Petiole abscission in cotton: Structural and molecular changes associated with abscission

Flower and boll abscission in cotton limit yield potential, and delayed abscission of later formed leaves contributes to increased staining and trash in lint during harvesting. The purpose of this study was to determine the cytological and ultrastructural changes occurring during abscission and to isolate and characterize genes associated with abscission. The long-term goal of this research is to obtain results that may permit manipulation of cotton abscission to increase yields and improve lint quality. Abscission of cotyledonary petioles was induced in cotton explants by applying either lanolin or lanolin + 0.1% ethephon to cut petiole stumps. Prominent swelling of principally angular collenchyma cells in the subepidermal ground tissues on the adaxial side of the abscission zone of the petiole was observed prior to abscission. No enlargement or swelling of cells was observed on the abaxial side, and no cell divisions were observed prior to cell enlargement in the abscission zone. Middle lamella dissolution and partial degradation of the primary cell wall resulted in cell separation in the abscission zone prior to petiole abscission from the explant. Vesicles surrounded by a unit membrane appeared within the mid-cell wall regions as cell separation progressed. These anatomical and ultrastructural changes suggest that abscission-specific, cell wall hydrolytic enzymes are being secreted during abscission.;To identify genes associated with abscission in cotton, a cDNA library with a titer of 10;Abscission involves structural, physiological and molecular changes. The light microscope and ultrastructural observations reported in this study elucidate cellular events leading to cell separation in cotton, although some structural features of abscission remain unresolved. The abscission cDNA libraries, specifically the subtracted cDNA library, provide a wealth of clones for further identification and characterization of genes that may play important roles in abscission. Ultimately this research may lead to regulation of abscission, resulting in increased yield and improved lint quality of cotton.