In 1934, DU Bux aiid Nuernbergk (9) compiled from a nunmber of sources the first extensive phototropic dosage-response curve for oat coleoptiles. The Xvarious features of this curve, first positive curvature, firlst negative curvature, and second and third positive curvatuire, are now wvell knownv. The early (losage-respoIise Only very recently has the profound effect of re(l light oni the phototropic responise been appreciated (1,3,5,7,8). But here too the picture was confused. Some authors reporte(l anl increase in phototropic sensitivity (1,3,5) xvhat. and lhave draxv-n atteintioni to the fact that it is not simplv the total amount of light received by the plant that is imilportanlt. but the imlaninier in xv-hicbl it is a( illlnsstel-ed as x-ell. The present paper has tlhree objectives. The first is to obtain a series of (losage-response curves for phototropic tip curvature xvith several intensities of monoclhromiiatic lighlt and exactly-defilled conditions. The second is to clarify the effect of red light on phototropic sensitivitx un(ler a xvi(le range of definle(l con(litions of phototropic induction. The third is to provi(le the basis for a (letaile(l kinetic analysis ot phototropismii of oat coleoptiles (13). Materials & MethodsOats (,4zncna sativa L., cv. Victory) wvere germiiinate(l folloxving in detail a regimiie described elsewlxere (5). The only light used during handling was fromii 15 xv green fluorescent lights wrapped in one layer of green and txvo layers of amber cellulose acetate (Shades. Inc., San Francisco). The tranismissiOI of this combinationi of filtering mlaterial was determined wvith a Bausch and( Lomb Spectronic 505 recording spectrophotometer. It Mvas found to he greater than 0.1 %{ only in a narroxv region of the spectrum from 5220 to 5630 A. When used during early stages of growth of the seedlings, the light described produced no noticeable phototropic effects.After the coleoptiles had reached a length of 0.5 cnm, only a single lamp as above,v wrappedc witl two layers of each type of cellulose acetate, was used, and then only for a short time. If extreme care was not taken even with this latter illumination, enough irregularity andl curvature occurred to pro(luce large variability 248 www.plantphysiol.org on May 11, 2018 -Published by Downloaded from

A general procedure for the isolation of functionally intact phycobilisomes was devised, based on modifications of previously used procedures. It Phycobilisomes contain the phycobiliproteins which are major light-harvesting pigments in red and blue green algae (4). Isolation of PBS3 facilitates studies on characterization of their morphology, phycobiliprotein composition, and the interaction and reaggregation properties of the phycobiliproteins. PBS were first isolated without prefixation from the red alga Porphyridium cruentum in 0.5 M phosphate buffer on a sucrose step gradient at 4 C (6). The procedure was subsequently modified for some blue-green algae (1 1), but it was not generally applicable to other species, as judged from shorter wavelength fluorescence emission at 660 to 665 nm instead of 670 to 675 nm. Further modifications have been made and it was found that the most crucial condition to maintain PBS integrity, in addition to high ionic strength, is temperature. We have found that it is important that isolations be done at about 20 to 23 C, and that the phosphate buffer content be at 0.75 M (pH 6.8). The simplified procedure described here gives high PBS yields from red and blue-green algae thus far tried. These PBS exhibit the best energetic coupling of any obtainable, and are '

Allophycocyanin from dissociated phycobilisomes of Nostoc sp. occurs in three spectrally identifiable forms that fractionate on calcium phosphate adsorption chromatography as: allophycocyanin (APC) I (15-20%), APC I1 (4&50%), and APC I11 (3@40%). APC I has a single absorption maximum at 654 nm, and a fluorescence emission peak at 678 nm. The absorption peaks of APC I1 and 111 are both at 650nm, but the relative absorbance at 620/650nm of APCIII is less than that of APCII. The emission of both is maximum at 660nm. On zone sedimentation in sucrose, their S,,,, values of 6.0 0.2 (APC 111) were comparable to the order of their elution from Sephadex G-200. On SDS acrylamide gel electrophoresis two subunits were resolved with apparent molecular weights of 16,900 and 18,400 daltons. When stained by Coomassie blue, they were present in a ratio of 1a:lP in APC11 and 111, and a probable ratio of 2a:3P in APCI. The larger size of APCI may be accounted for by additional / 3 subunits, by the presence of an additional polypeptide of 35,000 daltons, or both. Over several days, bleaching as noted by a decrease in absorbance at 650nm, occurred in all three forms; in addition, the more pronounced bleaching at 650 nm, relative to 620 nm, results in APC 111 becoming spectrally identical to APC 11. A trace of a fourth pigment, probably comparable to allophycocyanin-B, was occasionally detected. The results suggest that several in vitro APC forms (sharing similar subunits) arise upon phycobilisome dissociation, and that APC I is the form most closely related to the final fluorescence emitter of intact phycobilisomes. In this form it probably serves as the bridging pigment in energy transfer from the phycobilisomes to chlorophyll. 0.1 (APC I), 5.0 & 0.1 (APC 11), and 5.3 INTRODUCTIONLight energy absorbed by phycobiliproteins is first funneled to photosystem 11, as recently reported for Porphyridiurn cruentum (Ley and Butler, 1976), and is finally distributed t o both photosystems, as for Anacystis nidulans, where 40% of the quanta absorbed by phycocyanin are contributed t o photosystem I and 60% t o photosystem I1 (Wang et a/., 1977). Phycobilisomes (PBsomes)?, which contain the phycobiliproteins, have allophycocyanin (APC) as the key pigment (Gantt et al., , 1977. Its position is analogous to that of the trap of the two photosystems, but rather than doing photochemistry, it collects excitation energy from the other biliproteins before funnelling it into the chlorophyll of the thylakoid. Phycobilisomes, isolated intact but stripped away from the chlorophyll-containing membranes, show a fluorescence maximum a t 6 7 5 4 8 0 n m (23"C), irrespective

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