Loss Of Photosynthetic Activity Research Articles

Pleiotropic effects of PipX, PipY, or RelQ overexpression on growth, cell size, photosynthesis, and polyphosphate accumulation in the cyanobacterium Synechococcus elongatus PCC7942.

The cyanobacterial protein PipY belongs to the Pyridoxal-phosphate (PLP)-binding proteins (PLPBP/COG0325) family of pyridoxal-phosphate-binding proteins, which are represented in all three domains of life. These proteins share a high degree of sequence conservation, appear to have purely regulatory functions, and are involved in the homeostasis of vitamin B6 vitamers and amino/keto acids. Intriguingly, the genomic context of the pipY gene in cyanobacteria connects PipY with PipX, a protein involved in signaling the intracellular energy status and carbon-to-nitrogen balance. PipX regulates its cellular targets via protein-protein interactions. These targets include the PII signaling protein, the ribosome assembly GTPase EngA, and the transcriptional regulators NtcA and PlmA. PipX is thus involved in the transmission of multiple signals that are relevant for metabolic homeostasis and stress responses in cyanobacteria, but the exact function of PipY is still elusive. Preliminary data indicated that PipY might also be involved in signaling pathways related to the stringent stress response, a pathway that can be induced in the unicellular cyanobacterium Synechococcus elongatus PCC7942 by overexpression of the (p)ppGpp synthase, RelQ. To get insights into the cellular functions of PipY, we performed a comparative study of PipX, PipY, or RelQ overexpression in S. elongatus PCC7942. Overexpression of PipY or RelQ caused similar phenotypic responses, such as growth arrest, loss of photosynthetic activity and viability, increased cell size, and accumulation of large polyphosphate granules. In contrast, PipX overexpression decreased cell length, indicating that PipX and PipY play antagonistic roles on cell elongation or cell division. Since ppGpp levels were not induced by overexpression of PipY or PipX, it is apparent that the production of polyphosphate in cyanobacteria does not require induction of the stringent response.

Photosynthetic Carbon Uptake Correlates with Cell Protein Content during Lipid Accumulation in the Microalga Chlorella vulgaris NIES 227

Large-scale microalgae cultivation for biofuel production is currently limited by the possibility of maintaining high microalgae yield and high lipid content, concomitantly. In this study, the physiological changes of Chlorella vulgaris NIES 227 during lipid accumulation under nutrient limitation was monitored in parallel with the photosynthetic capacity of the microalgae to fix carbon from the proxy of oxygen productivity. In the exponential growth phase, as the biomass composition did not vary significantly (approx. 53.6 ± 7.8% protein, 6.64 ± 3.73% total lipids, and 26.0 ± 9.2% total carbohydrates of the total biomass dry-weight), the growth capacity of the microalgae was preserved (with net O2 productivity remaining above (4.44 ± 0.93) × 10−7 g O2·µmol PAR−1). Under nutrient limitation, protein content decreased (minimum of approx. 18.6 ± 6.0%), and lipid content increased (lipid content up to 56.0 ± 0.8%). The physiological change of the microalgae was associated with a loss of photosynthetic activity, down to a minimum (1.27 ± 0.26) × 10−7 g O2·µmol PAR−1. The decrease in photosynthetic O2 productivity was evidenced to correlate to the cell internal-protein content (R2 = 0.632, p = 2.04 × 10−6, N = 25). This approach could serve to develop productivity models, with the aim of optimizing industrial processes.

Sugar metabolism as input signals and fuel for leaf senescence.

Senescence in plants is an active and acquired developmental process that occurs at the last developmental stage during the life cycle of a plant. Leaf senescence is a relatively slow process, which is characterized by loss of photosynthetic activity and breakdown of macromolecules, to compensate for reduced energy production. Sugars, major photosynthetic assimilates, are key substrates required for cellular respiration to produce intermediate sources of energy and reducing power, which are known to be essential for the maintenance of cellular processes during senescence. In addition, sugars play roles as signaling molecules to facilitate a wide range of developmental processes as metabolic sensors. However, the roles of sugar during the entire period of senescence remain fragmentary. The purpose of the present review was to examine and explore changes in production, sources, and functions of sugars during leaf senescence. Further, the review explores the current state of knowledge on how sugars mediate the onset or progression of leaf senescence. Progress in the area would facilitate the determination of more sophisticated ways of manipulating the senescence process in plants and offer insights that guide efforts to maintain nutrients in leafy plants during postharvest storage.

