Comparative ultrastructure of Layer I receptor mosaics in principal eyes of jumping spiders: the evolution of regular arrays of light guides

Summary Previous work has shown that the mosaics of Layer I receptive segments in the tiered principal (AM) retinae of most jumping spiders (Salticidae) are organised as regular arrays of light guides which are competent to sustain fine visual discriminations. The retinae are narrow strips which arise in development by lateral compression of a primordial hemispherical monolayer of nascent receptive segments. Foveal Layer I receptive segments each contain a single rhabdomere in most species, but simple geometry suggests that the developmental route will generate a vertical suture line of sampling ambiguity in which contiguous rhabdomeres of adjacent segments act as single light guides. In members of two primitive subfamilies, the Lyssomaninae and Spartaeinae, such suture lines are indeed present; their optical consequences are discussed in the context of the evolution of foveal rhabdomeres that are long light guides. In several notionally advanced subfamilies collectively termed the Salticinae here for convenience, suture lines have been eliminated by rotations of the positions of single rhabdomeres with respect to the longitudinal axes of their receptive segments. The resulting mosaic patterns of rhabdomere distribution are similar in genera distantly related within the Salticinae, and are not bilaterally symmetrical with respect to horizontal axes bisecting the boomerang-shaped receptor fields. The basic pattern is not disturbed in genera in which Layer I receptive segments are separated from neighbours by a structureless extracellular matrix. This separation of segments conserves the organisation found in juvenile jumping spiders designated as 2nd instar by Blest (1988). The present material confirms that the evolution of retinal tiering preceded that of a foveal Layer I mosaic of high acuity in the Lyssomaninae as well as Spartaeinae (Blest and Carter 1987). The evolutionary history of Layer I in the Salticinae remains obscure.     

Secondary retinae of a primitive jumping spider,Yaginumanis (Arachnida,Araneida, Salticidae)

Summary Retinae of the secondary eyes of a primitive salticid spider, Yaginumanis sexdentatus (Yaginuma 1967) are described at the ultrastructural level. The structures of the anterior lateral, posterior lateral and posterior median eyes are identical. Receptor somata lie in the retinal cups. Each receptor bearing twin rhabdomeres is ensheated by (i) much-divided processes of non-pigmented glial cells whose somata lie distally in the retinal cups; and (ii) four processes of pigmented glial cells whose somata lie basally, below the receptive segments. Pigment granules in the latter are concentrated in the basal retina, and are not present at the level of the rhabdoms. The present findings support the placement of Yaginumanis in a newly erected Subfamily Spartaeinae by Wanless (1984), because of the likelihood of homology in the fine structural organisation of the secondary retinae of this genus and of the genus Portia.     

A new mechanism for transitory,local endocytosis in photoreceptors of a spider,Dinopis

Summary Intermediate segment outgrowths (ISOs) are transitory specialisations of the plasma membrane of intermediate segments of the posterior median photoreceptors of Dinopis. Local regions form outgrowths into the glial partitions separating the receptors and remain connected to their parent intermediate segments by narrow necks. ISOs, only a few m in diameter, are sites of intense endocytosis. Coated pits in their plasma membranes give rise to saccular internalisations. Unusual, slender, endocytotic tubules either pinch off coated vesicles, or become detached to yield a tubular detritus. Products of endocytosis are assembled to yield multivesicular and dense bodies, which are usually surrounded by smooth saccules derived from the endoplasmic reticulum of the intermediate segment. ISOs also contain arrays of tubules, thought to be stacks of haemocyanin molecules. There are usually at least 10 times the number of empty ISOs as full and active outgrowths. The number of active ISOs increases rapidly at dawn to peak at about 3 h after sunrise and then rapidly declines. The present sample suggests that the number of empty ISOs increases steadily throughout the day. Thus, ISOs turn over and are probably rapidly formed and short-lived. The contents of ISOs are observed to be evicted into the intermediate segments, where they presumably join the population of secondary lysosomes and are digested. The cyclical activity of ISOs is greatest after shedding of rhabdomeral membrane at dawn (Blest 1978). ISOs are thought to be concerned with the return to the receptors of a minor fraction of rhabdomeral material lost to extracellular space during shedding of the microvillar membrane.The authors thank Professor D.T. Anderson, F.R.S., for use of field facilities of the Crommelin Biological Field Station of Sydney University at Warrah, Pearl Beach, N.S.W., and Andrew and Sally Austin and Carolyn Lawson-Kerr for help in the field. We are indebted to Rod Whitty and the Electron Microscopy Unit for support during these studies, and to Gary Brown for preparing Figs. 1 and 16     

