Changes in auxin patterns in developing gynophores of the peanut plant (Arachis hypogaea L.)

The peanut plant (Arachis hypogaea L.) produces flowers aerially, but buries the recently fertilized ovules in the soil in order for the fruit and seeds to mature underground. The organ that carries the seeds into the soil is called the gynophore. The growth of the peanut gynophore is regulated primarily by indole-3-acetic acid (IAA). A monoclonal antibody raised against IAA was used to successfully detect and localize this growth substance in the tissues of developing peanut gynophores. Five different stages of development were analysed: (1) before fertilization; (2) after fertilization; (3) during downwards growth; (4) at soil penetration; and (5) at the early stages of fruit formation. While no auxin signal is visible in the unfertilized ovules and ovary region, an asymmetric signal is observed in the gynophore wall after fertilization. During downwards growth, the auxin signal is located in both the meristematic region and in the area encircling the seeds, as well as in the cortex and epidermis region of the elongation zone. Upon soil penetration, the auxin signal in the meristematic region disappears, and most of the signal is detected in the gynophore wall near the tip. At the early stages of peanut fruit development, auxin signal is found at the lowermost area of the bending fruit, which eventually causes the fruit to be positioned horizontally. The results of this study suggest that the possible source of auxin within the gynophore may be the area of the gynophore wall close to the tip.