Experiments with lettuce seeds during the first hours of imbibition showed that oxygen is necessary to sustain high adenine nucleotide ratios and consequently, energy charge values are higher than 0.8 as is usually the case in normally metabolizing tissues. The origin of the energy-rich bonds needed for the biosynthetic work done by germinating seeds during the first min and h after imbibition is a question for debate (7,9,11,15). Some seeds have active fermentative metabolism even in air but 02 is always necessary to permit normal germination. In other seeds, such as lettuce seeds, ATP production from fermentation is very low (17 and unpublished results).In the last 15 years, many improvements in the techniques for extracting mitochondria have permitted researchers to obtain from many plant tissues particles exhibiting very high respiratory control and P/O ratios close to the generally accepted theoretical values. To date, mitochondria extracted from dry or imbibed seeds before the protrusion of the radicle are loosely coupled and do not exhibit respiratory control (27). In germinating seeds, as well as in many plant tissues, a significant percentage of the 02 uptake has been reported to be cyanide-insensitive (11). Many authors have claimed that cyanide is unable to inhibit the germination of seeds (10, 25) and sometimes a stimulatory effect was reported (23).These observations led to the hypothesis that an unknown metabolic pathway was operative until the deficient Cyt oxidase pathway was able to function fully (9,11, 25 Pradet (13), demonstrated that cyanide at low concentration is a potent inhibitor of lettuce seed germination if volatility and chemical instability are controlled. This result was recently confirmed by Yu et al. (26).In vivo studies of adenine nucleotides during lettuce seed germination show that a high ATP level depends upon 02 (14,15, 17). From a comparison between the rate of ATP utilization and 02 uptake, Pradet (15) postulated that oxidative phosphorylation should operate during the beginning of germination. The experiments presented in this paper were done to obtain further evidence on the occurrence of oxidative phosphorylation in vivo during imbibition of lettuce seeds. The rate of energy-rich bond production was estimated from energy charge values (1, 17, 19, 20). Anoxia, cyanide, and FCCP3 were used to limit ATP synthesis. MATERIALS AND METHODSImbibition. Lettuce seeds (Lactuca sativa var. Reine de Mai, pleine terre) were immersed and agitated in water or solutions containing inhibitor for the required time at 20 C.Anoxic Treatments. The presoaked seeds were placed on wet filter papers in stoppered beakers and gassed. The stoppered beakers were fitted as described by Raymond and Pradet (17) to kill the seeds under N2. The O2 content of N2 was controlled at the exit of the beakers as described before (17). The O2 partial pressure in N2 was lower than 10 Pa.Killing, Sampling, Enzyme Inactivation, and Nucleotide Extractions. Metabolic activity was stopped by pouring cold ...
Eliminating heavy metals in the environment by phytoremediation is a method that uses, generally, plants with a low biomass yielded and feeble depth of root system. For the purpose of improving this technique, we have tested four varieties of productive specie with high yields, the rapeseed (Brassica napus L.). In particular, we have studied metal stress effect on biomass, growth, and endogenous Zn and Cd content. Metal treatment caused significant dry weight differences between metal-treated and control plants. A significant genotypic difference has been noticed between the four cv. For two varieties, Jumbo and Drakkar, the accumulation is more important in the stems and petioles, whereas, this accumulation is at a maximum level in the root system for the two varieties, Cossair and Pactol. Chlorophyll and carotenoïd content, as well as lipid peroxidation, known as stress markers, were also evaluated. Metal treatment led to an increase in the amount of malondialdehyde (MDA) in the leaves. However, the increase of Zn and Cd levels in the tissue culture was followed by a decrease in the photosynthetic pigments. To cite this article: A.
Bulbing was studied in shallot plants cultured in vitro. Bulbing occurred under a 16 h photoperiod with fluorescent + incandescent light and 30-50 g 1(-1) sucrose in the culture medium. Exogenous gibberellin (10 microM GA3) inhibited leaf and root growth and bulbing. When added to the medium at a concentration of 10 microM, three inhibitors of gibberellin biosynthesis (ancymidol, flurprimidol and paclobutrazol) promoted bulb formation and the percentage of bulbing. When ancymidol was used in combination with GA3, it did not reverse the effect of GA3 applied alone. Under treatments with 30-70 g l(-1) sucrose, bulbing ratios greater than those found in control plants were achieved by addition of ancymidol, and bulb fresh weight was increased in the same way. Ancymidol caused a 66% decrease in sucrose content in leaf bases but greatly increased the glucose, fructose and fructan contents. The increase in fructan content by ancymidol could result from the three-fold rise in total [14C]sucrose uptake per plant from the culture medium associated with a marked increase in leaf base labelling at the expense of root labelling. The possible role of ancymidol is discussed and evidence supports a major regulatory role for gibberellins in bulbing.
International audienceTo gain more insight into the impact of zinc on the primary metabolites in rapeseed, plants were regenerated in vitro in the presence of zinc (0.1–1 mM), acclimatized, transferred to a greenhouse, and treated with 2 mM ZnSO4. The main metabolites, including soluble carbohydrates and free amino acids, were analyzed by nuclear magnetic resonance spectroscopy, and further confirmed by spectrophotometry and enzymatic analyses. Exposure of these greenhouse-grown plants to ZnSO4 led to both a significant rise of the total amino acid level and an increase of proline accumulation in the different tissues. Moreover, the control plants, regenerated without zinc stress, exhibited a significant reduction of soluble carbohydrate levels, whereas the plants derived from Zn-treated regenerants exhibited significantly higher levels of both glucose and sucrose. These levels increased proportionally with the Zn concentration in the regeneration step
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