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Localization of the self- and the interspecific-incompatibility reactions in style sections of Lilium longiflorum
Plant Science Letters, 10 (1977) 199--203
199
© Elsevier/North-Holland Scientific Publishers, Ltd.
LOCALIZATION OF THE SELF- AND THE INTERSPECIFICINCOMPATIBILITY REACTIONS IN STYLE SECTIONS OF LILIUM LONGIFLORUM*
PETER D. ASCHER
Department of Horticultural Science, University of Minnesota, St. Paul, Minn. 55108
(U.S.A.) (Received April 6th, 1977) .(Accepted June 10th, 1977)
SUMMARY
Both compatible and incompatible pollen tubes growing from the ovarian to the stigmatic end of Lilium longiflorum style sections reached lengths not significantly different from similar tubes growing from the stigmatic to the ovarian end. Similarly, there was no significant difference in pollen tube lengths following interspecific pollinations of ovarian versus stigmatic ends of style sections. Neither the self- nor the interspecific-incompatibility reactions appear to be due to localized stylar barriers to pollen tube growth in L. longiflorurn.
INTRODUCTION
Gametophytic self incompatibility, a common mechanism enforcing outbreeding in Angiosperms, occurs when the self-incompatibility (S) allele in the pollen tube matches one of the S alleles in the style, and results in a physiological disturbance of pollen tube growth such that the incompatible tube fails to achieve complete stylar penetration and fertilization. The length to which an incompatible pollen tube grows before manifestation of the self-incompatibility reaction appears relatively constant within a species [1,2], a fact which led early authors to propose a particular region in the style to be responsible for the physiological barrier. Emerson [3] reported that the entire style of Oenothera organensis supported the gametophytic self-incompatibility reaction since pollen tubes passing through stylar ~afts were inhibited within an incompatible stock at the same length as those growing from the stigma, regardless of
*Paper Number 9857 of the Scientific Journal Series of the University of Minnesota Agricultural Experiment Station. This work was supported in part by the United Bulb Company, Mount Clemens, Michigan.
200 the length of the compatible scion. However, incompatible pollen tubes of Oe. organensis seldom penetrate more than 1 mm of the 150 mm style [4], while incompatible tubes of most species possessing gametophytic self incompatibility reach 0 . 2 5 - 0 . 7 5 the length of the style. In addition to a gametophytic self-incompatibility system which limits incompatible pollen tubes to a b o u t half the length of the style in the time compatible tubes penetrate the whole style, Lilium longiflorum, the Easter lily, exhibits several forms of interspecific incompatibility which inhibit pollen tubes near the stigma or halfway down the style [5,6]. Characteristically, all pollen tubes in a style interspecifically pollinated in a short-growth combination stop growth at the base of the stigmatic cavity, the entrance to the style proper. These pollen tubes apparently do not continue growth with extended incubation and may be dead [6]. The severity and uniformity of this inhibition in many different interspecific combinations could suggest a localized barrier to interspecific pollen tube growth in the Easter lily style. While studying chemotropic guidance of pollen tube growth in the style, M y o d o [7] removed the stigma and ovary from pistils of self-compatible L. formosanum, cut the remaining section of the style in half and pollinated the resulting 4 ends. M y o d o concluded from this experiment that polarity existed in the L. formosanum style. Pollen tubes in the ovarian section of the style grew several millimeters than those in the stigmatic sections. This study convincingly illustrated to me that lily pollen tubes grew from the ovarian end of the style toward the stigma relatively as efficiently as from the stigma to the ovary. Using this information, I compared pollen tube growth in Easter lily styles pollinated at the stigmatic end with growth in styles pollinated at the ovarian end to determine whether the lily style limits self- or interspecificincompatible pollen tube growth by means of localized barriers. MATERIALS AND METHODS Flowers were harvested one day after anthesis from greenhouse-grown lilies. Following removal of the pistil by cutting through the ovary with a triangular needle, the flowers were placed in water to serve as a pollen source. Both the stigma and the ovary were cut from each pistil with a sharp razor blade. In order to equalize the apertures at each end of the style, a 10--12 mm section was removed from the stigmatic end while a 2--3 mm section was removed from the ovarian end. Before pollination the appropriate end of each style section was dipped into stigmatic exudate collected from L. longiflorum flowers. Style sections were pollinated either at the stigmatic end or at the ovarian end by touching the exudate-moistened, cut surface to an anther. Pollinated styles were incubated on moistened filter paper in 150-ram Petri dishes for 48 h at 22°C. At the termination of incubation, the styles were cut longitudinally with a razor blade, stained with aqueous aniline blue, and the longest pollen tube in each half style measured from the point of pollination to the tube tip with the aid of a dissecting microscope. Half-style values formed
