bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chlorophyll(ide) forms after partial phototransformation of protochlorophyll(ide) in etiolated wheat leaves
Authors: Klockare Birgitta , Virgin Hemming I. 
Published: April 2006

Dark‐grown wheat leaves (TriticumL. cv. Starke II Weibull) were illuminated repeatedly with light flashes giving partial phototransformation of protochlorophyllide to chlorophyllide. After short flashes (e.g. 15 ms red light, 250 W m−2), transforming only a minor part of the protochlorophyllide present, the first more stable chlorophyll(ide) measured ca 15 s after the phototransformation had its absorption maximum in the red around 672 nm. It stayed there during the following 30 min in darkness. After longer flashes (e.g. 125 ms), transforming a larger portion of the protochlorophyllide, the chlorophyll(ide) formed had its maximum absorption more towards 684 nm and shifted to 672 nm during a subsequent period in darkness. Thus, in this case a Shibata shift took place.The conditions which produce the “stable” 672 nm form, without a Shibata shift, are discussed. The presence of large amounts of non‐transformed protochlorophyllide remaining after the phototransformation seems to be important. Under such conditions it is possible that the Shibata shift is completed within a very short time.Also the possible existence of two kinds of phototransformable protochlorophyllide is discussed. According to this idea one of the two protochlorophyllide forms produces a chlorophyllide absorbing at 672 nm shortly after phototransformation without having passed a Shibata shift. The other protochlorophyllide form photo‐transforms to a chlorophyllide which proceeds through the Shibata shift.
Induced pore formation in membranes of cortex cells in excised Sorghum roots: its effect on membrane potential and nucleotide leakage
Authors: Lerner H. R. , Denti A. Ballarin , Pradet A. 
Published: April 2006

Measurements of membrane potentials were used for screening various molecules capable of inducing pore formation in cellular membranes for their ability to penetrate into excised roots of Sorghum bicolor (L.) Moench.Poly‐l‐lysine (30 000 MW) and amphotericin B did not affect cortical cells even though they affected epidermal cells; the lysine polymer and the amphotericin B micelle were apparently too large to diffuse into the roots. Polymyxins and filipin depolarized the epidermal cells as well as the cells of the cortex. Depolarization of cortical cells by filipin was slower than that by polymixins.Leakage of adenylate nucleotides was measured to obtain information concerning the size of the pores induced by polymyxins. Incubation with 200 μg/ml polymyxin B caused leakage of ATP from root segments. Leaked nucleotides were found in the medium; however, with time they were dephosphorylated, presumably by cell wall phosphatases. In situ ATP formation was observed when root segments were incubated with polymyxin, ADP, Pi, succinate and glucose, confirming that the induced pores were larger than the size of a nucleotide.
Kinetics of indole acetic acid‐induced growth in hypocotyl sections of Vigna mdiata
Authors: Bouchet Marie‐Hélène , Prat Roger , Goldberg Renée 
Published: April 2006

The kinetics of auxin‐induced elongation of segments from Vigna radiata (L.) Wilczek hypocotyls have been investigated using auxanometer measurements. Doseresponse curves were established for several well‐defined parameters of the growth response. The experimental data revealed that different kinetic parameters were affected differently by increasing auxin concentrations. The dose‐response curves are slightly sigmoid for fresh weight, nearly bell‐shaped for total elongation or maximal elongation rate, and nearly linear for maximal growth acceleration. The effects of auxin concentration on regulation of growth orientation are discussed.A biphasic response is observed mainly with segments taken from the middle of the hypocotyl (‘C’) which exhibit maximal growth rates. Segments from other levels, with lesser growth potentials, exhibit a very weak response. The two successive phases may then require different maturation states. Kinetics of the acceleration curves are very similar all along the hypocotyl and remain very homogeneous with increasing IAA concentrations.
Long‐term effects of low levels of SO2 on bean plants (Phaseolus vulgaris). I. Immission‐response pattern of net photosynthesis and transpiration during life‐long, continuous measurements
Authors: Saxe Henrik 
Published: April 2006

