Division and DNA distribution in ribosome-deficient plastids of the barley mutant “albostrians”

The ribsome-deficient plastids of the albino leaves of the barley mutant albostrians divide at about the same rate as normal plastids and contain similar levels of plastids DNA to the normal plastids. Double-ring structures were observed around the neck of constricting dumbbell-shaped, ribosome-deficient plastids in the basal intercalary meristem of albino leaves. In the distal region of albino leaves the ribosome-deficient plastids contain a rudimentary thylakoid system often closely associated with DNA nucleoids. It is suggested that nuclear coded proteins synthesized within the cytoplasm are responsible for the formation of the double-ring structures and the rudimentary thylakoids of albino plastids.     

Identification of surface exposed amino acids of isolated and membrane-bound CF1 by protease accessibility

In order to compare surface-exposed amino acids in isolated and membrane-bound CF₁ the technique of limited proteolysis was employed. The cleavage sites of several proteases were identified by sequence analysis of the resulting peptides after isolation by SDS-PAGE. In isolated CF₁ the N-terminal region of the subunit was found to be highy sensitive to proteases; the accessible peptide bonds included E17-G18, R21-E22, E22-V23, and K24-V25. Additional protease-attacked bonds in subunit were S86-S87, xE125-S126. and R127-L128. In the subunit of isolated CF₁ the bonds L14-E15 and V76-A77 were identified as being accessible. All identified protease accessible amino acids are located at the protein surface according to a molecular model of CF₁ computed after the crystal structure of mitochondrial F₁ by S. Engelbrecht (1997). In membrane bound CF₁ the primarily accessible peptide bond of the N-terminal domain of is R21-E22. After this bond is cleaved by trypsin, the K24-V25 becomes accessible to further trypsin attack. Moreover, the peptide bonds R14O-S141 and G16O-R161 are cleaved. According to the Engelbrecht model G16O is almost completely shielded and actually this amino acid was hardly accessible to protease in isolated CF₁. The subunit in general is much more sensitive to proteolysis in membrane-bound than in solubilized CF₁. In the subunit of membrane-bound CF₁ a papain-sensitive bond G102-G103 was identified. The results indicate major structural alterations when CF₁ is extracted from the CF₀CF₁ complex. Thiol modulation, i.e. reduction of the regulatory disulfide bond between C199 and C205 of y subunit, enhances the accesibility of a number of peptide bonds, in particular G160-R161, to proteolytic attack by papain. In contrast, thylakoid membrane energization results in masking of this peptide bond.     

Nitrate reductase is not accumulated in chloroplast-ribosome-deficient mutants of higher plants

The activities of nitrite reductase (EC 1.7.7.1) are 60–70% of wild-type activity in pigment-deficient leaves of the chloroplast-ribosomedeficient mutants albostrians (Hordeum vulgare) and iojap (Zea mays). The activity and apoprotein of nitrate reductase (EC 1.6.6.1.) are lacking in the barley mutant. Only very low activities of nitrate reductase can be extracted from leaves of the maize mutant. The molybdenum cofactor of nitrate reductase and xanthine dehydrogenase (EC 1.2.3.2) is present in maize and barley mutant plants. However, it is not inducible by nitrate in pigment-deficient leaves of albostrians. From these results we conclude: (i) Nitrite reductase (a chloroplast enzyme) is synthesized in the cytoplasm and does not need the presence of nitrate reductase for the induction and maintenance if its activity. (ii) The loss or low activity of nitrate reductase is a consequence of the inability of the mutants to accumulate the apoprotein of this enzyme. (iii) The chloroplasts influence the accumulation (i.e. most probably the synthesis) of the nonchloroplast enzyme, nitrate reductase. The accumulation of nitrate reductase needs a chloroplast factor which is not provided by mutant plastids blocked at an early stage of their development.Abbreviations CRM cross-reacting material - Mo-co molybdenum cofactor - NiR nitrite reductase - NR nitrate reductase     

Isolation and characterization of a barley mutant with abscisic-acid-insensitive stomata

