Stimulation of ethylene production in apple tissue slices by methionine

Methionine can induce more than a 100% increase in ethylene production by apple tissue slices. The increased amount of ethylene derives from carbons 3 and 4 of methionine. Only post-climacteric fruit tissues are stimulated by methionine, and stimulation is optimum after 8 months' storage. Copper chelators such as sodium diethyl dithiocarbamate and cuprizone very markedly inhibit ethylene production by tissue slices. Carbon monoxide does not effect ethylene production by the slices. These data suggest that the mechanism for the conversion of methionine to ethylene, in apple tissues, is similar to the previously described model system for producing ethylene from methionine and reduced copper. Therefore, it is suggested that one of the ethylene-forming systems in tissues derives from methionine and proceeds to ethylene via a copper enzyme system which may be a peroxidase.     

Metabolism in plant storage tissue slices

The tissue of resting plant storage organs such as carrots, red beets, sugar beets or potato tubers can be activated by slicing into thin disks and incubation of these fragments in a moist atmosphere for different periods of time (“aging”). Activation comprises the turning-on of various genes with subsequent synthesis of transfer-, ribosomal and messenger RNAs and their transport into the cytoplasm. The immediate consequence of all these primary reactions is a vigorous synthesis of various enzymes and structural proteins which enable the cell to greatly enhanced metabolic activities. Thus, degradation of storage polymers and the procession of the resulting products through glycolysis, the pentose phosphate shunt and the shikimateprephenate-pathway and cellulose biosynthesis occur. Deinhibition of the tricarboxylic acid cycle opens the flow of metabolites into fatty acid, phospholipid and steroid biosynthesis, simultaneously providing the respiratory chain with electrons. In spite of functional modifications within the electron transport chain, the enhanced respiration of tissue slices serves as an energy source for the various energy-dependent reactions of the cell such as syntheses and the uptake of solutes. All of these activities accompany a concomitant dedifferentiation process and ultimately lead to renewed redifferentiation of the tissue slice cell.     

The accumulation and storage of nitrogen by herbaceous plants

Abstract Accumulation of nitrogen (N) by plants in response to N supply outstripping demand is contrasted with storage of N, which implies that N in one tissue can be reused for the growth or maintenance of another. Storage can, therefore, occur in N-deficient plants; accumulation can not. The consequence of accumulation and storage of N is considered, particularly in relation to the reproductive growth of annual plants, which can often use a great deal of stored N. Nitrate and proteins are the forms of N most often stored in vegetative tissues and, quantitatively, ribulose 1,5-bisphosphate carboxylase/oxygenase is often the most important protein store. While storing nitrate will be less costly to the plant in terms of energy, protein stores offer several possible advantages. These advantages are (i) maximizing the potential for carbon assimilation, (ii) avoiding problems with the regulation of leaf turgor and (iii) allowing the reduction on nitrate to occur in the young, fully illuminated leaf.     

Studies on the utilization of methionine sulfoxide and methionine sulfone by rumen microorganisms in vitro

Summary.  An in vitro experiment was conducted to test the ability of mixed rumen bacteria (B), protozoa (P), and their mixture (BP) to utilize the oxidized forms of methionine (Met) e.g., methionine sulfoxide (MSO), methionine sulfone (MSO₂). Rumen contents were collected from fistulated goats to prepare the microbial suspensions and were anaerobically incubated at 39°C for 12 h with or without MSO (1 mM) or MSO₂ (1 mM) as a substrate. Met and other related compounds produced in both the supernatants and hydrolyzates of the incubation were analyzed by HPLC. During 6- and 12-h incubation periods, MSO disappeared by 28.3 and 42.0%, 0.0 and 0.0%, and 40.6 and 62.4% in B, P, and BP suspensions, respectively. Rumen bacteria and the mixture of rumen bacteria and protozoa were capable to reduce MSO to Met, and the production of Met from MSO in BP (156.6 and 196.1 μmol/g MN) was about 17.3 and 14.1% higher than that in B alone (133.5 and 171.9 μmol/g MN) during 6- and 12-h incubations, respectively. On the other hand, mixed rumen protozoa were unable to utilize MSO. Other metabolites produced from MSO were found to be MSO₂ and 2-aminobutyric acid (2AB) in B and BP. MSO₂ as a substrate remained without diminution in all-microbial suspensions. It was concluded that B, P, and BP cannot utilize MSO₂; but MSO can be utilized by B and BP for producing Met. Received December 28, 2001 Accepted May 21, 2002 Published online October 14, 2002 Acknowledgements The authors are extremely grateful to Professor H. Ogawa, the University of Tokyo, Japan and Dr. Takashi Hasegawa, Miyazaki University, Japan for inserting permanent rumen fistulae in goats. We would like to thank MONBUSHO for the award of a research scholarship to Mamun M. Or-Rashid since 1996–2001. Authors' address: Shaila Wadud, Laboratory of Animal Nutrition and Biochemistry, Division of Animal Science, Miyazaki University, Miyazaki 889-2192, Japan, Fax. +81-985-58-7201, E-mail: rafatkun@hotmail.com     

