Michel Gendraud

Dormancy in vegetative buds of peach : relation between carbohydrate absorption potentials and carbohydrate concentration in the bud during dormancy and its release

The absorption of sucrose and sorbitol by the bud and the stem of Prunus persica was evaluated during the rest period. The utilization of p-chloromercuribenzenesulfonic acid (PCMBS), an inhibitor of sucrose transporter, allowed estimation of the active absorption of sucrose in different isolated organs (bud, buds underlying tissues and stem). It was assumed that the sink capacities of tissues depended on their potential to absorb carbohydrates by active transport. Endogenous carbohydrate levels in the tissues were also measured. In the bud, the qualitative and quantitative distribution of carbohydrates could be related to the absorption potential of the bud. During dormancy, the bud exhibited a low absorption potential and increased its sucrose concentration by starch hydrolysis. Soluble sugars accumulated during winter. During dormancy release, the bud was able to absorb carbohydrates allowing carbon storage. The data presented led to the proposal of a scheme of events occurring during bud dormancy and its release.

Bud break delay on single node cuttings and bud capacity for nucleotide accumulation as parameters for endo- and paradormancy in peach trees in a tropical climate

Abstract Two tests, one biological the other biochemical, were used to determine the nature of growth inhibition during ‘winter’ rest of leaf buds of peach trees cultivated in the tropical climate of Reunion Island. The ‘cuttings’ test measures the growth capacity of the bud attached to a shoot segment and thus may reveal either paradormancy or endodormancy. The ‘nucleotides’ test, which determines the ability of the bud alone to increase its nucleoside triphosphate pool subsequent to an exogenous supply of adenosine, is a marker of endodormancy. Results show that, although it is only of slight intensity, endodormancy does occur in buds in a tropical climate. They also show that what is recorded as bud growth inhibition can be paradormancy at the beginning of the rest period and endodormancy later, which supports the idea that endodormancy is the result of a gradual shift of the sources of growth inhibition from the shoot to the bud itself. They finally suggest that the reverse sequence could occur with dormancy release and that long-range inhibitions could be the cause of erratic budbreak under a tropical climate.

Plant Responses to High Frequency Electromagnetic Fields

High frequency nonionizing electromagnetic fields (HF-EMF) that are increasingly present in the environment constitute a genuine environmental stimulus able to evoke specific responses in plants that share many similarities with those observed after a stressful treatment. Plants constitute an outstanding model to study such interactions since their architecture (high surface area to volume ratio) optimizes their interaction with the environment. In the present review, after identifying the main exposure devices (transverse and gigahertz electromagnetic cells, wave guide, and mode stirred reverberating chamber) and general physics laws that govern EMF interactions with plants, we illustrate some of the observed responses after exposure to HF-EMF at the cellular, molecular, and whole plant scale. Indeed, numerous metabolic activities (reactive oxygen species metabolism, α- and β-amylase, Krebs cycle, pentose phosphate pathway, chlorophyll content, terpene emission, etc.) are modified, gene expression altered (calmodulin, calcium-dependent protein kinase, and proteinase inhibitor), and growth reduced (stem elongation and dry weight) after low power (i.e., nonthermal) HF-EMF exposure. These changes occur not only in the tissues directly exposed but also systemically in distant tissues. While the long-term impact of these metabolic changes remains largely unknown, we propose to consider nonionizing HF-EMF radiation as a noninjurious, genuine environmental factor that readily evokes changes in plant metabolism.

Localization in sucrose gradients of pyrophosphatase activities in the microsomal fraction of Jerusalem artichoke (Helianthus tuberosus L.) tubers

Summary Three distinct Mg 2+ -PPases have been detected in the microsomal vesicles from Jerusalem artichoke. Separation of the different membranes on a linear sucrose gradient showed that these activities were associated with tonoplast (d = 1.11-1.12), Golgi (d = 1.14-1.15) and plasma membrane (d = 1.17-1.18). PPase activity located in the plasmalemma enriched fractions seemed to be different from ATPase activity, considering the effects of the well known effectors of the plasmalemma ATPase type.

Saccharose and sorbitol transporters from plasmalemma membrane vesicles of peach tree leaves

The mechanisms of saccharose and sorbitol transport in Prunus persica leaves were investigated in plasma membrane vesicles purified by aqueous 2-phase partitioning and equilibrated in pH 7.5 buffer containing K+. The imposition of an artificial proton motive force energized an active uptake of both saccharose and sorbitol. The maximum uptake rate of saccharose was 2.5 times higher than that of sorbitol. Saccharose and sorbitol uptake exhibited saturation kinetics suggesting they were carrier-mediated. Apparent Km for the saccharose and the sorbitol uptake were 0.36 and 0.67 mM, respectively. Active absorption of saccharose was completely inhibited by a non-permeant thiol reagent, PCMBS, contrary to sorbitol absorption. These results suggested that saccharose and sorbitol were transported at least by two different carriers.