A barley (Hordeum vulgare L.) mutant (cool) with leaf transpiration unaffected by the application of 1 mM abscisic acid (ABA) was isolated from the population of M2 seedlings using thermography (electronic visualization, and quantitation of the temperature profiles on the surface of the leaves). Stomata of the mutant plants were insensitive to exogenously applied ABA, darkness, and such desiccation treatments as leaf excision and drought stress. The evaporative cooling of the leaves of the cool barley was always higher than that of the wild-type barley, even without ABA application, indicating that the diffusive resistance of the mutant leaves to water loss was always lower. Guard-cell morphology and stomatal density as well as ABA level and metabolism were seemingly unaltered in the mutant plants. In addition, gibberellin-induced -amylase secretion and precocious embryo germination in the mutant barley was inhibited by ABA to the same extent as in the wild-type barley.Abbreviations ABA (±) cis-trans abscisic acid - GA gibberellin     

Factor analysis of fluctuation in populations ofPseudomonas syringae pv.savastanoi on the phylloplane of the olive

Populations ofPseudomonas syringae pv.savastanoi on the surface of olive leaves were monitored quarterly from 1974 to 1981. Seven microbiological parameters were measured: the density of the bacteria on the leaves unfolded in March, in June, and in September; the density of the bacteria on random leaves; the mean vigor of bacterial isolates obtained at each sampling time; and the similarity between the isolates, based on both the simple matching coefficient and the pattern coefficient. Seven environmental parameters were also recorded: the mean temperature, the rainfall, and the frequency and velocity of east and west winds during a period of 30 days before each sampling; the rate of turnover of the leaves during the same period; the number of pollen grains on the leaves at the time of sampling; and the 5-day biochemical oxygen demand of the wash water of leaves in each sample. Factor analysis led to extraction of 7 factors that accounted for 70.69%–92.80% of the maximum variance of every microbiological parameter and 68.92%–96.62% of the maximum variance of every environmental parameter. The factors were identified as cambial activity, leaf age, summertime, time of blossoming, summer rains, winter rains, and warm weather fronts. More than 43% of the total parameter variance was loaded in the first 2 factors. Higher communality values (>86% of maximum variance) were obtained for the microbiological parameters based on the distribution of phenotypic characters among the bacterial isolates than for those based on bacterial densities on the phylloplane.     

Expression,purification, characterization,and deletion mutations of phosphorylase kinase γ subunit: identification of an inhibitory domain in the γ subunit

A catalytic fragment, _1-298, derived from limited chymotryptic digestion of phosphorylaseb kinase (Harris, W.R.et al., J. Biol. Chem., 265: 11740–11745, 1990), is reported to have about six-fold greater specific activity than does the subunit-calmodulin complex. To test whether there is an inhibitory domain located outside the catalytic core of the subunit, full-length wild-type and seven truncated forms of were expressed inE. coli. Recombinant proteins accumulate in the inclusion bodies and can be isolated, solubilized, renatured, and purified further by ammonium sulfate precipitation and Q-Sepharose column. Four out of seven truncated mutants show similar ( _1-353 and _1-341) or less ( _1-331 and _1-276) specific activity than does the full-length wild-type , _1-386. Three truncated forms, _1-316, _1-300, and _1-290 have molar specific activities approximately twice as great as those of the full-length wild-type and the nonactivated holoenzyme. All recombinant s exhibit similarK _m values for both substrates, i.e., about 18M for phosphorylaseb and about 75 M for MgATP. Three truncated s, _1-316, _1-300, and _1-290, have a 1.9- to 2.5-fold greater catalytic efficiency (V _max/K _m) than that of the full-length wild-type and a 3.5- to 4.5-fold greater efficiency than that of the truncated _1-331. This evidence suggests that there is at least one inhibitory domain in the C-terminal region of , which is located at _301-331· _1-290, but not _1-276, which contains the highly conserved kinase domain, is the minimum sequence required for the subunit to exhibit phosphotransferase activity. Both _1-290 and _1-300 have several properties similar to full-length wild-type , including metal ion responses (activation by free Mg²⁺ and inhibition by free Mn²⁺) pH dependency, and substrate specificities.     

