Protein Turnover in Isolated Barley Leaf Segments and the Effects of Stress

Leaf segments prepared from the first leaves of barley (Hordeumvulgare) exhibit a rapid loss of protein when given a matricstress with polyethylene glycol. Protein synthesis was reducedby the stress but a greater effect of stress was seen on proteindegradation. Growing leaves were exposed to ³H₂O for 4 d ormore to label total protein, and the half-life of protein 2-³H,in the isolated segments prepared from such leaves, was shownto be c. 140 h in the absence of stress. Stress reduced thisto c. 62 h. A short pulse with ³H₂O preferentially labels rapidlyturning-over protein and a 24 h pulse given to isolated leafsegments labelled proteins with a half-life of c. 64 h in thepresence or absence of stress. Degradation of the 24 h pulse-labelledproteins was inhibited by cycloheximide. Proline accumulationoccurred in the stressed segments and was inhibited by cycloheximide.The results are discussed in the light of current views concerningprotein degradation and possible relationships between proteolysisand proline accumulation.     

Nucleic Acid Metabolism during Greening and Unrolling of Barley Leaf Segments

Barley (Hordeum vulgare) leaf segments unroll and green when illuminated. Illuminated segments also have an increased capacity for RNA synthesis. Part of this increased RNA synthesis may be attributed to an increased RNA polymerase activity. In addition, following illumination there is an increased formation of polysomes.     

Effects of Sucrose on Petiolar Carbohydrate Accumulation and Photosynthesis in Excised Sinapis Cotyledons

Petioles of Sinapis cotyledons cultured in 6x10^–2 M sucrosein the light increased 28-fold in total carbohydrate contentover a 7-d period compared with an 8-fold increase in petiolesof cotyledons cultured on water. The starch and reducing sugarfractions were the major components of this accumulation. Labelledsucrose applied to the petiole base moved quickly up the petioleand into the main veins of the lamina. Some basipetal redistributionoccurred subsequently and after 24 h radioactivity accumulatedstrongly at the petiole base. Culture in sucrose reduced basalaccumulation and increased acropetal movement of the label. Fixation of ¹⁴CO₂ by petioles remained constant when cotyledonswere cultured in water, whereas in sucrose, fixation fell by50 per cent during the first 2 d. The pattern of inhibitionof fixation matched the pattern of sucrose distribution in thepetiole. Petiolar chlorophyll content remained constant in controlsbut fell rapidly after 4 d culture in sucrose. The results are discussed in relation to the role of petiolarcarbohydrate accumulation in the regulation of CO₂ fixation,primordium development, and senescence in this system.     

Effects of Growth Regulators on Ribonucleic Acid Metabolism of Barley Leaf Segments

Illumination or gibberellic acid treatment of etiolated barley leaf segments stimulates unrolling and results in an increased level of RNA. In contrast, segments treated with abscisic acid do not unroll and have a lower content of RNA. Gibberellic acid treatment enhanced the capacity of segments to incorporate radioactivity from ³²P-orthophosphate into all the RNA components detected by gel electrophoresis; abscisic acid greatly restricted the incorporation of precursors into all the RNA fractions. In conjunction with a changed capacity for RNA synthesis it was observed that abscisic acid-treated segments had a lowered soluble DNA-dependent RNA polymerase level in comparison to gibberellic acid-treated or illuminated segments. However, the influence of growth regulators on RNA polymerase content of the segments was associated with general effects on protein level rather than a specific effect on the synthesis of polymerase enzyme.     

Photosynthesis and Light Activation of Ribulose 1, 5-bisphosphate Carboxylase in the Presence of Starch