A possible role for extra-cellular ATP in plant responses to high frequency, low amplitude electromagnetic field.

In parallel to evoking the accumulation of stress-related transcripts, exposure to low level 900 MHz EMF affected the levels of ATP, the main energy molecule of the cell. Its concentration dropped rapidly (27% after 30 min) in response to EMF exposure, along with a 18% decrease in the adenylate energy charge (AEC), a good marker of cell energy status. One could interpret this decrease in ATP and AEC in a classical way, i.e., as the result of an increase in cellular energy usage, but recent work brings exciting new insights in pointing out a signalling function for ATP, especially in the stress physiology context where it could trigger both reactive oxygen species and calcium movement (this latter being involved in plant responses to EMF exposure). In this addendum, we discuss our results within this new perspective for ATP function.

Effect of exogeneous methyl oleate on the time course of some parameters of Streptomyces hygroscopicus NRRL B-1865 culture

Addition of methyl oleate to a Streptomyces hygroscopicus NRRL B-1865 culture modified the metabolic properties of this strain. This addition decreased the pH of the medium, increased the valine uptake of the cells and reduced their consumption of glucose until the beginning of antibiotic biosynthesis, which was delayed. At the same time, an increase in growth (× 1.8) and a marked improvement in antibiotic production (× 20) could be observed. The use of labelled methyl oleate showed that methyl oleate was not a precursor of antibiotics produced by S. hygroscopicus NRRL B-1865. It is suggested that methyl oleate addition may cause some alteration in membrane permeability, inducing an increase in H+ extrusion and stimulating the accumulation of branched amino acids, known to be direct precursors of polyether antibiotics.

Determination of the growth potential of strawberry plants (Fragaria × ananassa Duch.) by morphological and nucleotide measurements in relation to chilling

Early strawberry fruit production requires that non-dormant strawberry plants be covered during winter. Two methods were used to study the breaking of dormancy of Elsanta strawberry plants following chilling at temperatures below 8 °C. First, a morphological test using the petiole lengths of plants transferred from a nursery to a growth chamber was used. Second, the nucleotide contents before and after incubation of samples in an adenosine solution were measured by bioluminescence. The results show that these two methods can reveal changes in the growth potential of strawberry plants, and, therefore, the release from dormancy. Key words: Dormancy, strawberry plant, nucleotide, growth potential, Fragaria

Change in intracellular pH in Tetrahymena pyriformis GL in relation to the toxicity level of the lonophorous antibiotic nigericin

Nigericin, a carboxylic poly ether antibiotic, is toxic towards Tetrahymena pyriformis GL [1, 7, 12, 13]. Nigericin transports K(+) across biological membranes along the gradient. This transport is generally equilibrated by an influx of H(+) ions. The toxicity of nigericin (at low 10 mg · l(-1) and high 30 mg · l(-1) levels) was studied by measuring the intracellular pH of Tetrahymena pyriformis GL by means of two labelled molecules: (14)C-DMO and (3)H-inulin. This measurement of pHi requires prior knowledge of the number of cells and their volume. The results reveal a correlation of the toxicity of nigericin, acidification of the intracellular environment and increase in cell volume leading to the return of pHi to control values.

Study of H+-nutrient co-transport in peach-tree and the approach to their involvement in the expression of vegetative bud growth capability

Summary Sucrose and sorbitol are the predominant forms of photosynthetically reduced carbon transported in Prunus persica . The mechanisms of sucrose and sorbitol transport were investigated in plasma membrane vesicles isolated from peach tree leaves. The maximum uptake was obtained for sucrose (2.5 times higher than sorbitol uptake). Active absorption of sucrose was completely inhibited by a non-permeant thiol reagent, PCMBS, contrary to sorbitol absorption. These results suggested that sucrose and sorbitol were transported at least by two different carriers. The absorption of exogenous sucrose and sorbitol in the bud and the underlying territories of the bud and their distribution in the single node cuttings were evaluated during the vegetative rest period. The utilization of PCMBS, an inhibitor of sucrose transporter, allowed for the estimation of the active absorption of sucrose in different isolated territories. It was assumed that the sink capacities of tissues depend on their potentialities to absorb carbohydrates by H + /symport. The presence of unlabelled sucrose during PCMBS pretreatment decreased the inhibition exerted by PCMBS: it suggested that the inhibitor was bound specifically on the sucrose transporter. The «active» absorption related to the transporter could therefore be distinguished from the total absorption, including diffusion. The evolution of exogenous sucrose and sorbitol was evaluated during the vegetative rest period, in isolated territories and in single node cuttings. In natural conditions, three periods were disclosed: 1) from September to October, the bud, intrinsically able to grow, was inhibited by the stem; 2) from November to December the bud was in a state of deep dormancy, and it was intrinsically unable to absorb nutrients; and 3) January was characterized by the reacquisition of bud growth potential and bud burst. Concerning sorbitol, a similar evolution was observed but it seemed that sorbitol was principally utilized a few days before budburst.