Senescence of attached leaves: Regulation by developing pods

Analysis of total nitrogen, chlorophyll content, ribulose-1,5-bisphosphate carboxylase/oxygenase activity and net photosynthesis rate was carried out on the leaves that support the developing pods in pigeon pea [ Cajanus cajan (L.) Millsp. cv. Prabhat] at several stages during pod filling. A continuous loss in all the above-mentioned parameters was observed during the course of pod development. When no pods were allowed to develop by continuous flower removal treatment, there was a considerable delay in loss of all these metabolic parameters. Excision of pods after their mid-development resulted not only in no further loss, but also in a significant recovery both of total nitrogen and of other investigated characteristics.     

Phosphorylation of chloroplast membrane proteins partially protects against photoinhibition

Thylakoids isolated from peas (Pisum sativum cv. Kelvedon Wonder) and phosphorylated by incubation with ATP have been compared with non-phosphorylated thylakoids in their sensitivity to photoinhibition by exposure to illumination in vitro. Assays of the kinetics of fluorescence induction at 20° C and the fluorescence emission spectra at-196° C indicate a proportionally larger decrease in fluorescence as a result of photoinhibitory treatment of non-phosphorylated compared with phosphorylated thylakoids. It is concluded that protein phosphorylation can afford partial protection to thylakoids exposed to photoinhibitory conditions.Abbreviations and symbols DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - F ₀ Level of chlorophyll fluorescence when photosystem 2 traps are open - F _m Level of chlorphyll fluorescence when photosystem 2 traps are closed - P Maximum level of fluorescence reached in the absence of DCMU - PSI (II) photosystem I(II)     

Simultaneous and independent effects of abscisic acid on stomata and the photosynthetic apparatus in whole leaves

(±)-Abscisic acid (ABA) at 10^-5 M was added to the transpiration stream of leaves of 16 species (C₃ and C₄, monocotyledons and dicotyledons). Stomatal responses followed one of three patterns: i) stomata that were wide and insensitive to CO₂ initially, closed partially and became sensitive to CO₂; ii) for stomata that were sensitive to CO₂ before the application of ABA, the range of highest sensitivity to CO₂ shifted from high to low intercellular partial pressures of CO₂, for instance in leaves of Zea mays from 170–350 to 70–140 bar; iii) when stomata responded strongly to ABA, their conductance was reduced to a small fraction of the initial conductance, and sensitivity to CO₂ was lost. The photosynthetic apparatus was affected by applications of ABA to various degrees, from no response at all (in agreement with several previous reports on the absence of effects of ABA on photosynthesis) through a temporary decrease of its activity to a lasting reduction. Saturation curves of photosynthesis with respect to the partial pressure of CO₂ in the intercellular spaces indicated that application of ABA could produce three phenomena: i) a reduction of the initial slope of the saturation curve (which indicates a diminished carboxylation efficiency); ii) a reduction of the level of the CO₂-saturated rate of assimilation (which indicates a reduction of the ribulose-1,5-bisphosphate regeneration capacity); and iii) an increase of the CO₂ compensation point. Photosynthesis of isolated mesophyll cells was not affected by ABA treatments. Responses of the stomatal and photosynthetic apparatus were usually synchronous and often proportional to each other, with the result that the partial pressure of CO₂ in the intercellular spaces frequently remained constant in spite of large changes in conductance and assimilation rate. Guard cells and the photosynthetic apparatus were able to recover from effects of ABA applications while the ABA supply continued. Recovery was usually partial, in the case of the photosynthetic apparatus occasionally complete. Abscisic acid did not cause stomatal closure or decreases in the rate of photosynthesis when it was applied during a phase of stomatal opening and induction of photosynthesis that followed a transition from darkness to light.Abbreviations and symbols A rate of CO₂ assimilation - ABA (±)-abscisic acid - c _a partial pressure of CO₂ in the ambient air or in the gas supplied to the leaf chambers - c _i partial pressure of CO₂ in the intercellular spaces of a leaf - e _a partial pressure of H₂O in the air - g conductance for water vapor - J quantum flux - T ₁ leaf temperature     

Regulation of photosynthetic carbon assimilation at the cellular level: a review

In green leaves and a number of algae, photosynthetically derived carbon is ultimately converted into two carbohydrate end-products, sucrose and starch. Drainage of carbon from the Calvin cycle proceeds via triose phosphate, fructose 6-phosphate and glycollate. Gluconeogenesis in photosynthetic cells is controlled by light, inorganic phosphate and phosphorylated sugars. Light stimulates the production of dihydroxyacetone phosphate, the initial substrate for sucrose and starch synthesis, and inhibits the degradative pathways in the chloroplast. Phosphate inactivates reactions of synthesis and activates reactions of degradation. Among the phosphorylated sugars a special role is allocated to fructose 2,6-bisphosphate, which is present in the cytoplasm at very low concentrations and inhibits sucrose synthesis directly by inactivating pyrophosphatedependent phosphofructokinase. The synthesis of sucrose plays a central role in the partitioning of photosynthetic carbon. The cytoplasmic enzymes, fructose bisphosphate phosphatase and sucrose phosphate synthase are likely key points of regulation. The regulation is carried out by several effector metabolites. Fructose 2,6-bisphosphate is likely to be the main coordinator of the rate of sucrose synthesis, hence of photosynthetic carbon partitioning between sucrose and starch.Paper presented at the FESP meeting (Strasbourg, 1984)     

