Incompatible Pollen Research Articles

Effects of Temperature, Light, Nutrients and Carbon Dioxide on the Strength of the Self-Incompatibility Response in Detached Flowers of Lycopersicon peruvianum

The effects of temperature, light, nutrients and CO2on the gametophytic self-incompatibility response in a clone of Lycopersicon peruvianum have been quantified using fluorescence microscopy of style squashes prepared from detached flowers held under experimental conditions for 48 h after self pollination. Self-incompatibility was significantly weakened by raising the temperature from 15 °C to 22 or 25°C, and by incubating flowers without an energy source - i.e. in the dark and/or without externally supplied sucrose. The sucrose effect was not duplicated by equimolar mannitol or a full mineral nutrient solution plus vitamins. CO2 applied at 5% in air for 8 h after pollination had no detectable effect on pollen tube arrest. Observed weakening effects were not sufficient for use in production of selfed seed. They indicate, however, that self-incompatibility in this clone of L. peruvianum is a temperature-sensitive, energy-dependent process, and support the oppositional model of self-incompatibility in which incompatible pollen tubes are actively inhibited.

Tests of the heterosis model

An alternative to the classical model of self-incompatibility indicates that genetic control of self-incompatibility could involve more than one locus and function through passive failure of incompatible pollen tubes rather than through their active inhibition. Both aspects of the alternative model have been tested and, in each case, the data support the classical single-locus oppositional interpretation rather than the alternative. On the basis of these data, and others now available, we conclude that, in the Solanaceae, and presumably also in some others, self-incompatibility is better explained by the classical interpretation. Several points, however, remain to be resolved.

テッポウユリの異品種の花柱および前受粉した雌ずいの花柱を組合せて接合した花柱内における花粉管伸長

The self-incompatibility in Lilium longiflorum was investigated using the differently grafted pistils. Pistils of Lilium longiflorum cv. Georgia and Hinomoto were cut transversely into two parts at 15 or 25mm from stigma tips. They were then grafted in different combinations with silicone rubber tube (2.5mm in inner diameter). Pollen tube growth in the grafted pistils was somewhat reduced as compared with that in the intact style, but the incompatibility responses of the pollen tubes could be studied in the grafted styles.In the pistils grafted with different cultivar, the appearance of self-incompatible responses was observed on the style from the same cultivar. The ovary end portion of the grafted styles seemed to be more influential.In the pistils grafted with cross-pre-pollinated pistil segment, the incompatible pollen tube growth was faster than in the pistils grafted with non- or self-pre-pollinated pistil segments. The necessary condition for the rapid growth of pollen tube was generated in the styles after cross-pollination, with a qrobable velocity of 0.5cm/h from the stigma to the ovary.In self-pre-pollinated pistils, the necessary condition for the rapid growth of pollen tube seemed not to be generated in the style and further any inhibitor for the pollen tube growth was not produced.

Arabinogalactan-Proteins of the Female Sexual Tissue of Nicotiana alata

Arabinogalactan-proteins (AGPs), isolated from the pistils of Nicotiana alata, an ornamental tobacco, are developmentally regulated. Both the total amount and concentration of AGP in the stigma increase during flower development, reaching 10 micrograms AGP/stigma at maturity. In contrast, AGP concentration in the style remains constant throughout the maturation period reaching 12 micrograms AGP/style at maturity. The classes of AGP present in the stigma and style during flower development, separated according to their charge by crossed-electrophoresis, are different and change during development. Pollination of flowers of N. alata with compatible or incompatible pollen results in a significant and reproducible increase in the amount of AGPs in the stigma, but not the style, compared with control unpollinated pistils. Pollination with ethanol vapor inactivated pollen also results in an increase in the amount of AGP in the stigma, but this is less than half that observed following pollination with viable pollen. There are no significant differences in the classes of AGP, based on crossed-electrophoresis, present in the pistil following pollination.