Subunit movement during catalysis by F1-F0-ATP synthases

The catalytic portion (F₁) of ATP synthases have the subunit composition ₃, ₃, , , . This composition imparts structural asymmetry to the entire complex that results in differences in nucleotide binding affinity among the six binding sites. Evidence that two or more sites participate in catalysis, alternating their properties, led to the notion that the interactions of individual pairs with the small subunits must change as binding site properties alternate. A rotation of the subunit within the ₃₃ hexamer has been proposed as a means of alternating the properties of catalytic sites. Evidence argues that the rotation of the complete subunit during ATP hydrolysis is not mandatory for activity. The subunit of chloroplast F₁ may be cleaved into three large fragments that remain bound to F₁. This cleavage enhances ATPase activity without loss of evidence of site-site interactions. Complexes of ₃₃ have been shown to have significant ATPase activity in the absence of . Mg²⁺ATP affects the interaction of with the different subunits, and induces other changes in F₁, but whether these changes are induced by catalysis, or are fast enough to be involved in the catalytic turnover of the enzyme has not been established. Likewise, changes in structure and in binding site properties induced in thylakoid membrane bound CF₁ by formation of an electrochemical proton gradient may activate the enzyme rather than be apart of catalysis. Mechanisms other than rotary catalysis should be considered.     

Tentoxin effects onSorghum: The role of polyphenol oxidase

Summary In an ultrastructural and cytochemical study of tentoxin-treatedSorghum bicolor (L.) Moench, both bundle sheath and mesophyll plastids were severely affected, Plastids from chlorotic leaf areas lacked most internal membranes yet had plastid ribosomes and large fibrillar areas of plastid DNA. In recovered areas (mottled yellow and green), cells were found that had plastids of near-normal ultrastructure as well as the severely affected plastid-types found in chlorotic leaf areas. Polyphenol oxidase (PPO) cytochemistry of these mottled leaf areas indicated that all recovered mesophyll plastids had PPO whereas all the abnormal mesophyll plastids showed no activity. Because bundle sheath plastids ofSorghum have no PPO activity at any developmental stage, yet are affected by tentoxin, PPO cannot be uniquely affected by this toxin. We suggest that tentoxin may affect the transport of cytosolic proteins into the plastid.     

The photosynthetic F1-α3β3 and α1β1 catalytic core complexes

Minimal photosynthetic catalytic F₁() core complexes, containing equimolar ratios of the and subunits, were isolated from membrane-bound spinach chloroplast CF₁ and Rhodospirillum rubrum chromatophore RrF₁. A CF₁-₃₃ hexamer and RrF₁-₁₁ dimer, which were purified from the respective F₁() complexes, exhibit lower rates and different properties from their parent F₁-ATPases. Most interesting is their complete resistance to inhibition by the general F₁ inhibitor azide and the specific CF₁ inhibitor tentoxin. These inhibitors were earlier reported to inhibit multisite, but not unisite, catalysis in all sensitive F₁-ATPases and were therefore suggested to block catalytic site cooperativity. The absence of this typical property of all F₁-ATPases in the ₁₁ dimer is consistant with the view that the dimer contains only a single catalytic site. The ₃₃ hexamer contains however all F₁ catalytic sites. Therefore the observation that CF₁-₃₃ can bind tentoxin and is stimulated by it suggests that the F₁ subunit, which is required for obtaining inhibition by tentoxin as well as azide, plays an important role in the cooperative interactions between the F₁-catalytic sites.Abbreviations CF₀F₁ chloroplast F₀F₁ - CF₁ chloroplast F₁ - CF₁ chloroplast F₁ subunit - CF₁ chloroplast F₁ subunit - CF₁() a complex containing equal amounts of the CF₁ and subunits - MF₁ mitochondrial F₁ - RrF₀F₁ Rhodospirillum rubrum F₀F₁ - RrF₁ R. rubrum F₁ - RrF₁ R. rubrum F₁ subunit - RrF₁ R. rubrum F₁ subunit - RrF₁() a complex containing equal amounts of the RrF₁ and subunits - Rubisco Ribulose-1,5-bisphosphate carboxylase - TF₁ thermophilic bacterium PS3 F₁     

Chloroplast acclimation to low osmotic potential

Photosynthetic potential of isolated chloroplasts was investigated during in situ water deficits. An eight day stress cycle imposed on spinach plants reduced leaf _w by 0.57MPa, and leaf by 0.50MPa, resulting in partial turgor maintenance during the stress cycle. Pressure/volume curves confirmed the occurrence of osmotic adjustment. Leaf depression was associated with an altered response of chloroplasts to low in vitro. Optimum reaction medium for photosynthesis shifted from –1.04 to –1.57MPa, and low was not as inhibitory to photosynthesis of plastids pre-exposed to stress in situ. These data indicate that chloroplasts acclimate to low external in response to leaf water deficits. This response was still evident four days after a stress cycle ended, but was nearly reversed eight days after stress. Repeated stress cycles in situ did not increase the degree of chloroplast acclimation to low in vitro. Fast dehydration of leaves did not induce this apparent chloroplast acclimation.Abbreviations osmotic potential - _w water potential - PEG polyethylene glycol 8000 - MPa megapascals     

