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Despite the advances in the physiology of fruit ripening, the role and contribution of water pathways are still barely considered. Our aim was therefore to characterize aquaporins, proteins that render the molecular basis for putative regulatory mechanisms in water transport. We focused our work on strawberry (Fragaria × ananassa) fruit, a non-climacteric fruit of special interest because of its forced brief commercial shelf life. A full-length cDNA was isolated with high homology with plasma membrane (PM) intrinsic proteins (named FaPIP1;1), showing a profile with high expression in fruit, less in ovaries and no detection at all in other parts. Its cellular localization was confirmed at the PM. As reported in other plasma membrane intrinsic proteins subtype 1 (PIP1s), when expressing the protein in Xenopus leavis oocytes, FaPIP1;1 shows low water permeability values that only increased when it is coexpressed with a plasma membrane intrinsic protein subtype 2. Northern blotting using total RNA shows that its expression increases during fruit ripening. Moreover, functional characterization of isolated PM vesicles from red stage fruit unequivocally demonstrates the presence of active water channels, i.e. high water permeability values and a low Arrhenius activation energy, both evidences of water transport mediated by proteins. Interestingly, as many ripening-related strawberry genes, the expression pattern of FaPIP1;1 was also repressed by the presence of auxins. We therefore report a fruit specific PIP1 aquaporin with an accumulation pattern tightly associated to auxins and to the ripening process that might be responsible for increasing water permeability at the level of the PM in ripe fruit. [ABSTRACT FROM AUTHOR]

To investigate selenium tolerance mechanisms in Arabidopsis thaliana, genetic and physiologic studies were performed in the three Arabidopsis accessions Landsberg erecta (Ler), Columbia (Col) and Wassilewskija (Ws). Accession Ler was significantly less tolerant to selenate than Ws and Col, whereas Ws was less tolerant to selenite than the others. Analysis of selenium tolerance in F1 and F2 plants obtained from crosses between these accessions suggest that multiple genes are involved in selenate tolerance and a single major gene controls selenite tolerance in these populations. Bulked segregant analysis in two F2 populations indicated that molecular marker ciw7 on chromosome 4 is linked to selenite tolerance, and three molecular markers on chromosomes 1, 3 and 5 (nga111, ciw4 and ciw8, respectively) are linked to selenate tolerance. The ecotypic variation in selenite tolerance appeared to be correlated with root levels of non-protein thiols. Also, the shoot tissue levels of selenocysteine (SeCys) and selenocystine were correlated with tolerance to both selenate and selenite. Judging from RT-PCR results, several sulfate transporters and S assimilatory enzymes appear to be upregulated by selenate and selenite at the transcriptional level. A potential SeCys methyltransferase was expressed at lower levels in selenite-sensitive Ws than in the other two, when grown on selenite. Together, these studies show that there is substantial intraspecific variation in tolerance to selenate and selenite in Arabidopsis, and provide insights into the genetic and biochemical mechanisms underlying the observed ecotypic differences. [ABSTRACT FROM AUTHOR]

Chlorophyll (Chl) and total soluble protein decreased and proteolytic activity increased over a 12-day period during dark-induced senescence in detached leaves of Tara, a yellowing cultivar (Y) of Dendranthema grandiflora. In Boaldi, a non-yellowing cultivar (NY), Chl and soluble protein remained near initial levels and little change in proteolytic activity was observed. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of soluble proteins showed no major differences in banding patterns between the two cultivars at day 0; however, all of the resolved proteins were diminished in Tara by day 12. On the other hand, in NY Boaldi, the intensity of the protein bands did not change over the 12-day period. Attached and detached leaves exhibited similar senescence patterns for each cultivar. Ethylene (100 µl l-1 ) accelerated the rate of Chl loss in detached leaves of Tara, but had no effect on Boaldi. These observations suggest that Boaldi is a stay-green genotype, possibly a functional type. The results are discussed in relation to the role of ethylene in chrysanthemum leaf senescence. [ABSTRACT FROM AUTHOR]

