Glandular Trichomes of Soybean Leaves: Cytological Differentiation from Initiation Through Senescence

The development and ultrastructure of glandular trichomes of Glycine max (soybean) leaves have been characterized from initiation through maturation and senescence on mature leaves. They develop from a single epidermal cell and at maturity contain five cells in a linear arrangement, including a basal cell that is continuous with the epidermal layer The nuclei of the upper four cells are centrally placed At initiation of secretion the cuticle separates from the primary cell wall at a region between the uppermost two cells The gland cells are enriched in dictyosomes, rough endoplasmic reticulum, and small vesicles. Plasmodesmata occur in high frequency between gland cells but are fewer between the basal cell and adjacent leaflet cells. The plastids of the upper two cells are unique in that they are closely associated with the nuclei and contain membrane aggregations surrounded by osmiophilic globules, membrane-bound crystalline structures, and starch granules but no grana or thylakoids During gland senescence the dictyosomes degenerate to form membrane pockets of coated vesicles along the cell periphery. Double-walled "macrotubules" 60-70 nm in diameter, which have not been reported in plant cells, appear at about the same time