Occurrence of unidentified bodies that resemble “plastid initials” in poplar cells after breaking of dormancy in midwinter

Summary Electron-microscopic studies of plastids in cortical cells of poplar (Populus euramericana cv. gelrica) were carried out to examine whether any structural changes were initiated after breaking of dormancy in midwinter under non-growing conditions. After the breaking of dormancy, ultrastructural changes became evident and the profiles of plastids became heterogeneous. Organelles resembling the plastid initials proposed by Mühlenthaler and Frey-Wyssling in 1965 were frequently observed concomitant with changes in the plastid envelope. The formation of plastid initials appeared to be initiated by the formation of septa in pre-existing plastids. After this stage, narrow connections appeared between the initials and the parent plastids. Approximately 50 days after the breaking of dormancy in late March, further heterogeneity in the profiles of plastids was observed. At this stage, young plastids (plastids without starch granules) were frequently observed and the formation of plastid initials was hardly ever observed. These observations suggest that the plastid initials may be present for only a limited period in the cortical cells of the poplar and may be the precursors of the proplastids. Similar ultrastructural profiles were found in cortical cells of mulberry and in leaf buds of apple trees, suggesting that such changes in the ultrastructure of plastids are a general feature of perennials.     

Spectroscopic studies of bound cytochrome c and an iron-sulfur center in a purified reaction center complex from the green sulfur bacterium Chlorobium tepidum

Flash-induced optical kinetics at room temperature of cytochrome (Cyt) c ₅₅₁ and an Fe-S center (CF_A/CF_B) bound to a purified reaction center (RC) complex from the green sulfur photosynthetic bacterium Chlorobium tepidum were studied. At 551 nm, the flash-induced absorbance change decayed with a t _1/2 of several hundred ms, and the decay was accelerated by 1-methoxy-5-methylphenazinium methyl sulfate (mPMS). In the blue region, the absorbance change was composed of mPMS-dependent (Cyt) and mPMS-independent component (CF_A/CF_B) which decayed with a t _1/2 of 400–650 ms. Decay of the latter was effectively accelerated by benzyl viologen (Em –360 mV) and methyl viologen (–440 mV), and less effectively by triquat (–540 mV). The difference spectrum of Cyt c had negative peaks at 551, 520 and 420 nm, with a positive rise at 440 to 500 nm. The difference spectrum of CF_A/CF_B resembled P430 of PSI, and had a broad negative peak at 430435 nm.Abbreviations (B)Chl (bacterio)chlorophyll - Cyt cytochrome - F_A, F_B and F_X iron-sulfur center A, B and X of Photosystem I - CF_A, CF_B and CF_X F_A-,F_B- and F_X-like Fe-S center of Chlorobium - mPMS 1-methoxy-5-methylphenazinium methyl sulfate - PSI Photosystem I - RC reaction center     

