The synthesis andaccumulation of proteinase inhibitor I in excised tomato leaves can be induced with oligosaccharides obtained by fungal endo-a-1,4-polygalacturonase digestion of a pectic polysaccharide (Mr 5000-10,000) isolated from tomato leaves. Active oligosaccharides were-also released from isolated tomato leaf cell walls by endopolygalacturonases partially purified from tomato plants. It.is suggested that oligosaccharides, released from plant cell wall pectic polysaccharides by either endogenous or exogenous endopolygalacturonases at a wound or infection site, may have hormone-like roles in regulating plant defense responses in unwounded tissues many centimeters away from the site of release.Severe wounding of tomato or potato leaves by attacking pests or other mechanical damage releases a putative wound hormone that is transported throughout the plants where it induces leaves to initiate synthesis and accumulation of two proteinaceous inhibitors of serine endopeptidases (1). This proteinase inhibitorinducing factor (PIIF) has been consistently associated with polysaccharides ofwidely varying sizes (2), suggesting that PIIF activity may be intrinsic to a specific saccharide sequence or structure.Recently, a highly active tomato PIIF fraction of Mr 5000-10,000 was shown to be pectic polysaccharide. It has a composition similar to that of an enzymically produced fragment of sycamore cell walls, of Mr 200,000, that was shown to have activity similar to that oftomato PIIF (3). This evidence suggested that PIIF activity may be associated with a structural component of plant cell walls. However, in view.of the large sizes of.both the tomato pectic polysaccharide and the sycamore cell wall fragment, it is questionable whether they would be rapidly transported through the plant vascular system after wounding in vivo.-In this communication we report that an endopolygalacturonase purified from.the fungus Rhizopus stolonifer (4) degrades tomato PIIF into oligosaccharides that are active inducers of proteinase inhibitor I when supplied to excised tomato leaves. We also show that a mixture of two endopolygalacturonases, partially purified from. tomato fruit, degrades both tomato PIIF and purified tomato cell walls into PIIF-active oligosaccharides. These results suggest that PIIF activity produced in vivo by cell damage resides in small hydrolytic fragment(s) of plant cell walls. MATERIALS AND METHODSTomato PIIF is a partially purified, highly methylated soluble pectic polysaccharide of Mr 5000-10,000 on the basis of its elution profile from Sephadex G-50 when compared to protein standards (unpublished data). Acid-demethylated tomato PIIF polysaccharide was prepared by dissolving 50 mg oftomato PIIF in 5 ml of 2 M trifluoroacetic acid and heating under reduced pressure at 859C for 1 hr. The reaction mixture was chilled in an ice bath and then centrifuged at 25,000 X g for 10 min. The supernatant was lyophilized to remove the trifluoroacetic acid. The residue was dissolved in water, adsorbed on DE-52 (Whatman),...
Among the many plant mineral nutrients, potassium (K) stands out as a cation having the strongest influence on quality attributes that determine fruit marketability, consumer preference, and the concentration of critically important human-health associated phytonutrients. However, many plant, soil, and environmental factors often limit adequate uptake of K from the soil in sufficient amounts to satisfy fruit K requirements during development to optimize the aforementioned quality attributes. The objectives of this review are 1) to summarize published study abstracts on the effects of soil and/or foliar K fertilization as well as diverse K forms, on fruit phytonutrient concentrations; and 2) to illustrate the important role of K forms on fruit quality with a case study of Cucumis melo L (muskmelon) fruit produced with optimal soil applied K . The muskmelon studies will compare commercial sources (forms) of K applied to examine seasonal effects (spring vs. autumn) and the number of foliar K applications during fruit development on fruit marketability (maturity, yield, firmness, soluble solids, sugars, relative sweetness), consumer preference attributes (sugar content, sweetness, texture), and phytochemical concentrations (K, ascorbic acid, and β-carotene concentrations). Numerous studies have consistently demonstrated that specific K fertilizer forms, in combination with specific application regimes, can improve fruit quality attributes. Potassium fertilizer forms in order of effectiveness (Glycine (Gly)-complexed K=K 2 SO 4 ≥KCl>no K> KNO 3 ) when applied wet (foliar or hydroponic) vs. dry (soil) were generally superior in improving fruit marketability attributes, along with many humanhealth nutrients. The muskmelon case study demonstrated that two K forms: Gly-complexed K and K 2 SO 4 , combined with a silicone-based surfactant, applied weekly, as a foliar spray, during fruit development, from both autumn and spring-grown plants, had the greatest impact on improving fruit marketability attributes (maturity, yield, firmness, and sugars), as well as fruit quality attributes (human-health bioactive compounds K, ascorbic acid, and β-carotene). Among several foliar applied K salts studied under field conditions so far, salts with relatively low salt indices appeared to have the greatest impacts on fruit quality when applied during the mid-to late-season fruit development periods.
aktuell-magazin TICKER Kunstlicht macht Spinat wertvoller Lässt man frischen Spinat bis zu neun Tage in einer rund um die Uhr beleuch-teten Auslage (bei ca. 0 °C), wird er kei-neswegs zu welkem Biomüll. Das fluo-reszierende Licht, das Supermärkte zur
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