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Control of root growth: effects of carbohydrates on the extension, branching and rate of respiration of different fractions of wheat roots (1993)

Bingham, I. J. ; Stevenson, E. A.

Oxford, UK : Blackwell Publishing Ltd

Physiologia plantarum 88 (1993), S. 0

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ISSN: 1399-3054

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: Rates of extension, numbers of laterals and rates of respiration were measured in different fractions of wheat (Triticum aestivum L. cv. Alexandria) roots following changes in carbohydrate supply. The supply of carbohydrate was varied by selective pruning and exogenously fed sugars. Pruning shoots to a single leaf (leaf-pruning) reduced the rate of O2 uptake by intact roots. Rates were not stimulated by shortterm feeding of sucrose (25 mM), but were stimulated by the uncoupler p-trifluoro-methoxy(carbonylcyanide)phenylhydrazone (FCCP). Feeding glucose to roots of leaf-pruned and non-pruned plants for 16–24 h increased the rate of O2 uptake. It is concluded that respiration is under fine control by adenylates and coarse control by carbohydrate supply, with carbohydrates regulating directly the rate of some energy consuming process(es). These energy consuming processes are located in growing tissue fractions. Feeding glucose to leaf-pruned and non-pruned plants increased rates of O2 uptake in seminal root tips, the zone of developing lateral primordia and mature root sections with elongating laterals, but had no effect on mature sections from which the laterals had been excised. Leaf-pruning reduced the extension rate of seminal axes and first-order laterals when measured over 24 h. Feeding glucose to roots from the time of pruning increased the rate, but did not fully restore it to control values. Pruning roots to a single seminal axis (root-pruning) and feeding glucose to non-pruned plants had no effect on the extension rate of the seminal axis or its laterals over this time period, although rates were increased by root-pruning when measured over 3 days. The number of lateral root primordia was reduced by leaf-pruning and increased by root-pruning and feeding glucose. The results are discussed in terms of the role of carbohydrates in the control of root growth and branching.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1399-3054.1993.tb01772.x

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Regeneration of NADH in a bioreactor using yeast cells immobilized in alginate fiber: I. Method and effect of reactor variables (1993)

Stevenson, E. ; Ibbotson, P. G. ; Spedding, P. L.

New York, NY [u.a.] : Wiley-Blackwell

Biotechnology and Bioengineering 42 (1993), S. 43-49

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ISSN: 0006-3592

Keywords: calcium alginate reactor ; NADH regeneration ; Saccharomyces cerevisiae ; yeast ; Chemistry ; Biochemistry and Biotechnology

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology

Notes: Saccharomyces cerevisiae cells immobilized in a calcium alginate fiber reactor were used as a source of alcohol dehydrogenase for the NAD+-to-NADH reaction. The reaction was catalyzed by enzyme in cells on the surface of the fiber. Internal diffusional effects were present. The enzyme cell concentration was optimized by harvesting cells finally grown under anaerobic conditions. The results were expressed as an apparent reaction rate constant that was independent of NAD+ and excess ethanol concentration, was slightly affected by flow rate above a minimum value, and increased with immobilized cell concentration in the fiber. The reaction was complete after 6 to 7 h under optimal conditions of 36°C and 9.5 pH. The latter was 0.5 pH units above the free enzyme optimum, indicating that microenvironmental effects were in evidence. © 1993 John Wiley & Sons, Inc.

Additional Material: 12 Ill.