David A. Walker

Photosynthesis and phosphate: a cellular affair?

Abstract New data indicate that supply of orthophosphate to the chloroplast can, in some circumstances, become the process that limits photosynthesis in vivo . Phosphate availability seems to be finely regulated by the interaction of chloroplast, cytosol and vacuole.

PYRUVATE CARBOXYLATION AND PLANT METABOLISM

The discovery and elucidation of 8-carboxylation of pyruvate 8-Carboxylases of plants . . . . . . ( I ) Oxaloacetic decarboxylase . . . . . (2) Malic enzyme . . . . . . (3) Phosphoenolpyruvate carboxylase . , . . (4) Phosphoenolpyruvate carboxykinase . . . The role of pyruvate carboxylation in plant metabolism . (I) Respiration . . . . . . . . (2) Photosynthesis . . . . . . . (3) Crassulacean acid metabolism . . . . . (4) Fat metabolism . . . . . . . (5) Carbon dioxide fixation by roots Conclusions . . . . . . . . . Summary . . . . . . . . . References . . . . . . . . . Addendum . . . . . . . . . . . . . . 215 . 216 . 220 . 220 . 220 . 223 . 226 . 227 . 227 . 232 . 239 . 244 . 247 . 248 . 248 249 254

[15] Isolation of intact chloroplasts: General principles and criteria of integrity

Publisher Summary This chapter discusses method for the isolation of intact chloroplasts. The intact chloroplast comprises three distinct entities: (1) the thylakoid membranes, which contain the pigments, components of the electron-transport chain, and the coupling factor for photophosphorylation, (2) the stroma, which contains soluble proteins including those necessary for photosynthetic carbon reduction, plus metabolites and other salts, and (3) the envelope membranes, which enclose the organelle and also contain the metabolite translocators. Intact chloroplasts capable of high rates of photosynthesis can be prepared from many species, such as cereals, only by first digesting the leaves with cellulase and pectinase to obtain protoplasts and then rupturing these to release the chloroplasts. The metabolic activity of isolated chloroplasts cannot exceed that of the parent tissue, but in addition, healthy and rapidly growing plants generally have softer leaves that contain smaller amounts of interfering substances (such as phenolics, oxalate, etc.), and thus more readily yield intact chloroplasts with high rates of photosynthesis.

Energetics of photosynthesis in Zea mays. I. Studies of the flash-induced electrochromic shift and fluorescence induction in bundle sheath cells

Bundle sheath strands free of mesophyll contamination were isolated from 3–4-week-old leaves of maize (Zea mays L.). Patterns of electron flow in the preparations were studied in the presence of physiological substrates. Relative electron flow rates were estimated from the flash-induced electrochromic band shift changes (P-518) and cytochrome f turnover. Induction of chlorophyll fluorescence was also measured. Little Photosystem II activity was found to be present, the principal pathway of electron flow being Photosystem I-driven cyclic electron transfer. The latter was activated through reductive poising by NADPH, generated via malate decarboxylation or (less efficiently) from dihydroxyacetone phosphate. The actions of these electron donors and of oxygen, nitrite and methyl viologen as electron acceptors in redox poising the Photosystem I-driven cycle were investigated and are discussed in relation to the regulation of photosynthesis in the bundle sheath.

Energetics of photosynthesis in Zea mays. II. Studies of the flash-induced electrochromic shift and fluorescence induction in mesophyll chloroplasts

Abstract Patterns of electron transfer in isolated mesophyll chloroplasts of maize (Zea mays L.) were studied in the presence of the physiological substrates, oxaloacetate, 3-phosphoglycerate and pyruvate. Flash-induced absorbance changes due to the electrochromic pigment band-shift (P-518) were used to estimate relative electron flow rates through the cyclic and non-cyclic pathways of electron transport. Further information on the redox state of electron carriers and the activity of coupled electron flow was obtained from measurements of fluorescence induction and of actinic-light-induced fluorescence changes. The results demonstrate the importance of correct redox poising for optimal rates of photosynthesis and are discussed in relation to the operation and regulation of photosynthesis in the C4 system.

Tell me where all past years are

This is about a young man who wished to go to sea like his father and finished up, instead, in photosynthesis. It describes how he served his apprenticeship in England and the United States and how he was then lucky enough to find himself in the laboratory of Robin Hill, one of the all-time greats in this field. It discusses some of the events that led, via mitochondria in castor beans and carboxylating enzymes in Crassulacean plants, to the isolation of fully functional chloroplasts and the manner in which the first polarographic measurements of CO2-dependent O2 evolution contributed to present understanding of the movement of molecules through the chloroplast envelope. It describes some of the problems with materials and apparatus which were commonplace forty years ago and reflects on the advantages of working in foreign places and the pleasures of becoming a member of a truly international community.

Inhibition of Tumor Necrosis Factor Alpha (TNFα) Expression and Function In Vitro by Modified Antisense Oligonucleotides

Abstract Antisense oligonucleotides containing C-5 hexynyl/propynyl modified pyrimidines were synthesized using solid phase phosphoramidite chemistry. These modified oligonucleotides were found to have significant inhibitory activity against TNFα production in vitro.