The immission‐response effect of five low levels of sulfur dioxide on net photosynthesis and transpiration was studied during continuous measurements in near‐complete life cycles of whole bean plants (Phaseolus vulgaris L. cv. Processer) grown in a controlled environment. Sixteen plants were grown in individual water cultures in each of five 100 1 glass assimilation chambers with a new type of exposure system with separate root aeration. SO2 immission ranged from 10 μg m−3 to 950 μg m−3 during 12‐h day‐time exposure periods, five days a week, while a low, natural background of NOx was accepted.The SO2‐induced photosynthetic reductions were in the short term, but in particular on the long‐term level very closely related with stomatal conductance (significance level better than 0.0005). However, a causal coherence was not inferred. Physiological inhibitions were composed of: (1) A reversible component (night and week‐end recovery) and (2) an irreversible component (related to reduced green leaf area). The pattern of leaf growth was studied, with the conclusion that SO2 reduced leaf area by promoting senescence, rather than by interfering with leaf emergence and development.
Adventitious root formation ‘in vitro’ in apple rootstocks (Malus pumila) II. Uptake and distribution of indol‐3yl‐acetic acid during the auxin‐sensitive phase in M.9 and M.26
Authors: James David J. 
Published: April 2006

During the auxin‐sensitive phase of root initiation, rates of 3‐indolyl‐ [2‐14C] acetic acid (IAA) uptake into the 1 cm bases of shoots of the apple rootstock M.9 (Malus pumila Mill.) ‘in vitro’ were not significantly affected by the presence of 10−3M phloroglucinol (PG) using either liquid or agar‐solidified media. The use of a liquid medium did however reduce rates of uptake over a 10‐day period of auxin application. The distribution of labelled IAA between the 1‐cm base and the shoot remainder was not affected by PG.Exposure of shoots of the difficult‐to‐root M.9 and the easy‐to‐root M.26, to 2.8 × 10−5M IAA containing [2‐14C] IAA revealed no positive correlation between the amount of label taken up by the 1‐cm base and rooting performance. M.9 bases absorbed almost twice as much label as M.26 after 9 days but had produced only one‐third as many roots. Measurements of label distribution between the 1‐cm base and the shoot remainder showed that less than 10% of the label moved to the shoot remainder over a 6‐day period of auxin application. Dose‐response curves of IAA and rooting over the range 1 × 10−5M and 3 × 10−3M showed that root number in M.9 was at an optimum at 1 × 10−3M IAA after 6 days whilst M.26 required only 1 × 10−4M for a similar response. These data support the hypothesis that differences in rooting of the two rootstocks reflect differences in the endogenous metabolism of exogenous IAA and not differences in its rates of uptake or distribution in the shoots.
Effects of agar brand and concentration on the tissue culture medium
Authors: Debergh P. C. 
Published: April 2006

In tissue‐cultured Cynara scolymus L. (globe artichoke) vitrification (hyperhydric transformation) can only be overcome by increasing the concentration of agar. However, with increasing concentrations of Difco Bacto agar (8–15 g/I) the availability of labelled kinetin is decreased. There is some evidence for postulating that cytokinins under inductive conditions of low agar concentration or high matrix potential are evocators of vitrification.Both the brand and concentration of agar also affect the chemical and physical characteristics of a culture medium.Impurities introduced with the agar are responsible for significant differences in the concentration of an element in comparable media with different levels of agar, and are easily detected by conductance.Penetrometer measurements also show large ranges in solidity of media with increasing concentrations, not only within the type of agar, but also for the same concentration within different brands.
Highly purified intact chloroplasts from mesophyll protoplasts of the C4 plant Digitaria sanguinalis. Inhibition of phosphoglycerate reduction by orthophosphate and by phosphoenolpyruvate
Authors: Hallberg Mats , Larsson Christer 
Published: April 2006