201 sub-samples in completely random experimental designs containing 4 treatments and 8 replications or 8 treatments and 4 replications. RESULTS AND DISCUSSION Intraspecific pollen tubes growing from the ovarian end toward the stigmatic end of L. longiflorum style sections reached lengths not significantly different from tubes growing in the normal, stigma to ovary direction whether the tubes were compatible or incompatible (Fig. 1). The Easter lily cultivars "Ace", "Arai" and "Nellie White" are self-incompatible clones b u t are cross compatible in all combinations. Because of the uneven trimming of pistils (removal of 10--12 mm from the stigmatic end and 2--3 mm from the ovarian end), the presence of a physiological barrier to incompatible pollen tube growth halfway down the style from stigma to ovary should have resulted in significantly longer incompatible pollen tube growth from the ovarian end of the style. These results indicate that the self-incompatibility reaction in L. longiflorum, like that in Oe. organesis [3], does n o t result from a barrier in a particular sector of the style. Short-growth interspecific incompatible pollen tubes growing from the ovarian end toward the stigmatic end of Easter lily style sections reached lengths n o t significantly different from those growing from the stigmatic to ovarian end (Table I). A physiological barrier to interspecific pollen tube
Ig Incompatible Compatible
J 0
gol
a
,
I
,
stigmatic I ovarian I stigmatic~ ovarian 'NELLIE WHITE' J 'ARAI'
stigmatic,I ovarian 'ACE'
Fig. 1. Pollen tube lengths after 48 h growth in L. longiflorum style sections compatibly or incompatibly pollinated at the stigmatic or the ovarian end. Differences within cultivars, designated by letters above histogram bar, were determined by Duncan's New Multiple Range test, 0.01 level.
202 TABLE I P O L L E N T U B E L E N G T H S IN m m 48 h A F T E R I N T E R S P E C I F I C O R S E L F P O L L I N A T I O N O F L I L Y S T Y L E S E C T I O N S AT E I T H E R THE S T I G M A T I C (TOP) O R O V A R I A N ( B O T T O M ) E N D O F THE S E C T I O N Style
Pollen
Site o f p o l l i n a t i o n Top
Lilium longiflorum "Ace .
.
.
L. longiflorum "Nellie W h i t e "
L. X " E n c h a n t m e n t "
.
L. × " T h u n d e r b o l t " "Golden Clarion" Bright S t a r "
l s d . 05
Bottom
1.9 3.6 4.1
2.0 2.6 5.8
n.s. n.s. n.s.
L. X " B l a c k D r a g o n " "Enchantment"
4.5 1.5 7.3 6.9 46.4
3.2 1.0 5.1 6.6 50.9
n.s. n.s. n.s. n.s. n.s.
L. × " E n c h a n t m e n t "
43.1
40.4
n.s.
L. regale L. auratum L. henryi
growth located at the base of the stigmatic cavity would have been removed by the trimming of the pistils. Therefore, interspecific pollen tube growth from either end of the style sections should have been longer than normal. However, the pollen tube lengths observed in Easter lily style sections are either the same as or slightly shorter than those observed in intact pistils pollinated on the stigma [5,6]. Apparently the short-growth interspecific-incompatibility reaction is n o t restricted to a particular portion of the L. longiflorum style. Following sell pollination, pollen tubes of the MidCentury Hybrid lily " E n c h a n t m e n t " nearly penetrate the entire 50--60 m m style in 48 h growth at 22°C and reach the same length in intact Easter lily styles pollinated on the stigma and incubated under the same conditions [5]. Although apparently self compatible and possessing pollen tubes capable of growing the same rate in L. longiflorum styles as in its own styles, " E n c h a n t m e n t " must be considered half-growth incompatible when used as a pollinator of Easter lily styles, for the pollen tubes do n o t penetrate the 100-ram styles before floral senescence. The lengths of " E n c h a n t m e n t " pollen tubes growing ovarian to stigmatic end did n o t differ significantly from those of tubes growing in the reverse direction in either " E n c h a n t m e n t " or L. longiflorum styles (Table I). These experiments indicate that neither the self- nor the interspecificincompatibility reactions are localized in particular portions of the L. longiflorurn style. Both of these incompatibility reactions would appear to be the result of interactions of pollen tubes and stylar tissue with the length of the inhibited pollen tubes determined by the interaction rather than by the position of the pollen tube in the style.
203 REFERENCES 1 2 3 4 5 6 7
J. Brewbaker, J. Hered., 48 (1957) 271. K.K. Pandey, Evolution, 14 (1960) 98. S. Emerson, Bot. Gaz. Chicago, 101 (1940) 890. S. Emerson, Genetics, 23 (1938) 190. P.D. Ascher and L.W. Drewlow, Plant Sci. Lett., 4 (1975) 401. P.D. Ascher and S.J. Peloquin, Am. J. Bot., 55 (1968) 1230. H. Myodo, J. Fac. Agric. Hokkaido Univ., 52 (1962) 70.
