RELATIONSHIPS BETWEEN TAPETUM, LOCULUS, AND POLLEN DURING DEVELOPMENT

Various parts of the anther (walls, tapetum, locular fluid, meiocytes, microspores) cooperate for correct pollen development. To show the different types of relationships possible between these parts, we considered the following characteristics, alone and in combination: types of tapetum, types of pollen-dispersing unit, form of loculus, amount of locular space and fluid, number of pollen grains in transverse sections of the anther and in the loculus, and hydration status of pollen at dispersal. The different relationships between pollen, loculus, and tapetum should enable uniform nourishment of grains in the loculus and ensure a high percentage of viable grains. Two opposite modes were identified: direct and indirect nourishment of grains, the latter occurring when locular fluid is more or less abundant between the tapetum and the grains. The amount of space between developing grains determines different manners of grain nourishment and modes of pollen presentation for dispersal. Cyclosis, which is presumably related to production and release of nutrients into locular fluid, has been described in cytoplasm of all types of tapetum. In loculi containing many grains, we postulate the existence of mechanisms causing movement of locular fluid and pollen grains, enabling uniform nourishment of grains. When the tapetum degenerates, the grains begin to mature, consuming substances (usually starch) stored in the anther wall. This phase concludes with resorption and/or evaporation of locular fluid and partial dehydration of pollen to different degrees in different species. Dehydration may end before, during, or after opening of the anther or flower.