Date of Award

Spring 1975

Document Type

Thesis - Restricted

Degree Name

Master of Science (MS)

Department

Biology

Abstract

During the transition from larval to adult tissues, the fat body of holometabolous insects undergoes striking intracellular changes. Light and electron microscopic observations on 4th instar larvae of Sciara coprophila (Diptera) reveal that shortly after molt to the last larval instar, each fat body cell is divided into two distinct zones. Zone 1 contains lipid bodies in a PAS-positive region of cytoplasmic components. Zone 2 contains the nucleus, mitochondria, golgi, rough endoplasmic reticulum (RER), and an extensive network of membranes that form "intracellular channels". As larvae approach pupation, there is a great increase in the area occupied by Zone 1 components and a decrease in the frequency of many of the organelles of Zone 2. During this period, two types of membrane-bound proteinaceous granules (PG) appear. The first type of PG exhibits a dense homogenous matrix, the precise origins of which are not established. On the basis of morphological evidence, it seems probable that these early appearing homogenous PG form either in conjunction with the RER, or by a coalescence of vesicles from the smooth endoplasmic reticulum (SER). A second, larger heterogenous type of PG regularly appears during later stages of larval development and is autophagic in nature. This class of granules may represent smaller PG of earlier larval stages that increase in size simply through accumulation of mitochondria, RER and other cellular components. Alternatively, the large PG may be a separate class of residual bodies, that arise independently through the progressive condensation of organelles within autophagic vacuoles.

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