On the use of Avena protoplasts to study chloroplast development

Different methods were tested to isolate protoplasts from etiolated, partially greened, and light-grown leaves of Avena sativa. Preparations with high yields and high photosynthetic capacities (time of illumination 4 h) were obtained when small transverse leaf segments were incubated for 2 h at 30°C in 2% cellulysin (Calbiochem), 0.6 M mannitol, and 0.5% bovine serum albumin (BSA) at pH 5.6, without shaking. As measured by light-dependent O₂ evolution or fixation of labeled bicarbonate, protoplasts exhibited rates of up to 124 mol per mg of chlorophyll per h at 20°C and saturating bicarbonate, which were nearly identical to those found with intact leaves. The assay conditions necessary for this activity were 0.6 M sorbitol, 50 mM N-2-hydroxy-ethylpiperazine-N-2-ethane sulfonic acid (pH 7.6), and 10 mM NaHCO₃. If plastids were isolated from these protoplasts, sorbitol was 0.45 M, including 10 mM ethylenediaminetetraacetate (EDTA). under these conditions, rates of photosynthesis were up to 125 (light-grown) and 71 (6 h illuminated) mol O₂ evolved or ¹⁴CO₂ fixed per mg of chlorophyll per h, compared to 3.5 mol·mg chl^-1·h^-1 obtained with mechanically isolated plastids. With this system, CO₂-dependent O₂ evolution was already detected after 3 h of illumination of etiolated tissue, but could only be observed at pH values between 7.6 and 8.6, in the presence of EDTA. At lower pH (7.3) or at pH 7.6 in the absence of EDTA, light-dependent O₂ evolution up to 24 h of greening was only measurable with 3-phosphoglycerate as the substrate. The possible effects of EDTA in this respect as well as the advantages of using protoplasts or plastids isolated from protoplasts for developmental studies are discussed.Abbreviations BSA bovine serum albumin - EDTA ethylenediamine tetraacetic acid - HEPES N-2-hydroxyethyl-piperazine-N-2-ethane-sulphonic acid - MES 2(N-morpholino) ethane sulphonic acid - PGA 3-phosphoglycerate     

Assembly-dependent expression of antigenic epitopes by β2-microglobulinb

In this report we provide evidence for the expression of antigenic epitopes on mouse (₂-microglobulin^b _2m ^b) that result from assembly with cognate H-2 class I heavy chains. For the cell line 69.9.15 (₂m^a × ₂m^b), which expresses a mutant cytosolic form of H-2K^b and wild-type H-2D^b, flow cytometry with rabbit antiserum against mouse ₂m displayed ₂m expression by cells grown in the presence or absence of fetal calf serum. By contrast, the epitopes identified by the ₂m^b-specific monoclonal antibody (mAb) S19.8 and clone 23 were not expressed by 69.9.15 cells grown in serum-containing conditions, and although S19.8 reactivity was weakly recovered by culture in the absence of serum, no such reacitivity was observed with clone 23. Strong expression of these epitopes was achieved following transfection of 69.9.15 cells with the wild-type H-2K ^b gene, indicating that the ₂m^b epitopes defined by mAb S19.8 and clone 23 were expressed when ₂m^b was assembled with an appropriate heavy chain. In support of this conclusion, we observed the recovery of the S19.8 and clone 23 epitopes by in vitro assembly of H-2K^b heavy chains with ₂m^b in the presence of the VSV N protein p52–59; however, such epitopes were expressed neither by ₂m^b prior to heterodimer assembly nor by non-conformed ₂m^b present in tissue culture supernatants recovered from H-2 class I surface positive cells. Taken together, these data indicate that in addition to the property of ₂m to modify the antigenicity of the MHC class I heavy chains, ₂m epitopes are induced in a reciprocal manner by assembly with MHC class I heavy chain molecules. Correspondence to: R. A. Zeff.     

Refinement of the protein backbone angle ψ in NMR structure calculations

Cross-correlated relaxation rates involving the C-H dipolar interaction and the carbonyl (C) chemical shift anisotropy (CSA) have been measured using two complementary 3D experiments. We show that the protein backbone angle can be directly refined against such cross-correlated relaxation rates (^{H C,C}) and the three-bond H/D isotope effect on the C chemical shifts (³C _(ND)). By simultaneously using both experimental parameters as restraints during NMR structure calculations, a unique value for the backbone angle is defined. We have applied the new refinement method to the -Spectrin SH3 domain (a -sheet protein) and to the Sgs1p HRDC domain (an -helical protein) and show that the quality of the NMR structures is substantially improved, judging from the atomic coordinate precision and the Ramachandran map. In addition, the -refined NMR structures of the SH3 domain deviate less from the 1.8 Å crystal structure, suggesting an improved accuracy. The proposed refinement method can be used to significantly improve the quality of NMR structures and will be applicable to larger proteins.     