Owing to a typographical error three equations were omittedfrom page 1294. The correct paragraphs are set out below. The component K₁ corrected for the difference in temperaturebetween the enzyme assay and the leaf and was calculated accordingto the Arrhemus equation. where v10 and v18 are the reaction velocities of carboxylationat 10?C and 18?C, respectively and A is the activation energy(A = 90 kJ mol^–1, as determined for purified wheat RuBPCOby M?chler, Keys and Cornelius, 1980) The components K2 corrected for the difference in CO₂ partialpressure between enzyme assay and leaf and for competitive inhibitionof carboxylation by O₂ and was calculated according to the modifiedMichaelis Menten equation where v_c, is the carboxylation velocity under leaf conditions,V_c. is the maximum carboxylation velocity as determined in theenzyme assay, K_c, and K_o are the Michaelis constants for carboxylationand oxygenation, respectively (K_o = 159 Pa CO₂. K_o = 35.3 kPaO₂, as interpolated for 18?C from spinach data as determinedby Jordan and Ogren, 1984), O is oxygen partial pressure inair and C₁ is intercellular CO₂ partial pressure in leaves (C₁= 29.1 ? 0.8 Pa (? s c , n = 15)) The component K3 corrected for the decrease in CO₂ fixationin leaves due to photorespiration and was calculated accordingto equation 3 Equation 3 is denved from the equation for the substrate specificityof RuBPCO, S= v_c/v_oC (Laing, Ogren, and Hageman, 1974), andfrom the equation for the stoichiometry of photorespiratoryCO₂ release, F=v_c–1/2 v_o, where v_c, and v_c are reactionvelocities of carboxylation and oxygenation, O and C are partialpressures of 02 and intercellular CO₂, F is net photosynthesisand S is the substrate specificity of RuBPCO (S= 3061 Pa/Pa,as interpolated for 18?C from spinach data as determined byJordan and Ogren, 1984)     

Accumulation of Reserve Carbohydrate by Rumen Protozoa and Bacteria in Competition for Glucose

The aim of this study was to determine if rumen protozoa could form large amounts of reserve carbohydrate compared to the amounts formed by bacteria when competing for glucose in batch cultures. We separated large protozoa and small bacteria from rumen fluid by filtration and centrifugation, recombined equal protein masses of each group into one mixture, and subsequently harvested (reseparated) these groups at intervals after glucose dosing. This method allowed us to monitor reserve carbohydrate accumulation of protozoa and bacteria individually. When mixtures were dosed with a moderate concentration of glucose (4.62 or 5 mM) (n = 2 each), protozoa accumulated large amounts of reserve carbohydrate; 58.7% (standard error of the mean [SEM], 2.2%) glucose carbon was recovered from protozoal reserve carbohydrate at time of peak reserve carbohydrate concentrations. Only 1.7% (SEM, 2.2%) was recovered in bacterial reserve carbohydrate, which was less than that for protozoa (P < 0.001). When provided a high concentration of glucose (20 mM) (n = 4 each), 24.1% (SEM, 2.2%) of glucose carbon was recovered from protozoal reserve carbohydrate, which was still higher (P = 0.001) than the 5.0% (SEM, 2.2%) glucose carbon recovered from bacterial reserve carbohydrate. Our novel competition experiments directly demonstrate that mixed protozoa can sequester sugar away from bacteria by accumulating reserve carbohydrate, giving protozoa a competitive advantage and stabilizing fermentation in the rumen. Similar experiments could be used to investigate the importance of starch sequestration.     

Photosynthesis and Light Activation of Ribulose 1,5-bisphosphate Carboxylase in the Presence of Starch

Limitation of photosynthesis and light activation of ribulose,1,5-bisphosphate carboxylase (RuBPCO) were examined in the 5thleaf of seedlings of red clover (Trifolium pratense L. cv. Renova)for 5 d following an increase in photosynthetic photon fluxdensity (PPFD) from 200 to 550µmol quanta m^–2 s^–1.Net photosynthesis and its stimulation at 2.0 kPa O₂ initialactivity of rapidly extracted RuBPCO, standard activity of RuBPCOafter incubation of the extracts in the presence of CO₂, Mg²⁺,and inorganic phosphate and contents of soluble protein, starch,soluble sugars, and various photosynthetic metabolites weredetermined. Photosynthesis decreased and starch content increased.No decrease in photosynthesis was found if, when PPFD was increased,all leaves except the investigated 5th leaf were removed, suggestingthat the decrease in photosynthesis was due to accumulated carbohydrates.The stimulation of photosynthesis at 2.0 kPa O₂ did not decreaseand the ratio of the total foliar steady-state contents of triosephosphate to 3-phosphoglycerate increased suggesting that thedecrease in photosynthesis was not due to limiting inorganicphosphate in chloroplasts. Intercellular CO₂ partial pressureand RuBP content were not decreased. Nevertheless, the ratioof photosynthesis to initial RuBPCO activity decreased, suggestingthat the catalysis per active RuBPCO site was decreased. Theincrease in PPFD in the growth cabinet and the PPFD at whichleaves were preconditioned for 1 h, affected not only initialactivity but also the standard activity of RuBPCO. The resultssuggest that a varying proportion of RuBPCO was bound to membranesand was contained in the insoluble fraction of the extracts.A comparison of photosynthesis with extracted RuBPCO activitysuggested that membrane bound RuBPCO did not contribute to photosyntheticCO₂ fixation and that the binding and release to and from membranesmodulated actual RuBPCO activity in vivo. Key words: Photosynthesis, ribulose 1,5-bisphosphate carboxylase, starch     

