Developmental and Structural Section
Zitnak, Tim , Posluszny, U , Gerrath, Jean .
Developmental morphology of the cucurbit axillary complex: Is there any dioecy in the Cucurbitaceae?
Apical meristem development and branching of many Cucurbitaceae species is of interest due to the node’s complex nature. However, few complete ontogenetic studies exist. A series of studies has been undertaken to provide a set of morphological characteristics by examining the ontogeny of several species of vine-forming Cucurbitaceae with different tendril architecture. Shoot architecture, phyllotactic patterns, and floral development have been examined. Ontogeny was examined using epi-illumination light microscopy and scanning electron microscopy. Studies have been done for Echinocystis lobata (Michaud), Sicyos angulatus (L.) and Ecballium elaterium (L.). For all species examined, each leaf has a complex axillary structure that is offset from the leaf axil. This axillary complex undergoes a series of asymmetric divisions giving rise to structures in a consistent spatial sequence: a male inflorescence, female inflorescence, axillary bud and, with the exception of E. elaterium, a tendril. The axillary bud does not undergo dormancy but develops into either a compressed, quiescent shoot or continues growth to produce a branch. All species have the same spatial sequence of axillary structures. However, each species displays different timing patterns for the initiation and development of these structures. Some of these timing patterns appear to correspond to the pattern of production of male and female flowers. Male and female flower primordia are always present even if the node appears unisexual. The tendril of S. angulatus is likely homologous to a shoot complex with the tendril stalk being homologous to a shoot and the tendril arms homologous to leaves.
Some species of Cucurbitaceae have been considered dioecious but been determined to be monoecious. Many have a reproductive life cycle spanning several years so these determinations can take years. This study shows that even though a plant may appear to be of only one gender, primordia of the opposite gender may have been produced. Ontogenetic studies could more readily provide evidence that cucurbits that are apparently dioecious are actually monoecious. Increasing fruit in cultivated Cucurbitaceae and decreasing fruit in weed species are global objectives. Published experiments focus on gender change. However, based on morphological observations, changes may be the result of an inhibition or abortion of a primordium and not a change in its gender. This needs to be considered when examining biological pathways which affect sex expression.
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1 - University of Guelph, Department of Molecular and Cellular Biology, Guelph, ON, N1G 2W1, Canada
2 - University of Guelph, Molecular and Cellular Biology, Guelph, Ontario, N1G 2W1, Canada
3 - University of Northern Iowa, Department of Biology, Cedar Falls, Iowa, 50614-0421, USA
Presentation Type: Oral Paper:Papers for Sections
Location: 551A/Convention Center
Date: Tuesday, August 3rd, 2010
Time: 2:15 PM