Occurrence of glutamate dehydrogenase isoenzymes during growth of Oocystis alga

Oocystis sp., a unicellular green alga, contained two glutamate dehydrogenase isoenzymes: one was specific for NADH and the other for NADPH. Activity staining after gel electrophoresis indicated that one component in NADH-GDH was not specific for the cofactor and three components in NADPH-GDH. The optimal concentration of substrate, purification procedure and kinetic properties of both glutamate dehydrogenase (GDH) enzymes in vitro are presented. The kinetics of growth, nutrient removal and enzyme activities for Oocystis growing in wastewater showed that ammonia was preferentially utilized over nitrate and the medium was depleted before the maximum population was obtained in indoor culture. There was a sharp increase in NADPH-GDH activity following the exhaustion of ammonia from the medium but NADH-GDH activity remained unchanged. The NADPH-GDH activity at the outset increased exponentially with time in greenhouse culture but then decreased sharply accompained by a rapid increase in biomass and nitrite concentration. The K(m) values for ammonia in this algal GDH was high, while glutamate synthase activity was not detected; this suggests that Oocystis may adapt to conditions of ammonia limitation by producing large quantities of NADPH-GDH instead of using glutamate synthase pathway.     

l-Arginine and l-Canavanine Metabolism in Jack Bean, Canavalia ensiformis (L.) DC. and Soybean, Glycine max (L.) Merr

Studies have been conducted with the arginase (l-arginine amidinohydrolase, EC 3.5.3.1) of two legumes: jack bean, Canavalia ensiformis (L.) DC., a l-canavanine-containing plant and soybean, Glycine max, a canavanine-free species. Analyses of the arginase obtained from gradient-purified mitochondria of these legumes revealed that the arginine-dependent (ADA) and canavanine-dependent activities (CDA) were localized within this organelle.     

Reduced osmotic potential inhibition of photosynthesis : site-specific effects of osmotically induced stromal acidification

The effects of reduced reaction medium osmotic potential (0.67 molar sorbitol as compared to a control treatment with 0.33 molar sorbitol) on the enzymic steps of the photosynthetic carbon reduction cycle were investigated using isolated spinach (Spinacia oleracea L. var Longstanding Bloomsdale) chloroplasts. Reversal of reduced osmotic potential inhibition of photosynthetic rates by a stromal alkalating agent (NH₄Cl) was associated with specific steps of the cycle. Low osmotic potential induced stromal acidification was found to be facilitated by osmotically induced chloroplast shrinkage. However, the action of the alkalating agent was found not to be associated with reversal of osmotically induced morphological changes of the stromal compartment.

Labeled metabolite analyses indicated that the osmotic stress treatment caused the substrate for fructose 1,6-bisphosphatase (FBPase) to build up in the absence of NH₄Cl, and the substrate for phosphoribulokinase to increase in the presence of NH₄Cl. These data were interpreted as indicating that the most severe effect of osmotic stress on photosynthesis is at the site of FBPase, and that this inhibition is mediated by osmotically induced stromal acidification. Phosphoribulokinase activity inhibition at the low osmotic potential treatment was apparently less severe and not mediated by stromal acidification. A third site of osmotic inhibition, which was reversed by NH₄Cl, and therefore was assumed to be mediated by stromal acidification, was at the step of ribulose 1,5-bisphosphate carboxylase.

Additions of NH₄Cl also enhanced the activity of the pH-insensitive phase of the photosynthetic carbon reduction cycle, 3-phosphoglyceric acid reduction, at the stress treatment. This effect was thought to be mediated by the removal of the block at FBPase. A model was proposed to outline the relative severity of osmotic stress effects at various sites of the photosynthetic carbon reduction cycle.

     

Nuclear medicine-important advances in clinical medicine: the role of nuclear and ultrasonic thyroid imaging

The Scientific Board of the California Medical Association presents the following inventory of items of progress in nuclear medicine. Each item, in the judgment of a panel of knowledgeable physicians, has recently become reasonably firmly established, both as to scientific fact and important clinical significance. The items are presented in simple epitome and an authoritative reference, both to the item itself and to the subject as a whole, is generally given for those who may be unfamiliar with a particular item. The purpose is to assist busy practitioners, students, research workers or scholars to stay abreast of these items of progress in nuclear medicine that have recently achieved a substantial degree of authoritative acceptance, whether in their own field of special interest or another.The items of progress listed below were selected by the Advisory Panel to the Section on Nuclear Medicine of the California Medical Association and the summaries were prepared under its direction.     

An Ontogenetic Study of Canavanine Formation in the Fruit of Jack Bean, Canavalia ensiformis (L.) DC

An ontogenetic study of canavanine formation in the fruit of jack bean, Canavalia ensiformis (L.) DC. was conducted. Evidence was presented to show that the ovary wall is the reservoir for seed canavanine. The testa possesses sufficient canavanine to account for the continued elevation in seed canavanine after the pod senesces. The seed canavanine concentration is not constant inasmuch as the canavanine content per milligram dry weight or soluble protein increases abruptly with seed growth and levels off only with the onset of fruit ripening.     

The ommatidium of the termite mastotermes darwiniensis

An electron microscope study of the compound eye of the termite Mastotermes darwiniensis shows that the ommatidia have both primitive and specialized features. The ommatidia are of the apposition type with eight similar retinular cells, a fused rhabdom, irregularly orientated rhabdomere tubules and no tracheae. The retinula cells contain lipid. The cone cells have unusual processes, which thicken towards the basement membrane and contain rough endoplasmic reticulum, granules and dense bodies. These processes may act as a primitive transport system for nutrients.     

Effects of Phenylmercuric Acetate on Stomatal Movement and Transpiration of Excised Retula papyrifera Marsh. Leaves

Effects of 10⁻³m, 10⁻⁴m, and 10⁻⁵m phenylmercuric acetate (PMA) on stomatal movement and transpiration of excised Betula papyrifera leaves were investigated. Duco cement leaf prints and transpiration decline curves were used for the analysis of stomatal condition. PMA induced stomatal closure and decreased transpiration. Stomata of leaves treated with any of the 3 PMA concentrations closed earlier and at a higher relative water content than did stomata of untreated leaves. As determined from transpiration decline curves, PMA at 10⁻³m caused an increase in apparent “cuticular” transpiration. However, the increase appeared to result largely from some PMA-poisoned stomata which remained open for prolonged periods. Considerable PMA toxicity was observed, with 10⁻³m and 10⁻⁴m concentrations causing browning of leaves. PMA treatment caused a decrease in chlorophyll content, even at a low PMA concentration (10⁻⁵m) which influenced stomatal response only slightly and did not cause evident browning of leaves. The time and degree of stomatal opening varied with stomatal size. Large stomata tended to open earlier and close later than small stomata. Hence, in Betula papyrifera stomata of various size classes were considered as physiologically different populations.     

Statocysts of medusae and evolution of stereocilia

Ectodermal sensory cells of the statolith each bear one nonmotile kinocilium, and in some hydromedusae bear stereocilia which are defined as distinct from microvilli by having fibrillar rootlets. The progressive elaboration of stereocilia can be traced. A hypothesis in which jellyfish statocysts evolve from vibration receptors avoids the difficulty of the uselessness of incipient gravity organs. Comparative study suggests that the kinocilium or its basal body is the transducer.