Phytotoxic effects of essential oils in controlling weed species Digitaria horizontalis and Cenchrus echinatus

In certain plant species, essential oils have been reported to inhibit seed germination and cause toxicity and have been associated with a loss of photosynthetic activity. This study aimed to evaluate the effects of essential oils and their major compound citronellal on the germination and growth of crabgrass (Digitaria horizontalis) and burrgrass (Cenchrus echinatus). Essential oils from E. citriodora and C. nardus and pure citronellal compound were used at concentrations of 1% and 10% and 20% to test seed germination and phytotoxic effects, respectively, in the plants. The treatments application was done when the plants were at the four-leaf stage. Seed germination was reduced drastically (97–99% reduction relative to untreated controls), with citronellal showing more drastic reductions than essential oils. In addition, evaluated the phytotoxic effects of essential oils on plant height and dry mass of shoots and roots were evaluated. The negative effects of the oils were seen 12 h following the treatment. The application of the oils at a concentration of 20% reduced the accumulation of dry mass of shoots and roots; however, the number of tiller only affected stomatal opening in burrgrass. Finally, the oils reduced chlorophyll and total protein content in the weeds by more than 80% and 90%, respectively. Therefore, these oils may have application as potential bioherbicides to controlling weeds.

Understanding the evolution of holoparasitic plants: the complete plastid genome of the holoparasite Cytinus hypocistis (Cytinaceae).

Background and Aims Plant plastid genomes are highly conserved in size, gene content and structure; however, parasitic plants are a noticeable exception to this evolutionary stability. Although the evolution of parasites could help to better understand plastome evolution in general, complete plastomes of parasites have been sequenced only for some lineages so far. Here we contribute to filling this gap by providing and analysing the complete plastome sequence of Cytinus hypocistis, the first parasite sequenced for Malvales and a species suspected to have an extremely small genome. Methods We sequenced and assembled de novo the plastid genome of Cytinus hypocistis using a shotgun approach on genomic DNA. Phylogenomic analyses based on coding regions were performed on Malvidae. For each coding region present in Cytinus, we tested for relaxation or intensification of selective pressures in the Cytinus lineage compared with autotrophic Malvales. Key Results Cytinus hypocistis has an extremely divergent genome that is among the smallest sequenced to date (19·4 kb), with only 23 genes and no inverted repeat regions. Phylogenomic analysis confirmed the position of Cytinus within Malvales. All coding regions of Cytinus plastome presented very high substitution rates compared with non-parasitic Malvales. Conclusions Some regions were inferred to be under relaxed negative selection in Cytinus, suggesting that further plastome reduction is occurring due to relaxed purifying selection associated with the loss of photosynthetic activity. On the other hand, increased selection intensity and strong positive selection were detected for rpl22 in the Cytinus lineage, which might indicate an evolutionary role in the host-parasite arms race, a point that needs further research.

Physiological and biochemical alterations on maize leaves infected by Stenocarpella macrospora

This study aimed to analyze the antioxidant system responses and photosynthetic performance of maize cultivars (ECVSCS155 and HIB 32R48H) infected by Stenocarpella macrospora. The activities of some antioxidant enzymes and metabolites and the concentration of reactive oxygen species in maize leaves as well as chlorophyll a fluorescence imaging parameters were assessed. For both cultivars, the enzymatic and non-enzymatic components of the antioxidant system were dramatically altered in the infected leaves. As the disease symptoms became more noticeable, enzyme activities (e.g., peroxidases and catalases) and the concentration of ascorbate and glutathione decreased accordingly. The concentrations of hydrogen peroxide and malondialdehyde equivalents increased, thereby contributing to the intensification of lipid peroxidation upon damage to cell membranes caused by fungal infection. Decreases in maximum fluorescence, maximum PSII quantum efficiency, effective PSII quantum yield and quantum yield of regulated energy dissipation coupled with increases in initial fluorescence and quantum yield of non-regulated energy dissipation were directly related to the progressive loss of photosynthetic activity coupled with the development of oxidative stress during the S. macrospora infection process.