Deacclimation of Scots pine (Pinus sylvestris) in northern Finland (65°N) was studied from the perspective of protein metabolism, which was related to nitrogen fertilization. Two-year-old seedlings were fertilized with calcium ammonium nitrate (0, 442 and 884 kg N ha-1) in the summer prior to the study. Needles were harvested for analyses at 3-week intervals during the natural deacclimation period from mid-March to the beginning of June 1998. Deacclimation was followed by monitoring various physiological variables: freezing resistance decreased and osmotic potential increased during the experiment and needle dry weight increased from bud flushing onwards. The concentration of soluble proteins in needles was higher in fertilized seedlings but decreased transiently in the 884 kg N ha-1 fertilized seedlings before budbreak. The abundance of several small polypeptides (17–32 kDa) decreased in the spring. A 60-kDa protein, identified by immunoblotting as a dehydrin, was detected in all treatments. The quantity of this dehydrin decreased with resumption of growth, along with the appearance of 50- and 56-kDa dehydrins. The concentration of these dehydrins decreased during dehardening more rapidly in fertilized seedlings than in the control plants. The fertilized seedlings started to grow earlier than the unfertilized plants. In conclusion, nitrogen fertilization provided good reserves for new growth but did not affect deacclimation of pine needles. [ABSTRACT FROM AUTHOR]

Twenty day-old winter rape (Brassica napus L. var. oleifera L. cv. Jantar) seedlings, grown in nutrient solution, were exposed to different shoot/root temperature (i. e. 20/20, 20/3, 3/20 and 3/3°C) for 2 or 4 weeks. Chilling treatments modified markedly the pattern of plant growth as indicated by changes in dry matter accumulation in individual plant parts (leaves, hypocotyls, roots) and decreased leaf specific area. Growth of roots was less sensitive to low temperature than that of shoots. This was reflected by a decrease in shoot/root biomass ratio. Chilling treatments increased freezing resistance, decreased water content and water potential and modified reducing sugar, soluble protein and phospholipid contents in the leaves. A biphasic character of tissue responses to chilling temperature was observed, the most remarkable changes being registered during the first 7 or 14 days of the treatment. Effects of root or shoot exposure to chilling temperature on ice nucleation temperature, LT50, water potential, accumulation of sugars and phospholipids in leaves were additive. All the observations point to the important role of the root system in plant acclimation to cold. Its impact on water status of leaves is emphasized and some mechanisms of root involvement in acclimation processes are proposed. [ABSTRACT FROM AUTHOR]

Apples (Malus domestica Borkh.) were heated for 4 days at 38°C immediately after harvest and then placed at 20°C for 7–10 days. Protein synthesis, ethylene production and fruit softening were reversibly inhibited by the heat treatment. Fruit respiration, membrane permeability and chlorophyll degradation in the fruit peel were enhanced during the treatment. The heat-treated apples ripened normally but more slowly than untreated apples. We hypothesize that heat treatment differentially affects processes which normally increase simultaneously during fruit ripening, by inhibiting those processes which require de novo protein synthesis and enhancing those that do not. [ABSTRACT FROM AUTHOR]

Inhibition of phosphoenolpyruvate carboxylase (EC 4.1.1 31) from the C4-halophyte Salsola soda L. by NaCl is competitive to phosphoenolpyruvate (PEP). Physiological (betaine. glycerol) and synthetic (polyethylene glycol) osmotica and the allosteric activator glucose-6-phosphate (G6P) increase the apparent affinity of the enzyme for PEP and also alleviate the inhibition by NaCl. Physiological osmotica that either increase the Km(PEP) (proline) or are neutral (sorbitol), do not protect the enzyme against NaCl attack. In the absence of cosolutes and G6P, the enzyme is self-protected when its concentration in the assay medium is increased to more physiological values. In addition, the amount of betaine needed for complete protection is inversely related to native protein concentration in the assay. Exogenous protein (bovine serum albumin or bovine skin gelatin) have no effect on either Km(PEP) or extent of NaCl inhibition. These results can be better explained with the exclusion volume theory and the inferred assumption that both cosolutes and high protein concentration strengthen intrinsic aggregation properties of enzymes. It is suggested that the extremely high phosphoenolpyruvate carboxylase concentration in the cytoplasm and the accumulation of compatible solutes in response to water stress fully protect the enzyme in vivo against the chaotropic effects of NaCl. [ABSTRACT FROM AUTHOR]

