Metabolism of separated leaf cells: I. Preparation of photosynthetically active cells from tobacco

Suspensions of mesophyll cells, prepared from tobacco leaves by treatment with pectinase, fixed CO₂ by photosynthesis. The products of carbon assimilation were similar for both cells and intact tissue. The cells sustained a constant fixation rate for 20 to 25 hours. For optimal CO₂ fixation, enzymatic maceration of the tissue was accomplished in 0.8 m sorbitol, but photosynthesis was optimal in 0.6 m sorbitol at pH 7 to 7.5. A hypertonic environment during maceration, which results in cell plasmolysis, is essential to maintain intact plasmalemmas and hence photosynthetically active cells. For sustained CO₂ fixation, light intensities below 500 foot-candles were required. Higher light intensities (to 1000 foot-candles) gave high initial rates of CO₂ fixation, but the cells bleached and were inactive on prolonged incubation. At pH 7.0 the bicarbonate concentration at maximal velocity of CO₂ fixation was about 1.5 mm and the apparent Km for bicarbonate was 0.2 mm.     

Preceramic transhumance and andean food production

Thomas Lynch (1971) has recently attempted to document the fact that the preceramic hunter-gatherers of Peru were mobile throughout a range of altitudinal zones and that the fields of movement of these preceramic populations may well have been continuous, since the members of each group exploited the resources of different habitats in terms of regular annual cycles. However, it is equally clear that these long, linear fields of the preceramic populations began to be fragmented at some point in lime. We believe that the termination of the proposed period of transhumance constitutes an extremely interesting problem. At the present time this feature has been discussed only in terms of data from the Peruvian coast. In this paper we employ some of Lynch’s data and observations in an attempt to demonstrate (I) that a minimum of modification of the preceramic pattern of food procurement within the highlands was required to convert hunter-gatherers into food producers; and (2) wild tubers played a crucial role in this process.     

Capsella embryogenesis: The suspensor and the basal cell

Summary The suspensor and basal cell ofCapsella were examined with the electron microscope and analyzed by histochemical procedures. The suspensor cells are more vacuolate and contain more ER and dictyosomes, but fewer ribosomes and stain less intensely for protein and nucleic acids than the cells of the embryo. The end walls of the suspensor cells contain numerous plasmodesmata but there are no plasmodesmata in the walls separating the suspensor from the embryo sac. The lower suspensor cells fuse with the embryo sac wall and the lateral walls of the lower and middle suspensor cells produce finger-like projections into the endosperm. At the heart stage the suspensor cells begin to degenerate and gradually lose their ability to stain for protein and nucleic acids.The basal cell is highly vacuolate and enlarges to a size of 150 X 70. An extensive network of wall projections develops on the micropylar end wall and adjacent lateral wall. The nucleus becomes deeply lobed and suspended in a strand of cytoplasm traversing the large vacuole. The cytoplasmic matrix darkens at the late globular stage and histochemical staining for protein becomes very intense. The basal cell remains active after the suspensor cytoplasm has degenerated. It is proposed that the suspensor and basal cell function as an embryonic root in the absorption and translocation of nutriments from the integuments to the developing embryo.Research supported by NSF grant GB 3460 and NIH grant 5-RO 1-CA-03656-09.     

Orchid embryology: Pollen tetrads of Epidendrum scutella in the anther and on the stigma

Summary The pollinium of Epidendrum scutella, both in the anther and on the stigma, was examined with the electron microscope. The sporoderm of the outer tetrads has a sexine and an intine while that of the inner tetrads lacks a sexine, and an intine is formed only after the pollinium is on the stigma. A fibrous wall layer apparently holds the tetrads together. The cytoplasm is filled with plastids, mitochondria, polysomes, vacuoles and vesicles of various sizes, and endoplasmic reticulum (ER) with narrow cisternae. The vegetative nucleus is oval in form and contains a large nucleolus. The generative nucleus is deeply lobed and contains a well-developed nucleolus. The generative cytoplasm lacks both plastids and mitochondria and has little ER. Dictyosomes are present as well as assorted vesicles. A pocket is present between the plasma membrane of the generative cell and the wall; it contains assorted membranes and ribosome-like particles. After the pollen is on the stigma the wall surrounding the generative cell begins to disappear and gaps develop in it.This investigation was carried out during the tenure of a research fellowship from the Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina.Research supported by grants from National Science Foundation (GB-3460) and the Miller Institute for Basis Science at the University of California, Berkeley. The authors would like to thank Miss Mary Ashton for her assistance in the research.     

Effect of growth rate on histidine catabolism and histidase synthesis in Aerobacter aerogenes

A study was made of how the catabolism of a carbon and energy source is affected by the biosynthetic demands of growing bacterial cells. Cultures of Aerobacter aerogenes in l-histidine medium were grown in a chemostat at rates determined by the supply of either sulfate or a required amino acid, l-arginine. It was discovered that the rate at which these cells grow under a biosynthetic restriction determines both the rate and the pattern of histidine degradation. (i) Histidine catabolism is partially coupled to the growth rate. This coupling is achieved by catabolite repression of histidase (histidine ammonia lyase; EC 4.3.1.3.), and also by a slightly decreased in vivo function of this enzyme at low growth rates. (ii) The looseness of the coupling results in a direct relationship between growth rate and growth yield, and possibly is correlated with an altered pattern of carbon flow from histidine. (iii) Sudden decreases in growth rate cause total repression of histidase synthesis for substantial periods of time. (iv) Sudden release of biosynthetic restriction leads rapidly to an increase in the functioning of the cells' complement of histidase, an increase in the rate of synthesis of this enzyme, and an increase in the growth yield from histidine.     

Effect of Processing on the Microflora of Norwegian Seaweed Meal, with Observations on Sporendonema minutum (Høye) Frank and Hess

Meal from the brown seaweed Ascophyllum nodosum (L.) Le Jol. is mainly used as an animal feed supplement. Since moist weed often develops a marked mold growth and since little was known about the microflora of seaweed meal, a cultural procedure was developed to enumerate the populations of bacteria, yeasts, and molds of seaweed meals manufactured by different drying processes. The microflora could be supported by a variety of media varying in levels of nutrition and in the source and concentration of salts. Fresh weed contained less than 10(3) bacteria and less than 10(2) yeasts and molds per g (dry weight). The type and extent of microbial populations in seaweed meal appeared to be dependent upon the method of seaweed drying. Rotary drum-drying at temperatures decreasing from 800 to 80 C maintained or reduced the microbial populations to 10(3) organisms per g (dry weight). Although meals with high nutritional quality can be obtained with warm air- or rock-dried weed, these conditions can also permit bacterial and mold development. Extended rock-drying in variable weather conditions and prolonged storage of moist weed, both of which decrease the nutritional quality, also lead to high bacterial numbers and to a marked development of the halophilic brown mold Sporendonema minutum which attained populations of 10(8) viable spores per g of dried weed. A poultry diet containing 5% badly molded weed had no apparent toxic or growth-depressing effect when fed to chicks.     

Comparative control of a branch-point enzyme in microorganisms

Thirty-two genera of microorganisms were identified with one of six distinctive control patterns for the enzyme 3-deoxy-d-arabino-heptulosonate-7-phosphate synthetase. These patterns included sequential feedback inhibition, isoenzyme feedback inhibition, cumulative feedback inhibition, and three (apparent) simple one-effector patterns. Documentation is provided of an overwhelming tendency for control patterns to be strongly conserved among the member species of the various genera that were examined.