The role of sucrose as a signaling molecule in plants was originally proposed several decades ago. However, recognition of sucrose as a true signal has been largely debated and only recently this role has been fully accepted. The best-studied cases of sucrose signaling involve metabolic processes, such as the induction of fructan or anthocyanin synthesis, but a large volume of scattered information suggests that sucrose signals may control a vast array of developmental processes along the whole life cycle of the plant. Also, wide gaps exist in our current understanding of the intracellular steps that mediate sucrose action. Sucrose concentration in plant tissues tends to be directly related to light intensity, and inversely related to temperature, and accordingly, exogenous sucrose supply often mimics the effect of high light and cold. However, many exceptions to this rule seem to occur due to interactions with other signaling pathways. In conclusion, the sucrose role as a signal molecule in plants is starting to be unveiled and much research is still needed to have a complete map of its significance in plant function.

1990. Suerose and fruetan metabolism of different wheat cultivars at chilling temperatures. -Physiol. Plant. 78; 554-559.Four wheat (Tritieum aestivum L.) varieties cultivated in different climates from subtropics to North Patagonia were used to study sucrose and fructan metabolism in plants when submitted to a cold period. Higher levels of sugars were found in the more cold tolerant cultivars. Sucrose synthase (EC 2.4.1.13) and sucrose phosphate synthase (EC 2.4.1.14) activities showed a 2-3 fold increase when plants were grown at 4°C for 10 days. The more cold-tolerant wheat cultivars also showed the higher levels of enzyme activities. These metabolieal changes were not due to anatomical or morphological differences produced during growth at 4°C. Materials and methods:. .;:•*•,;: Plant materialFour wheat (Triticum aestivum L.) eultivars adapted to different clitnates were used. Cultivar Trigal 800 and cv. Buck Patacon seeds were kindly provided by Ing. J.

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Temperature change induces morpho-physiological responses, whose significance for plant function under this modified environmental condition is mostly unclear. Plastic responses to temperature changes from optimal (25°C) to chilling (5°C) conditions or vice versa, as compared with constant temperature treatments, were studied in spring and winter wheat. Plants grown at 5°C had smaller leaves, less stomata and larger root systems than their counterparts grown at 25°C. Plants at 5°C therefore had larger effective root : shoot ratio, defined as the ratio between total area of roots and stomata. Spring and winter cultivars differed in root growth, leaf growth and stomatal frequency following a shift in temperature. Nevertheless, both cultivar types reached similar effective root : shoot ratios, which were typical for each temperature. We also found changes in leaf thickness, transverse vascular bundle area and xylem : phloem ratios. Shifting temperature triggered rapid changes in leaf and root carbohydrate content and osmotic potential. Our results suggest that temperature-induced plasticity may play a role in ameliorating possible water deficits caused by large soil–air temperature differentials in natural environments.

The role of Ca(2+) in the induction of enzymes involved in fructan synthesis (FSS) mediated by sucrose was studied in wheat (Triticum aestivum). Increase of FSS enzyme activity and induction of the expression of their coding genes by sucrose were inhibited in leaf blades treated with chelating agents (EDTA, EGTA and BAPTA). Ca(2+) channel blockers (lanthanum chloride and ruthenium red) also inhibited the FSS response to sucrose, suggesting the participation of Ca(2+) from both extra- and intra- cellular stores. Sucrose induced a rapid Ca(2+) influx into the cytosol in wheat leaf and root tissues, shown with the Ca(2+ )sensitive fluorescent probe Fluo-3/AM ester. Our results support the hypothesis that calcium is a component of the sucrose signaling pathway that leads to the induction of fructan synthesis.

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Four wheat (Triticum aestivum L.) varieties cultivated in different climates from subtropics to North Patagonia were used to study sucrose and fructan metabolism in plants when submitted to a cold period. Higher levels of sugars were found in the more cold tolerant cultivars. Sucrose synthase (EC 2.4.1.13) and sucrose phosphate synthase (EC 2.4.1.14) activities showed a 2–3 fold increase when plants were grown at 4°C for 10 days. The more cold‐tolerant wheat cultivars also showed the higher levels of enzyme activities. These metabolical changes were not due to anatomical or morphological differences produced during growth at 4°C

The induction of fructosylsucrose-synthesizing activity (FSS) by sugars was tested using detached primary leaf blades of several wheat (Triticum aestivum L.) cultivars, immersed in different sugars solutions for 24 h in the dark. The highest induction was brought about by sucrose, while glucose, fructose and maltose also caused significant induction. 5-Ketofructose, 3-methylglucose and 6-deoxyglucose, which cannot be metabolized by plants, produced no induction at all. The fact that mannose also failed to induce FSS and that mannoheptulose did not inhibit the induction by sucrose suggests that the hexokinase-sensing system may not be involved. The protein phosphatase inhibitor okadaic acid and the calmodulin-dependent protein kinase antagonist W7 inhibited FSS induction while some types of protein kinase inhibitors, such as staurosporine and genistein, had less or no effect, respectively. Cycloheximide and cordycepin completely inhibited the induction response, indicating that transcription and translation are necessary for the FSS induction. Northern blot experiments using a sucrose:fructan-6-fructosyl transferase probe gave a clear indication that the mRNA for this enzyme, which is almost absent in control leaves, is dramatically increased after a 24-h treatment with 500 mM sucrose, and confirmed the inhibition produced by protein kinase and protein phosphatase inhibitors. Our data indicate that protein kinase and protein phosphatase activities take part in the chain of events that intervenes in the induction of fructan synthesis by sugars.