Effects of Ear Removal on Photosynthesis, Carbohydrate Accumulation and on the Distribution of Assimilated 14C in Wheat

Removal of an ear from a tiller of a wheat plant growing inthe field did not result in any marked change in the net photosyntheticrate of the subtending flag leaf, even during the period whenthe ear would normally have received large amounts of assimilatefrom the flag leaf. Following ear removal, there was an increasein the amount of ethanol-soluble and ethanol-insoluble carbohydratesin the remaining organs of the tiller. ¹⁴C labelling studiesshowed that a new pattern of translocation was established within2–3 days of ear removal, and the tiller exported assimilateto other tillers on the plant, and possibly to the roots.     

水杨酸和茉莉酸甲酯对丹参幼苗叶片显微结构、光合及非结构糖积累的影响

研究了水杨酸(SA)和茉莉酸甲酯(MeJA)处理对丹参(Salvia miltiorrhiza Bunge)幼苗叶片显微结构、叶片光合能力及幼苗中非结构糖积累的影响.结果显示:SA处理增加了丹参幼苗叶片气孔密度;叶肉细胞排列紧密、体积减小,叶肉细胞内叶绿体数目减少,但叶绿体体积增大,叶绿体基粒片层结构的数目增加;叶片中叶绿素a、b含量、叶气孔导度、蒸腾速率以及净光合速率均增加;同时,幼苗根中和叶片中酸性转化酶活性降低,幼苗地上部分蔗糖含量及可溶性糖总量显著高于对照.MeJA处理减少了叶片气孔密度,气孔发育畸形;叶肉细胞间隙增大,栅栏细胞层数减少,叶肉细胞内叶绿体数目减少,叶绿体体积减小,叶绿体基粒片层结构被破坏;叶片中叶绿素a及类胡萝卜素含量、叶片的净光合速率低于对照,叶气孔导度、蒸腾速率增强;同时,幼苗根中及叶中酸性转化酶活性增加,幼苗根中蔗糖含量及可溶性糖总量显著低于对照.可见,SA处理能促进植物叶片显微结构发育,增强叶片光合能力,抑制蔗糖降解并促进蔗糖积累;而MeJA处理则破坏了植物叶片显微结构,降低了叶片光合能力,促进了蔗糖降解并减少蔗糖积累.     

Influence of Rate of Development of Leaf Water Deficits upon Photosynthesis, Leaf Conductance, Water Use Efficiency, and Osmotic Potential in Sorghum

This study reports the effect of rate of development of leaf water deficits in soil-grown sorghum (Sorghum bicolor) on the relationship of net photosynthesis, leaf conductance, and water use efficiency to leaf water potential, and on the degree of solute accumulation (osmotic adjustment). Recovery of these processes on rewatering, and responses during a second stress cycle were also studied. The most rapid rate of stress (1.2 MPa day^?1) resulted in no solute accumulation and the lowest rate of net photosynthesis and leaf conductance for any given leaf water potential during stress. Stress at 0.7 and 0.15 MPa day^?1 led to equal solute accumulations of approximately 0.6 MPa, but net photosynthesis, leaf conductance, and water use efficiency at a given leaf water potential were lower with the faster rate of stress (0.7 MPa day^?1). Additionally, leaf conductance at a given leaf turgor potential was lowest at the 1.2 MPa day^?1 stress rate, slightly higher at the intermediate rate of stress, and clearly highest at the slowest rate of stress. Recovery of both net photosynthesis and leaf conductance upon rewatering was rapid, taking less than 3 days, but full recovery of osmotic potential took between 6 and 11 days. One slow stress cycle had no influence on relationships during a second cycle. The concept of a threshold leaf water potential for stomatal closure is discussed and the conclusion reached that stomatal closure occurs slowly over a wide range of leaf water potential (> 1.0 MPa), the range being greater for slower rates of stress.     

