Sex expression cucumber

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Review of sex expression in cucmber and ethylene.

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Sex determination in cucumber

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Perfect flowers or Hermaphroditic flowers Both male and female reproductive parts are present on the same flower

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Perfect flowers or Hermaphroditic flowers Both male and female reproductive parts are present on the same flower

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Monoecious plants – Imperfect flowers Separate male and female flowers are present on the same plant

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Dioecious plants – Imperfect flowers Male and female flowers are present on individual separate plants

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ABC model of floral development

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Attainment of unisexuality in flowers by means of homeotic transformation has not been reported as a mechanism of sex determination in natural population.

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Sex determination in cucumber ♂ flower ♀ flower

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Male cucumber flowers are composed of four whorls of organs (from the outer to the inner whorl): five sepals, five yellow petals, five stamens, and three arrested carpel primordia in the fourth whorl. In contrast, stamens are arrested in their development in the female flower , and the three carpel primordia develop further to an inferior ovary, a short style, and three separated stigmas . ♂ flower ♀ flower

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Developmental arrest of whorl 4 in male and whorl 3 in female flowers Flower Morphology of Wild-Type Cucumber Plants. (A) Longitudinal section through male flower buds at two developmental stages. The carpel primordia are arrested in whorl 4. Stamen primordia arise from the flanks of the petals and produce sporogenous tissue. (B) Longitudinal section through a young wild-type male cucumber flower at a later developmental stage just before opening of the flower . The anthers start to produce pollen. (C) Macroscopic view of a male flower. A pair of sepals and petals were removed to allow a view inside. The arrested carpel primordia are visible at the bottom of the flower. (D) Longitudinal section through a female flower bud. Stamen and carpel primordia develop in whorls 3 and 4, respectively. The sepals cover the flower completely. (E) Longitudinal section through a female flower bud at a later developmental stage. The stamen primordia are arrested, and in the fourth whorl an inferior ovary and superior stigmas develop. (F) Macroscopic view of a female flower at a stage just before opening of the flower. As in (C), a pair of sepals and petals have been removed to allow a view inside the flower. The whorl numbers indicate the positions of the floral organs within the flower. O, ovary. Bars in (A), (B), (D), and (E) 5 1 mm.

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Genetic and environmental control of cucumber sex determination Genotypes Gynoecious - F-M- - ♀ Andromonoecious - ffmm - ♂ and ♀ Monoecious - ffM- - ♂ and ♀ Hermaphrodite - F-mm - ♀ Ethylene and ethephon – induction of ♀ flowers AVG and AgNO 3 – induction of ♂ flowers

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Sex of different cultivars used in this study

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Development of flower buds in gynoecious cucumber plants

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Development of flower buds in gynoecious cucumber plants

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Development of flower buds in monoecious cucumber plants

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Development of flower buds in monoecious cucumber plants

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AVG masculinizes between node 8 and 13, Ethephon feminizes between nodes 10 and 14 Floral stages immediately before and after differentiation of stamen primordia are responsive to both AVG and ethephon treatments

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The expression patterns for CS-ACS2 , CS-ERS , CS-ETR1 , and CS-ETR2 are all different among monoecious , gynoecious and andromonoecious plants. CS-ACS2 and CS-ETR2 are expressed in identical domains in monoecious plants and overlapping domains in gynoecious plants. In andromonoecious plants, none of the ethylene receptors transcripts accumulated in the stamen primordia . Atleast one ethylene receptor transcript is expressed in the stamen and pistil primordia of monoecious and gynoecious flowers, and pistil primordium of andromonoecious flowers.

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Cells producing and sensing ethylene are identical. Eg . Overlapping CS-ACS2 and CS-ETR2 mRNA expression in monoecious and gynoecious plants, direct determination of female flowers by inducing pistil development. Cells producing and sensing ethylene are adjacent. Eg . mRNA expression of CS-ACS2 in adaxial side of petals but all the receptors in stamen primordia in monoecious plants. (diffusion?) Cells producing and sensing ethylene are distant. Eg . mRNA expression of CS-ACS2 in pistil primordia but that of receptors in the stamen primordia . (diffusion?)

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