C. Kevers

Peroxidase activity and endogenous free auxin during adventitious root formation

That endogenous free auxin has a central role in the process of adventitious root formation is generally accepted [27, 28, 35,46,49, 61]. The concept however has been developed more from the observation that exogenously applied auxins invariably induce the formation of a greater number of roots per cutting than other chemicals, than from established correlation between the auxin content or the auxin variation of cuttings and their rootability. In the mind of many plant physiologists, the exogenously supplied auxins, whatever synthetic, simply grow the bulk of endogenous auxins and act in a similar manner. This concept is out of date, as clearly shown on the one hand by the relationships between exogenous and endogenous auxins in cell cultures [52, 64], and on the other hand by recent analyses of the fate of exogenously supplied auxins in cuttings [7, 68]. The cell signaling eventual role of exogenous auxins supplied to cuttings thus has seldom been distinguished from the role of the endogenous ones. Literature concerning the estimation of endogenous auxin levels at the time of cutting excision in relation with their rooting capacities or concerning the variation of the levels in the course of adventitious rooting was until recently very discrepant [15,36]. First, there were relatively few studies using unequivocal physico-chemical techniques of auxin analyses. Second, it was not clearly stated what developmental stage of rooting was sampled (induction preceding cell reactivation and division, organization of the primordia, growth of the newly formed roots), nor was the physiological condition of the stock plant taken into consideration.

Vitrification: Morphological, Physiological, and Ecological Aspects

Vitrification (synonyms: glassiness, translucency, vitrescence, hyperhydric malformations) is a physiological disorder frequently affecting herbaceous and woody plants during their in vitro vegetative propagation. The descriptions of these conditions given by various authors are very similar although often vitrification is not properly recognized (see 3.1. and 4 below). In general stems of vitrified plantlets are broad, thick and translucent; leaves are thick, wrinkled and/or curled, frequently very elongated, and easily breakable. Some researchers have ascribed the malformations to chlorophyll deficiency and general cell hyperhydricity (23, 45).

Atypical metabolisms and biochemical cycles imposing the cancerous state on plant cells

The biological, morphological and biochemical characteristics which define plant cancer cells at the end of a neoplasic progression in the absence of pathogens and which distinguish them from tumorous cells are summarized. Such plant cancer cells have in common with animal cancer cells many metabolic disturbances. The present paper reviews the biochemical changes in nitrogen, carbon, sugar and heme metabolisms which contribute to polyamine (PAs) accumulation. It indicates how these changes are interconnected and even form between each other biochemical cycles which likely maintain these cells in their irreversible state. The role of these cycles in the maintenance of such cells under a probable permanent oxidative stress is debated.

Erythromycin as a tool to investigate the tetrapyrrole biosynthetic pathways in habituated and normal sugarbeet calli

Erythromycin (ERT) has been shown to reduce the 5-aminolevulinic acid (ALA) synthesizing capacity of a normal (N) chlorophyllous sugarbeet callus, grown under light, in contrast to a habituated achlorophyllous non-organogenic (HNO) callus of the same species. Similar effects were obtained on total hemes and on catalase which is a hemoprotein used as marker. The effect of ERT, which is an inhibitor of plastid differentiation and of chlorophyll synthesis, was reversed in the N callus by a supply of glycine and succinate. The compounds are the precursors of ALA synthesized through 5-aminolevulinic acid synthase (ALAS) which is implied in the Shemin pathway. The involvement of ALAS appeared to be favoured when plastids were undifferentiated (HNO callus) or when plastids were inefficient (N callus under darkness or under light after ERT treatment).

Flowering abundance of strawberry depending on the number of subcultures in vitro

Some difficulties have arisen over the years with the use of micropropagated strawberry plants, or runner plants derived from them. These have included delayed fruiting and the size of individual fruits from such plants which tends to be smaller than from conventionnaly runner-propagated plants [13]. The smaller size of the fruits might come from a tendency of micropropagated strawberries to produce more flowers, particularly when originated from shoots raised after a high number of multiplication cycles [7]. The present work aimed to study the flowering abundance in relation with the number of subcultures on the multiplication medium and also correlate this flowering behaviour with other morphogenetic traits. Particular attention has been paid to rooting because flowering and rooting are known to be antagonistic developmental processes [3, 8, 9].