Growth and Photosynthesis in the First Leaf of Barley The Effect of Time of Application of Nitrogen

Using Proctor barley grown in sand under controlled-environmentconditions it was shown that when application of nitrogen, asnitrate, was delayed beyond day 4, at which time the first leafwas beginning to unfold, absolute and relative growth-ratesof seedlings were reduced so that the young plants were significantlysmaller. Delay in nitrate application led to reduction in length,breadth, area, and dry weight of the first leaf, and also toa lower photosynthetic activity on day 8, as measured by infra-redgas analysis. Measurement of the uptake of ¹⁴CO² by first leaves showed thatapplication of nitrate on days 2 or 4 led to high rates of fixationof carbon over the period days 8–12, whereas applicationon days 6 or 8 led to a substantially lower maximum rate offixation which was maintained for a shorter period. When nitratewas applied on day 8 total fixation of carbon over the perioddays 7–14 was only 60 per cent of that for leaves on plantsfor which nitrate was supplied on day 2. When amounts of carbon fixed were compared on a leaf dry-weightbasis, maximum values were found to be similar for all treatments,suggesting that the differences in fixation per leaf resultmainly from the effect of treatment on leaf area. For all treatmentsit was confirmed that a decline in photosynthetic activity occurredby day 14. This was not correlated with photosynthetic activityin the second leaf, nor with emergence of the third leaf. Analysis of different parts of the lamina of the first leafshowed all to be affected by the timing of the supply, bothin growth and in photosynthetic activity. Leaf dry weight didnot increase after day 8 for any treatment, yet when nitratewas applied on day 8 plants showed a fourfold increase in photosyntheticrate. The significance of this in relation to carboxylationand other resistances in photosynthesis is discussed.     

光合单位的周转率与叶片光合速率的关系

利用闪光技术,测得若干高等植物叶片的光合单位为 1450～2050 Chl/CO_2。在含O_2 2％及CO_2浓度和光通量密度都饱和的条件下,测得叶片的连续光合速率为25～70μmol CO_2 m~(-2) s~(-1)。从上述数据及叶片叶绿素含量计算,得叶片光合单位的周转率已达80～160次/s。这样的周转速率与Emerson当初用改变闪光间暗间隔而测到的光合单位周转时间相似(即<10 ms/次,或>100次/s),从而证实了光合单位的周转与光合速率直接有关。这样的速率可称之为叶片光合的理论速率。     

Involvement of Cl in the Increase in Proline Induced by ABA and Stimulated by Potassium Chloride in Barley Leaf Segments

Stimulation by sodium or potassium chloride of the ABA-induced increase in proline was synergistically enhanced by CaCl₂ or MgCl₂ as well as by 1,3-bis[tris(hydroxymethyl)methylamino] propane chloride (BTP-Cl), N-methyl-d-glucamine chloride (NMG-Cl), or 2-amino-2-hydroxymethyl-1,3-propandiol chloride (TRIS-Cl). This enhancing effect did not depend on the osmolarity and occurred when Cl⁻ was higher than K⁺ in the incubation medium, but not vice versa. When CaCl₂ or MgCl₂ or NMG-Cl were added, the higher the Cl⁻:K⁺ ratio in the external solution the higher was the increase in proline. When the excess of Cl⁻ to K⁺ was obtained with BTP-Cl the highest enhancing effect resulted with a Cl⁻:K⁺ ratio of 3:1 while, at a 5:1 ratio, the KCl stimulation was completely suppressed. The inhibiting effect of proline accumulation by NH₄⁺ and 4,4′-diisothiocyano-2,2′-disulfonic acid stilbene was reversed to varying degrees depending on the magnitude of the excess of Cl⁻ on K⁺ concentration in the medium. Also, the inhibition of proline accumulation obtained by tetraethylammonium chloride, monensin, and d-mannose was similarly reverted. These data suggest that Cl⁻ elicits an increase in ABA-induced proline which needs the simultaneous presence of K⁺ (or Na⁺) to take place.     

Glucose Uptake Rate by Saccharomyces Cerevisiae in the Presence of Promoters of Alcoholic Fermentation Using 14C-Labelled Glucose

The glucose uptake rate by Saccharomyces cerevisiae in various densities of glucose and molasses solutions was found to be about one third up to two fold higher in the presence of promoters -alumina and kissiris in comparison with their absence in the free cells. This study was accomplished by using ¹⁴C-labelled glucose, which is a convenient method.     

The Effects of Grain Nitrogen and Applied Nitrate on Growth, Photosynthesis and Protein Content of the First Leaf of Barley Cultivars

Five cultivars of barley with widely differing grain nitrogencontents were compared. In the absence of exogenous nitratesupply plants grown from high nitrogen grain showed a more rapidleaf emergence, greater leaf size, especially of the first leaf,higher photosynthetic rate and greater total souble proteinand Fraction 1 protein content of the first leaf, than plantsgrown from low nitrogen grain. However, early supply of nitrateto plants grown from low nitrogen grain enabled these to performas well as those from grain with a high nitrogen content. Regressionanalysis showed that Fraction 1 content of the first leaf isclosely correlated with grain nitrogen which exerts a progressivelygreater effect on content of this protein as application ofexogenous nitrate is delayed. The more rapid photosyntheticrate of plants grown with high nitrogen, and the consequentgreater rate of dry matter accumulation, is attributable mainlyto effects of nitrogen availability on leaf area and much lessto effects on leaf protein.     

