The Role of Anaerobic Respiration in Germinating Muskmelon Seeds: I. IN RELATION TO SEED LOT QUALITY

Five muskmelon (Cucumis melo L.) cultivar seedlots from a commercialsource and freshly produced seeds of two cultivars, when artificiallyaged, were found to differ in their viability and vigour asdetermined by germination tests. Furthermore, the various commercialseedlots without ageing also exhibit a range of deteriorationlevels. Low vigour seeds had higher respiratory quotient valuesthan the high vigour seeds as a result of a higher level ofCO₂ production. This high level of CO₂ evolution in low vigourseeds may have been due to anaerobic respiration. Levels of acetaldehyde and ethanol produced by imbibing seedswere negatively associated with seed viability and vigour. After6 h of imbibition low vigour seeds produced significantly moreethanol and acetaldehyde than high vigour seeds. After 24 hof imbibition, ethanol continued to accumulate in the commercialseedlots up to 10-fold the amount produced after 6 h of imbibition,whereas, acetaldehyde levels increased less. However, in thefreshly produced, artificially aged seeds (except the most extremeageing), ethanol levels were reduced and no acetaldehyde productioncould be detected, indicating re-utilization of ethanol. It is suggested that ethanol production in the first hours ofimbibition can be used as a reliable index to predict germinationin muskmelon seedlots. Key words: Germination, Cucumis melo L., Seeds, Anaerobic respiration     

Anaerobic Metabolism in Germinating Seeds of Echinochloa crus-galli (Barnyard Grass) : METABOLITE AND ENZYME STUDIES

Echinochloa crus-galli, a problem weed in rice fields, has the rare ability to germinate and to grow in a totally oxygen-free environment. After 7 days growth in the light or dark under N₂, E. crus-galli var. oryzicola produces a 2- to 3-centimeter nonpigmented shoot.     

Cd2+处理对菹草叶片保护酶活性和细胞超微结构的毒害影响

以不同浓度Cd^2 处理5d的菹草为实验材料,测定了叶片SOD,POD,CAT等生理生化指标的变化,并用透射电镜观察了Cd^2 对叶细胞超微结构,尤其是对叶绿体,线粒体和细胞核的损伤情况。结果表明：SOD活性,叶绿素含量随Cd^2 处理浓度的增加而下降,而CAT和POD活性都是在1mg／L浓度下达到峰值,而后降低。SOD对Cd^2 毒害最敏感,其次为POD和CAT。电镜观察发现：随Cd^2 浓度的增加,对细胞超微结构的损伤程度也加剧。表现为叶绿体膨大,被膜断裂、消失和叶绿体解体;线粒体变形,脊突膨大和空泡化;细胞核核仁分散,核膜断裂,核空泡化。并探讨了Cd^2 对植物的毒害机制。     

CHEMICAL ANTAGONISM OF IONS : II. ANTAGONISM BETWEEN ANIONS AND ALSO BETWEEN CATIONS AND ANIONS IN THEIR EFFECT ON OXALATE ACTIVITY.

Sulfate ions (SO₄ ⁼) produce an anomalous effect on the ionization of oxalate diion, opposite in direction to the effect of Mg⁺⁺ ions. This effect of sulfate is antagonized by the presence of Cl^- ions according to the equation: See PDF for Equation where f'' is the antilog of the increase in pK₂'' due to the sulfate. In solutions containing up to 0.03 molar MgSO₄ the effect of Mg⁺⁺ predominates over that of SO₄ ⁼. Above 0.1 molar the effect of SO₄ ⁼ predominates and tends to neutralize the initial deviation. In solutions containing fixed amounts of MgCl₂ and varying amounts of NaSO₄ (or vice versa) the effects of these two salts sharply antagonize each other in all proportions.     