Proteomics Links the Redox State to Calcium Signaling During Bleaching of the Scleractinian Coral Acropora microphthalma on Exposure to High Solar Irradiance and Thermal Stress

Shipboard experiments were each performed over a 2 day period to examine the proteomic response of the symbiotic coral Acropora microphthalma exposed to acute conditions of high temperature/low light or high light/low temperature stress. During these treatments, corals had noticeably bleached. The photosynthetic performance of residual algal endosymbionts was severely impaired but showed signs of recovery in both treatments by the end of the second day. Changes in the coral proteome were determined daily and, using recently available annotated genome sequences, the individual contributions of the coral host and algal endosymbionts could be extracted from these data. Quantitative changes in proteins relevant to redox state and calcium metabolism are presented. Notably, expression of common antioxidant proteins was not detected from the coral host but present in the algal endosymbiont proteome. Possible roles for elevated carbonic anhydrase in the coral host are considered: to restore intracellular pH diminished by loss of photosynthetic activity, to indirectly limit intracellular calcium influx linked with enhanced calmodulin expression to impede late-stage symbiont exocytosis, or to enhance inorganic carbon transport to improve the photosynthetic performance of algal symbionts that remain in hospite. Protein effectors of calcium-dependent exocytosis were present in both symbiotic partners. No caspase-family proteins associated with host cell apoptosis, with exception of the autophagy chaperone HSP70, were detected, suggesting that algal loss and photosynthetic dysfunction under these experimental conditions were not due to host-mediated phytosymbiont destruction. Instead, bleaching occurred by symbiont exocytosis and loss of light-harvesting pigments of algae that remain in hospite. These proteomic data are, therefore, consistent with our premise that coral endosymbionts can mediate their own retention or departure from the coral host, which may manifest as “symbiont shuffling” of Symbiodinium clades in response to environmental stress.

Response of chlorophyll d-containing cyanobacterium Acaryochloris marina to UV and visible irradiations

We have previously investigated the response mechanisms of photosystem II complexes from spinach to strong UV and visible irradiations (Wei et al J Photochem Photobiol B 104:118-125, 2011). In this work, we extend our study to the effects of strong light on the unusual cyanobacterium Acaryochloris marina, which is able to use chlorophyll d (Chl d) to harvest solar energy at a longer wavelength (740nm). We found that ultraviolet (UV) or high level of visible and near-far red light is harmful to A. marina. Treatment with strong white light (1,200μmolquantam(-2)s(-1)) caused a parallel decrease in PSII oxygen evolution of intact cells and in extracted pigments Chl d, zeaxanthin, and α-carotene analyzed by high-performance liquid chromatography, with severe loss after 6h. When cells were irradiated with 700nm of light (100μmolquantam(-2)s(-1)) there was also bleaching of Chl d and loss of photosynthetic activity. Interestingly, UVB radiation (138μmolquantam(-2)s(-1)) caused a loss of photosynthetic activity without reduction in Chl d. Excess absorption of light by Chl d (visible or 700nm) causes a reduction in photosynthesis and loss of pigments in light harvesting and photoprotection, likely by photoinhibition and inactivation of photosystem II, while inhibition of photosynthesis by UVB radiation may occur by release of Mn ion(s) in Mn4CaO5 center in photosystem II.

Metabolic and Molecular Events Occurring during Chromoplast Biogenesis

Chromoplasts are nonphotosynthetic plastids that accumulate carotenoids. They derive from other plastid forms, mostly chloroplasts. The biochemical events responsible for the interconversion of one plastid form into another are poorly documented. However, thanks to transcriptomics and proteomics approaches, novel information is now available. Data of proteomic and biochemical analysis revealed the importance of lipid metabolism and carotenoids biosynthetic activities. The loss of photosynthetic activity was associated with the absence of the chlorophyll biosynthesis branch and the presence of proteins involved in chlorophyll degradation. Surprisingly, the entire set of Calvin cycle and of the oxidative pentose phosphate pathway persisted after the transition from chloroplast to chromoplast. The role of plastoglobules in the formation and organisation of carotenoid-containing structures and that of theOrgene in the control of chromoplastogenesis are reviewed. Finally, using transcriptomic data, an overview is given the expression pattern of a number of genes encoding plastid-located proteins during tomato fruit ripening.

