Photolability of Photosynthesis in Two Separate Mutants of Scenedesmus obliquus

Abstract

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...

Photoinhibition of photosynthesis in chilled potato leaves is not correlated with a loss of Photosystem-II activity

“…In addition, it was observed that the photoinhibition of P700 activity was closely correlated with the changes in ~bp (Tables 6 and 8). Previous in vitro studies of isolated thylakoid membranes and microalgae (Harvey and Bishop 1978, Gerber and Burris 1981, Satoh and Fork 1982 have also related photoinhibition to a selective loss of active P700. In contrast, chilling potato leaves in light did not induce or enhance photodamage of the PS II function (Fig.…”

Temperature/light dependent development of selective resistance to photoinhibition of photosystem I

“…Until recently, PSII has been generally thought to be the primary target for photoinhibition although photoinactivation of PSI was also reported in in vitro systems [5–7]. Since the initial reports on PSI photoinhibition in vivo in algal systems [8, 9]and intact spinach leaves [10], there have been several additional reports of selective inhibition of PSI related photochemical activities under either weak illumination in chilling sensitive plants [11–13]or under high light in potato leaves [14]. In these reports, it was demonstrated that during light stress at low temperatures the maximum quantum yield of electron transport through PSI, the pool of photooxidizeable reaction center pigment of PSI (P700), and the efficiency of P700 oxidation were dramatically reduced [11–14].…”

Photosynthetic characteristics of phycoerythrin-containing marine Synechococcus spp. II. Time course responses of photosynthesis to photoinhibition

“…The Photosystem I activity measured here (P700 photo-oxidation in Triton-solubilized membranes) is independent of noncyclic electron flow and Photosystem I1 activity. Losses in P700 activity have also been observed in response to photoinhibitory light levels in a benthic diatom (Gerber & Burris 1981) and the green algae Scenedesmus obliquus (Harvey & Bishop 1978) and Dunaliella tertiolecta (Falkowski 1984).…”