Effect of Exogenous Nitrate on Anaerobic Metabolism in Excised Rice Roots: II. FERMENTATIVE ACTIVITY AND ADENYLIC ENERGY CHARGE

Reggiani, R., Brambilla, I. and Bertani, A. 1985. Effect ofexogenous nitrate on anaerobic metabolism in excised rice roots.II Fermentative activity and adenylic energy charge.—J.exp. Bot 36: 1698–1704. The presence of nitrate in the culture medium of excised sterilerice roots stimulated CO₂ and ethanol evolution and, to a smallerextent, alanine accumulation. The increased anaerobic carbohydrateconsumption observed in roots grown on nitrate is consistentwith the constantly higher level of adenylic energy charge.An hypothesis serving to explain the evidence concerning theeffect of nitrate on anaerobically grown rice roots is proposed. Key words: Anaerobiosis, ethanol, nitrate, alanine, adenylic energy charge     

The Role of Boron in Plant Growth: II. THE EFFECT ON GROWTH OF THE RADICLE

Estimates of cell number, cell volume, respiratory rate, nitrogen,sugar, and nucleic acid content were made on 1 mm. sectionsof the radicles of field bean at frequent intervals during thefirst 96 hours of growth in nutrient solutions with and withoutboron. The primary effects of deficiency were cessation of cell divisionand enlargement of the apical cells. The increased volume ofthe apical cells may have been due to either a longer periodbeing available for development as the rate of mitosis decreased,or to an unusually rapid rate of cell extension. The resultsindicated that cell division did not cease for lack of availablesugar nor as a result of failure to synthesize protein or nucleicacids. It is suggested that in the absence of boron divisionceases because abnormalities in the formation of the cell wallprevent the cell from becoming organized for mitosis. In particularthe hypothesis that boron is concerned with the formation of‘pectin’ from uridinediphosphate-D-glucose is examinedin the light of published evidence.     

Effects of Anoxia on Wheat Seedlings: II. INFLUENCE OF O2 SUPPLY PRIOR TO ANOXIA ON TOLERANCE TO ANOXIA, ALCOHOLIC FERMENTATION, AND SUGAR LEVELS

Prior exposure of roots of intact wheat seedlings for 15–30h to hypoxia (0016-006 mol m 02) greatly increased their toleranceto subsequent anoxia, as assessed by the ability of the rootsto elongate upon return to air. Such hypoxically pretreatedroots had 2–4-fold higher activities of pyruvate decarboxylase(PDC) and 35–l7-fold higher activities of alcohol dehydrogenase(ADH) in their 0–1 mm apices and 0–5 mm root tipsthan in apices and tips of roots pretreated in air (026–031mol m3 02). The ADH/ PDC ratio increased I 3–5-fold duringhypoxic pretreatment. Furthermore, the rate of alcoholic fermentationby 0–5 mm tips of the hypoxically pretreated roots was14-4-fold faster than in tips from aerobically pretreated roots.No consistent difference between 02 pretreatment was found foralcoholic fermentation by tissues taken between 10 and 20 mmfrom the root tip. The observed activities of PDC and rates of alcoholic fermentationindicate that alcoholic fermentation is usually rate-limitedby PDC in 0–1 mm apices and 0–5 mm tips of wheatroots. Comparisons with data in the literature indicate thatwheat has at most a small Pasteur effect, which may explainwhy wheat is more intolerant to anoxia than rice. Exogenous glucose delayed the loss of elongation potential inboth aerobically and hypoxically pretreated roots. In the absenceof glucose, more than 85% of aerobically pretreated roots hadlost their elongation potential after 9 h anoxia, compared with30% in the presence of glucose. After 21 h anoxia nearly allaerobically pretreated roots had lost their elongation potential,compared with 10% and 0% of hypoxically pretreated roots inthe absence and presence, of glucose, respectively. The protective effect of glucose was presumably not due to anendogenous sugar deficiency; at the start of anoxia, 0–1mm apices of aerobically pretreated roots contained sufficientsugar for 23 h of their measured rate of ethanol synthesis yet,85% of these apices had lost their elongation potential afteronly 9 h of anoxia. It is suggested that in wheat roots, lowrates of synthesis of ethanol and hence of ATP, lead to injuryof cells, in turn generating a requirement for exogenous glucose,despite high endogenous sugar concentrations. Key words: Wheat seedlings, anoxia, glucose, O₂ pretreatment, alcoholic fermentation     

CHEMICAL ANTAGONISM OF IONS : I. EFFECT OF Na-Mg AND K-Mg MIXTURES ON THE ACTIVITY OF OXALIC DIION.

