Leaf cell water and enzyme activity.

This work supports further the thesis that under conditions of water stress, cell water content may supersede hormonal regulation in effecting enzyme activity, thus becoming a regulatory factor in cellular metabolism. Addition of NaCl to the root medium of barley plants (Hordeum vulgare L.) markedly increased leaf RNase activity parallel to an increase of leaf water saturation deficit (WSD). Kinetin and abscisic acid, applied to the salinated plants, also modified RNase activity, as well as leaf-WSD. The familiar pattern of effects of these hormones on leaf RNase as well as leaf chlorophyll content was inverted, kinetin effected a relative increase in RNase activity and a decrease in leaf chlorophyll, whereas abscisic acid effected a relative decrease in RNase activity and maintained chlorophyll content. A close relationship between enzyme activity and leaf WSD became evident when leaf RNase and protease activities in the salinated plants were plotted against leaf WSD. This close relationship was maintained irrespective of the hormonal treatments, which in themselves markedly modified leaf WSD. As predicted, high relative humidity which relived the leaves from salt-induced water stress prevented the salt-induced rise in RNase activity.

Effect of Nitrogen on Polysaccharide Production in a Porphyridium sp.

Porphyridium cultures grown on either nitrate or ammonium as the nitrogen source showed similar patterns of growth and cell wall polysaccharide production. The effect of nitrogen on growth and cell wall polysaccharide production was studied by applying three regimens of supply: batch mode, in which nitrate was supplied at the beginning of the experiment and became depleted at day 6; continual mode, in which nitrate was added daily; and deficient mode, in which the cells were cultured in a nitrate-free medium. Growth was similar in the batch- and continual-mode cultures, whereas it was totally inhibited in the deficient-mode culture. Polysaccharide content (per volume) was highest in the batch-mode culture and lowest in the deficient-mode culture. However, polysaccharide production per cell was similar in the continual- and deficient-mode cultures, the highest value being found in the batch-mode culture. In addition to its effect on polysaccharide content, nitrogen affected the polysaccharide distribution between soluble and bound polysaccharides. In the deficientmode culture, most of the cell wall polysaccharide was dissolved in the medium.

Leaf water content and hormone effects on ribonuclease activity.

In barley (Hordeum vulgare) leaves in which the water balance was not hampered, kinetin and abscisic acid effected the well documented decrease and increase, respectively, in RNase activity. When the plants were exposed to water shortage, leaf-water saturation deficit increased steadily, with kinetin enhancing and abscisic acid retarding the rise. Under drought, the pattern of hormonal effects was inverted, with kinetin enhancing RNase activity over and above the activity assayed in abscisic acid-treated leaves. A very close relationship between RNase activity and water saturation deficit was found and significantly, it was maintained irrespective of the hormonal treatment, which in itself markedly modified leaf-water saturation deficit. The inverted effects of kinetin and of abscisic acid on RNase activity under conditions of water shortage were interpreted as resulting primarily from the effects of these hormones on leaf-water. It is suggested that under conditions of increased water deficiency in the plant, cell-water supersedes hormonal regulation in effecting RNase activity.

Relationship between the Unicellular Red Alga Porphyridium sp. and Its Predator, the Dinoflagellate Gymnodinium sp.

Contamination of algae cultivated outdoors by various microorganisms, such as bacteria, fungi, algae, and protozoa, can affect growth and product quality, sometimes causing fast collapse of the cultures. The main contaminant of Porphyridium cultures grown outdoors in Israel is a Gymnodinium sp., a dinoflagellate that feeds on the alga. Comparison of the effects of various environmental conditions, i.e., pH, salinity, and temperature, on Gymnodinium and Porphyridium species revealed that the Gymnodinium sp. has sharp optimum curves, whereas the Porphyridium sp. has a wider range of optimum conditions and is also more resistant to extreme environmental variables. The mode of preying on the alga was observed, and the specificity of the Gymnodinium sp. for the Porphyridium sp. was shown. In addition, Gymnodinium extract was shown to contain enzymatic degrading activity specific to the Porphyridium sp. cell wall polysaccharide.

Chelating Properties of Extracellular Polysaccharides from Chlorella spp.

Chlorella stigmatophora LB 993 was grown in artificial seawater under controlled conditions. The production of cell wall polysaccharides attached to the cells and dissolved in the growth medium was monitored during algal growth. Preliminary characterization of the dissolved polysaccharides of C. stigmatophora and other Chlorella species is presented. The capacity of dissolved polysaccharides of C. stigmatophora to bind toxic heavy metals was also studied and compared with that of polysaccharides produced by other marine Chlorella species. The differences in metal-complexing capacity observed for dissolved polysaccharides obtained from various Chlorella species is attributable to differences in the composition of the polysaccharides, notably the uronic acids content.

Polyamine Biosynthetic Enzymes in the Cell Cycle of Chlorella: Correlation between Ornithine Decarboxylase and DNA Synthesis at Different Light Intensities.