199
© Elsevier/North-Holland Scientific Publishers, Ltd.
LOCALIZATION OF THE SELF- AND THE INTERSPECIFICINCOMPATIBILITY REACTIONS IN STYLE SECTIONS OF LILIUM LONGIFLORUM*
PETER D. ASCHER
Department of Horticultural Science, University of Minnesota, St. Paul, Minn. 55108
(U.S.A.) (Received April 6th, 1977) .(Accepted June 10th, 1977)
SUMMARY
Both compatible and incompatible pollen tubes growing from the ovarian to the stigmatic end of Lilium longiflorum style sections reached lengths not significantly different from similar tubes growing from the stigmatic to the ovarian end. Similarly, there was no significant difference in pollen tube lengths following interspecific pollinations of ovarian versus stigmatic ends of style sections. Neither the self- nor the interspecific-incompatibility reactions appear to be due to localized stylar barriers to pollen tube growth in L. longiflorurn.
INTRODUCTION
Gametophytic self incompatibility, a common mechanism enforcing outbreeding in Angiosperms, occurs when the self-incompatibility (S) allele in the pollen tube matches one of the S alleles in the style, and results in a physiological disturbance of pollen tube growth such that the incompatible tube fails to achieve complete stylar penetration and fertilization. The length to which an incompatible pollen tube grows before manifestation of the self-incompatibility reaction appears relatively constant within a species [1,2], a fact which led early authors to propose a particular region in the style to be responsible for the physiological barrier. Emerson [3] reported that the entire style of Oenothera organensis supported the gametophytic self-incompatibility reaction since pollen tubes passing through stylar ~afts were inhibited within an incompatible stock at the same length as those growing from the stigma, regardless of
*Paper Number 9857 of the Scientific Journal Series of the University of Minnesota Agricultural Experiment Station. This work was supported in part by the United Bulb Company, Mount Clemens, Michigan.
200 the length of the compatible scion. However, incompatible pollen tubes of Oe. organensis seldom penetrate more than 1 mm of the 150 mm style [4], while incompatible tubes of most species possessing gametophytic self incompatibility reach 0 . 2 5 - 0 . 7 5 the length of the style. In addition to a gametophytic self-incompatibility system which limits incompatible pollen tubes to a b o u t half the length of the style in the time compatible tubes penetrate the whole style, Lilium longiflorum, the Easter lily, exhibits several forms of interspecific incompatibility which inhibit pollen tubes near the stigma or halfway down the style [5,6]. Characteristically, all pollen tubes in a style interspecifically pollinated in a short-growth combination stop growth at the base of the stigmatic cavity, the entrance to the style proper. These pollen tubes apparently do not continue growth with extended incubation and may be dead [6]. The severity and uniformity of this inhibition in many different interspecific combinations could suggest a localized barrier to interspecific pollen tube growth in the Easter lily style. While studying chemotropic guidance of pollen tube growth in the style, M y o d o [7] removed the stigma and ovary from pistils of self-compatible L. formosanum, cut the remaining section of the style in half and pollinated the resulting 4 ends. M y o d o concluded from this experiment that polarity existed in the L. formosanum style. Pollen tubes in the ovarian section of the style grew several millimeters than those in the stigmatic sections. This study convincingly illustrated to me that lily pollen tubes grew from the ovarian end of the style toward the stigma relatively as efficiently as from the stigma to the ovary. Using this information, I compared pollen tube growth in Easter lily styles pollinated at the stigmatic end with growth in styles pollinated at the ovarian end to determine whether the lily style limits self- or interspecificincompatible pollen tube growth by means of localized barriers. MATERIALS AND METHODS Flowers were harvested one day after anthesis from greenhouse-grown lilies. Following removal of the pistil by cutting through the ovary with a triangular needle, the flowers were placed in water to serve as a pollen source. Both the stigma and the ovary were cut from each pistil with a sharp razor blade. In order to equalize the apertures at each end of the style, a 10--12 mm section was removed from the stigmatic end while a 2--3 mm section was removed from the ovarian end. Before pollination the appropriate end of each style section was dipped into stigmatic exudate collected from L. longiflorum flowers. Style sections were pollinated either at the stigmatic end or at the ovarian end by touching the exudate-moistened, cut surface to an anther. Pollinated styles were incubated on moistened filter paper in 150-ram Petri dishes for 48 h at 22°C. At the termination of incubation, the styles were cut longitudinally with a razor blade, stained with aqueous aniline blue, and the longest pollen tube in each half style measured from the point of pollination to the tube tip with the aid of a dissecting microscope. Half-style values formed