Depletion of Vipp1 inSynechocystissp. PCC 6803 affects photosynthetic activity before the loss of thylakoid membranes

A vipp1 mutant of Synechocystis sp. PCC 6803 could not be completely segregated under either mixotrophic or heterotrophic conditions. A vipp1 gene with a copper-regulated promoter (P(petE)-vipp1) was integrated into a neutral platform in the genome of the merodiploid mutant. The copper-induced expression of P(petE)-vipp1 allowed a complete segregation of the vipp1 mutant and observation of the phenotype of Synechocystis 6803 with different levels of vesicle-inducing protein in plastids 1 (Vipp1). When P(petE)-vipp1 was turned off by copper deprivation, Synechocystis lost Vipp1 and photosynthetic activity almost simultaneously, and at a later stage, thylakoid membranes and cell viability. The photosystem II (PSII)-mediated electron transfer was much more rapidly reduced than the PSI-mediated electron transfer. By testing a series of concentrations, we found that P(petE)-vipp1 cells grown in medium with 0.025 muM Cu(2+) showed no reduction of thylakoid membranes, but greatly reduced photosynthetic activity and viability. These results suggested that in contrast to a previous report, the loss of photosynthetic activity may not have been due to the loss of thylakoid membranes, but may have been caused more directly by the loss of Vipp1 in Synechocystis 6803.

Defoliation effects on carbon and nitrogen substrate import and tissue‐bound efflux in leaf growth zones of grasses

ABSTRACTGrassland plants suffer regular defoliation, causing loss of photosynthetic activity and internal resources. Consequently, re‐foliation may be substrate‐limited. The present study was undertaken to test the hypothesis that decreased C import in leaf growth zones is (partially) compensated by: (i) mobilization of substrate within growth zones; and (ii) increased efficiency of substrate use in leaf area expansion; but (iii) that these processes depend on the C status of growth zones at defoliation. Mixtures of a C3 (Lolium perenne L.) and a C4 grass (Paspalum dilatatum Poir.) were grown at 15 °C (C3 dominance) and 23 °C (C4 dominance). Individual plants thus grew in contrasting (light and temperature) environments before being defoliated. Defoliation caused a drastic and immediate decrease in C import, but effects on leaf area expansion were buffered by biomass mobilization in the growth zone and increases in specific leaf area of produced tissue. Thus, over the first 2 d post‐defoliation, the amount of leaf area produced per unit imported C increased by 39 to 102% depending on treatment. The magnitude of these buffering responses was correlated with the concentration of water soluble carbohydrates in the growth zone at defoliation. Similar responses were observed for N, although defoliation effects were smaller and delayed relative to those on C import. This study demonstrates refoliation is sustained by short‐term mobilization of reserves within the growth zone and reduced costs of produced leaf area, but that these mechanisms depend on growth zone C status at defoliation.

The last step of the ethylene biosynthesis pathway in turnip tops (Brassica rapa) seeds: Alterations related to development and germination and its inhibition during desiccation.

The involvement of ethylene in zygotic embryogenesis is a little known aspect of the growth and development in higher plants. In the present work, we study the alterations of the last step of the ethylene biosynthesis pathway during the formation period of turnip tops (Brassica rapa cv. Rapa) seeds and its repercussions in the germination process and post-germinative growth. For this, we chose 11 different phases of silique development, the first being the recently fertilized pistil and the last being the silique just prior to its dehiscence (ca. 2 months post-anthesis). In the 11 phases, ethylene production was detected in both whole silique (with or without seeds) and in the seeds enclosed by the silique wall. The levels of ACC, ACO and ethylene production proved high in seeds belonging to: (1) the pod in the very early phases, when the seeds were growing but without photosynthetic competence; (2) the silique at maximum growth, in which the seeds will initiate desiccation and loss of photosynthetic activity. During the phases prior to dehiscence, there was a marked inhibition in the last step of the ethylene biosynthesis pathway. In viable dry seeds, no ACO activity was detected and the ACC levels were 4-fold lower than at the onset of the silique senescence. Germination brings about a net synthesis of ACC with respect of the stores dry seed. This fact, together with other results presented in this work, point towards, as in other seeds, a dependence of ethylene synthesis for radicle emergence. The possible role played by the silique wall in the control of ethylene biosynthesis during zygotic embryogenesis, as well as the participation of ethylene as a hormonal signal in the triggering of seed desiccation in Brassica rapa cv. Rapa, are discussed in depth.