Magnesium ions decrease the activity of divalent organic anions much more than the normal decrease produced by sodium ions. The effect is very large with short chain acids, particularly oxalic acid. The addition of sodium or potassium ions produces a marked decrease in the effect of magnesium diions on the activity of oxalate diions. Quantitative data on 0.005 molar solutions of oxalic diion over a wide range of concentrations of MgCl₂ and of NaCl (or KCl) show that the following equation is obeyed: See PDF for Equation where A is an empirical value dependent on the concentration of oxalate diion (0x⁼). This equation has been shown to hold down to zero ionic strength of Na⁺ and K⁺, and hence to be valid in the physiological range. These observations are of biological interest since the activity of proteins should (like oxalic acid) show a similar antagonism.     

Enzymic Mechanism of Starch Breakdown in Germinating Rice Seeds: 9. DE NOVO SYNTHESIS OF beta-AMYLASE

Germinating rice seeds were fed with [³⁵S]methionine and the incorporation of ³⁵S into β-amylase demonstrated by quantitative immunoprecipitation using rabbit anti-β-amylase immunoglobulin G fraction. Separation of the antigen-antibody complex by Na-dodecylsulfate gel electrophoresis and subsequent radioautography clearly showed the radioactive labeling of the β-amylase molecule. The specific radioactivity of β-amylase derived from scutellum by immunoprecipitation was significantly greater than that of the endosperm. The results strongly indicate that at the onset of germination of rice seeds β-amylase is synthesized de novo in the scutellum and that in later stages there occurs activation of an inactive, latent form of the enzyme associated with starch granules in the endosperm. In later stages of germination this activated form of the enzyme becomes dominant.     

Glutamine Synthetase of Germinating Peanuts : PROPERTIES OF TWO CHROMATOGRAPHICALLY DISTINCT FORMS AND THEIR ACTIVITY TOWARD 4-METHYLENEGLUTAMIC ACID

Glutamine synthetase activity, extracted from an acetone powder of 7-day germinated peanuts (Arachis hypogaea L.), was precipitated by ammonium sulfate (40-60% saturation) and further purified by gel filtration and calcium phosphate gel treatment. When it was adsorbed to and subsequently eluted from a column of diethylaminoethyl-cellulose, two peaks of activity (designated glutamine synthetase 1 and 2) were obtained which were enriched 150- and 20-fold, respectively, over the initial extract. Glutamine synthetase 1 was present in ungerminated seeds and in the cotyledons during germination; glutamine synthetase 2 appeared during germination and was found largely in the developing plant. Compared with glutamine synthetase 2, glutamine synthetase 1 appeared to have a slightly smaller molecular weight and was more stable to heat and storage. The catalytic properties of the two forms were essentially the same. Whereas neither form catalyzed gamma-glutamyltransferase activity with 4-methyleneglutamine, both glutamine synthetases 1 and 2 catalyzed an ATP- and NH(4) (+)-dependent conversion of [(14)C]-4-methyleneglutamic acid to [(14)C]-4-methyleneglutamine, but the K(m) value for 4-methyleneglutamic acid was 10-fold greater and the V(max) only one-fourth that measured with l-glutamic acid. This is the first report of glutamine synthetase activity with 4-methyleneglutamic acid as substrate, although the level of this activity does not appear adequate to account for the rapid synthesis of 4-methyleneglutamine observed in germinating peanuts.     

THE EFFECT OF RADIOACTIVE RADIATIONS AND X-RAYS ON ENZYMES : III. A UNIT OF MEASURE OF ACTIVITY FOR RADIUM EMANATION.

In this communication we have introduced a unit to express activity or power of a given preparation of radium emanation. We have named this unit the curie-power and defined it as the activity of 1 curie of radium emanation and its radioactive products in equilibrium with it. We suggest the introduction of this unit in order that we may make a more comprehensive statement of our experimental observation. In the radiochemical reaction effected by the radiations (beta and gamma) from radium emanation in which enzymes are inactivated the chemical change in a given system is a function of the product of two variables; namely, the average activity of the radium emanation, P_a, expressed in terms of the unit millicurie-power, and time, t, expressed in hours. This product has the dimensions of energy and is identical with W which is measured in terms of the energy unit, millicurie-power hours.     