A phospholipase inhibitor, manoalide, and a G-protein activator, Mas-7, both affect the turnover of phototransductive membranes by crab retinas in darkness With a model for the regulation of rhabdomeral membrane turnover

(1) In vitro retinas of a crab, Leptograpsus, were treated with a phospholipase inhibitor, manoalide, or a G-protein activator, Mas-7. Both drugs address early stages of the phototransduction cascade. (2) Manoalide inhibited the light-dependent reduction of rhabdoms during the `day' phase of the light cycle, but did not induce rhabdom overgrowth. Following a period of darkness manoalide failed to affect the diminution of illuminated rhabdoms. (3) The diminution of rhabdoms that follows photoreceptor depolarisation induced by 100 mmol · l<sup>−1</sup> K<sup>+</sup> in darkness was not affected by 2␣μmol · l<sup>−1</sup> manoalide. (4) When retinas in the `night' phase were treated with Mas-7 in darkness, rhabdom diameters were augmented, concurrently with endocytosis of photoreceptor plasma membranes. (5) The results of combining manoalide and Mas-7 with actinomycin D, U-57908 or okadaic acid, drugs used in previous studies to manipulate steps notionally lower in the transduction cascade, lead to a hypothetical model for the regulation of phototransductive membrane turnover by arthropods. Accepted: 3 October 1996     

Photoreceptor membrane breakdown in the spider Dinopis: The fate of rhabdomere products

Summary Photoreceptor membrane breakdown at dawn in the posterior median eyes of the spider Dinopis is described. Coated and smooth vesicles are shed into the receptor cytoplasm and are assembled into multivesicular bodies of two kinds: (i) Coated vesicles form loosely-assembled multivesicular bodies (mvbs) whose bounding membranes are derived from endoplasmic reticulum. (ii) Smooth vesicles generated by the mass disintegration of membrane aggregate to yield tightly-assembled multivesicular bodies which are not membrane-bound. Both types are either lysed in the inter-rhabdomeral cytoplasm, or degrade via multi-lamellar bodies to residual bodies (rbs) while they are being transported to the intermediate segments. Two systems are associated with lysis. Nebenkerne produced by the rapid differentiation of GERL in the intermediate segments fuse with membrane-bound mvbs or rbs and may inject them with hydrolases. Partially-differentiated rigid tubules (Blest et al., 1978) travel to the receptive segments together with RER from the intermediate segments and also fuse with or engulf mvbs. Both systems may contain pro-enzymes which are activated at their target sites. No evidence of a close or necessary geometrical relationship between GERL and Golgi bodies has been seen, and there is no clear demarcation between RER, smooth ER and GERL which is entering into continuity with or engulfing mvbs. The implications of these findings for hypotheses about the origins of isolation membranes and autolytic systems in invertebrate systems are briefly discussed.The authors thank Professor D.T. Anderson, F.R.S., for our use of field facilities at the Crommelin Biological Field Station of Sydney University at Warrah, Pearl Beach, N.S.W., Andrew & Sally Austin and Sally Stowe for help in the field, and Joanne Maples for technical assistance. Professor T.H. Waterman and Dr. V.B. Meyer-Rochow kindly gave us access to certain of their results prior to publication. We are indebted to Rod Whitty and the Electron Microscopy Unit for advice and support throughout these studies     

