Analysis of NaCl toxicity in Chlorella sorokiniana showed decreased growth rates, increased dry weight per cell, increased intracellular Na+ and Cl-, more total chlorophyll per cell, a decreased chlorophyll a to chlorophyll b ratio, increased rates of 02 evolution, and decreased rates of CO2 fixation when the extracellular concentration of NaCl was increased from zero to 0.3 M. Cultures did not grow at concentrations greater than 0.3 M NaCl unless 10 mM calcium salts were present. Inclusion of that concentration of Ca2+ extended the tolerance to 0.5 M NaCl before growth stopped. Increasing the light intensity from 1.2 to 9.4 mw/cm2 increased growth rates for cultures in 0.10 to 0.45 M NaCl. At 14 mw/cm2 added Ca2+ reduced growth rates of cultures in 0.3 M NaCl compared to controls without added Ca2 . Maximal growth rates for cultures in NaCl media were achieved by addition of 10 mM CaSO4 and maintenance of the light intensity at 9.4 mw/cm2. The maximal growth rate of the organism was 9.6 doublings/day achieved at 2.7 mw/cm2 for control cultures. In 0.3 M NaCl the growth rate was 4.3 doublings/day at 2.7 mw/cm2 and 8.2 doublings/day at 9.4 mw/cm2 with 10 mM CaSO4 added.Increasing light intensities from 2.7 to 9.4 to 14 mw/cm2 decreased Physiological mechanisms of salt tolerance have been primarily concerned with ionic compositions and fluxes. Regulation of ionic composition in marine algae consists of Na+ exclusion with accumulation of K+ and C1-and generally requires cellular energy and the presence of Ca2`(27). Studies of ionic fluxes in the red marine alga Gracilaria foliifera (12), in the fresh water algae Hydrodictyon africanum (23) and Chlorella pyrenoidosa (2), and on the internodal cells of Nitella translucens (18) have demonstrated light-dependent active transport for Na+ exclusion and K+ and Cl-accumulation. Work on the red marine alga Porphyra perforata showed a requirement for Ca2+ in the medium for intracellular retention of K+ (7).Two considerations indicate that light-dependent ion fluxes in green plants are controlled by photosynthetic rather than respiratory energy. First, light generally has little effect on ion fluxes in nongreen tissue, and second, the action spectrum of ion fluxes in green tissue matches that of chlorophyll absorption (23). The activation of K+ and Cl-fluxes in Nitella was separated respectively between photosynthetic systems II and I (18). Under conditions of either DCMU inhibition or far red light irradiation, where system I was functional, K+ absorption was not affected and Cl-absorption was reduced compared to conditions where both photosystems were operative (2, 18, 24). The selective participation of these systems was also reported in Chlorella pyrenoidosa (2) and Hydrodictyon africanum (24). System I was also implicated in Na+ efflux (24).Direct involvement of ATP from cyclic photophosphorylation for light-dependent Na+ and K+ fluxes was established by using uncouplers of phosphorylation. Addition of carbonylcyanide-m-chlorophenylhydrazone (2,17,25,28) and i...

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Division rates of Nannochloris oculata Droop (Chesapeake Bay clone) were recorded in semicontinuous cultures grown at 81 combinations of light intensity, temperature, salinity and nitrogen source. A maximal growth rate of 2.1 doublings 1 day occurred at 30 C, 15‰ salinity with a light intensity of 11,300 lux (1.350 mW/cm2) using ammonium or urea as nitrogen sources. Several generalizations about the autecology of this organism result: (1) salinity optima were between 5–15‰ in all instances. (2) the lack of growth at 10 C and the universal improvement in growth with temperature elevation to 30 C indicates a rather high temperature optimum. (3) there is a trend of decreasing light optimum with temperature decreases below the optimum. The source of nitrogen providing the best growth was shown to be dependent on light, temperature, salinity and interactions among these variables. For nitrate and ammonium cultures, temperature had the greatest influence on growth rate, followed by light and then salinity. For urea cultures, the order was temperature, salinity, then light. Interactions of all combinations of variables were significant with the temperature‐salinity‐light interaction most pronounced with urea cultures. Demonstration of interactions among environmental variables and nitrogen nutrition suggests that some conclusions based on surveys employing fixed variables alone may be unreliable.

Stutmmary. Glucose culttures of Chiorella vulgaris were growin in white light, in molnochromatic light, and in (larkiness. Differenice spectra showecd that all wavelengths resulted in increased pigmienitationl over the dark controls.Cells irradiated with the 600 mML beam showed a much higher absorption in the blue end of the spectrum w-ith respect to the red end than is normally found in absorption spectra of white-light growNn Chlorclla cells.Drv weight comparisonis between monochromatic light and dark controls showed the controls to be somewhat highler. This demonstrated that the monochrom,atic irradiation produced pigment synthesis but no increase in growth. Dark (22), and sporulation in fuingi (2) are all photochemical phenomiena stimulated by radiation with wavelengths between 400 and 750 m,u. Less well-known phenomena, such as the inhibition of cell division by light (19) and the stimulation of heterotrophic cell growth by brief illumination in the dark (9, 10), have been observed in the algae. In the latter cases, nothing is known of the segments of cellular physiology which respond initially to the light.Of considerable importance, in understanding the system of energy conversion in plants, is the mechamism by which certain plants, classified as obligate autotrophs, are prevented from growing on any reduced carbon source in the dark. Obligate phototrophy is common in the algae (23), but might be unexpected in as vigorous and ubiquitous a genus as Chlorella.

Sum mary. C/llorella vidgaris Beyerinck (Emiiersoin's strain), fails to grow in the (lark even when sugars are provided. This phenomenon w-as clearly demoilstrated in the alga. C. vulgar-is, for wlhich the growth rate in darkness on a glucose medium remained constant for 2 days anid then declined to approach zero. Pigmiient concenitrations also declined in darkness. Changes in flow rate of 1 % CO,-in-air fromii zero to 7 ml.per mninute caused a progressive increase in the dark growth rate over a 5-day period, hut did not maintain growth in the dark. Rates above 7 ml per imiinute produced no changes in growth rates. The respiration of gltucose by the alga was stim-aulated 1y low intensities of white light. This response was not iimmediate, but was clearly l)resent after the third day of incubation.Malonate anid cyanide were inhibitory to growth of C. vldgaris on inorganic medium Dr glucose miiedium under 300 ft-c of white liglht. These data suggested that succinic dehvdrogeenase and cytochrome oxidase systems were present.Substances inhibitorv-to growth were excreted into the mlediumii under dark-growth coniditions, and 2 of these substances were ilidelltified as formic and acetic acids.