Morpho-Histological and Cytological Study on Meristematic Nodule Induction and Shoot Organogenesis in Paeonia Ostii ‘Feng Dan’

This is the first report concerning the sequence of morpho-histological and cytological events occurring during organogenesis from cotyledon-derived meristematic nodules (MNs) in Paeonia ostii ‘Feng Dan’. Sections were made and studies were carried out with dissecting microscope, light microscope, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observation. Histological studies revealed a complex developmental process of morphogenesis that including five stages: (1) callus originated from cell division in both cambial and cortical regions, and type I - yellow compact callus with densely arranged clumps were identified as embryogenic callus. (2) pre-nodular structure consisted of organization center (a central area of vascularization surrounded by meristematic cell layers) and an epidermis-like layer; (3) independent MNs comprised of organization center, a cortical-like area of parenchymatous cells and an epidermal-like area; (4) nodular clusters displayed vigorously internal meristematic cell division and generated a relative movement towards the nodules periphery, establishing vascular connection with primordia; (5) successive new elongated shoots with complete vascular system and axillary bud primordia were developed. SEM observations showed three types of extracellular matrix (ECM), a smooth membranous layer, fibrillar structures and granular mucilage-like secretions on embryogenic callus, and recorded its dynamic morphological changes. Ultrastructural analysis revealed striking changes of chloroplast morphology and starch content during MNs morphogenesis. This study allows a better understanding of in vitro regeneration via MN culture and provides references for protocol optimization and genetic transformation.

Center and surround mechanisms of opponent-color X and Y ganglion cells of retina of macaques

1. Opponent-color ganglion cells of macaques can be classed as X or Y. Cells with a cone-specific receptive-field organization (center and surround receiving input from spectrally different cone types) have a linear summation, whereas cells with a cone-mixed organization (center and surround partly mediated by input from the same cone type) have a nonlinear summation. 2. Pure center and pure surround responses of Y-cells have a fast decay and show conspicuous transients at stimulus offset and onset; pure responses of X-cells have a slow decay and show fewer transients, especially at stimulus offset. 3. Sensitivity profiles based on pure responses elicited in conditions of chromatic adaptation of the opponent responses show that Y-cells have unimodal center and unimodal surround profiles, whereas X-cells have unimodal center and bimodal surround profiles. 4. Responses receiving contribution from both opponent mechanisms (mixed) have different time course and pattern in X- and Y-cells. Mixed response of Y-cells show a discontinuity in cell firing during the transient (on) component of cell activity, which has a higher sensitivity than other waveform changes produced by concurrent stimulation of the opponent mechanism. This discontinuity occurs with stimulus conditions that also elicit proximal negative responses in the local electroretinogram and appears to be due to a centrally located process having some degree of rectification.