The time course of the induction of callose in wounded pea roots

Summary Initial study indicated that much callose is produced in pea root tissues during the preparation of fresh hand-cut sections or during conventional fixation in formalin-acetic acid-alcohol, glutaraldehyde or acrolein. In contrast, there is little callose in freeze-substituted tissues and this is mostly in sieve tubes and considered endogenous. Freeze-substitution was subsequently used to monitor wound-induced callose development in the various tissues of pea roots. This development was fastest in the phloem, first detected 1 minute post-wounding and complete by 3 hours. In some parenchyma cells full development was delayed by 20 hours. By 100 hours, wound callose was no longer detectable in parenchyma cells but remained undiminished in the phloem. The implications of these results for all studies involving callose localization are discussed.Abbreviations C callose - FAA formalin-acetic acid-alcohol - GMA glycol methacrylate - P phloem - PAS periodic acid-Schiffs - PF phloem fibres - PP pith parenchyma - PW post-wounding     

Effects of ovariectomy on energy metabolism in exercising rat muscle studied by 31P-NMR

The effects of ovariectomy on metabolism of high-energy phosphate compounds during and after exercise were studied in hindleg muscles of 14 rats. Sciatic nerve stimulation was used to establish different work loads, and the changes in inorganic phosphate-to-phosphocreatine ratios (Pi/PCr) were recorded by 31P nuclear magnetic resonance (NMR) in vivo. Four weeks after ovariectomy, there was evidence of significantly higher Pi/PCr during work at stimulation rates greater than 0.5 Hz. The slope for the stimulation rate-to-Pi/PCr relationship decreased from 1.98 +/- 0.15 to 1.36 +/- 0.2 Hz/Pi/PCr after ovariectomy. The normalized tension output of these muscles, tested separately using identical stimulation protocols, was not changed with ovariectomy. Thus the relationship between work (tension-time integral) and bioenergetic cost (Pi/PCr) suggested reduced maximal enzyme activity (Vmax) by 9-17% as a result of lack of ovarian sex hormones, but no change in Michaelis-Menten constant (Km) was found. Postexercise recovery was also significantly slower (3.27 +/- 0.54 PCr/Pi units per minute compared with 4.04 +/- 1.08 in controls). It is suggested that reduced levels of ovarian sex hormones decrease oxidative phosphorylation. Cytochrome oxidase activity was reduced in these muscles by 40%, but other mitochondrial enzyme systems may be affected as well. The possible significance of these data is the implication of a reduced capacity for menopausal women or amenorrheic female athletes to perform prolonged intensive exercise.     

Water efflux from the surface of field-grown grass roots. Observations by cryo-scanning electron microscopy

The objective of this study was to compare whole plant growth and physiological responses to salt stress of two Acacia nilotica subspecies (ssp. cupressiformis and ssp. tomentosa ). Salt stress was induced by adding NaCl at different concentrations to the nutrient solution: 0, 75, 100 and 200 m M . After one month under such stress, plants were still healthy and actively growing in both subspecies up to 100 m M NaCl. Water potential (Ψ) and osmotic potential (π) decreased with salinity and the lower π enabled the plants to maintain turgor. Höfler diagrams confirmed that osmotic adjustment had occurred under all treatments. Furthermore, the point of zero turgor occurred at a higher relative water content. An increase in the elastic modulus (ɛ) was observed under stress (low elasticity of the cell wall). Both osmotic adjustment and a high ɛ modified the capacity of both subspecies to maintain a positive water balance. Accumulation of ions (Na⁺, K⁺ and Cl⁻) and proline could explain such osmotic adjustment. Acacia nilotica ssp. cupressiformis showed a higher absorption of K⁺ than ssp. tomentosa up to 100 m M NaCl treatment.     

Histochemical localization of β-glycosidases in roots ofZea mays II. Changes in localization and activity ofβ-glucosidase in the main root apex

Summary High-glucosidase activity has been demonstrated histochemically in the epidermis, and outer cortex of the root meristem, and in the peripheral cells along the flanks of the root cap. Low enzyme activity is found in the central part of the root cap and in the developing stele. Enzyme activity increases in cells just before they elongate and declines after elongation. The-glucosidase activity is located peripherally in the cells and usually occurs in the form of networks of strands and particles.     

A histological study of lateral root initiation and development inZea mays

Summary A light microscopic study has been made of the origin and development of lateral roots inZea mays.The initiation of a lateral occurs adjacent to a xylem pole and involves an increase in cytoplasmic basophilia and subsequent divisions of cells of the pericycle and the parenchyma of the stele of the mother root.Cells derived from the parent pericycle form most of the young lateral but its epidermis and root cap are composed of cells of endodermal origin.Two different types of polysaccharides are secreted by cells of the young lateral root. One type which is PAS-positive and non-metachromatic, is produced by the epidermal cells, while the other type, metachromatic and only slightly PAS-positive, is secreted by the root cap cells.     

Purification of a branched-chain keto acid dehydrogenase from Pseudomonas putida.

We purified branched-chain keto acid dehydrogenase to a specific activity of 10 mumol/min per mg of protein from Pseudomonas putida grown on valine. The purified enzyme was active with 2-ketoisovalerate, 2-ketoisocaproate, and 2-keto-3-methylvalerate in a ratio of 1.0:0.8:0.7 but showed no activity with either pyruvate or 2-ketoglutarate. There were four polypeptides in the purified enzyme (molecular weights, 49,000, 46,000, 39,000, and 37,000). The purified enzyme was deficient in the specific lipoamide dehydrogenase produced during growth on valine (molecular weight, 49,000). Branched-chain keto acid dehydrogenase required L-valine, oxidized nicotinamide adenine dinucleotide, coenzyme A, thiamine pyrophosphate, and magnesium chloride. A partially purified preparation catalyzed the oxidation of 2-keto-[1-14C]isovalerate to [14C]carbon dioxide, isobutyryl-coenzyme A, and reduced nicotinamide adenine dinucleotide in equimolar amounts. Both the Km and the Vmax for 2-ketoisovalerate were affected by the addition of L-valine to the assay mixture. However, only the Vmax values for oxidized nicotinamide adenine dinucleotide and coenzyme A were affected when L-valine was present. This suggested that valine acted by affecting the binding of branched-chain keto acids to subunit E1 of the complex.     

Muscle metabolism in older subjects using 31P magnetic resonance spectroscopy.

We used phosphorus magnetic resonance spectroscopy to study the calf muscles of elderly normal (mean +/- SD) (80.0 +/- 5.12 years), elderly impaired (80.7 +/- 0.58 years), old normal (66.8 +/- 1.92 years), and young normal people (24.6 +/- 4.72 years). Relative levels of inorganic phosphate (Pi), phosphocreatine (PCr), and adenosine triphosphate were measured with a 1.9-tesla, 30-cm bore magnet at rest and following plantra flexon exercise. No differences were found at rest or during recovery from exercise in the elderly normal subjects with respect to gender or the presence of stable medical problems treated with medication. At rest there was an age-related decrease in the ratio of PCr/Pi. After exercise, the time constant of PCr recovery increased with age. A mild 7-week exercise regimen consisting of plantar flexion had no effect on time constant of PCr recovery in the elderly subjects. Four elderly impaired subjects had lower PCr/Pi ratios at rest and slower time constant of PCr recovery after exercise than normal elderly subjects. We conclude that gender and the presence of stable medical problems had no effect on muscle metabolism in the elderly and that the elderly recovered slower than young controls. This slower recovery was not corrected with a mild exercise program.