蓖麻蚕前胸腺细胞超微结构的变化与蜕皮激素分泌活动的关系

ULTRASTRUCTURAL CHANGCS OF THE PROTHORACIC GLAND CELLS DURING ECDYSONE SECRETION AT LAST TWO LARVAL INSTARS OF PHILOSAM1A CYNTHIA RICINA

本研究叙述蓖麻蚕Philosamia cythia ricini四龄及五龄幼虫前胸腺蜕皮激素分泌活动各不同时期所显示的腺细胞超微结构变化。从幼虫蜕皮后至进入眠期之间的腺细胞结构可分为三个时期,(1)不活动期:细胞核呈圆形,核内密布染色质及核仁,细胞质内有结构完整的线粒体、粗面及滑面内质网、核糖体和高尔基氏体;细胞外围的细胞间区内有许多小囊泡及多泡囊。(2)活动期:细胞结构变化为细胞核膜出现内陷、外突,形成波浪形的核周膜;线粒体变形,出现内嵴稀疏的空心线粒体。(3)激素释放期:细胞核变形,形成若干长短不一向外伸出的指状突,有些伸达细胞边缘;其余细胞器退化,其后仅余残缺的高尔基氏体,稀疏的核糖体,线粒体的内崤逐渐消失,成为空腔扩大的及空腔内藏“膜轮”的线粒体,和一些溶解体及大形“膜轮”。

The prothoracic glands (PG) of Philosamia cynthia ricina are composed of a number of single cells loosely attached to each other to form the long convoluted band-like paired organs. Attached to the tracheae near the prothoracic spiracle, the main part of the gland is more or less flat and broad band-like in appearance. Four branches extend out from the gland: anterior, latero-ventral, latero-dorsal and posterior. The glands produce ecdysone regulating ecdy-sis, and in each moulting stage they go through a cycle of secretory activity. Based on the ul-trastructural changes of PG cells in the last two larval instars the cycle can be divided into three phases: 1. resting or inactive phase after moult, 2. active phase in mid-intermoult, and 3. release phase preceding moult.In the resting phase immediately after moult, the final disintegration of the previous cellular structures still remains perceivable. Shortly fter feeding starts (about 12 hours after moult) the cellular ultrastructures restitute the original characteristics of the resting stage. The nucleus is ovoid or elliptical in form, predominated with euchromatin and heteroch-romatin. The cytoplasmic organelles restore gradually. The mitochondria are rod-shaped with a dense matrix of flat lamellar cristae. The rough endoplasmic reticulum (RER) lies in the cytoplasm where a large number of ribosomes accumulate. The smooth en-'doplasmic reticulum (SER) is intermingled with mitochondria. The Golgi complexes containing numerous vesicles are randomly distributed in the cytoplasm. The periphery of each glandular cell is surrounded with a rather thick peripheral intercellular space (PIS) containing vesicles, multivesicular sacs, tracheoles and nerves, with the outer surface surrounded by basal lamina and inner side attached to the plasma membrane.In mid-intermoult, some ultrastructural changes occur in the cells. The nuclear membrane assume a wave-like appearance, and ribosomes, mitochondria and RER appear in the perinu-clear region. Later on the mitochondria progressively become elongated or rounded and even irregular in profile.The release phase is characteristerized by the gradual morphological involution of PG cells, which is marked by a number of irreversible changes at the beginning. The most striking change occurs in the mitochondria: the cristae disintegrate gradually and finally disappear and vacuoles are formed. The central cavities of mitochondria may become much dilated and the 'membrane whorl' occasionally appears inside. The RER disintegrates gradually in the loosely organized cytoplasm which contains lysosomes. The nucleus becomes extremely evagi-nated and protrude out finger-like protuberances, some of which extend out almost reaching the' periphery region of plasma membrane.