During the life cycle of Chlorella vulgaris Beijerinck var vulgaris fa. vulgaris growing synchronously, the specific activity of ornithine decarboxylase peaked at the 2nd hour of the cycle, whereas that of arginine decarboxylase changed only slightly, increasing towards the end of the cycle. The endogenous level of putrescine and spermidine on a per cell basis increased gradually up to the 8th hour of the cycle, and declined thereafter. Thus, the peak of ornithine decarboxylase activity and the polyamine increase preceded both DNA replication (which took place between the 6th and 8th hours of the cycle) and autospore release (which started at the 8th hour). A 2-fold increase in the light intensity caused doubling of the DNA content, resulting in doubling of the number of autospores per mother cell. It also brought about a 2-fold increase in the specific activity of ornithine decarboxylase and polyamine content, the peaks being at the same hour of the cycle under high and low light intensities. The increase in cell number and polyamine content in a Chlorella culture grown under high light intensity was inhibited by alpha-difluoromethyl ornithine, a specific inhibitor of ornithine decarboxylase, this inhibition being partially reversed by putrescine.It is suggested that in C. vulgaris the sequence of events which relates polyamine biosynthesis to cell division is as follows: increased ornithine decarboxylase activity, accumulation of polyamines, DNA replication, and autospore release.

Acetohydroxy Acid Synthase Activity in Chlorella emersonii under Auto- and Heterotrophic Growth Conditions.

Acetohydroxyacid synthase (AHAS) activity was studied in the green unicellular alga Chlorella emersonii. This activity and its regulation was compared in the algae grown autotrophically and heterotrophically on glucose in the dark. No evidence for the existence of more than one enzyme was found. The activity in crude extracts from either heterotrophically or autotrophically grown cells showed a K(m) for pyruvate of 9 millimolar, a 22-fold preference for 2-ketobutyrate over pyruvate as the second substrate, 50% inhibition by 0.5 millimolar valine, and 50% inhibition by 0.3 micromolar sulfometuron methyl (SMM). Spontaneous mutants of the alga resistant to SMM were isolated, which appeared to be single gene mutants containing SMM-resistant AHAS activity. Hence, AHAS appears to be the sole direct target site of SMM in C. emersonii. The fact that the mutants had equivalent SMM resistance under auto- and heterotrophic conditions further supports the conclusion that the same enzyme functions under both physiological regimes. The addition of valine and isoleucine leads to partial relief of SMM inhibition of biomass increase, but not of SMM inhibition of cell division.

Participation of ornithine decarboxylase in early stages of tomato fruit development.

The apparent association of ornithine decarboxylase (ODC) with rapid cell proliferation in developing tomato (Lycopersicon esculentum Mill. cv. Pearson ms-35) fruits has been previously described. Further evidence is provided by the use of two ODC inhibitors, alpha-difluoromethylornithine (alpha-DFMO) and alpha-methylornithine (alpha-MO). Fruit development was inhibited by these inhibitors if applied during the period of intensive cell division. When applied in vitro, the two inhibitors were shown to inhibit the activity of ODC but not that of arginine decarboxylase (ADC). When applied in vivo, alpha-DFMO, a catalytic irreversible inhibitor, caused 97.1% reduction of ODC activity in the dialyzed extract from the treated ovaries, while it had no effect on ADC. On the other hand, alpha-MO, a reversible inhibitor, did not reduce the activity of these two enzymes in the dialyzed extracts when applied in vivo. The dialysis procedure probably removed alpha-MO from the enzyme fraction. Putrescine, the product of both ODC and ADC, alleviated the inhibition of fruit development but did not restore ODC activity to the control level. These results suggest that in the young developing tomato fruit, ODC is the enzyme responsible for the synthesis of putrescine, which is essential for the early stages of fruit development. The reduced activity of ODC elicited by putrescine suggests a mechanism of feedback regulation by enzyme repression or release of an ODC anti-enzyme.

Soluble polysaccharide and biomass of red microalga Porphyridium sp. alter intestinal morphology and reduce serum cholesterol in rats.

The present study investigated the effects of the red microalga Porphyridium sp. on gastrointestinal physiology and lipid metabolism in male Sprague-Dawley rats. Diets containing dietary fibre from pelleted red microalgal cells (biomass) or their sulfated polysaccharide, pectin or cellulose (control) were fed to rats for a period of 30 d. All three fibre-supplemented diets increased the length of both the small intestine and colon, with a significantly greater effect in rats fed the algal polysaccharide. The polysaccharide also increased mucosa and muscularis cross-sectional area of the jejunum, and caused hypertrophy in the muscularis layer. The algal biomass significantly lowered gastrointestinal transit time by 44% in comparison with the control rats. Serum and mucosal cholecystokinin levels were lower in rats on the pectin and polysaccharide diets, while cholecystokinin levels in rats fed algal biomass were not different from those in the control animals. In comparison with the control diet, all the experimental diets significantly lowered serum cholesterol levels (22-29%). Feeding of non-fermentable algal polysaccharide or biomass significantly increased faecal weight and bile acid excretion compared with pectin-fed or control rats. The algal polysaccharide and biomass were thus shown to be potent hypocholesterolaemic agents active at low concentrations in the diet. Both metabolic and morphological changes were observed following consumption of algae, suggesting several possible mechanisms by which the alga affects lipid metabolism. The results presented in the present study encourage the use of red microalga as a functional food.