Photosynthetic Gene Expression in Amaranth, an NAD-ME Type C4 Dicot

Post-transcriptional regulation determines initial C4 gene expression patterns in developing leaves of Amaranthus hypochondriacus, an NAD-ME type C4 dicot. RuBPCase, PEPCase, and PPdK mRNAs are abundant in meristems and in leaf primordia, but are utilised only during specific developmental stages. While each enzyme shows independent patterns of initial mRNA and polypeptide accumulation, cell-specific localisation of the polypeptides occurs prior to cell-specific localisation of the mRNAs. In mature three-coloured leaves of A. tricolor, loss of photosynthetic activity correlates with reductions in the transcription rates of some plastid-encoded genes, reduction and loss of coordination in the translation of RuBPCase polypeptides, and loss of cell-specific accumulation of RuBPCase mRNAs (but not the polypeptides). The mitochondrial NAD-dependent malic enzyme (NAD-ME) provides an example of a basic metabolic enzyme that has acquired specialised gene expression patterns allowing it to function in the C4 pathway. NAD-ME occurs preferentially in photosynthetic tissues, and is specific to bundle sheath cells throughout development. NAD-ME synthesis is regulated by light and development at transcriptional and post-transcriptional levels. The findings summarised here indicate that C4 genes are independently regulated by multiple control mechanisms in response to developmental, environmental, and metabolic signals.

Inhibition of the phosphate transporter during isolation of intact chloroplasts from leaves of sunflower

Chloroplasts isolated from spinach leaves by the mechanical method were intact and exhibited high rates of CO2-dependent oxygen evolution whereas chloroplasts isolated from sunflower leaves by the same technique were also intact but showed only low rates of oxygen evolution. The rate of uptake of orthophosphate (Pi) from the suspending medium with sunflower chloroplasts was less than 20% of that in spinach chloroplasts. The apparent Km for Pi transport was lower in sunflower chloroplasts but uptake was competitively inhibited by 3-phosphoglycerate in chloroplasts from both species. Uptake of malate (via the dicarboxylate transporter) and of ATP (via the adenine nucleotide transporter) was also reduced in sunflower chloroplasts compared to spinach chloroplasts. The endogenous Pi content and total exchangeable phosphate pool of sunflower chloroplasts were less than half that in spinach chloroplasts.Addition of a number of possible protective agents to the grinding medium failed to prevent the loss of photosynthetic activity during mechanical isolation of sunflower chloroplasts. Grinding mixtures of spinach and sunflower leaves together indicated that spinach chloroplasts were not inhibited by the sunflower leaf extract. Chloroplasts isolated from sunflower leaves via protoplasts had high rates of CO2-dependent oxygen evolution. The Vmax and Km for Pi uptake, endogenous Pi content and total exchangeable phosphate pool of chloroplasts isolated from sunflower protoplasts were all similar to spinach chloroplasts. It is concluded that inner envelope membrane proteins are damaged during mechanical isolation of sunflower chloroplasts. The decrease in activity of the phosphate transporter and loss of endogenous phosphate may contribute to the low rates of photosynthesis observed in chloroplasts isolated by the mechanical method from leaves of sunflower and possibly other species.

Maximising Photosynthetic Activity and Cell Integrity in Isolated Bundle Sheath Cell Strands From C4 Species

Bundle sheath cells prepared from C4 leaves have a variety of experimental applications because of their high permeability to metabolites. We determined the factors affecting the physical and metabolic integrity of Panicum miliaceum bundle sheath cell strands immediately following isolation and during subsequent storage. Cell integrity was monitored by determining chloroplast intactness (as ferricyanidedependent O2 evolution) and photosynthetic activity (usually as HCO3-, 3-phosphoglycerate- or C4 acid-dependent O2 evolution). In freshly isolated cell preparations, at least 85-90% of the chloroplasts were apparently intact and there was no significant decline in this value during storage for up to 5 h. With the best extraction conditions, light-dependent O2 evolution in response to adding HCO3- or C4 acids ranged between 3 and 6 �mol min-1 mg-1 chlorophyll. Preillumination of leaves was critical for good isolated cell photosynthetic activity and the activity due to C4 acids in particular was increased substantially by including EDTA. During storage for up to 5 h at 0°C as much as 80% of the capacity for HCO3-- or C4 acid-dependent O2 evolution was lost; this loss was very largely prevented by storing the cells with EDTA. Large kinetic lags (induction phase) also developed during storage of cells. Both the loss of photosynthetic activity and the kinetic lags were reduced or eliminated by including photosynthetic intermediates such as dihydroxyacetone phosphate or ribose 5-phosphate in the storage medium. Under the best conditions, bundle sheath cell preparations could be stored for at least 3 h with little apparent change in cell integrity or metabolic capacity.

