sporadic attention. Here, we report an attempt to determine whether aniline blue and lacmoid are indeed specific for visualizing callose. We also re-evaluate, based on a check for stain specificity, the localization of callose in elongatingLz'/z'wm Iongifiorum, cv. 'Ace' pollen tubes. Specificity of these stains was checked by chemical and enzymatic extraction procedures which solubilize proteins and polysaccharides. Results herein question the generally accepted validity of the fluorescent-aniline blue method for detecting callose. Lacmoid either possesses an affinity for both callose and protein or for callose as a glycoprotein. As for callose localization, the walls of the non-growing region of the lily pollen tube contain callose, probably as a glycoprotein. Presence of the callosic glycoprotein in the wall of the growing tube-tip is dependent on tube length. Callose plugs exhibiting an affinity for aniline blue or lacmoid were never seen. Phase-contrast microscopy revealed non-stainable wall ingrowths in fixed-tubes and free-moving cytoplasmic masses within living tubes.

Callose deposition and plug formation in Petunia pollen tubes in situ

In Petunia pollen tubes growing in the style there appear to be two ways of callose deposition. The first one is callose deposition outside the plasma membrane as a distinct layer closely appressed to the cell wall. The second one is callose deposition within the cytoplasm as distinct callose grains, leading to the formation of callose plugs. This second way is accompanied by a characteristic ultrastructure of the cytoplasm, namely strong electron-density of the plasma matrix, partial absence of the plasma membrane and the absence of plastids and dictyosomes. For both ways of callose deposition a mechanism is proposed and the function of callose plugs is discussed.

FORMATION OF CALLOSE AND LIGNIN DURING LEAF ABSCISSION

Deblading of bean leaves promoted the formation of callose and lignin in the abscission zone. The abscission layer became evident three days after deblading. The greatest increase in callose occurred in about two layers of cells during the development of the abscission layer. Four days after deblading, only a few layers of cells on the distal side of the abscission layer showed an increase in lignin. Lignification continued to expand to 8–10 layers of cells at the time of separation. After separation, the lignified cells remained with the petiole. Sieve elements in the abscission zone were covered with callose plugs and the vessels were occluded with tyloses.