Ethylene and not embolism is required for wound-induced tylose development in stems of grapevines

Abstract

The pruning of actively growing grapevines (Vitis vinifera) resulted in xylem vessel embolisms and a stimulation of tylose formation in the vessels below the pruning wound. Pruning was also followed by a 10-fold increase in the concentration of ethylene at the cut surface. When the pruning cut was made under water and maintained in water, embolisms were prevented, but there was no reduction in the formation of tyloses or the accumulation of ethylene. Treatment of the stems with inhibitors of ethylene biosynthesis (aminoethoxyvinylglycine) and/or action (silver thiosulfate) delayed and greatly reduced the formation of tyloses in xylem tissue and the size and number of those that formed in individual vessels. Our data are consistent with the hypotheses that wound ethylene production is the cause of tylose formation and that embolisms in vessels are not directly required for wound-induced tylosis in pruned grapevines. The possible role of ethylene in the formation of tyloses in response to other stresses and during development, maturation, and senescence is discussed.

Figure 1.

Images of experimental treatments. A, A rubber tube traps the cut end of stem at one end and is connected at the other end to a 3-mL syringe that collects gas evolved from the cut end. B, The stem is cut in degassed water, and the cut end is capped with a water-filled rubber bulb to avoid exposure of the cut surface to air in experimental periods. Scale bar = 4 cm. [See online article for color version of this figure.]

Figure 2.

Cryo-SEM of vessels 4 mm under the cut surface in samples at day 6 after cutting. A, Gas-filled vessel in stem cut in air and capped with an air-filled rubber pipette bulb. B, Ice-filled vessel in stem cut in water and capped in a water-filled rubber pipette bulb. The textured substance in the vessel is ice. Images in A and B are representative of 40 to 60 vessels observed in each of two or three replications of stem sections per treatment. Occasionally, gas-filled vessels were observed in stem sections cut under water (less than 10%) and only very rarely was an ice-filled vessel observed in stem sections cut in air. C, Water (ice)-filled vessels (two vessels at the left) and tyloses formed in a water-filled vessel (the vessel at the right) in stems cut in water and capped in a water-filled rubber pipette bulb. Surface ice was evaporated to reveal the tylose structure.

Figure 3.

Tylose development in stems 4 mm under the cut surface at day 8. In stems cut in air (A) and in stems cut under water (B), most vessels contained tyloses. Scale bar = 200 μm.

Figure 4.

Pattern of ethylene concentration evolved from the cut end of grape stem. Data are for samples of gas collected for 1 h and are normalized to 7.2-mm-diameter shoot. A, Stem cut and remained in air (white circle) or cut in water and then exposed to air after 2 h (black circle), both without the treatment of an ethylene inhibitor. B, Stem cut in AVG (white circle), STS (black circle), or STS followed by AVG (gray circle) solutions and then exposed to air after 2 h. Data are from one replication and are representative of three or four replications for each treatment, although the timing of the peaks did not coincide exactly in each experiment. Vertical shaded and white bars indicate approximate nighttime and daytime, respectively.

Figure 5.

Tylose morphology 4 mm under the cut surface in stems treated without ethylene inhibitors (A–C) and in those with ethylene inhibitors (D–F). A, No tyloses were present in stems at day 0. B, In stems cut in air, most vessels were completely occluded by multiple compactly arranged tyloses at day 9. C, In stems cut in water and then exposed to air (controls for ethylene inhibitor treatments), most vessels were again completely occluded by multiple compactly arranged tyloses at day 9. D and E, In stems cut in and treated with AVG, no tyloses were present at day 9 (D), and few, small tyloses (arrows) occurred in few vessels at day 13 (E). F and G, In stems cut in and treated with STS, few small tyloses (arrow) were present in few vessels at day 9 (F), and tyloses were still few but larger in some vessels at day 13 (G). H and I, In stems treated with STS followed by AVG, tyloses did not develop in most vessels at day 9 (H) and were small and few and present in few vessels at day 13 (I). Scale bar = 200 μm in A to C, 50 μm in D to H, and 100 μm in I.

Figure 6.

Frequency of tyloses at 4 mm under the cut surface of stems treated with and without ethylene inhibitors (AVG, STS, or STS followed by AVG). Each datum is presented as the mean with one sd (n = 3).