Pollen tube growth in tristylous Pontederia cordata (Pontederiaceae)

Pollen tube growth rates in legitimate cross- and self-pollinations were compared by controlled hand pollination in two varieties of Pontederia cordata L. (Pontederiaceae). In each pollen–stigma combination pollen germinated readily on stigmas and pollen tubes penetrated stigmatic tissue. Pollen tube length in styles was positively correlated with pollen size. In most pollinations legitimate pollen tubes grew more rapidly in styles than self pollen tubes. This difference was statistically significant in most comparisons. Inhibition of incompatible pollen tubes was either in the style or ovary. It is suggested that the mechanisms of incompatibility may differ among the floral morphs and depend on the particular pollen size involved in pollinations. The observed differences in pollen tube growth of legitimate cross- and self-pollinations in P. cordata suggest that the species is primarily outbreeding.

GERMINATION OF CORYLUS AVELLANA L. (HAZEL) POLLEN: HYDRATION AND THE FUNCTION OF THE ONCUS

SUMMARY As reported by Schoch-Bodmer fifty years ago, the onci play an important part in accommodating volume changes in the 3-porate pollen of Corylus avellana L. during cycles of dehydration and rehydration. The onci, which are rich in pectins judging from their cytochemical properties, possess a remarkable fine-structure, characterised by densely packed, convoluted lamellae. Staining responses suggest that the protein content of the body of the oncus is low, although esterase activity is distributed throughout. During germination a granular sporopollenin seal at the preferred aperture is disrupted by the gelatinisation of underlying pectins, and the pollen tube emerges as an outgrowth from the inner cellulosic layer of the intine. This process is preceded by the release of proteins from each aperture site. The source of this outflow is a protein-rich umbonate cap, 1–3 μm in thickness, lying beneath the pore over the body of the oncus and extending under the encompassing exine annulus. The nexine is absent from the annulus, so that the apertural proteins are continuous with the interbacular material. This implies that in this pollen type there are no clearly separate “gametophytic” and “sporophytic” domains. As in species of Compositae and Cruciferae with a similar sporophytic type of self-incompatibility (SI) system, incompatible pollen of C. avellana is inhibited on the stigma surface, the stigma papillae responding rapidly to the presence of the incompatible pollen by synthesis of internal callose. This suggests that the S-factors are held in the pollen wall, and it is possible that they form one component of the poral proteins. In the light of recent reports of sporophytic proteins held at the apertural sites in various angiosperm pollens, the possibility is considered that the poral proteins of C. avellana are also of sporophytic origin, at least in part. Should they contain tapetum-derived S-factors a ready explanation of the sporophytic control of the SI system is at hand.

Stylar peroxidase and incompatibility reactions in Petunia hybrida.

Self-, cross- and non-pollinated styles of Petunia hybrida were treated with 3-3'-diaminobenzidine for the ultrastructural localization of peroxidase activity. Wall peroxidases were absent in cross-pollinated styles, but they were detectable as an osmiophilic deposit on the cell walls of the outer portion of the transmitting tissue in self- and non-pollinated styles. The cell layer showing peroxidase activity was thicker in the self-pollinated styles than in the non-pollinated ones. In accordance with current hypotheses on the mechanism involved in pollen incompatibility process, it is suggested: that wall peroxidases present in the cells of the outer portion of the transmitting tissue are involved in the gametophytic self-incompatibility of Petunia; that self-pollination causes an increase in the number of cells involved in the rejection process; that non-pollinated styles, which are characterized by the presence of cell wall peroxidases in the outer portion of the transmitting tissue, are 'prepared' to a certain extent for the rejection of incompatible pollen tubes. The removal of peroxidase activity thus seems to be an important step in the compatible pollination process.

Late-acting self-incompatibility in angiosperms

In most self-incompatible (SI) plants, pollen tube growth in self-pollinated flowers is inhibited on the stigma or in the style. SI systems that operate in the ovary have been assumed to be extremely rare. Evidence from many plant species is presented to show that the SI barriers in the ovary, described here as late-acting SI systems, are quite common. The late-acting SI systems are divided into four categories: (1) ovarian inhibition of incompatible pollen tubes before the ovule is reached; (2) prefertilization inhibition in the ovule; (3) post-zygotic rejection of the embryo, and (4) ovular inhibition for which the cytological details have not been established.

