Restart of lignification in micropropagated walnut shoots coincides with rooting induction

in Biologia Plantarum (2003), 47(1), 1-5

The lignin content of walnut shoots did not change during in vitro shoot Multiplication. Lignin content started to increase as soon as shoots were passed to a rooting medium with auxin. Exogenous auxin ... [more ▼]

The lignin content of walnut shoots did not change during in vitro shoot Multiplication. Lignin content started to increase as soon as shoots were passed to a rooting medium with auxin. Exogenous auxin (applied for rooting) Caused a transient elevation of the endogenous free indoleacetic acid (IAA) content with a Simultaneous decrease of peroxidase activity. These events typically marked the completion of the rooting inductive phase (before any visible histological event. that is before the cell divisions beginnin- the rootin- initiation phase). This meant that either the given exogenous auxin or the endogenous IAA has served as signal for the stimulation of lignification. Continued increase of lignification in the shoots required completion of root formation; this increase indeed was slown down when root emergence did not occur. It was further shown that lionification varied conversely to the content of the Soluble Phenol Content. itself apparently being related to the activity of phenylalanine ammonia-lyase activity. [less ▲]

Biosynthesis of peroxidases: a role as interplay between primary and hormonal metabolisms

in Acosta, M.; Rodriguez-lopez, J.-N.; Pedreno, Maria-A (Eds.) Plant perodixases - Biochemistry and physiology - VI international plant peroxidase symposium Proceedings (2002)

Hyperhydric, fully habituated (growth independent from exogenous auxin and cytokinin), fully heterotrophic (achlorophyllous, dependent on sucrose supply, nevertheless able to fix CO2 non ... [more ▼]

Hyperhydric, fully habituated (growth independent from exogenous auxin and cytokinin), fully heterotrophic (achlorophyllous, dependent on sucrose supply, nevertheless able to fix CO2 non-photosynthetically) and non-organogenic (complete loss of any organogenic totipotency) sugarbeet cells in culture were characterized by a very low peroxidase activity, among other deficient heme compounds. This deficiency resulted from the lack of synthesis of the precursor aminolevulinic acid (ALA) through the chloroplastic Beale pathway; the low productive unusual ALA synthesis through the mitochondrial Shemin pathway (commonly used by animals and fungi) functioned but further at a limited rate due to inhibition of ALA-dehydratase by benzoic derivatives, predominant among the phenolic acids of these cells (compared to normal ones). A thorough investigation of the metabolic and hormonal functioning of these neoplastic cells showed that the above deviation originated from a disturbed nitrogen metabolism that diverted glutamate from the Kreb's cycle into polyamine (over) synthesis, which had also as consequence a low ethylene production. The Kreb's cycle could be replenished by oxaloacetate and malate deriving from the anaplerotic fixation of CO2 onto phosphoenolpyruvate. A privileged pentose phosphate pathway (PPP) allowed the formation of substrates for a non-limited biosynthesis of (endogenous) auxins and cytokinins. The PPP, through NAD(P)H formation, enhanced nitrogen metabolism, but also, together with a putative H2O2 accumulation (originated from high superoxide dismutase activity and high polyamine oxidation combined with low catalase activity), favoured the alternative respiratory pathway. These results not only illustrate a novel view of integration of hormonal metabolisms with the C and N primary and secondary ones but also allow to consider the biosynthesis of peroxidases in an interplay or mediating role between them. [less ▲]

A comparison of respiratory pathways in fully habituated and normal non-organogenic sugarbeet callus

in Journal of Plant Physiology (2000), 156(3), 312-318

The respiration of cells and isolated mitochondria of a habituated non-organogenic (HNO) cell line (auxin- and cytokinin-independent) and of a normal (N) cell line (auxin- and cytokinin-requiring) from ... [more ▼]

The respiration of cells and isolated mitochondria of a habituated non-organogenic (HNO) cell line (auxin- and cytokinin-independent) and of a normal (N) cell line (auxin- and cytokinin-requiring) from sugarbeet (Beta vulgaris L.) was investigated. Oxygen uptake by both cells and mitochondria of the HNO fine was higher than that of the N line. Respiration in the presence of cyanide (i.e. capacity of the alternative pathway) was also higher in the HNO callus as compared with the N one. The measurements of O-2 uptake from isolated HNO and N mitochondria showed that addition of a mixture of substrates (NADH, succinate, malate and NAD) resulted in a higher respiration via the CN-resistant pathway in mitochondria From HNO cells. The activity of cytochrome c oxidase was twice as high as in the N cells as compared with the HNO cells. Immunoblots also showed that a higher alternative oxidase protein was present in HNO cells than in the N cells. A model showing the relationships between the different metabolic pathways previously studied in the HNO cells and the higher respiration via the CN-resistant pathway in the HNO cells is proposed. [less ▲]

Interactions between polyamine and ethylene metabolisms in a hormone autonomous sugarbeet callus

in Journal of Plant Physiology (2000), 157(1), 24-30

In a fully habituated non-organogenic sugarbeet callus (HNO) overproducing polyamines and underproducing ethylene (in comparison with its normal hormone-dependent counterpart), the question raised about a ... [more ▼]

