Multicellular Secretory Trichome Development on Soybean and Related Glycine Gynoecia

Multicellular glandular trichomes form on gynoecia of wild annual Glycine species, annual soybean cultivars, and wild perennial Glycine species. These trichomes occur from the ovary base to the style base and, in perennial species, along the style as well. Trichomes form at least 2 d before anthesis, and new trichomes develop throughout flowering and also on young seed pods. Trichome structure is similar in all taxa examined, usually five to seven linearly arranged cells. Stalk cells with callose walls become highly vacuolate, and their cytoplasms have reduced numbers of Golgi bodies and endoplasmic reticulum. During secretion, two to four distal cells develop dense cytoplasms containing both prominent Golgi bodies with large vesicles and endoplasmic reticulum with enlarged lumens. Both organelles are involved in forming carbohydrate/protein secretory products. Internal secretion begins with products exuding between the plasmalemma and the primary wall of each distal cell. Secretion progresses between the primary wall and the outermost cuticle that entirely covers the trichome, which is thicker and more highly modified than a normal cuticle. This cuticle separates from cell walls in secretion regions. Products are exuded outside, occur on the inner surface of trichome and gynoecium, and are more obvious in perennial than in annual taxa. The composition and function of products are unknown.