Purified mesophyll protoplasts from the C4 plant Digitaria sanguinalis were used to prepare intact mesophyll chloroplasts with low cytoplasmic contamination. The procedure involved breakage of protoplasts, differential centrifugation, partition in a dextran‐polyethylene glycol two‐phase system, and Percoll density gradient centrifugation. The final chloroplast preparation contained about 80% intact chloroplasts with a phosphoenolpyruvate carboxylase contamination of 0.2–1% of the original protoplast activity, corresponding to 1–6 μmol 14CO2 fixed/mg Chl h. The purified chloroplasts showed substrate‐dependent oxygen evolution in the range of 40–150 μmol substrate reduced/mg Chl h, with phosphoglycerate or oxaloacetate as substrate. Both reactions were stimulated 1.5 fold by pyruvate and further by addition of the other substrate. These measurements indicated that phosphoglycerate reduction was limited by substrate transport across the chloroplast envelope. Without added substrate, the chloroplasts consumed oxygen via pseudo‐cyclic electron transport in the light. Also this reaction was stimulated by pyruvate.Phosphoglycerate‐dependent oxygen evolution was inhibited by Pi and by phosphoenolpyruvate to about the same extent with purified chloroplasts, but only by Pi with protoplast extracts. This suggests that phosphoglycerate, Pi and phosphoenolpyruvate share a common carrier, similar to the Pi‐translocator in C3 chloroplasts, and that the lack of inhibition obtained with phosphoenolpyruvate and unpurified chloroplasts is artefactual, possibly due to oxaloacetate formation from added phosphoenolpyruvate and concomitant stimulation of oxygen evolution by oxaloacetate reduction. Furthermore, the results suggest that phosphoenolpyruvate is transported with a Km similar to that of Pi in C4 mesophyll chloroplasts.
Kinetics of the reactivation of the Hill reaction in CO2‐depleted chloroplasts by addition of bicarbonate in the absence and in the presence of herbicides
Authors: Snel Jan E. H. , van Rensen Jack J. S. 
Published: April 2006

In isolated broken chloroplasts photosynthetic electron transport requires the presence of CO2 and/or bicarbonate. This bicarbonate effect on electron flow was measured in a medium containing 100 mM sodium formate. In this medium a dark incubation time with bicarbonate is required for the reactivation of the Hill reaction. We have measured the kinetics of the reactivation of electron flow by varying the dark incubation of CO2‐depIeted pea (Pisum sativum L., cv. Rondo) chloroplasts with bicarbonate. The half‐time of this reactivation appears to be 25 s when 2 mM bicarbonate is added.The dinitrophenol herbicide, i‐dinoseb, is shown to be a competitive inhibitor of the bicarbonate dependent Hill reaction with an inhibitor constant (Ki) of 31 nM. In the presence of 100 nM i‐dinoseb or 100 nM DCMU the half‐time of the reactivation by 2 mM bicarbonate appears to increase to about 58 s. We provide an explanation for these phenomena by analyzing the bicarbonate‐thylakoid interaction on the basis of a simple reaction scheme. The binding of bicarbonate to the thylakoids appears to be a second order reaction with pseudo‐first order kinetics. According to our analysis, any inhibitor, which is competitive with respect to the bicarbonate stimulation of the Hill reaction, should increase the half‐time of the reactivation of the Hill reaction.
α‐Aminoisabutyric acid, propyl gallate and cobalt ion and the mode of inhibition of ethylene production by cotyledonary segments of cocklebur seeds
Authors: Satoh Shigeru , Esashi Yohji 
Published: April 2006

Using cotyledonary segments of cocklebur (Xanthium pennsylvanicum Wallr.) seeds, the inhibitory effect of α‐aminoisobutyric acid (AIB) on ethylene production was compared with that of propyl gallate and CoCl2. Of these inhibitors only AIB was effective in causing the accumulation of endogenous free 1‐aminocyclopropane‐l‐carboxylic acid (ACC) in the tissue. The degree of inhibition of ethylene production by AIB decreased markedly with increasing concentrations of pre‐loaded ACC, while the inhibition by propyl gallate and CoCl2 changed little. Kinetic analysis showed that AIB competitively inhibited the conversion of pre‐loaded ACC to ethylene, but propyl gallate and CoCl2 did not. Short‐chain organic acids and analogues of AIB, such as acetic, propionic, butyric and cyclopropanecarboxylic acids, did not inhibit ethylene production by the segments. Thus, additional support for the competitive mode of inhibitory action of AIB on the conversion of free ACC to ethylene was provided.A conjugated hydrolysable ACC was found to be present in abundance in cotyledons of this seed. However, its content in the tissue was hardly affected by treatment with the three inhibitors and by administration of exogenous ACC, suggesting that the conjugated ACC was not directly involved in ethylene production.
Lipid composition in leaves of cucumber genotypes as affected by different temperature regimes and grafting
Authors: Horváth I. , Vigh L. , van Hasselt Ph. R. , Woltjes J. , Kuiper P. J. C. 
Published: April 2006

