Cell Surfaces in Plant-Microorganism Interactions

Abstract

MATERIALS AND METHODSEthylene production and cell wail hydroxyproline-rich glycoprotein (HRGP) biosynthesis are greatly enhanced in melon (Cucumin melo cv.Cantaloup charentais) seedlings infected with CoUetotrichum lagenariwm.Short-term experiments performed in the presence of specific inhibitors of the ethylene pathway from methionine, namely L-canaline and aminoethoxyvinylglycine, indicate that under non-toxic conditions, both ethylene and I'4Clhydroxyproline deposition in the cell wall of infected tissues are significantly lowered. On the contrary, treatment of healthy tissues with 1-aminocyclopropane 1-carboxylic acid, a natural precursor of ethylene, stimulates both the production of the hormone and the incorporation of I'Clhydroxyproline into cell wall proteins.The data provide the first evidence of the in vivo effect of ethylene on the cell wall hydroxyproline-rich glycoprotein biosynthesis in plants.It has been reported in previous papers (10, 11) that melon seedlings respond to a fungal attack by the accumulation of HRGP2 in their cell walls. Special attention has been paid to this modification of the cell surface for it involves glycoproteins, a class of components often mediating cell to cell interactions (5). Availability of plants with higher or lower than normal amounts of cell wall hydroxyproline allowed us to ascertain that the enrichment of diseased plants in HRGP is closely associated to their defense against microorganisms (9). Indirect evidence suggests a role for ethylene in the regulation of this mechanism. When supplied exogenously to intact plants, this hormone promotes an enrichment of the cell wall in hydroxyproline (24) corresponding to an enrichment in HRGP (9). A similar hydroxyproline response occurs after wounding of plant tissues (7), a process otherwise well-known to stimulate the production ofethylene (13). Inasmuch as large amounts of this hormone are often released by infected plants (1,22) Patil and Tang (21), and then diluted to appropriate concentrations with 50 mm phosphate buffer (pH 6.0). AVG and ACC were each dissolved and adjusted to I x lo-3 M in 50 mm phosphate buffer (pH 6.0). Appropriate dilutions were then made with the same buffer.Ethylene Measurement. The production of ethylene was measured from excised seedlings, petiole of the first leaf, and from C. lagenarium, as follows. Four excised seedlings (without roots) were enclosed for 24 h in 570-ml serum flasks stopped with serum caps, and containing 30 ml of the usual growth medium (28). Newly excised seedlings were used everyday. The petioles were cut into 5-mm segments as previously indicated (9), and divided into lots of 2 g. The segments of each lot were incubated for 4 h under the light in 13 ml serum vials, stopped with serum vaccine caps, containing 6 ml of a medium consisting of 2% sucrose in 50 mm K-phosphate buffer (pH 6.0). A CO2 trap made of filter paper soaked with 200 td of 1 N KOH was inserted into each vial.Measurements of ethylene from C. lagenarium were performed on a 6-d-old culture i...

Cell Surfaces in Plant-Microorganism Interactions

“…However, this assumption is questionable in instances where the rise in ethylene production is an early event which happens soon after inoculation (21,25). In infected melon seedlings, for instance, ethylene is enhanced 30 h after inoculation; that is about 2 d before the appearance of symptoms (26,32). At that time, neither the main hydrolytic activities usually displayed by pathogens (2, 10), nor the pathogen itself (30) are quantitatively detectable; so far no toxin release could be detected either.…”

“…Knowledge of host-pathogen interactions which lead to the increased production of ethylene such as in the melon-Colletotrichum lagenarium system (26,32) is of prime importance in understanding the role ofthis hormone in cell wall modifications.…”

“…Colletotrichum lagenarium was obtained by liquid culture on a glucose-ammonium nitrate synthetic medium (10); 12-d-old culture was routinely used. A liquid culture of Phytophtora parasitica was obtained as indicated for Phytophtora megasperma (5).In previous studies, ethylene was reported to play a role in the accumulation of HRGP2 in the cell wall of diseased plants, and this accumulation was shown to be associated with the plant's defense mechanism (11,12,32). Knowledge of host-pathogen interactions which lead to the increased production of ethylene such as in the melon-Colletotrichum lagenarium system (26,32) is of prime importance in understanding the role ofthis hormone in cell wall modifications.…”

Response to Xanthomonas campestris pv.vesicatoria in Tomato Involves Regulation of Ethylene Receptor Gene Expression

“…SA in particular is essential in mounting the resistance response in many plantpathogen interactions (Delaney et al, 1994). Ethylene regulates several genes involved in defense responses, including those encoding PR proteins such as chitinases, ␤-1,3-glucanases, and PR1 (Deikman, 1997), phytoalexin synthesis enzymes (Ecker and Davis, 1987), defensin (Penninckx et al, 1996), and hydroxy-Pro-rich glycoproteins (Toppan et al, 1982). Since ethylene induces the expression of many defense-related genes, increasing ethylene synthesis during infection would be one way of initiating a defense response.…”

Effect of Submergence on the Cell Wall Composition of Deep-Water Rice Internodes

“…However, in rapidly growing rice internodes, we found an increased hydroxyproline content in the cell walls which are expected to be softer than the cell walls of nongrowing internodes. It is known that hydroxyprolinerich glycoproteins accumulate in response to added ethylene (22,25). Submergence causes ethylene accumulation in rice internodes (17).…”