Exogenous sugars overcome incompatibility in hazelnut (Corylus avellana L.)

Petreatment of hazelnut (Corylus avellana L.) stigmas with L M or 2 M sugar solutions before pollination with incompatible pollen, or pollination with 1∶1 mixtures of incompatible pollen and finely ground sugars, prevented rejection of incompatible pollen by the stigma surface. Lower sugar concentrations or lower ratios of sugar to pollen were less effective. No specificity for overcoming incompatibility was observed among 18 simple sugars and related sugar compounds.

Discriminating styles (DS) and pollen-mediated pseudo-self compatibility (PMPSC) in Petunia hybrida hort

Discriminating styles (DS) in Petunia hybrida discriminate among incompatible pollen sources with pollen-mediated pseudo-self compatibility (PMPSC) similarly to those in Nemesia strumosa. Both species exhibit a single-locus gametophytic self-incompatibility system. Correlation of PMPSC to PSC level of the male was not universal and DS/PMPSC operated in heterozygous S genotypes. PSC levels of progenies generated from compatible or incompatible bud pollination were not significantly different from those of open-flower pollination of a DS plant with a given male, suggesting that DS did not select among male gametophytes for increased PSC.

ON THE DARWINIAN HYPOTHESIS OF THE ADAPTIVE SIGNIFICANCE OF TRISTYLY.

Darwin proposed that the function of the stamen-style polymorphism in heterostylous plants is to increase the probability of legitimate (compatible) pollinations among the floral morphs. Conspicuous pollen trimorphism in tristylous Pontederia cordata enables a test of the hypothesis. Comparison of the composition of pollen loads in naturally pollinated stigmas of intact and emasculated flowers were made at a population in Paugh Lake, Ontario, which was visited primarily by bumblebees. The magnitude of legitimate pollination was analyzed by ANOVA. In intact flowers, significant legitimate pollination was detected in the long-styled morph only. Following emasculation legitimate pollination was evident in the long- and short-styled morphs, with the mid-styled morph just short of displaying significant legitimate pollination. Similar results were obtained by chi-square analysis. It has been suggested that heterostyly may reduce mutual interference between maternal and paternal reproductive function. Two aspects of pollen-stigma interference were investigated in P. cordata. The potential importance of stigmatic or stylar clogging by incompatible pollen was examined by controlled field pollinations and measurements of seed set. The results indicate that prior application of large amounts of incompatible pollen has no significant effect on the seed set of open-pollinated inflorescences. Comparison of legitimate pollen capture in intact and emasculated flowers provided no evidence that the presence of stamens within flowers of the floral morphs interferes with the receipt of legitimate pollen. Pollen-stigma interference remains to be demonstrated in heterostylous plants.

Self-incompatibility in ryegrass IX. cross-compatibility and seed-set in autotetraploid Lolium perenne L.

The results of the experiments presented in the two previous papers of this set showed that 35 autotetraploid ryegrass plants fell into 18 different incompatibility classes and, in particular, that only one S-Z pair in the pollen needs to be matched in the stigma for incompatibility to occur (Fearon, Hayward and Lawrence, 1984a, b). These results were obtained by pollinating tetraploids with pollen from diploids and vice versa. In the experiment described in the present paper, the classification and conclusions of these earlier experiments are put to the test by crossing the tetraploid plants inter se. The results completely confirm those of the earlier experiments. In addition, they show that there is no dominance between the alleles at either locus in the pollen and that incompatibility only occurs when both an S and a Z allele are matched in the stigma. Two implications of these results are considered. First, that only one S-Z pair in the pollen needs to be matched in the stigma strongly suggests that the growth of incompatible pollen is positively inhibited, rather than that of compatible pollen being positively stimulated. Second, it is shown theoretically that a consequence of this mechanism is that the level of cross-compatibility is appreciably lower in populations of tetraploids relative to those of diploids in which few, but equally frequent alleles are segregating at each locus. If the number of alleles that are segregating in the population exceeds twelve, however, this difference in level of cross-compatibility becomes negligible. The implications of this outcome for plant breeding are briefly considered.