A Simple Bioassay for Herbicidal Substances of Microbial Origin by Determining de novo Starch Synthesis in Leaf Segments

A simple and sensitive assay system was developed in the search for new herbicidal substances. The system is based on the following two phenomena observed in photosynthesis: (1) de novo starch synthesis, determined in excised leaf segments of barnyard millet (Panicum crus-galli), a C₄ plant, and Italian ryegrass (Lolium multiflorum Lam.), a C₃ plant; and (2) oxygen evolution in the cells of Scenedesmus obliquus, detected by using an oxygen electrode. The system can detect photosynthesis-inhibiting herbicides at a concentration as low as 0.1 ppm. After assaying 6,500 microbial culture broths, 6 culture filtrates were selected for further study.     

Variations in the Photosynthesis Rate and Activity of Photosynthetic Enzymes in Maize Leaf Tissue of Different Ages

Highly good correlations for the extractable activities of ribulose-1,5-bisphosphatecarboxylase, pyruvate,P_i dikinase, phosphoenolpyruvate carboxylase,NADP-malate dehydrogenase and NADP-malic enzyme and the rateof photosynthesis were found in maize leaves of various ages.The activities of the first two enzymes were similar to, orslightly higher than, the photosynthesis rate, whereas the activitiesof the other enzymes were 2 to 6 times higher than the photosynthesisrate. These results suggest that pyruvate,P_i dikinase and ribulose-1,5-bisphosphatecarboxylase may be rate-limiting factors in maize. (Received May 12, 1984; Accepted July 5, 1984)     

Photosynthesis of Lamina and Sheath of Barley Leaves

Apparent photosynthesis, in mg. CO₂ absorbed per dm.² per hour,of the sheath and enclosed stem of a barley leaf was about 50per cent. of that of the lamina of the same leaf, when the photosynthesizingarea was measured as one side of the lamina and the outer exposedsurface of the sheath. Apparent photosynthesis of a particularlamina or sheath was about 70 per cent. of that of the one aboveon the same stem. Respiration per dm.², though not per g. dry weight, of sheathwith enclosed stem was greater than of lamina in one experimentdone with low-intensity illumination so that true rates of photosynthesisof lamina and sheath were similar. Differences in respirationrates per unit area of laminae and sheaths probably accountedfor most of the greater apparent photosynthesis of the formerin other experiments done with higher intensity illumination. It is suggested that for growth-analysis studies the size ofthe photosynthetic system of cereals should be measured as thatof one side of the leaf laminae plus the outer surface of thecombined leaf sheaths. In the later stages of growth the surfacearea of exposed stem and peduncle should also be included.     

Maintenance of High Photosynthetic Rates during the Accumulation of High Leaf Starch Levels in Sunflower and Soybean

Sunflower (cv. “Mammoth Greystripe”) and soybean (Merr. cv. “Amsoy 71”) leaves were exposed to continuous light for at least 52 hours in an attempt to determine the relationship between leaf starch levels and photosynthetic rates. Immature rapidly expanding and relatively mature slowly expanding sunflower leaves were studied. After 52 hours continuous light, the rapidly expanding leaves accumulated high starch levels (3.3 milligrams per square centimeter, 43% of dry weight) with only about a 10% decline from the initial photosynthetic rate of 42 milligrams CO₂ per square decimeter per hour. Under the same conditions, the slowly expanding leaves accumulated less starch, but the photosynthetic rate declined 30%. Soybean leaves, which were slowly expanding, accumulated less starch than sunflower leaves (2.1 milligrams per square centimeter, 34% of dry weight), and their photosynthetic rates declined only about 10% after 54 hours continuous light.     

改良的半叶法测定茶光合速率时韧皮部处理方法的比较

采用环割、ＴＣＡ（三氯醋酸）化学抑制、石蜡烫伤茶叶叶柄韧皮部,以阻止光合产物外运,并通过石蜡切片观察韧皮部破坏程度与其光合速率的关系。结果表明：环割能有效去除韧皮部,阻止光合产物运输,光合速率高;其次TCA 抹,能致使输导系统筛管塞堵子,光合产穆能外运;最后是石蜡烫伤,产生结晶簇结输导组织和运输带来了障碍。