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Lemna minor fronds transferred to a sterile culture medium containing 50% (v/v) deuterium oxide ((2)H2O) rapidly undergo a loss of soluble protein with a corresponding increase in free amino acids. The loss of protein is due to two factors: (i) the inhibition of protein synthesis for 4 h followed by a slower rate of synthesis than normal, (ii) a rapid 9-10 fold increase in protein degradation. In plants grown for longer periods (3-6 days) in 50% (2)H2O medium, protein synthesis is inhibited by 20% and the rate constant of degradation is 2-3 times that measured in fronds growing in normal (H2O containing) complete medium. The initial loss of protein is not due to the breakdown of any specific protein fraction. Investigation of several enzymes indicates that all proteins are catabolised in response to (2)H2O treatment. The implications of these results with regard to the interpretation of density-labelling experiments are discussed.

Homogenates of etiolated wheat leaves contain increased levels of acidic gibberellin (GA)-like substances following treatment with red light. Differential centrifugation of homogenates indicates that the response is confined to the 1000 g (or plastid) fraction. Irradiation of suspensions of intact etioplasts also increases the level of extractable GA-like activity. Phytochrome can be detected spectrophotometrically in preparations of etioplasts. The response in etioplasts can be inhibited by chloramphenicol, but not by cycloheximide, and partially by Amo 1618. The GA-like substances produced in etioplasts seem capable of passing into the surrounding medium within 20 min.

Disruption of preparations of intact etioplasts isolated from wheat (Triticum aestivum L.) leaves in the dark leads to an increase in the level of extractable gibberellin-like (GA-like) activity. Irradiation of disrupted preparations with red light causes an alteration in the Rf of part of the GA-like activity. A study of sub-etioplast fractions prepared by gradient centrifugation indicates that the phytochrome and the GA-like substances are associated principally with the etioplast envelope.

A new terminology for intermediates observed in the phototransformation of phytochrome (P) is proposed. At 0°C freeze dried tissue of Pisum sativum seedlings containing P in the red absorbing form (Pr) does not undergo complete photoconversion to the far red absorbing form (Pfr) but forms intermediates which revert to Pr in darkness. Use of low temperature techniques and comparison with reactions in fresh tissue allow identification of the intermediates with those observed earlier. They consist of a mixture of the first photoproduct, lumi-R and its dark relaxation product, meta-Ra. Similarly, Pfr forms a mixture of its first photoproduct, lumi-F and its dark relaxation product, meta-Fa. The dark reversion of lumi-R to Pr and of lumi-F to Pfr have also been observed in freeze-dried tissue. Reactions occurring in this material at 0°C are proposed to be essentially restricted to photoreactions of the chromophore and relaxations of the products. Before complete phototransformation of Pr to Pfr and vice versa is possible an aqueous matrix is required for protein/chromophore conformational relaxations to occur.

The rapid increase in acidic gibberellin-like (GA-like) activity occurring in etiolated wheat (Triticum aestivum L.); leaf tissue in response to red light is phytochrome controlled. The production of some of the GA-like activity appears to possess a similar escapetime from far-red reversibility to leaf unrolling and is sensitive to Amo 1618. Application of these GA-like substances to leaf sections maintained in the dark causes unrolling. Increased GA-like activity can also be detected in non-irradiated portions of partly irradiated leaves.

Transfer of Lemna minor fronds to culture medium containing 50% (v/v) deuterium oxide induces a large increase in the rate of protein breakdown, which is not due to an increase in the activity of acidic or neutral proteolytic enzymes or peptidases. Biochemical and ultrastructural evidence indicates that deuterium oxide affects the properties of certain membranes, particularly the tonoplast, and allows vacuolar proteolytic enzymes to pass into the cytoplasm and cause the increased protein breakdown.

CoASH, Mg(2+), ATP and (-)-carnitine were found to be essential for the production of palmitoylcarnitine from palmitate by purified barley etio-chloroplasts. It was concluded that long-chain acyl CoA synthetase (palmitoyl CoA synthetase, EC 6.2.1.3) and carnitine long-chain acyl-transferase (carnitine palmitoyltransferase, EC 2.3.1.21) activity were present in the etio-chloroplasts. It is suggested that the long-chain acylcarnitine formed may move more easily through membrane barriers than the long-chain acyl CoA compound. Also or alternatively this enzyme may spare CoA by transferring long-chain acyl groups from long-chain acyl CoA to carnitine.

Irradiation with red light causes a phytochrome dependent increase in the extractable amount of acidic gibberellin-like activity in plastid preparations from etiolated leaves of Triticum aestivum L.

Etio-chloroplasts of barley, purified on sucrose density gradients were shown to possess carnitine long-chain acyltransferase (carnitine palmitoyltransferase, EC 2.3.1.21) activity and carnitine short-chain acyltransferase (carnitine acetyltransferase EC 2.3.1.7) activity. These enzymes may play a role in the transport of acyl groups as acylcarnitines through the membrane barrier of barley etio-chloroplasts and also 'or alternatively' may spare CoA by transferring short- and long-chain acyl groups from short-and long-chain acyl CoA to carnitine.