How spatangoids produce their traces: relationship between burrowing mechanism and trace structure

Kanazawa, K. 1995 11 30 How spatangoids produce their traces: relationship between burrowing mechanism and trace structure.
Two spatangoid echinoids, Echinocardium cordatum and Lovenia elongata , were allowed to produce their traces in poorly and well-sorted sediments in aquaria. In poorly sorted sediments they formed distinct traces, comparable to fossil traces. Sorting of sediment occurred during transportation by the lateroventral spines and brought about characteristic patterns in grain size at the bottoms of the burrows and in redeposited sediment, which made the traces visible. Differences in the burrowing mechanism between E. cordatum and L. elongata are reflected in their trace structures. E. cordatum formed a laminated backlill structure which resulted from periodic accumulation of excavated sediment behind it, while L. elongata simply pushed excavated sediment by compression to the posterior sides of the test, so that their traces lack a distinct laminated structure and the width of the trace becomes larger than that of the animal. In well-sorted sediment, the echinoids burrowed in the same way as in poorly sorted sediment, but no visible trace was produced other than a drain tube. These observations reasonably explain some characteristic modes of occurrence of fossil spatangoid traces. Their different morphological expressions depend on sediment texture and the uneven lithification of traces. Spatangoids, trace, burrowing mechanism .     

Regulation of cyclic electron flow in C3 plants: differential effects of limiting photosynthesis at ribulose‐1,5‐bisphosphate carboxylase/oxygenase and glyceraldehyde‐3‐phosphate dehydrogenase

Cyclic electron flow around photosystem I (CEF1) is thought to augment chloroplast ATP production to meet metabolic needs. Very little is known about the induction and regulation of CEF1. We investigated the effects on CEF1 of antisense suppression of the Calvin–Benson enzymes glyceraldehyde‐3‐phosphate dehydrogenase (gapR), and ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) small subunit (SSU), in tobacco (Nicotiana tabacum cv. Wisconsin 38). The gapR, but not ssuR, mutants showed substantial increases in CEF1, demonstrating that specific intermediates, rather than slowing of assimilation, induce CEF1. Both types of mutant showed increases in steady‐state transthylakoid proton motive force (pmf) and subsequent activation of the photoprotective q_E response. With gapR, the increased pmf was caused both by up‐regulation of CEF1 and down‐regulation of the ATP synthase. In ssuR, the increased pmf was attributed entirely to a decrease in ATP synthase activity, as previously seen in wild‐type plants when CO₂ levels were decreased. Comparison of major stromal metabolites in gapR, ssuR and hcef1, a mutant with decreased fructose 1,6‐bisphosphatase activity, showed that neither the ATP/ADP ratio, nor major Calvin–Benson cycle intermediates can directly account for the activation of CEF1, suggesting that chloroplast redox status or reactive oxygen species regulate CEF1.     

Depletion of stromal Pi induces high 'energy-dependent' antenna exciton quenching (qE) by decreasing proton conductivity at CFO-CF1 ATP synthase

This work tests two models to account for the effects of depletion of stromal inorganic phosphate (P_i), which results in down-regulation of light capture via the exciton quenching (q_E) mechanism and has been proposed to act in feedback regulation of the light reactions. In both models, antenna down-regulation is activated by acidification of the lumen, despite the fact that linear electron flow (LEF) (and associated proton flux) is decreased upon P_i depletion. In one model, an imbalance of ATP or NADPH activates cyclic electron transfer around photosystem I (CEF1), increasing proton influx to the lumen. In the second, the effective conductivity of the CF_O-CF₁ ATP synthase to protons ( g _H⁺) is decreased, retarding proton efflux from the lumen. Sequestering of P_i by mannose infiltration increased sensitivities of q_E and pmf to LEF. The effects were attributable to decreases in g _H⁺, but not to CEF1 and were largely reversed by subsequent P_i feeding. Rapid recovery of g _H⁺ in the dark suggested that dark-labile metabolic pools are responsible for regulation of the ATP synthase. Overall, these results support models where accumulation of Benson–Calvin cycle intermediates or lowering of stromal P_i below its K _Mat the ATP synthase, retards proton efflux from the lumen, leading to build-up of pmf and subsequent down-regulation of photosynthetic light capture.     

Integrating the proton circuit into photosynthesis: progress and challenges

The formation of trans-thylakoid proton motive force (pmf) is coupled to light-driven electron transfer and both powers the synthesis of ATP and acts as a signal for initiating antenna regulation. This key intermediate has been difficult to study because of its ephemeral and variable qualities. This review covers recent efforts to probe pmf in vivo as well as efforts to address one of the key questions in photosynthesis: How does the photosynthetic machinery achieve sufficient flexibility to meet the energetic and regulatory needs of the plant in a varying environment? It is concluded that pmf plays a central role in these flexibility mechanisms.     

NEW ARGININE-CONTAINING PEPTIDES ISOLATED FROM CHLORELLA CELLS

Seven kinds of arginine-containing peptides were isolated fromthe cells of Chlorella ellipsoidea, and their structures wereinvestigated. Their amino acid make-ups and quantities presentin randomly grown algal cells were found to be as follows (indecreasing order of contentin moles per dry weight of cells): Arg-Arg, Arg-Arg-Glu, Arg-Arg-Arg, Arg-Glu> Arg-(Arg₂, Glu)-Glu>Arg-(Arg₃,Glu), Arg-(Glu, Asp) Using synchronously mass-cultured algal cells, the quantitiesof these peptides as they changed during the algal life cyclewere followed. It was found that, except in the case of Arg-Arg-Arg,the contents (in moles per dry weight of cells) of the peptides(i) markedly increased during the stages from D_n to L₁, (ii)remained almost constant or more or less appreciably increasedduring the stages from L₁ to L₃, and (iii) decreased sharplyduring the transformation of L₃-cells (via L₄) into D_n-cellsin the dark. The content of Arg-Arg-Arg remained almost constantduring the period from D_n to L₃, and on transference of L₃-cellsin the dark it increased temporarily and then decreased duringthe transformation of L₄-cells into D_n-cells. Significance andpossible roles of these peculiar peptides in the life cycleof Chlorella were discussed. (Received May 10, 1965; )     

Specific inhibitory effect of copper on cellular division in Chlorella

By growing Chlorella ellipsoidea synchronously by the techniqueof TAMIYA et al. with some modifications, it was demonstratedthat cellular division of ripened cells (L₂- and L₃-cells) inthe dark is specifically inhibited—especially stronglyat pH 6.3—by cupric ion present in the medium. The possibleattack site of cupric ion in cellular division of this algais discussed. (Received March 12, 1969; )