Photoreceptor membrane breakdown in the spider Dinopis: Localisation of acid phosphatases

Summary The ultrastructural localisation of acid phosphatases (AcPhs) during the normal daily breakdown of rhabdomere membrane in Dinopis has been examined using -glycerophosphate and p-nitrophenyl phosphate as substrates. Results are related to the classification of organelles in the receptors given by Blest, Powell and Kao (1978). Weak and infrequent reactions are obtained in multivesicular bodies (mvbs) and multilamellar bodies (mlbs) derived from them. Residual bodies (rbs) begin to react strongly as they lyse. Source of AcPhs is endoplasmic reticulum which has barely differentiated towards the GERL configuration; it becomes reactive as it is incorporated into secondary lysosomes. GERL tubules, Y-bodies and vesicles respond erratically and weakly, and are also incorporated into rbs. No evidence was found for a significant participation of Golgi bodies in these processes, and acid phosphatase cytochemistry fails to reveal a topographical relationship between GERL in these cells and Golgi saccules. Coated vesicle clusters found in the predawn receptive segments are AcPh-negative; this implies that their previous identification as GERL-derived Nebenkerne carrying hydrolytic enzymes to newly-formed mvbs (Blest, Kao and Powell, 1978) is dubious. Isolation bodies and autophagic vacuoles enclosing other organelles in pathological receptors give strong reactions while adjacent secondary lysosomes derived from rhabdomere membrane and associated GERL give weak ones. It is concluded that rhabdomere-derived rb lysis is more tightly regulated than other autophagic processes, and it is suggested that a high degree of control is necessary in a receptor which may repeat the autophagy of a large mass of transductive membrane at least 60–100 times in the course of its working life.The authors thank Professor D.T. Anderson F.R.S. for the use of field facilities at the Crommelin Biological Field Station of Sydney University at Warrah, Pearl Beach, New South Wales throughout all these studies; Dr. Gary Griffiths (EMBO, Heidelberg) and Dr. Alex Pyliotis (Biochemistry, SGS, Australian National University) for some helpful comments on acid phosphatase histochemistry; Sally J. Stowe for help in the field; and Rod Whitty and the staff on the Electron Microscopy Unit for advice and support. Figure 28 was prepared by Chris Snoek     

Trichoderma spp. and Bacillus spp. as growth promoters in maize (Zea mays L.)

Microbes that are beneficial to plants are used to enhance the crop growth, yield and are alternatives to chemical fertilizers. Trichoderma and Bacillus are the predominant plant growth-promoting fungi and bacteria. The objective of this study was select, characterize, and evaluate isolates of Trichoderma spp. and Bacillus spp. native from the northern region of Sinaloa, Mexico, and assess their effect on growth promotion in maize (Zea mays L.). In greenhouse conditions, four Trichoderma isolates and twenty Bacillus isolates, as well as two controls, were tested in a completely randomized design with three replicates. We selected the two best strains of Trichoderma and Bacillus: TB = Trichoderma asperellum, TF = Trichoderma virens, B14 = Bacillus cereus sensu lato and B17 = Bacillus cereus, which were evaluated in the field in a completely randomized blocks in factorial arrangement design with three replicates applying different rates of nitrogen fertilizer (0, 150 kg N/ha, and 300 kg N/ha). Treatments 5 (B17 = B. cereus) and 11 (TF = T. virens) both fertilized with 150 kg N/ha showed similar yields and they did not reveal significant differences from the treatments fertilized with 300 kg N/ha. This indicated that treatment 5 (B17= B. cereus with 150 kg N/ha) and treatment 11 (TF= T. virens with 150 kg N/ha) were efficient as growth promoters, by not showing significant differences in root volume and dry weight of foliage. The results indicated a reduction of 50% in the rate of nitrogen to fertilizer required for maize (Zea mays L.) crops. These microorganisms Trichoderma and Bacillus could be an alternative to reduce the use of chemical fertilizers in maize.