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In finding out the catalase contents of plant sources a decisive role is played by their acid contents. When, during the process of crushing the specimens, the enzyme gets into contact with the acid cell sap it can be irreversibly destroyed, in extreme cases within a few seconds, either completely or to a considerable degree. If the plant parts are crushed in a neutral buffer solution the enzyme of some plants with almost neutral cell saps remains essentially undamaged. In plants, however, with cell saps of strong acidity even then a great part of the catalase is destroyed, apparently at the moment of crushing. For determining the true contents of catalase within the plant sources in question -- and possibly also the contents of other enzymes -- it is necessary to neutralize the cell sap in vivo before extraction. This tan be done by placeing the specimens in a diluted solution of ammonia, since the undissociated NH3 which it contains can easily permeate through the living protoplasm into the cell sap. Special attention should be paid to breaking up the specimens into small parts before placing them in the solution of ammonia. Otherwise the infiltration would be very slow. As indicators for the completion of the neutralization or alkalization of the cell saps we can use the lower epidermis of many leaves, tinted red by anthocyan. They change to blue in the alkaline range. After being thus treated -- it was done for this study with the leaves of Tradescantia gnianensis, Begonia conchifolia, Oxalis floribunda, Saxifraga sarmentosa, and Echeveria elegantissima -- the catalase activity of the extracts proved to be very much higher in plants with cell saps of strong acidity (Begonia. Oxalis) -- and sometimes also considerably higher in plants with almost neutral cell saps (Saxifraga) -- than that of the untreated leaves. If the specimens are exposed to ammonia for too long this activity decreases again. The maximum activity achievable by their placing in ammonia for a certain time can very well serve as a yard-stick for determining their true catalase contents, insofar as no other enzyme-checkers besides H'-ions are concerned. This clearly shows that some of the numerous difficulties, which botanic enzyme chemistry bas to cope with, may be overcome by orienting the studies and methods towards cell physiology. In accordance with other authors a clear correlation between the chlorophyll contents and the catalase contents, but no strict proportionally, was found. [ABSTRACT FROM AUTHOR]

1. Uptake of Ca45 by potato tuber slices was determined at +2° C and + 25° C. The Q10 was nearly 3. Since the conditions were such as to preclude active accumulation, it is suggested that the number of adsorption loci increases with respiration rate. 2. Proteins obtained by fractionation method 1 (7) accounted for a very small but definite fraction of the total Ca45 accumulated. Quantitative measurements of the protein fractions and of the dialysate showed that large amounts of Ca45 were lost during dialysis. 3. Fractionation method 2, which avoids (NH4)2SO4 precipitation and dialysis for three of the five fractions, permitted a much greater recovery of the absorbed Ca45 in the proteins. The granules showed the greatest activity per mg. The three undialyzed fractions accounted for 90-99 per cent of the protein activity though comprising only 35-40 per cent of the proteins. 4. Active accumulation (for 24 hours vs. 1 hour in the above absorption experiments) resulted in the same distribution among the fractions though the differences were more pronounced and the total uptake greater. 5. Uptake of P32 resulted in essentially the same distribution of activities among the protein fractions as in the case of Ca45. 6. A working hypothesis to explain these results is tentatively proposed. [ABSTRACT FROM AUTHOR]

Presents a table of physiological contents. Biochemistry and metabolism; Ecophysiology, stress and adaptation; Identification of guttation fluid proteins.