The effect of pollination intensity and incompatible pollen on seed set in Turnera ulmifolia (Turneraceae)

Controlled pollination experiments were performed on the self-incompatible distylous herb Turnera ulmifolia L. to investigate the effects of pollination intensity and large amounts of incompatible pollen on seed set. In the first experiment, known numbers of compatible pollen grains ranging from 1 to 100 were applied to stigmas of the floral morphs. In both morphs, increasing amounts of pollen generally resulted in increased levels of seed set, although considerable variance was observed at all pollination intensities. Approximately two to seven pollen grains are required to produce a single seed and more than 95 grains are required to achieve maximum seed set in T. ulmifolia. Regression analysis of the seed set data failed to detect a difference in the response of the floral morphs to pollination intensity. In the second experiment, known proportions of compatible and incompatible pollen were applied to stigmas at various time intervals. Most treatments involving mixtures of compatible and incompatible pollen had no significant effect on seed set when compared with the controls. Clogging was only observed in the long-styled morph when one anther of compatible pollen was applied to stigmas 1.5 and 3.0 h after pollination with five anthers of incompatible pollen. The clogging of stigmas by incompatible pollen seems unlikely to have played a major role in the evolution and maintenance of distyly in Turnera ulmifolia.

Review Lecture Self-incompatibility: phenomenology and physiology

Angiosperm self-incompatibility systems have been attracting increasing attention in recent years, both because of their importance in practical plant breeding and in acknowledgement of their considerable intrinsic interest as examples of cellular interaction and recognition. Progress has been made in analysing the genetics of complex multi-locus systems in certain primitive families, and the inhibition reaction itself has been more fully characterized in certain species. The review deals mainly with homomorphic, gametophytic self-incompatibility systems, concentrating on aspects of pollen-tube growth and pistil function that appear to play key roles in the discrimination between compatible and incompatible pollen. Various implications of a recently proposed hypothesis concerning the operation of gametophytic systems are also discussed.

Gametophytic Self-Incompatibility Reexamined

The conventional hypothesis of gametophytic self-incompatibility in the angiosperms involves one to four multiallelic incompatibility loci and the positive inhibition of incompatible pollen tubes. However, this concept does not accommodate recent experimental data indicating that there may be many loci. An alternative hypothesis which incorporates many loci and complementary pollen-style interactions suggests that there may be no S gene, as previously thought, and that gametophytic self-incompatibility is perhaps merely one aspect of extensive pollen-style interactions.

Nonreciprocal partial cross-incompatibility in maize

A case of cross-incompatibility among crosses in our genetics nursery was first observed in 1975. These crosses though involving controlling elements in maize (Zea mays L.) do not necessarily implicate these elements. When the derivative genotypes from the genetic stocks were crossed by specific male parents, ears with reduced seed set (RSS) were produced. In the reciprocal cross where these same genetic stocks were used as the male parent, ears with normal seed set (NSS) were obtained. The RSS effect is a heritable character caused by an incompatibility interaction between the female tissue and a specific pollen type. The genetic control of the incompatibility interaction has been hypothesized to be influenced by a cytoplasmic–chromosomal interaction in the female and a chromosomal factor in the pollen. The site of the incompatibility interaction is not on the silk surface because the incompatible pollen germinated and developed normally on the silk surface. Thus, the incompatibility interaction can occur either inside the silk or the ovule.

Pollen and pollination experiments. VIII. The effect of successive pollinations with compatible and self-incompatible pollen in apple and pear

In compatible pollen combinations, viable but infertile irradiated pollen Cr appears to compete much more in a mixture (the mentor pollen situation: C+Cr), than when used one day in advance (the pioneer pollen situation: Cr/C). Seed set of Cr/C was usually also greatly superior to that of C/Cr and, using, self, incompatible pollen S instead of Cr, S/C was nearly always much better than C/S. This is in accordance with the promotion of the second by the first (pioneer) pollen. Hence, when Cr or S are applied second in C/Cr or C/S, more ovules are rendered ineffective (blocked or aborted) than in the reverse combination when Cr or S act as pioneer pollen. These observations are consistent with the trend that the combinations C/ C+S, C+S, C/S tended to produce more selfed seeds in that order. Although mentor or pioneer pollen assist in removing the style barrier for self pollen, embryo abortions appears to be a second obstruction towards seed formation. Indications are that high spring temperature during pollination promote the production of selfed seeds in the presence of compatible pollen. The surfeit of self pollen in orchards with a minority of pollinators is not necessarily an unfavourable factor, it may both directly and indirectly contribute to fruit and seed set.