Enzymic Mechanism of Starch Breakdown in Germinating Rice Seeds: III. alpha-Amylase Isozymes

The formation of amylase isozymes in germinating rice (Oryza sativa) seeds was studied by isoelectric focusing on polyacrylamide gel disc electrophoresis. Time sequence comparisons of the amylase zymogram were made between extracts from gibberellic acid-treated embryoless and embryo-attached half-endosperm of rice seeds. In both cases, 4 major and 9 to 10 minor isozyme bands were detectable at the maximal stage of the enzyme induction. However, in the embryo-attached half-seeds, bands started to diminish after the 5th day of incubation, in agreement with the results of time sequence analyses of enzyme activities. Nearly identical patterns of amylase isozyme bands on a polyacrylamide gel disc electrophoresis in combination with isoelectric focusing indicate the intrinsic role of gibberellic acid in the starch breakdown in germinating rice seeds. We tentatively assign the newly synthesized enzymes to be α-amylases based on experimental results concerning the lability of the preparation on a prolonged treatment at pH 3.3 and the stability on heat treatment for 15 minutes at 70 C.     

Enzymic Mechanism of Starch Breakdown in Germinating Rice Seeds II. Scutellum as the Site of Sucrose Synthesis

In a close parallel to the developmental pattern of α-amylase activity, a rapid increase of maltase activity occurred in the endosperm tissue of germinating rice seeds after about 4 days of the seed imbibition. The overall pattern of the 2 hydrolytic enzyme activities strongly suggest that amylolytic breakdown is the major metabolic route of starch utilization in the germinating rice seeds. Results of the chemical analyses of sugar constituents as well as the measurements of sucrose synthetase activity show that the scutellum is the site of sucrose synthesis in the germinating rice seeds. It is thus supported that glucose derived from the reserve starch in endosperm is transported to scutellum, where it is converted to sucrose. Sucrose is further mobilized to the growing tissues, shoots and roots.     

Enzymic Mechanism of Starch Breakdown in Germinating Rice Seeds: 10. IN VIVO AND IN VITRO SYNTHESIS OF alpha-AMYLASE IN RICE SEED SCUTELLUM

Scutellar tissues were dissected from germinating rice seeds and the incorporation of [³⁵S]methionine into the α-amylase molecule was examined by in vivo and in vitro assay systems. Immunoprecipitation with monospecific anti-α-amylase immunoglobulin G raised against the purified enzyme preparation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography were used to identify α-amylase and its possible precursor molecule. Using freshly prepared scutellar tissues, it was demonstrated that α-amylase is synthesized de novo in the scutellar epithelium and secreted into endosperm. The synthesis of α-amylase directed by the polyadenylic acid-containing ribonucleic acid isolated from the scutellar tissues was also established using the translation system of either wheat germ extract or reticulocyte lysate. The immunoprecipitable product obtained in the in vitro translation system was smaller in molecular weight than that synthesized in vivo on the basis of mobilities in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Results are discussed in relation to the processing of the nascent polypeptide precursor of the enzyme molecule and the introduction of the oligosaccharide chain to the cleaved polypeptide to make up the mature form of α-amylase.     

THE POTENTIAL AND RESPIRATION OF FROG SKIN : I. THE EFFECT OF THE HOMOLOGOUS CARBAMATES. II. THE EFFECT OF CERTAIN LYSINS

Measurements of the O₂ consumption and of the potential of frog skin, made under comparable conditions, show that the homologous carbamates (ethyl, propyl, butyl, and amyl) reduce both the O₂ consumption and the potential, but not in a similar manner. In this respect, the effect of the carbamates is like the effect of reduction in O₂ tension. The simple lysins (saponin and the bile salts), on the other hand, abolish the potential without reducing the O₂ consumption at all. Irrespective of whether one considers the concentration of carbamate in the entire system or the amount of carbamate adsorbed by the frog skin, Traube''s rule relating the effect of a carbamate to its position in the homologous series does not seem to apply.     

Investigations of Carbon Transport in Plants: II. THE EFFECTS OF LIGHT AND DARKNESS AND SINK ACTIVITY ON TRANSLOCATION

The use of ¹¹C as a tracer has allowed repetitive measurementsof the speed of assimilate translocation to be made on singlemaize plants throughout prolonged periods of light and darkness.The speed appeared to double when the light was switched on.The time required to achieve a maximum speed, usually about3·5 cm min^–1, depended on the duration of the previousdark period. When the plant was transferred to darkness thespeed immediately decreased by about 20 per cent and continuedto decrease over the next 20 h to values of 0·5 to 0·9cm min^–1. The mean speed of translocation in tomato in the light, andother C3 plants, was usually about 1 cm min^–1. It wasreduced by 15–30 per cent when the fruit was removed orcooled from 26 to 10°C.