Departamento de Botânica, Instituto de Biociências, Universidade de São Paulo, Rua do Matão 277, São Paulo-SP, 05508-090, Brazil.
Centro de Microscopia Eletrônica, Universidade Federal de São Paulo, Rua Botucatu 862, São Paulo-SP, 04023-062, Brazil.
Protoplasma. 2022 Mar;259(2):399-412. doi: 10.1007/s00709-021-01671-9. Epub 2021 Jun 19.
Pollen grains have a relatively simple structure and microscopic size, with two or three cells surrounded by the protective sporoderm at maturity. The viability and efficiency of pollen transport from anther to stigma depends on pollen physiological properties, especially the relative water content of the vegetative cell. Pollen transport is a crucial fate for most angiosperms that depends on biotic pollinators and studies focusing on understanding the morpho-physiological properties of pollen grains are still scarce, especially to tropical open physiognomies as the Brazilian Cerrado. Therefore, we investigate some structural and physiological aspects of pollen grains from six native species naturally growing in one Cerrado area: Campomanesia pubescens (Myrtaceae), Caryocar brasiliense (Caryocaraceae), Erythroxylum campestre (Erythroxylaceae), Lippia lupulina (Verbenaceae), Pyrostegia venusta (Bignoniaceae), and Xylopia aromatica (Annonaceae). We selected dehiscent anthers and mature pollen grains to analyze (1) the anther wall and pollen microstructure, (2) the pollen water status at the time of anther dehiscence, and (3) the pollen chemical compounds. In all analyzed species, the anther and pollen developed in a successfully way, and except for Caryocar brasiliense, all species were able to emit pollen tubes in the germination tests. As expected for a dry and open environment, most species dispersed their pollen grains in a partially dehydrated form, as indicated by our harmomegathy experiment. As indicated by our study, the pollen ability in preventing dissection, maintaining its viability in a dry and hot environment during its transport from anther to stigma, may be related to the sporoderm apertures and to the reserve compounds, mainly carbohydrates in the form of hydrolysable starch grains.
花粉粒具有相对简单的结构和微观尺寸，成熟时由两个或三个细胞被保护的花粉壁包围。花粉从花药到柱头的活力和运输效率取决于花粉的生理特性，特别是营养细胞的相对含水量。花粉的运输是大多数被子植物的关键命运，依赖于有性传粉者，而专注于理解花粉粒形态生理特性的研究仍然很少，特别是在巴西塞拉多这样的热带开阔地貌中。因此，我们研究了在巴西塞拉多的一个地区自然生长的六个本地物种的花粉粒的一些结构和生理方面：毛曼橘（桃金娘科）、巴西栗（玉蕊科）、山石榴（石榴科）、马缨丹（马鞭草科）、美丽凌霄（紫葳科）和黄樟（樟科）。我们选择了开裂的花药和成熟的花粉粒进行分析：（1）花药壁和花粉的微观结构；（2）花药开裂时花粉的水分状态；（3）花粉的化学化合物。在所有分析的物种中，花药和花粉的发育都很成功，除了巴西栗之外，所有的物种在萌发测试中都能够发出花粉管。正如我们所预期的干燥和开阔的环境一样，大多数物种以部分脱水的形式分散花粉粒，这一点我们通过 harmomegathy 实验得到了证实。正如我们的研究所示，花粉粒在防止分裂、在从花药到柱头的运输过程中保持其在干燥和炎热环境中的活力的能力，可能与花粉壁的开口和储备化合物有关，主要是可水解淀粉粒形式的碳水化合物。