In a fully habituated non-organogenic sugarbeet callus (HNO) overproducing polyamines and underproducing ethylene (in comparison with its normal hormone-dependent counterpart), the question raised about a possible competition between these two metabolites for their common precursor, S-adenosyl-methionine (SAM). The experimental strategy consisted in determining the effects of exogenous polyamines and inhibitors of polyamine biosynthetic pathway on growth, polyamine accumulation and ethylene production. Exogenous putrescine or spermidine decreased polyamine contents and ethylene production. Inhibitors of the diamine putrescine biosynthesis, DFMO and DFMA, induced a reduction of both polyamine content and ethylene production with an increase of HNO callus growth. However, when a mixture of the two inhibitors was used, an increase of ethylene production was observed without any effect on growth. The inhibitors of spermidine synthase (CHA) and of SAM decarboxylase (MGBG) also decreased polyamine content and ethylene production with different effects on growth according to the concentrations used. The combination of the two inhibitors (CHA + MGBG) increased ethylene production of the HNO callus. The effect of growth regulators (auxin and cytokinin) on growth and ethylene production of HNO callus is also discussed. These results suggest that polyamines affect directly the ethylene biosynthesis. In the absence of an exogenous hormonal control, the lower ethylene metabolism of HNO callus could not be explained by a competition with polyamines for their common precursor. [less ▲]

Putrescine metabolism in a fully habituated nonorganogenic sugar beet callus and its relationship with growth

in Journal of Plant Physiology (1999), 154(4), 503-508

A fully-habituated and nonorganogenic (HNO) sugar beet callus was previously shown to overproduce polyamines, as compared with a normal (N) auxin- and cytokinin-dependent callus of the same strain ... [more ▼]

A fully-habituated and nonorganogenic (HNO) sugar beet callus was previously shown to overproduce polyamines, as compared with a normal (N) auxin- and cytokinin-dependent callus of the same strain. Because relationships were established between polyamine levels and metabolism with different growth and development processes, some key enzymes in the metabolic pathways of polyamines were investigated in the HNO callus, and their involvement in growth appraised. Putrescine was found to be the major free and conjugated polyamine in the HNO callus. It was biosynthesised preferentially via ornithine and ornithine decarboxylase (ODC), which is in agreement with the surplus of synthesised ornithine. Diamine (DAO) and polyamine (PAO)-oxidase activities were also highest in the HNO callus, as compared with the normal, with DAO being the more active. Transglutaminase activities (+/- Ca) were also higher in HNO than in normal callus. Addition of different polyamines or of inhibitors of their biosynthesis to the culture medium of the HNO callus modified the level of endogenous polyamines and affected callus growth. The results thus pointed out a higher polyamine metabolism, particularly of putrescine, in the actively growing auxin- and cytokinin-independent callus than in the normal one. They also provided evidence for the sensitivity of a habituated tissue type towards this class of growth regulators. [less ▲]

Differential growth dependency of normal and habituated sugarbeet cell lines upon endogenous ethylene production and exogenous ethylene application

in Physiologia Plantarum (1998), 103(2), 201-208

A fully habituated (auxin- and cytokinin-independent) nonorganogenic (HNO) sugarbeet (Beta vulgaris) callus produces very little ethylene as compared with a normal (N) hormone-requiring callus of the same ... [more ▼]

A fully habituated (auxin- and cytokinin-independent) nonorganogenic (HNO) sugarbeet (Beta vulgaris) callus produces very little ethylene as compared with a normal (N) hormone-requiring callus of the same strain. Both callus types react by growth changes to application of inhibitors of ethylene biosynthesis and ethylene action, of 1-aminocyclopropane-1-carboxylic acid (ACC) as the immediate precursor of ethylene, to transfer from light to darkness, and also to application of exogenous ethylene or an ethylene trapper. This indicates their growth dependency upon their endogenously biosynthesized ethylene and also their sensitivity to exogenous gas. However, the sensitivity was generally higher for the HNO callus producing naturally less ethylene. The weaker reaction of the HNO callus to the exogenous ethylene was attributed to its hyperhydric status (a water layer surrounding the cells). Because low ethylene production appears as a general characteristic of habituated cell lines, the causal and/or consequential relationships of this low ethylene production with other characteristics of habituated tissues (absence of exogenous hormones in the culture media, deficiency of cell differentiation, accumulation of polyamines in neoplastic tissues) are discussed. [less ▲]

Biosynthesis of 5-aminolevulinic acid via the Shemin pathway in a green sugar beet callus

in Biologia Plantarum (1998), 40(4), 493-497

5-Aminolevulinic acid synthase (ALAS) has been detected in a normal (auxin- and cytokinin-dependent) green sugar beet callus under light and under darkness. ALAS activity was lower when the callus was ... [more ▼]

5-Aminolevulinic acid synthase (ALAS) has been detected in a normal (auxin- and cytokinin-dependent) green sugar beet callus under light and under darkness. ALAS activity was lower when the callus was grown under light. The supply of precursors of the Shemin pathway (glycine and succinate) to dark-grown callus enhanced considerably the capacity of the 5-aminolevulinic acid (ALA) formation. Glutamate, gamma-aminobutyrate or a-ketoglutarate also increased ALA accumulation. Such an accumulation was also obtained after inhibition of polyamine synthesis. The results show that glutamate or its derivatives might feed the Shemin pathway in conditions preventing glutamate to be used through the Beale pathway. [less ▲]