The lipid composition of leaves has been investigated in different genotypes of cucumber (Cucumis sativus L.), which differ in temperature requirement for cultivation. In addition the effects of hardening by low but non‐chilling temperature, soil heating and grafting (on the chilling‐resistant C. ficifolia L.) on lipid composition have been studied. Content and composition of phospholipids and sterols were determined as well as phospholipid/sterol ratio, and fatty acid composition of total lipids and the different phospholipids.The effects of genetic differentiation and of the various culture treatments on lipid composition of the leaves were very different. Genetic differentiation was evident as higher levels of Iinolenic acid in several phospholipids in the more cold‐tolerant cultivars. Hardening the plants by low temperature resulted in a higher phospholipid level (especially phosphatidyl choline), more unsaturated phospholipid, and lowering of the sterol/phiospholipid ratio, all properties which may contribute to a higher membrane fluidity and lower growth temperature limit. Soil healing reduced the phospholipid level of the leaves slightly, and a higher content of 3‐trans‐hexadece‐noic acid in phosphatidyl glycerol was observed. Grafting cucumber on the cold‐resistant rootstock of C. ficifolia also raised the level of trans‐hexadecenoic acid in phosphatidyl glycerol. The role of this fatty acid in the functioning of the chloroplast is discussed.
Root growth and gravireaction: Influence of the shoot
Authors: Beffa Roland , Pilet Paul‐Emile 
Published: April 2006

The kinetics of root gravicurvature of intact maize (Zea mays L., cv. LG 11) seedlings can be separated into two steps. From 0 to 2 h, a rapid downward bending, enhanced by light, occurred. During the next 4 h (2 to 6 h) no further curvature appeared in the dark, whereas it continued in light. The final root gravicurvature was greater for light‐than dark‐treated seedlings. Growth was particulary inhibited during the first 2 h.When intact seedlings were placed horizontally and returned to the dark after a 4 h light pretreatment in a vertical position, only the second step (2 to 6 h) was changed. A negative gravitropism, associated with a stimulation of growth, appeared. Thus, when gravireaction took place in darkness, the final root gravicurvature was similar for the light‐pretreated intact seedlings and the dark control. Using apical root segments, this phase of negative gravicurvature was not observed although the stimulation of gravicurvature of light‐pretreated roots remained. Similar experiments were performed with seedlings having coleoptile or endosperm removed, after intact seedlings had been exposed to a light pretreatment, and gravireaction took place in the dark. Results indicated that these two organs could play an essential role in the development of gravicurvature and in the regulation of the light effects, respectively.
The physiological basis of seed dormancy in Avena fatua. II. On the involvement of alternative respiration in the stimulation of germination by sodium azide
Authors: Upadhyaya Mahesh K. , Naylor James ML , Simpson Graham M. 
Published: April 2006

Sodium azide, an inhibitor of cytochrome oxidase, has been shown to stimulate germination in several genetically pure lines of wild oats (Avena fatua L.). This effect of azide is completely inhibited by salicylhydroxamic acid, an inhibitor of alternative respiration. Sodium azide treatment, which induced germination, stimulated oxygen uptake by as much as 200 to 400%. The dose‐response curves for the stimulation of germination and of oxygen uptake by azide were very similar. The stimulation of oxygen uptake was completely inhibited by salicylhydroxamic acid and was not due to lipoxygenase activity. Thus, stimulation of salicylhydroxamic acid‐sensitive oxygen uptake (alternative respiration) is associated with and is necessary for the stimulation of germination in the presence of azide. However, it remains to be shown whether the induction of alternative respiration by azide is the direct cause of stimulation of germination.In the Montana 73, unlike other pure lines investigated, azide stimulated alternative respiration, but not germination. The lack of germination response in this line is considered to be due to an additional metabolic block in the processes leading to germination.
Structural modifications and δ‐aminolevulinate dehydratase synthesis/transport in cotyledons of far‐red irradiated radish
Authors: Brangeon Judy , Balangé Alain P. , Forchioni Arlette 
Published: April 2006

