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The ATP content of lodgepole – jack pine (Pinus contorta × banksiana) hybrids in the cordillerean–boreal transition zone was monitored during sulfur dioxide fumigations. Foliage was stabilized for analysis during the course of sulfur dioxide fumigations originating from a sour gas processing plant located in west-central Alberta. Controlled sulfur dioxide fumigations of seedlings were conducted in the laboratory to measure their effect upon ATP content. Field studies demonstrated that ATP concentrations of needle cells declined as sulfur dioxide concentration increased in the ambient air. An inverse linear relationship was found between ATP content and the measured sulfur dioxide concentration. The effect could be repeated in the laboratory with growth chamber cultured seedlings only in exceptional cases. It was repeated with detached branches from the field site exposed to sulfur dioxide under laboratory conditions. The results illustrate the fundamental differences between foliage preadapted to low-level sulfur dioxide fumigations and foliage grown under optimal conditions in a growth chamber.

Two separate mutants of the green alga, Senedesus oblquus, are described in which photosynthesis is sensitive to moderate intensities of white light (100 mw cm-'). Heterobtphic cultures of both mutants lose photosynthetic activity when exposed to white lght, the site of at least the initidal phase of this inactivation is within photosystem I. Although al whole cell and cell-free reactios typical of photosystem I exam_ied are hibited by irradiaton, the pincipal com nt of photosystem I affected is P-700. In l1ght-sensitive4 the ilnactivatin of P-700 activity is restored during the subseqnt dark period. This recovery is prevented by various antibotics and by anaerobic conditions. In light-sensitive41 P-700 'To whom reprint request should be addressed. Kok (20,21), and Forti and Jagendorf (13) demonstrated that Hill reaction activity was also adversely affected. This inhibition differed from that seen with intact green plant tissue since the effect required only light and not the combination of light plus 02-Moreover, PSII activity was more strongly affected than was PSI. Earlier Kok (23) had suggested somewhat reluctantly that photoinhibition involved a primary destruction of the photosynthetic pigment complex and secondary photooxidative reactions. Satoh (34-36) extended the isolated chloroplast studies and found that both PSI and PSII were inhibited by light; the inactivation of PSI required both light and 02 whereas PSII inhibition required only light. In our attempts to isolate specific photosynthetic mutant phenotypes of Scenedesmus obliquus A3 several LS4 types have been found. These include various pigment mutants unable to synthesize carotenoids, photosynthetic electron transport mutants which bleach when grown mixotrophically but show normal pigmentation when grown heterotrophically (6), and mutants which only grow heterotrophically, have near normal pigmentation but possess a photosynthetic activity sensitive to light. The initial phenotype is similar to the mutants developed in Chlorella by Claes (10) and later characterized as LS phenotypes by Kandler and Schotz (22). The second LS phenotype is normally characterized by a deficiency of Cytf and of cyclic photophosphorylation; the inability of this phenotype to form ATP photosynthetically apparently limits the rate of glucose uptake necessary to sustain growth in the light. The last group has been utilized in the current study and the behavior of two selected mutants, LS-4 and LS-41, is described. The purpose of the present investigation was to evaluate the underlying cause of the induced light lability in the two mutants, and also to examine further the basic mechanism of photoinactivation of the photosynthetic process. MATERIALS AND METHODS CULTURE OF ALGAL STRAINSThe techniques employed for maintenance of the normal and mutant strains of Scenedesmus have been described previously (4, 31). Cultures were normally harvested for use by centrifugation after 2 days of growth; at this time heterotrophic cultures were still within the logarithmic gr...

The pigment content and photosynthetic unit size of three herbs on the floor of a mature yellow oak (Quercus meuhlenbergii) forest were measured during most of the growing season. Two species, dutchman's breeches (Dicentra cucullaria) and Virginia bluebell (Mertensia virginica) are spring ephemerals, while Hepatica acutiloba has a semi‐evergreen habit. Although pigment composition changed in Dicentra, photosynthetic unit size only varied slightly. Mertensia was nearly invariant in pigment composition, but unit size was modified as the growing season progressed. The semi‐evergreen herb, Hepatica, underwent a remarkable alteration in pigment content, photosynthetic unit size, and number following overstory leaf expansion. The results indicate that an alteration of photosynthetic unit size is possible in fully expanded leaves of two forest floor herbs.