Manganese depletion in chloroplasts of Quercus rotundifolia during chemical simulation of lichen epiphytic states

Incubation of Quercus rotundifolia branches in culture media containing lichen substances isolated from Evernia prunastri thallus produces inhibition of Hill reaction in chloroptasts isolated from the leaves of the branches. Incubation with lichen substances diminishes the amount of chloroplastic manganese through a chelation process. This decrease causes the loss of photosynthetic activity because the Hill reaction is restored upon addition of exogenous manganese to the chloropiasts.

The retention of photosynthetic activity by senescing chloroplasts of oat leaves

The retention of photosystems I and II and or RuDP carboxylase activity in chloroplasts isolated from the first leaves of Victory oat (Avena sativa L.) seedlings was followed as the chloroplasts senesced in darkness. Both photosystems (PS) I and II retained their full activity after 3 days at 1°C, while even after 7 days at 1°C around 80% of the activity was still present. After 3 days at 25°C, PS I lost only 20% and PS II 50% of the initial activity. Acid pH increased the rate of decay of both systems, PS II falling almost to zero after 3 days at pH 3.5 (at 25°C). The preparations were almost bacteria-free, and addition of antibiotics not only did not improve their stability, but accelerated the rates of loss of photosynthetic activity. This is held to indicate that the enzymes are undergoing some turnover even in isolated chloroplasts. If the leaves were allowed to senesce in the dark first and the chloroplasts then isolated, their photosynthetic activities had greatly decreased, showing that senescence is more rapid in situ than in isolation. Under these conditions PS I decayed more rapidly than PS II. Ribulosediphosphate carboxylase, as measured by CO2 fixation, declined more rapidly than the photosystems, though the addition of kinetin and indole-3-acetic acid somewhat decreased the rate of loss, at least for the first 24 h. When the intact (detached) leaves were held in the dark, the rate of oxygen evolution declined rapidly, but in monochromatic blue light (450 nm) at 25°C about 30% of the initial rate was retained after 72 h.

Beiträge zum Stickstoffmetabolismus grüner Pflanzen II. Der Einfluss exogener Glucose auf die Aufnahme von Nitrat und Ammonium aus der Nährlösung und auf den Proteingehalt vonSpirodela oligorrhiza

The uptake of ammonium and nitrate by normal and glucose-stimulatedSpirodela oligorrhiza plants was investigated. Nitrate is used more rapidly by plants grown on glucose than by controls, suggesting a stimulation of nitrate assimilation by glucose. In plants growing on a normal nutrient, the contents of both water-soluble and water-insoluble proteins linearly increase with time and nitrogen uptake. In glucose-stimulated cultures soluble protein increases rapidly during the first 10 days of cultivation, but declines thereafter, while insoluble protein rises continuously over the whole period of time. The decreasing ratio of soluble and insoluble protein reflects an alteration of the protein and enzyme pattern, which is suggested to be the primary reason for the change of plastid ultrastructure and the loss of photosynthetic activity.

PHOTOREDUCTION BY CHLAMYDOMONAS

termed by Gaffron (1940), who has studied this process in some detail particularly in Scenedesmus (Gaffron, 1945). This process has been shown to occur also in a number of other species of green, blue-green, and red algae (Frenkel and Rieger, 1951). Algae which can carry out either photoreduction or normal photosynthesis under appropriate conditions are of particular interest; since they permit investigators to compare the effects of various physical and chemical agents on two photosynthetic reactions in which metabolic pathways differ in certain important respects. From such studies, Gaffron (1945) has drawn important conclusions about the nature of the catalytic systems involved. Of the algae known to carry out photoreduction, Chlamydomonas proves to be more suitable in certain respects than Scenedesmus, particularly because its adaptation to a metabolism involving molecular hydrogen is much more rapid (Frenkel, 1952). MATERIALS AND METHODS.-They are essentially the same as the ones described in an earlier paper (Frenkel, 1952). It should be added that Chlamydomonas is more sensitive to extensive handling, exposure to heat or prolonged cold storage than a number of algae which have been used in photosynthetic research, such as Chlorella or Scenedesmus. In preparing algal suspensions for manometric studies it is advisable to centrifuge cells for only five to ten minutes in a cooled centrifuge (5-10C.) at no more than 1000 X g. They should not be centrifuged and resuspended more than twice. Liquid cultures cannot be stored in the refrigerator for more than a few hours without considerable loss of photosynthetic activity. Agar slants can be stored for several weeks in a refrigerator with only