Mechanism of gene conversion in Ascobolus immersus. II. The relationships between the genetic alterations in b 1 or b 2 mutants and their conversion spectrum

Summary In order to establish a relationship between the type of genetic alteration occurring in the mutant and the conversion spectrum which is associated with it, an attempt was made to characterize the genetic alterations in a sample of five spore colour mutants by specific reversion.All the mutants revert by back-mutation. Reversion of one of them is possible by mutation in external suppressor gene: at least two of the external suppressors behave like super-suppressors. Reversion of two other mutants by intragenic second-site mutation and study of the intragenic suppressors indicate that they are of the frameshift type. One of the frameshift mutants (ICR₁₇₀ induced) reverts by two alkylating agents suggesting that it originates from base(s) addition. The inhability of ICR₁₇₀ to induce reversion of this mutant suggests the preferential occurrence of base addition in ICR₁₇₀ mutagenesis. Conversly the other frameshift mutant (induced by ethyl methanesulfonate) reverts strongly by ICR₁₇₀. Thus it is concluded that it originates from deletion.These two frameshift mutants and all the ICR₁₇₀ induced mutants give no or very few asci with postmeiotic segregation and either an excess of conversion towards the mutant type allele (addition type mutant) or towards the wild type allele (deletion type mutant).Evidence supports the hypothesis that mutants which give many asci with postmeiotic segregation originate from substitution.These data imply differential recognition of non-pairing and mispairing of bases and in the case of non-pairing, that the direction of conversion is determined by the non-pairing itself.     

Germ-free and barrier-raised TGFβ1-deficient mice have similar inflammatory lesions

Barrier-raised transforming growth factor 1 (TGF1)-deficient mice consistently die before 35 days of age of a severe multiorgan inflammatory disease that can affect the skeletal muscle, heart, liver, pancreas, salivary gland, lung, oesophagus and stomach. The underlying cause of this disease is not known. To determine whether abnormal responsiveness of the immune system to the presence of enteric flora plays a causative role, a colony of TGF1-deficient and wild-type mice were raised in a sterile environment. Seven germ-free TGF1-deficient and 5 germ-free TGF1 wild-type mice were examined. Lesion development was analysed and compared with historical data on 50 barrier-raised TGF1 mutant mice and 32 barrier-raised wild-type mice. All germ-free TGF1-deficient mice died shortly after weaning, as do their barrier-raised counterparts. There was a significant delay in death in germ-free TGF1-deficient mice compared with barrier-raised mutant mice. However, there was no difference in the type, severity or incidence of lesions between TGF1 mutant mice raised under germ-free or barrier conditions. Germ- free wild-type mice had no lesions. It is concluded that microorganisms play a minimal role in disease induction in TGF1-deficient mice     

In situ evidence that chilling in the light does not cause uncoupling of photophosphorylation or detachment of coupling factor in chilling-sensitive plants

The potential involvement of impaired photophosphorylation in the chilling sensitivity of photosynthesis in warm climate plant species has been a topic of investigation for more than two decades. With recent advances in the analysis of photosynthetic energy transduction in intact leaves, experiments are now possible that either address or avoid important uncertainties in the significance and interpretation of earlier in vitro work. Nevertheless, different laboratories using different techniques to analyze the effects of chilling in the light on photophosphorylation in intact cucumber (Cucumis sativus) leaves have come to very different conclusions regarding the role of impaired ATP formation capacity in the inhibition of net photosynthesis. In order to evaluate these discrepancies and bring this issue to a final resolution, in this investigation, we have made a detailed analysis of the decay of the flash-induced electrochromic shift and changes in chlorophyll fluorescence yield in cucumber leaves before, during and after a 5 h light-chill at chill temperatures of between 4 and 10°C. We feel that our findings address the major discrepancies in both data and interpretation as well as provide convincing evidence that photophosphorylation is not disrupted in cucumber leaves during or after light and chilling exposure. It follows that impaired photophosphorylation is not a contributing element to the inhibition of net photosynthesis that is widely observed in warm climate plants as a result of chilling in the light.Abbreviations CF chloroplast coupling factor or CF₁CF₀-ATP synthase - A₅₁₈ flash-induced electrochromic absorbance change measured at 518 nm - DCCD N,N'-dicyclohexylcarbodiimide - _H ⁺ transmembrane electrochemical potential of hydrogen ions - the electrical charge component of _H ⁺ - pH the hydrogen ion concentration component of _H ⁺ - F₀ and F_m the yields of chlorophyll fluorescence from dark-adapted material when all Photosystem II centers are open (F₀) or closed (F_m) - F₀' and F_m' F₀ and F_m measured in light-adapted material - F_s steady-state chlorophyll fluorescence yield in light-adapted material - Q_A primary quinone electron acceptor of Photosystem II - PPFD photosynthetic photon flux density