Studies on the self-incompatibility of Petunia hybrida in excised-style culture. Differences in self-incompatibility reaction among four clones

In Petunia clones with different S-alleles, self- or cross-pollinated excised-styles of 5, 10, 15, 20 or 25 mm were incubated on a standard agar medium for 24, 48 or 72 h. The length and number of protruding incompatible pollen tubes were compared with those of compatible ones. Throughout the experimental period, the length and number of incompatible pollen tubes of pollen from the S1S1-clone were always less than those of compatible ones. In pollen from S2S2-, S3S3- and S2S3-clones the incompatible pollen tube growth was barely arrested in 5 and 10 mm excised-styles during the first 24 h of incubation. However, inhibition of incompatible pollen tube growth was strengthened with the increase of both excised-style length and incubation period: this was clearly evident in 15 mm or longer excised-styles incubated for 48 h. Ratios of incompatible to compatible pollen tube length in excised-styles incubated for 72 h, were for S3S3 pollen tubes = 0.28, S1S1=0.48, S2S3 = 0.50, and S2S2 = 0.60, and ratios on tube numbers were S3S3 = 0.01, S1S1 = 0.1, S2S2 = 0.21, and S2S3 = 0.21. These results were in agreement with those of in vivo self-pollination. The incompatibility reaction seemed strongest in S3S3-, weaker in S1S1 - and weakest in S2S2- and S2S{3}-clones, and therefore the intensity of S-allele expression would be S3> S1> S2.

Pollen and pollination experiments. V. An empirical basis for a mentor pollen effect observed on the growth of incompatible pollen tubes in pear

The self-incompatible pear cultivar Doyenne du Comice was selfed with the aid of the mentor pollen technique (self pollen mixed 1:1 with compatible pollen) and the pioneer pollen method (compatible pollen applied 14 h in advance of the self pollen). Observations on tube growth in the style showed that inviable methylated pollen was ineffective either as mentor or pioncer pollen, having no effect on the performance of the self pollen which stopped growing at about one quarter of the style from the stigma. Calculations made on the basis of the obtained data indicated that the viable untreated or irradiated pioneer and mentor pollen, the former somewhat better than the latter, aided the self pollen tubes to reach the base of the style.

Studies on heteromorphic self-incompatibility systems: Physiological aspects of the incompatibility system of Primula obconica

In Primula obconica, a species with a heteromorphic self-incompatibility system, the distinction between compatible and incompatible pollen tubes takes place on the stigma surface in thrum flowers, self tubes growing randomly over the papillar cells. No differences were seen between self and cross tube behaviour on the pin stigma surface, but self tubes were inhibited within the stigmatic tissue with differences in tube length evident after 24 h. The stigma surface bears a proteinaceous pellicle and binds the lectin Concanavalin A. Removal of the stigma removes the incompatibility barrier in mature gynoecia. Bud pollination shows that pollen tubes cannot grow in a normal manner on immature stigmas; the random growth of tubes over the stigma surface resembles that of mature thrum selfs. Fewer compatible tubes reach the style base of young gynoecia and smaller numbers of seeds are set than in mature flowers. Pin and thrum pollen grains germinate and grow in aqueous media, thrum tubes growing longer than pin. The presence of H3BO4 and CaCl2 in the growth medium promotes tube elongation and lengths equivalent to compatible styles can be obtained. The pollen grains have proteinaceous materials in their walls which diffuse out on moistening. Prolonged washing in aqueous media removes these materials but the incompatibility reaction remains unchanged. Thus the incompatibility reaction is between pollen tubes and stigmatic tissue and differs from the homomorphic, sporophytic system where pollen wall proteins elicit the incompatibility response.