Effects Of Different Light Conditions On The Structure Of Compound Eyes In Shrimp Macrobrachium Nipponense

In this paper, the ultrastructures of compound eyes in blue and red light conditions were firstly studied with the transmission electron microscope in Macrobrachium nipponense. The changes of ultrastructural features of rhabdom and cells around were well observed, and were compared thoroughly with the features in full bright light and dark conditions. The functions and significances of related cells structures were discussed during the breakdown and rebuilding of the photoreceptor membrane. This work was of theoretical importance on the color visual research in crustacean. The results were reported as follows:M nipponense has reflecting superposition compound eyes. The facets of ommatidia that form the compound eyes are rectangle. There lie 512 ommatidia within one square millimeter in compound eyes. An ommatidium is composed of cornea, two corneagenous cells, four cone cells, eight retinular cells, rhabdom, distal pigment cells, distal and proximal reflecting pigment cells, In blue, red and in full bright light conditions, compound eyes exhibit obvious characters the disarrangement of microvilli in the rhabdom, the increased number of lamellar bodies, distal and proximal pigment granules covering the crystalline cone and rhabdom to prevent hard light damaging the ommatidia. During dark adaptation, the rhabdomal figures are regular, the distal pigment granules and proximal pigment granules are concentrated in the distal of crystalline tract and the proximal rhabdom respectively, and while retinular pigment granules are lacked in proximal of ommatidium.We firstly testified that the manipulative light conditions couldn't eliminate the circadian change of ultrastructures of compound eyes in M. nipponense. The compound eyes showed corresponding light adaptive features during the diurnal dark adaptation, and showed dark adaptive features to some extent during the nocturnal light adaptation. Many nerve endings both in retinular cells andproximal reflecting pigment cells indicated that the nervous system participated in the regulation of the intrinsic circadian rhythmicity.Both breakdown and resynthesis of microvilli in rhabdom are long-lasting sustained processes in M. nipponense. The lysosome system and the other cells amongst retinular cells carry out the breakdown of microvilli. The former includes coated vesicles, lysosome, lamellar bodies and oil droplets; and the latter include the hemocytes, proximal reflecting pigment cells and nerve glial cells. The multivesiculae bodies, as well as the rough and smooth endoplasmic reticulums, are considered as the sources of new membranes. Mitochondria provide energy not only for the degradation of microvilli, but also for the resynthesis of the photoreceptor membrane.The degree of ultrastructural changes of rhabdom during light and dark adaptation of compound eye had something to do with the intensity and wavelength of environmental light in M. nipponense. Analysis of variance showed there were obvious effects on the diameter and the length of rhabdom, and the distribution of proximal pigment in different light conditions. The varieties of the rhabdomal diameter were the least during day and night in blue light condition. With the increasing light adaptive time, the length of rhabdom trended to be longer and proximal pigment trended to spread more widely, but the variation was smaller in full bright light and short wave (blue) light conditions than that in long wave (red) light condition. The distribution of proximal pigment in blue light was broader than in red light, and that in full bright light was the shortest. The ultrastructure of the compound eyes responding to blue light was more sensitive than responding to red light in M nipponense.