RATES OF PHOTOSYNTHESIS AND RESPIRATION OF THE MOSS BRYUM SANDBERGII AS INFLUENCED BY LIGHT INTENSITY AND TEMPERATURE

Using differential respirometry and air enriched to 3% CO₂ (v/v), the rates of photosynthesis and dark respiration of the moss Bryum sandbergii were measured as influenced by temperature and light intensity. The optimal temperature for net (apparent) photosynthesis was between 24 to 30 C; however, the photosynthesis/respiration ratio was about 11 to 27 between 4 to 24 C and dropped to lower values at 34 C., which indicates a wide temperature tolerance for this moss in short-term experiments. The maximum temperature for photosynthesis was about 41 C and the minimum was below –5 C. At 20 C light saturation was approached at 6.2 mw cm^–2 (ca. 700 ft-c) but not completely reached at 12 mw cm^-2; the light compensation point was estimated to be 0.4 mw cm^-2 (ca. 40 ft-c). At 4 C light saturation and the compensation point were at lower levels and apparently solarization occurred at 12 mw cm^-2. Light intensity had little or no apparent effect on dark respiration. However, respiration increased with temperature over various ranges extending from –5 to 39 C with temperature quotients of about 2.5 to 1.2. The significance of these characteristics is discussed with respect to the ecological relationships of the species.     

THE RELATION BETWEEN CHLOROPHYLL CONTENT AND RATE OF PHOTOSYNTHESIS

1. Data are presented which support the conclusion of Emerson (1929) that the rate of photosynthesis is proportional to the chlorophyll content when the latter is varied by varying the iron supply. These data give a straight line passing through the origin, which is not true of Emerson''s results. 2. Similar data are presented which show that a similar relation exists when nitrogen controls the chlorophyll content. 3. Evidence is given which indicates that magnesium plays a part in the process of photosynthesis in addition to its effect upon the chlorophyll content.     

TOXICITY OF BISULFITE TO PHOTOSYNTHESIS AND RESPIRATION1

Inhabition of photosynthesis in Chloroccoum sp by bisulfileion was the reciprocal of the light intensity curve. Respiration was least affected of the bisulfite after endogenous substrate was reduced by incubation in darkness. Maximum areduction in growth occurred with bisulfile treatment at or above optimal growth temperatures. Maximum phytotoxicity correlated with conditions resulting in maximum metabolic activity. The order of toxicity was –H₂SO₃HSO₃^?SO₃.     

THE RELATION BETWEEN MAXIMUM RATE OF PHOTOSYNTHESIS AND CONCENTRATION OF CHLOROPHYLL

Willstätter and Stoll have studied the rate of photosynthesis as a function of chlorophyll content. However, their experiments fail to reveal any regular relationship between these two quantities, probably because, in order to obtain material differing widely in chlorophyll content, they were obliged to use leaves which were not comparable in other respects. The writer describes a method for varying the chlorophyll content per unit volume of cells of Chlorella vulgaris, maintaining other factors constant. Experiments are described which show that the maximum rate of photosynthesis is a smooth function of the chlorophyll content.     

THE ROLE OF RESPIRATION AND PHOTOSYNTHESIS IN THE CHLOROPLAST REGENERATION IN THE "GLUCOSE-BLEACHED" CELLS OF CHLORELLA PROTOTHECOIDES

1. As previously demonstrated, entirely chlorophyll-less cellsof Chlorella protothecoides are obtained when the alga is grownin a medium rich in glucose and poor in nitrogen source (urea).These cells, which are referred to as "glucose-bleached" cells,have neither discernible chloroplast structures nor photosyntheticactivity. When the "glucose-bleached" cells are incubated, inthe light, in a nitrogen-enriched mineral medium without addedglucose, they turn green, after an induction period, with regenerationof chloroplasts and development of the capacity for performingnormal photosynthesis. In the present study, changes in respiratoryactivity of algal cells during the process of greening (chloroplastregeneration) were followed, and the effects of various inhibitorsof respiration and photosynthesis on the greening process wereexamined. 2. The glucose-bleached cells showed a very low activity ofrespiration, and the activity increased markedly during an earlyphase of chloroplast regeneration, showing, however, a decreaseduring the subsequent phase of greening. 3. Some antimetabolites which inhibited the cell respiration,were found to suppress also the greening of cells. 2,4-Dinitrophenoland azide, potent inhibitors of oxidative phosphorylation, acceleratedconsiderably both the respiration and greening of algal cells.CMU inhibited completely photosynthesis of the greening cells,but suppressed only slightly the greening process. 4. Based on these results it was concluded that the primaryrole of respiration in the chloroplast regeneration in the glucose-bleachedcells is to produce oxidized carbon compounds (and perhaps reducedforms of NAD and NADP) for various biosynthetic reactions. Itwas further suggested that ATP may be supplied for the chloroplastregeneration by a certain means different from the oxidativephosphorylation or photophosphorylation. The activities of photosyntheticphosphorylation and CO₂-fixation developing in the greeningcells do not appear to play any essential role in the chloroplastregeneration. (Received December 27, 1965; )     

TOXICITY OF THE PESTICIDE ZECTRAN ON PHOTOSYNTHESIS,RESPIRATION, AND GROWTH IN FOUR ALGAE1,2

The insecticide Zectran decreased both respiration and photosynthesis in Oscillatoria terebriformis and Synechococcus lividus at concentrations between 0.5 and 12.5 ppm, whereas Navicula pelliculosa and Scenedesmus quadricauda were, relatively unaffected by these, same concentrations in the short-term, manometric experiments. In long-term growth experiments all 4 species exhibited a toxicity threshold between 1 and 10 ppm Zectran.     

LIMITATIONS OF PHOTOSYNTHESIS IN DIFFERENT REGIONS OF THE ZEA MAYS LEAF

The progressive development of the photosynthetic apparatus occurring along the length of the Zea mays leaf offers a convenient system with which to examine the limitations to photosynthetic CO₂ assimilation during biogenesis of a C₄ leaf. Changes in light-induced O₂ evolution and CO₂ assimilation, chlorophyll content, activity of PEP-carboxylase, NADP-malic enzyme and the 'R5P system' (consisting of d -ribose-5-phosphate-keto isomerase, ATP- d -ribulose-5 phosphate 1-phosphotransferase and d -ribulose-1,5-bisphosphate carboxylase) and fluorescence emission characteristics were examined along the length of the second leaf of 7-day-old plants grown under a diurnal light regime. The results suggest that the major limitation to CO₂ assimilation in the leaf sheath lies within the chlorenchyma and is either energy supply for carboxylation or the capacity of key photosynthetic enzymes. In the leaf blade stomatal resistance to CO₂ diffusion constitutes a major fraction of the total leaf resistance to CO₂ assimilation implicating the stoma as the major limiting factor to photosynthetic CO₂ assimilation.