Seed production in conifers involves an extended sequence of developmental events that may take as long as 3 years to complete. There is a conflict between two major processes: initial pollination of ovules and subsequent maturation of seeds after fertilization. The conflict arises because ovules must be exposed at first to receive pollen (the gymno-ovulate condition), and subsequently seeds must be protected during maturation (the angiospermous condition). The "Florin model", which shows that the coniferous cone was ancestrally a compound structure, provides a constructional "Bauplan" whose modifications can be understood by developmental study. In the majority of conifers there is no consistent ovule-bearing structure, even though this is required by the model; much of cone ontogeny is determined by intercalary meristematic activity that results in cone closure after pollination. Two main constructional types can be recognized. In Cephalotaxaceae, Cupressaceae, Sciadopityaceae, Taxaceae, and Taxodiaceae (all without saccate pollen), pollen structure and function is uniform and not associated with special modification of the ovulate cone at the time of pollen capture. In the Pinaceae and Podocarpaceae (mostly with saccate pollen), the ovulate cone is usually highly specialized with regard to pollen capture. In the former group, developmental emphasis is on postpollination events that lead to seed protection or are associated with seed dispersal. In the latter group, there is a duality in ovulate cone morphology, initially associated with pollination, and subsequently with seed protection and dispersal. The general conclusion is that the coniferous cone cannot be treated as a static entity for comparative purposes. The functional attributes of cone structures need to be considered in a very broad context when the evolution of the coniferous cone is discussed.Key words: conifers, development, pollen capture, seed cone.
Sacci of conifer pollen do not function primarily to increase the efficiency of wind pollination as is widely thought. Rather, they are bladders and cause pollen to float upwards in a liquid drop into the ovules. This observation is seemingly unsupported in the case of oriental spruce (Picea orientalis (L.) Link), which has saccate pollen. Ovulate cones are pendant at the time of pollination, which requires that pollen sink into the ovules. Pollen of oriental spruce floats at first but within 1-2 min sinks into the ovule. As sinking does not occur in saccate pollen of other Pinaceae, a variety of techniques was used to determine anatomical differences leading to this uncharacteristic tendency. Light, scanning electron, and confocal microscopy of the pollen surface yielded no significant appearing difference between pollen of oriental spruce and white spruce. However, transmission electron microscopy of freeze-fixed/freeze-substituted hydrated pollen revealed that the ektexine of oriental spruce pollen sacci is porous compared to that of white spruce. Confocal microscopy allowed examination of pollen hydration dynamics. Water enters pollen at the distal pole between sacci, and resulting rapid expansion of the tube cell forces air out of the saccate space. White spruce pollen remains buoyant because of enclosed air pockets in the saccus ektexine. Evolutionary change in pollen wall anatomy with resultant loss of saccus function is correlated with a change in ovulate strobilus orientation at pollination in oriental spruce. A suite of characters interact in the conifer pollination mechanism, and concerted change in these characters may lead to speciation.
The flowers of mangrove plants are pollinated by a variety of pollinators including birds, bats, and insects. This study analyzed the floral scent chemistry of mangroves on Iriomote Island (located near Taiwan) including Bruguiera gymnorrhiza (L.) Lamk. (Rhizophoraceae), Kandelia candel (L.) Druce (Rhizophoraceae), Rhizophora stylosa Griff. (Rhizophoraceae), Sonneratia alba J. Smith (Sonneratiaceae), Nypa fruticans (Thunb.) Wurmb. (Palmae), Lumnitzera racemosa Willd. (Combretaceae), Avicennia marina (Forsk.) Vierh. (Avicenniaceae or Verbenaceae), and Pemphis acidula Forst. (Lythraceae). A total of 61 chemicals (fatty acid derivatives, terpenoids, carotenoid derivatives, benzenoids, nitrogen-containing compounds, 13 unknown chemicals) were detected in the floral scents of the various species. The species displayed a distinct chemical profile ranging from only two chemicals in the floral scent of Kandelia candel to more than 25 chemicals in the floral scent of Nypa fruticans. All of the identified chemicals have been found in the floral scents of other angiosperms. The chemical profile of some species can be correlated with their floral morphology and pollinators.
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