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Photoassimilate produced by mature leaves is usually loaded into the phloem as sucrose. Transport of sucrose from the mesophyll cells to the phloem might involve an apoplastic step or be entirely symplastic, depending on species. Acid invertase occurs as both soluble and cell-wall-bound forms and has been detected in mature leaves. However, the ability of this enzyme to act as a regulator of carbon export and storage depends on whether it occurs either in the sucrose transport path (which could decrease export), or is located within the mesophyll cells (potentially resulting in intracellular futile cycling between sucrose synthesis in the cytoplasm and hydrolysis in the vacuole). Tissue-level localization of acid invertase was investigated by tissue printing, which establishes protein distribution within a leaf. Antiserum was raised against a synthetic peptide corresponding to a region close to the active site of acid invertase. Tissue prints from Pisum sativum L. and Hordeum vulgare L. showed invertase to be located in the vascular regions, which was not observed in Fuchsia hybrida L. This corresponds to differences in the presence of oligosaccharides in leaf extracts and in the pattern of plasmodesmatal connections between mesophyll cells and the vasculature. We hypothesize that the location of acid invertase activity is implicated in species-specific differences in sucrose and oligosacchande metabolism. [ABSTRACT FROM AUTHOR]

Leaf sucrose, starch, hexose and maximum extractable soluble acid invertase activity were compared throughout the day in source leaves of 13 plant species chosen for their putative phloem-loading type (apoplastic or symplastic). Four species which represent the different phloem-loading types (tomato, barley, maize and Fuchsia) were studied in detail. Using this information we wished to determine whether a positive correlation between foliar carbohydrates and acid invertase activity exists in leaves from different species and, furthermore, whether this relationship is determined by phloem-loading type. Acid invertase activity was relatively constant throughout the day in all species. The extent of sucrose, hexose and starch accumulation and the sucrose: starch ratio measured at a given time were species-dependent. No correlations were found between foliar soluble acid invertase activity and the hexose, sucrose or starch content of the leaves in any of the species, regardless of phloem-loading type. The species examined could be divided into three distinct groups: (1) high sucrose, low invertase; (2) low sucrose, low invertase; and (3) low sucrose, high invertase. The absence of an inverse relationship between leaf sucrose, hexose or starch contents and endogenous soluble acid invertase suggests that this enzyme is not directly involved in carbon partitioning in leaves but serves an auxiliary function. [ABSTRACT FROM AUTHOR]

An asporogenous strain of the pink snow mould fungus, Monographella nivalis (Schaffnit) E. Müller, anamorph Gerlachia nivalis Ces. ex Sac.) W. Gams & E. Müller (Syn. Fusarium nivale Ces. ex Sacc.), grew at 5 °C on a defined salts medium plus vitamins and utilized a variety of simple and polymeric carbohydrates as the sole carbon and energy source. Mycelium was grown at temperatures between 3 and 15 °C in aerated submerged fermentation culture in chemically defined mediam plus sucrose. Optimum growth rates of 0.035-0.033 h-1 occurred between 9 and 12 °C. Growth in a simple medium showed that all biochemical and physiological processes necessary for growth were functional at 3 °C. The growth performance of the organism at low temperatures was no better than would be expected from extrapolation of mesophilic growth responses to temperature. The optimum growth temperature of 9-12 °C showed that some biochemical or physiological process was impaired above 12 °C. Uptake and incorporation of 35S-methionine by mycelium at different temperatures showed that general protein synthesis increased up to 25 °C, and hence was not responsible per se for the sensitivity to temperatures above 12 °C. Heat shock proteins were synthesized at the relatively low temperature of 25 °C, consistent with the low temperature optimum for growth. When grown with sucrose as the sole carbon source, the mycelium catalyzed the extracellular hydrolysis of sucrose, releasing glucose and fructose together with a small amount of fructan trisaccharides and a trace of tetra- and penta-saccharides. Fructan accumulation was transient, corresponding with maximal rates of sucrose hydrolysis. Most biomass formation occurred in the absence of fructan in the culture, hence fructan was not necessary for growth at low temperature and did not appear to function as a cryoprotectant. Invertase activity was mostly (60-70%) bound to mycelium; the remainder was free in the culture supernatant. The regulation of invertase expression appeared to be by sucrose-induction, rather than by end-product repression. Rates of sucrose hydrolysis in culture were temperature-sensitive and were markedly depressed above 12c, indicating inhibition of invertase formation. [ABSTRACT FROM AUTHOR]

Discusses the distribution and activity of invertase in mature leaves of Lolium temulentum in relation to the anabolic and catabolic processes that occur in such tissues. Metabolism of sucrose in heterotophic epidermis and vasculature tissues; Changes in assimilate abundance; Patterns of gene expression; Metabolism of oligosaccharides based on sucrose.