δ‐Aminolevulinate dehydratase (ALAD) is synthesized in the cytoplasm and subsequently transported into the plastids in cotyledons of tar‐red irradiated radish (Raphanus sativus L. ev. Longue Rave Saumonée). The intra‐cellular localization of ALAD activity was determined under far‐red irradiation and darkness. After 60 h far‐red, ALAD was essentially eytoplasmic; 96 h far‐red corresponded to a peak in total ALAD activity, as well as the onset of massive ALAD transfer into the plastids, and after 120 h a maximum enzyme activity was located in the plastids. Under dark conditions, essentially no transport of ALAD was noted.Structural modifications of plastid‐eytoplasmic relationships were analysed at the three developmental periods under dark and far‐red conditions. 60 h far‐red induced a change in the “elasticity” of plastid envelopes leading to envelope proliferations and amoeboid shaped plastids. After 96 h tar‐red, membrane proliferations formed a highly evaginated plastid periphery. It is suggested that these membranes form a transport network between the two compartments. Also at 96 h, numerous vesicles, which appear to originate from the endoplasmic reticulum (ER), surround the plastid profile. On the basis of the structural observations, it is proposed that ALAD would be synthesized within the ER and transported toward the plastids via ER extensions, which take the form of smooth vesicles. Our hypothesis is that the transition vesicles and proliferations of the outer envelope membrane undergo a fusion process emptying the content of the vesicle into the intermembrane space of the envelope.
Acyltransferase capacity of membranes from cotyledons of germinating peas
Authors: Macey M. J. K. 
Published: April 2006

The incorporation of 1‐[14C]‐palmitate into the lipids of microsomal and mitochondrial membranes from peas (Pisum sativum L., var. Massey Gem) and the relative effects of ATP and coenzyme A(CoA) on the process have been examined. Both mitochondrial and microsomal pellets possessed acyltransferase capacity, which responded similarly to additions of ATP and CoA. Incorporation of 1‐[14C]‐palmitate into phospholipid was promoted by ATP alone, but incorporation into triacylglycerols was not. The addition of CoA alone did not promote incorporation. The addition of CoA and ATP further promoted incorporation into phospholipids and also stimulated incorporation into triacylglycerol. It was concluded that some CoA must be membrane‐bound and available for phospholipid but not for triacylglycerol synthesis. Phospholipase A, treatment of microsomal and mitochondrial phospholipids, previously labelled with 1‐[14C]‐palmitate in the presence of ATP and coenzyme A, showed that incorporation occurred only into the 2‐position of phosphatidyl choline and phosphatidyl ethanolamine.There was enough lyso‐phosphatidyl choline in the phospholipids of microcomal membranes (obtained from a 100 000 g pellet) to account for the observed incorporations of palmitate. Using microsomal membranes whose fatty acyl groups were pre‐labelled by incubation of tissue with 1‐[14C]‐acetate, no evidence of acyl exchange was found during subsequent incubations with unlabelled palmitate. Similar observations were made using oleate instead of palmitate. It was concluded that acyl‐CoA: 1‐acylglycerophosphocholine o‐acyltransferase (E.C. 2.3.1.23) was responsible for the observed acyl transfer to phosphatidyl choline.Sucrose gradient analysis of whole homogenates and of the 10 000 g pellet showed that both mitochondrial and rough endoplasmic reticulum possessed acyltransferase capacity, with the bulk of this residing in the mitochondria. The possible significance of this widely distributed membrane activity is briefly discussed.