Formation of methanethiol from methionine by leaf tissue

Leaf discs, but not detached leaves, exposed to L-methionine or S-methyl-L-cysteine emitted a volatile sulphur compound identified as methanethiol by different trapping systems and by GC. Methanethiol emission was analyzed using pumpkin (Cucurbita pepo) leaf discs. Emission was observed in darkness or light, however methanethiol emission was greately stimulated by light. Light-dependent emission started after a lag-time of 5–6 hr with an emission peak after 36–40 hr. Maximum rates obtained were in the range of 200 pmol methanethiol/min/cm² leaf area. After a period of 42 hr about 60–80% of total methionine sulphur added was released as methanethiol. Addition of chloramphenicol did not alter the induction period nor the maximum emission rate of methanethiol in response to L-methionine. Emission was also observed in response to S-methyl-L-cysteine; however, the shorter lag-period for methanethiol formation suggests metabolism via a different enzyme system. In a cell-free system of pumpkin leaves methanethiol formation occured in response to L-methionine. Feeding experiments with L-[³⁵S]methionine to leaf discs showed that more than 80% of methanethiol emitted was derived from the labelled methionine fed. These findings suggest that plants have the capacity to degrade L-methionine to methanethiol. Whole leaves fed L-methionine by the petiole system do not emit methanethiol, but this compound is formed and transported into the feeding solution. Thus, methanethiol is also produced by the intact leaf, but, in contrast to sulphide, is not released into the atmosphere. It is suggested that translocation of methanethiol may function as a signal for the regulation of sulphate uptake.     

The utilization of organic nitrogen compounds as sole nitrogen source by some freshwater phytoplankters

Seven organic compounds containing nitrogen were tested as potential sources of nitrogen for five different species of freshwater algae. The chlorococcal green algae Selenastrum and Ankistrodesmus were the most versatile with regard to nitrogen sources; the diatom Cyclotella also grew well upon some organic nitrogen compounds. The desmid Arthrodesmus grew fast only on urea, while Cryptomonas did not grow well upon any of the organic compounds tested.
More information is needed before the potential importance of organic nitrogen sources for freshwater phytoplankton can be assessed.     

Comparison of cold storage and perfusion of dog livers on function of tissue slices

We compared how two methods of hypothermic preservation affect physiological functions of tissue slices of dog liver. Livers were preserved by either (i) cold storage (CS) in Collins' solution or (ii) continuous perfusion (P) with a perfusate, containing hydroxyethyl starch, sodium gluconate, adenosine, and potassium phosphate, recently developed in our laboratory. Livers were cold stored for 6 to 8, 24, or 48 hr, and perfused for 24 or 72 hr. Tissue slices of preserved livers were incubated at 30 degrees C and analyzed for volume control, electrolyte-pump activity (K and Na), and adenine nucleotide concentration. Also, mitochondria were isolated after preservation to quantify respiratory activity. Slice functions of livers preserved for short periods (6 to 8 hr by CS and 24 hr by P) were similar to those for control livers. After normothermic incubation, the mean (+/- SD) water content of tissue (expressed per unit dry mass of tissue) was 2.3 +/- 0.3 kg/kg for control, 2.6 +/- 0.4 kg/kg for 6- to 8-hr CS, and 2.5 +/- 0.5 kg/kg for 24-hr P. Longer periods of preservation resulted in cell swelling, and water content was 3.3 +/- 0.4 kg/kg for 24- to 48-hr CS and 2.8 +/- 0.3 kg/kg for 72-hr P. The mean (+/- SD) K/Na ratio was nearly normal for livers preserved for short periods: 3.7 +/- 0.5 for control, 4.1 +/- 0.2 for 6- to 8-hr CS, and 3.3 +/- 0.4 for 24-hr P.(ABSTRACT TRUNCATED AT 250 WORDS)