201 sub-samples in completely random experimental designs containing 4 treatments and 8 replications or 8 treatments and 4 replications. RESULTS AND DISCUSSION Intraspecific pollen tubes growing from the ovarian end toward the stigmatic end of L. longiflorum style sections reached lengths not significantly different from tubes growing in the normal, stigma to ovary direction whether the tubes were compatible or incompatible (Fig. 1). The Easter lily cultivars "Ace", "Arai" and "Nellie White" are self-incompatible clones b u t are cross compatible in all combinations. Because of the uneven trimming of pistils (removal of 10--12 mm from the stigmatic end and 2--3 mm from the ovarian end), the presence of a physiological barrier to incompatible pollen tube growth halfway down the style from stigma to ovary should have resulted in significantly longer incompatible pollen tube growth from the ovarian end of the style. These results indicate that the self-incompatibility reaction in L. longiflorum, like that in Oe. organesis [3], does n o t result from a barrier in a particular sector of the style. Short-growth interspecific incompatible pollen tubes growing from the ovarian end toward the stigmatic end of Easter lily style sections reached lengths n o t significantly different from those growing from the stigmatic to ovarian end (Table I). A physiological barrier to interspecific pollen tube
Ig Incompatible Compatible
J 0
gol
a
,
I
,
stigmatic I ovarian I stigmatic~ ovarian 'NELLIE WHITE' J 'ARAI'
stigmatic,I ovarian 'ACE'
Fig. 1. Pollen tube lengths after 48 h growth in L. longiflorum style sections compatibly or incompatibly pollinated at the stigmatic or the ovarian end. Differences within cultivars, designated by letters above histogram bar, were determined by Duncan's New Multiple Range test, 0.01 level.
202 TABLE I P O L L E N T U B E L E N G T H S IN m m 48 h A F T E R I N T E R S P E C I F I C O R S E L F P O L L I N A T I O N O F L I L Y S T Y L E S E C T I O N S AT E I T H E R THE S T I G M A T I C (TOP) O R O V A R I A N ( B O T T O M ) E N D O F THE S E C T I O N Style
Pollen
Site o f p o l l i n a t i o n Top
Lilium longiflorum "Ace .
.
.
L. longiflorum "Nellie W h i t e "
L. X " E n c h a n t m e n t "
.
L. × " T h u n d e r b o l t " "Golden Clarion" Bright S t a r "
l s d . 05
Bottom
1.9 3.6 4.1
2.0 2.6 5.8
n.s. n.s. n.s.
L. X " B l a c k D r a g o n " "Enchantment"
4.5 1.5 7.3 6.9 46.4
3.2 1.0 5.1 6.6 50.9
n.s. n.s. n.s. n.s. n.s.
L. × " E n c h a n t m e n t "
43.1
40.4
n.s.
L. regale L. auratum L. henryi
growth located at the base of the stigmatic cavity would have been removed by the trimming of the pistils. Therefore, interspecific pollen tube growth from either end of the style sections should have been longer than normal. However, the pollen tube lengths observed in Easter lily style sections are either the same as or slightly shorter than those observed in intact pistils pollinated on the stigma [5,6]. Apparently the short-growth interspecific-incompatibility reaction is n o t restricted to a particular portion of the L. longiflorum style. Following sell pollination, pollen tubes of the MidCentury Hybrid lily " E n c h a n t m e n t " nearly penetrate the entire 50--60 m m style in 48 h growth at 22°C and reach the same length in intact Easter lily styles pollinated on the stigma and incubated under the same conditions [5]. Although apparently self compatible and possessing pollen tubes capable of growing the same rate in L. longiflorum styles as in its own styles, " E n c h a n t m e n t " must be considered half-growth incompatible when used as a pollinator of Easter lily styles, for the pollen tubes do n o t penetrate the 100-ram styles before floral senescence. The lengths of " E n c h a n t m e n t " pollen tubes growing ovarian to stigmatic end did n o t differ significantly from those of tubes growing in the reverse direction in either " E n c h a n t m e n t " or L. longiflorum styles (Table I). These experiments indicate that neither the self- nor the interspecificincompatibility reactions are localized in particular portions of the L. longiflorurn style. Both of these incompatibility reactions would appear to be the result of interactions of pollen tubes and stylar tissue with the length of the inhibited pollen tubes determined by the interaction rather than by the position of the pollen tube in the style.
203 REFERENCES 1 2 3 4 5 6 7
J. Brewbaker, J. Hered., 48 (1957) 271. K.K. Pandey, Evolution, 14 (1960) 98. S. Emerson, Bot. Gaz. Chicago, 101 (1940) 890. S. Emerson, Genetics, 23 (1938) 190. P.D. Ascher and L.W. Drewlow, Plant Sci. Lett., 4 (1975) 401. P.D. Ascher and S.J. Peloquin, Am. J. Bot., 55 (1968) 1230. H. Myodo, J. Fac. Agric. Hokkaido Univ., 52 (1962) 70.