Lora Jorge, Herrero Maria, Hormaza Jose I
Department of Pomology, Estación Experimental 'Aula Dei', CSIC, Apdo. 13034 50080 Zaragoza, Spain.
Department of Subtropical Fruits, Instituto de Hortofruticultura Subtropical y Mediterránea "La Mayora" (IHSM-UMA-CSIC) 29750 Algarrobo-Costa, Málaga, Spain.
Am J Bot. 2014 Sep;101(9):1508-18. doi: 10.3732/ajb.1400312. Epub 2014 Sep 14.
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Permanent tetrads are the most common form of pollen aggregation in flowering plants. The production of pollen in monads is plesiomorphic in angiosperms, but the aggregation into tetrads has arisen independently different times during the evolution of flowering plants. The causes behind the recurrent evolution of pollen aggregation from monads remain elusive. Permanent tetrad pollen is quite common in the Annonaceae, the largest family in the early-divergent order Magnoliales. In some genera, such as Annona, both tetrad- and monad-producing species can be found.•
In this comparative study of pollen development, we use immunolocalization, cytological characterization, and enzymatic assays of four species in the genus Annona and one species in its closely related genus Asimina that release pollen in tetrads and two species in the genus Annona that release pollen in monads.•
The main difference between species with tetrad and monad pollen is a delayed digestion of callose and cellulose at the pollen aperture sites that resulted in nonlayering of the exine in these areas, followed by a rotation and binding of the young microspores at the aperture sites.•
Small changes in development resulted in clear morphological changes on pollen dispersal time and open a window on the possible selective advantage of the production of aggregated pollen.
研究前提：永久四分体是开花植物中最常见的花粉聚集形式。在被子植物中，单核花粉的产生是原始的，但在开花植物的进化过程中，聚集成四分体的情况在不同时期独立出现。单核花粉反复进化为聚集花粉背后的原因仍然不明。永久四分体花粉在番荔枝科中相当常见，番荔枝科是早期分化的木兰目中最大的科。在一些属中，如番荔枝属，既能找到产生四分体花粉的物种，也能找到产生单核花粉的物种。
方法：在这项花粉发育的比较研究中，我们对番荔枝属的四个物种、与其密切相关的合瓣花属中一个产生四分体花粉的物种以及番荔枝属中两个产生单核花粉的物种进行了免疫定位、细胞学特征分析和酶活性测定。
主要结果：产生四分体花粉和单核花粉的物种之间的主要区别在于，花粉孔处胼胝质和纤维素的消化延迟，导致这些区域的外壁不分层，随后幼小花粉母细胞在孔处旋转并结合。
结论：发育过程中的微小变化导致了花粉传播时间上明显的形态变化，并为聚集花粉产生的可能选择优势打开了一扇窗。