Influence of structural and physical properties of the thylakoid membrane on QA - oxidation

Using isolated pea thylakoids, the relative rate of Q_A ^- oxidation has been estimated under various conditions, from the restoration of the induction curves following a dark period and from light 1-induced changes in modulated chlorophyll fluorescence excited by light 2.Alterations of _QinfA ^sup– oxidation rates were observed under conditions which affected the degree of thylakoid stacking, the lipid fluidity and the integrity of the membranes. The results are discussed in terms of the interactions between Q_A ^- and the plastoquinone pool with particular emphasis on lateral diffusion.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - EDTA Ethylenediaminetetracetate - Hepes N-2-hydroxyethyl piperazine-N-2-ethanesulphonic acid - NADP nicotinamide adenine dinucleotide phosphate     

Consequences of iron deficiency on photosynthetic and respiratory electron transport in blue-green algae

Growth of Aphanocapsa in low iron media resulted in a decrease of the endogenous iron pool. Below a critical concentration photosynthetic electron transfer was specifically depressed. This was caused by a strong inhibition of the synthesis of cytochromes b-559 of PSII, cytochromes b-563, f-557, and the Rieske Fe-S center of the cytochrome complex and especially the Fe-S centers of PSI. The influence of iron limitation on respiration and chlorphyll formation was negligible.Paper presented at the FESPP meeting (Strasbourg, 1984)     

Studies on 9-amino-6-chloro-2-methoxy acridine fluorescence quenching and enhancement in relation to energy transduction in spheroplasts and intact cells of the cyanobacterium Plectonema boryanum

The fluorescent probe 9-amino-6-chloro-2-methoxy acridine was used to study the energy transduction in the thylakoid and cell membranes of the cyanobacterium Plectonema boryanum. Apart from light-driven electron transfer, the dark endogenous respiration also leads to energization resulting in an ACMA fluorescence response, that is sensitive to the electron flow inhibitor 2, 5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, to the energy transfer inhibitors dicyclohexylcarbodiimide and venturicidine and to the uncoupler 5-chloro-3-t-butyl-2-chloro-4-nitrosalicylanilide.In spheroplasts, in which the cell membranes have lost their capacity to maintain a proton gradient, the respiration-and light-induced ACMA fluorescence changes (quenching) are similar to those in chloroplasts. In intact cells a combination of reversible quenching and enhancement of ACMA fluorescence was found. This dualistic behaviour is supposedly caused by an opposite orientation of the thylakoid and cell membranes. ACMA quenching at the level of the thylakoids was obtained either by respiratory or photosynthetic electron transfer and gave similar responses to those obtained in the spheroplasts. The slower ACMA fluorescence enhancement, only observed in cells with intact cell membranes, also evoked by both respiration and light-induced energization is sensitive to the compounds mentioned above and in addition to KCN.Our results support the view [8] that dark oxidation of substrates by O₂ proceeds via the thylakoid membrane and terminates at a CN^- sensitive oxidase located in the cell membrane which requires the involvement of a mobile cytoplasmic redox mediator.Abbreviations ACMA 9-amino-6-chloro-2-methoxy acridine - chl a chlorophyll a - DBMIB 2, 5-dibromo-3-methyl-6-isopropyl-p-benzoquinone - DCCD dicyclohexylcarbodiimide - DNP dinitrophenol - DNP-INT dinitrophenyl ether of 2-iodo-4-nitrothymol - FCCP carbonylcyanide-p-trifluoro-methoxy phenylhydrazone - S-13 5-chloro-3-t-butyl-2-chloro-4-nitrosalicylanilide - tricine N-2 (2-Hydroxy-1, 1-bis (hydroxymethyl) ethyl)-glycine - Tris Tris (hydroxymethyl) amino methane     

Morphometry of muscle fibre types in the carp (Cyprinus carpio L.)

Summary Ultrastructural parameters of muscle fibre types of the carp (Cyprinus carpio L.) were measured and compared with their contractile properties. In red fibres, which are slower than pink fibres, the relative length of the junction between the T system and the sarcoplasmic reticulum (T-SR junction) is smaller and the Z lines are thicker than in pink fibres. Pink fibres have a smaller relative length of T-SR junction than white fibres from the axial muscles. The two types of red fibres present in carp muscle also differ in their relative lengths of T-SR junction. Significant differences in the relative areas of the SR were not found.The relative volume of myofibrils in red fibres is two-thirds that in pink fibres, a difference that is not reflected in the maximal isometric tetanic tensions of these types. Red fibres, which are less easily fatigued than pink fibres, have larger relative volumes of subsarcolemmal and intermyofibrillar mitochondria. Small pink fibres have a larger relative volume of subsarcolemmal mitochondria than large pink fibres, but have a similar relative volume of intermyofibrillar mitochondria. Small and large pink fibres differ in the relative volumes of their membrane systems, but have similar relative lengths of T-SR junction.