Abstract
The stages of floral development in staminate and pistillate plants of hop (Humulus lupulus) were defined using scanning electron microscopy and light microscopy. Vegetative meristems of male and female plants are morphologically indistinguishable. On transition to the reproductive phase, inflorescence apices reduce greatly in size and striking developmental sex differences become apparent. The first sex-specific differences occur extremely early in floral ontogeny. Both male and female plants initiate inflorescence meristems at each leaf node, each meristem being enclosed within a bract. Male secondary inflorescence meristems give rise to clusters of asynchronously developing flowers. Female inflorescence meristems produce flowers arranged in 'cones'. Each male floral meristem initiates a whorl of five sepal primordia, followed by an inner whorl of five stamen primordia. There is no sign of carpel development at any stage. In females, two carpel primordia are initiated, surrounded at their base by a vestigial perianth whorl. No stamen development is observed. Several monoecious lines carry bisexual flowers, either within cymose panicles or within the basal bracts of terminal female inflorescences. Bisexual flowers usually possess perianth, stamen and carpel whorls. The central whorls are often highly variable, and range from a pair of stigmas fused to a thin central filament to a well developed gynoecium. Chimaeric central whorls consisting of fused staminoid-carpelloid structures also occur. Sex differences in unisexual hop flowers are determined at an extremely early stage in ontogeny. The inappropriate set of sex organs is suppressed before it becomes visible or, more probably, it is not initiated at all. Genes directing the development of sex are likely to act at an extremely early stage, well in advance of floral organogenesis. The sex chromosomes of dioecious hop plants are described, as well as the chromosome constitutions of monoecious plants and those carrying bisexual flowers.
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Claims 16
Claim · model-written summary
Male and female vegetative meristems are morphologically indistinguishable.
Verbatim
e0“Vegetative meristems of male and female plants are morphologically indistinguishable”
t0“hop”
Claim · model-written summary
At reproductive transition, inflorescence apices shrink and sex differences appear.
Verbatim
e0“On transition to the reproductive phase, inflorescence apices reduce greatly in size and striking developmental sex differences become apparent”
t0“hop”
Claim · model-written summary
Sex-specific differences occur extremely early in floral ontogeny.
Verbatim
e0“The first sex-specific differences occur extremely early in floral ontogeny”
t0“hop”
Claim · model-written summary
Both sexes initiate bract-enclosed inflorescence meristems at each leaf node.
Verbatim
e0“Both male and female plants initiate inflorescence meristems at each leaf node, each meristem being enclosed within a bract”
t0“hop”
Claim · model-written summary
Male secondary inflorescences form asynchronous flower clusters.
Verbatim
e0“Male secondary inflorescence meristems give rise to clusters of asynchronously developing flowers”
t0“hop”
Claim · model-written summary
Female inflorescences form flowers arranged in cones.
Verbatim
e0“Female inflorescence meristems produce flowers arranged in 'cones'”
t0“hop”
Claim · model-written summary
Male floral meristems initiate five sepals followed by five stamens.
Verbatim
e0“Each male floral meristem initiates a whorl of five sepal primordia, followed by an inner whorl of five stamen primordia”
t0“hop”
Claim · model-written summary
Male flowers show no carpel development.
Verbatim
e0“There is no sign of carpel development at any stage”
t0“hop”
Claim · model-written summary
Female flowers initiate two carpels and a vestigial perianth.
Verbatim
e0“In females, two carpel primordia are initiated, surrounded at their base by a vestigial perianth whorl”
t0“hop”
Claim · model-written summary
Female flowers show no stamen development.
Verbatim
e0“No stamen development is observed”
t0“hop”
Claim · model-written summary
Several monoecious lines carry bisexual flowers.
Verbatim
e0“Several monoecious lines carry bisexual flowers, either within cymose panicles or within the basal bracts of terminal female inflorescences”
t0“hop”
Claim · model-written summary
Bisexual flowers usually have perianth, stamen and carpel whorls.
Verbatim
e0“Bisexual flowers usually possess perianth, stamen and carpel whorls”
t0“hop”
Claim · model-written summary
Bisexual flower central whorls vary from fused stigmas to a developed gynoecium.
Verbatim
e0“The central whorls are often highly variable, and range from a pair of stigmas fused to a thin central filament to a well developed gynoecium”
t0“hop”
Claim · model-written summary
Chimaeric fused staminoid-carpelloid whorls also occur.
Verbatim
e0“Chimaeric central whorls consisting of fused staminoid-carpelloid structures also occur”
t0“hop”
Claim · model-written summary
The authors infer that inappropriate sex organs are suppressed before visibility or not initiated.
Verbatim
e0“The inappropriate set of sex organs is suppressed before it becomes visible or, more probably, it is not initiated at all”
t0“hop”
Claim · model-written summary
The authors suggest sex development genes act before floral organogenesis.
Verbatim
e0“Genes directing the development of sex are likely to act at an extremely early stage, well in advance of floral organogenesis”
t0“hop”