Uptake of 3-o-Methylglucose by Healthy and Hypomyces-infected Squash Hypocotyls

Abstract

Abstract. Rates of uptake of 3-o-methylglucose (MeG) by squash (Cucurbita maxima) hypocotyl sections from above lesions caused by Hypomyces solani f. sp. cecurbitae, race 1, are 2-fold greater than uptake by comparable tissues from healthy plants. Kinetic analyses indicate (i) that a single (constitutive) carrier system, with a Michaelis constant (Km) of 25 to 30 mm, mediates the transport of MeG into healthy hypocotyl cells and (ii) that an additional (inducible) system with a much lower Km (ca. 2 mM) is present in diseased hypoootyls. In both systems MeG uptake is inhibited competitively by glucose. The inducible transport system(s) in diseased tissues has a higher temperature coefficient, greater sensitivity to metabolic inhibitors and larger accumulation capacity than the one in healthy plants. While the nature of the oonstitutive system is ambiguous, the inducible carrier mechanism is a typical active transport system. These results indicate that increased rates of uptake and accumulation of metabolites by diseased tissues can be caused by new transport systems.Changes in host membrane permeability during pathogenesis have been noted in many plant diseases (13). In a recent study of permeability changes in Hypomyces-infected squash hypocotyls, it was concluded that the permeability of host cells in tissues above lesions did not differ from that of comparable cells in healthy plants (6). In fact, the functioning of plasma membranes as barriers to the movement of water and low molecular weight nonelectrolytes was not altered in individual cells until the fungus grew within their vicinity ( 1-3 cell diameters). Then, the permeability change was sudden, and the plasmolyzability of host cells was destroyed.Thatcher l (11) In this study, transport kinetics of 3-o-methylglucose are compared in healthy squash hypocotyls and hypocotyl tissues above lesions caused by Hypomnyces (Fusarium) solani f. sp. cucurbitae, race 1. With the use of a glucose derivative, 3-o-methylglucose, uptake by glucose transport systems can be investigated while complications from metabolic processes are avoided (8). Materials and MethodsInoculation Procedures. Cultures of the pathogen (Hypomnyces solani f. sp. cucurbitae Snyd. and Hans., race 1) were maintained as described previously (5). Squash (Cucurbita inaxima Dcne "Pink Banana") were grown in the greenhouse in U. C. mix (1). Three-to 6-day-old seedlings were inoculated with 1 ml suspensions of macroconidia (6 X 105/ml) at the base of hypocotyls. Uninoculated seedlings of identical plantings were maintained as controls. Lesions developed at the base of hypocotyls 5 to 7 days after inoculation. As in a previous study (6), seedlings with lesions 1 to 2 cm in length were used as experimental materials.Uptake of 3-o-methylglucose. Methods for studying uptake are modified from those described by Reinhold and Eshbar (8). Batches of 20 hypocotyl cross sections (ca. 1.5 mm thick) were rinsed briefly (30 sec), blotted dry, and weighed (400-500 mg fresh wt). Sections were taken from uninocu...

Induction and Development of Increased Ion Absorption in Corn Root Tissue

“…Chloramphenicol at bacteriostatic concentrations has no effect on the washing response or on uptake. Actinomycin D, cycloheximide, and 6-methylpurine strongly inhibited the development of increased absorption rates, which is in agreement with previous investigations (7,15,25), and which supports the general supposition that RNA 15 ,ug/ml; 6-methylpurine, 0.5 mM; and cycloheximide, 10 ueg/ml. and protein synthesis underlie the development of the washing response.…”

“…The apparent Km values do not change significantly with washing. This result is like that of Liittge and Laties (15) for corn roots, but is unlike that obtained with some other vegetative tissues (7,8,20,24,25). In corn roots the enhancement of accumulation rate must lie not with the formation of different and more efficient transport agents (or carriers), but rather with a greater quantity or a greater turnover of existing agents.…”

“…Washed tissue develops additional, high affinity mechanisms. Hancock (7,8) also reached this conclusion for 3-0-methyl glucose absorption in squash hypocotyl segments. He obtained evidence by use of cycloheximide and actinomycin D that RNA and protein synthesis were implicated in the washing response.…”

Effects of Helminthosporium carbonum Toxin on Absorption of Solutes by Corn Roots

“…Corrections were made for selfabsorption as needed. Uptake of 3-o-methyl-D-glucose was measured by the method of Hancock (7). Roots containing labeled leucine and glutamic acid were boiled and homogenized in water; counts for water extract and homogenate were combined to obtain total uptake, which was corrected for selfabsorption of tissue.…”

The sink-specific and stress-regulated Arabidopsis STP4 gene: enhanced expression of a gene encoding a monosaccharide transporter by wounding, elicitors, and pathogen challenge.

“…It has been suggested that the primary role of stress-induced cell wall invertases is the increased hydrolysis of extracellular sucrose and thus the productioii of sufficient hexoses as an energy source for the various stress responses (Sturm and Chrispeels, 1990). In fact, studies by Hancock (1969Hancock ( , 1970 clearly showed that the uptake of 3-O-methylglucose (3-OMG) into hypocotyl sections from wounded or infected squash is higher than it is in control sections, and this additional transport activity was assigned to an inducible transporter in diseased or wounded hypocotyls. The energy that is necessary for this additional transport could be provided by elicitor-induced dephosphorylation and activation of the respective H+-ATPase (Vera-Estrella et al, 1994).…”