Physical and chemical interactions between aphids and plants

Abstract

Aphids feed from sieve tubes deep inside the host plant. Therefore, aphids must be able to recognize their host plant(s) and to direct their stylets which must be long and thin enough to reach and puncture the sieve tubes at a particular site. Sieve tubes in angiosperms are longitudinal arrays of sieve element/companion cell modules which are highly sensitive to disturbance of any kind. The sieve tubes dispose of elaborate sealing mechanisms such as protein plugging and callose sealing which are triggered by a rise in calcium in the sieve tubes. Aphids seem to have developed a range of physical and chemical measures to limit the amount of calcium influx in response to stylet puncturing. Loss of sieve-element turgor pressure induced by stylet insertion is minimized by the minute stylet volume. Turgor-dependent Ca(2+) influx, possibly mediated by mechano sensitive Ca(2+) channels, must therefore be limited. The components of the sheath and watery saliva play a pivotal role in establishing the physical and chemical constraints on the rise of calcium. Most likely, sheath saliva prevents the influx of calcium from the apoplast by sealing the stylet puncture site while watery saliva may prevent plugging and sealing of sieve plates by potential interaction with SE sap ingredients.

A Diurnal Component to the Variation in Sieve Tube Amino Acid Content in Wheat

“…Many stylet bundles exude at a slow rate (between (Will and van Bel, 2006), and it is possible that these proteins act to affect exudation rates. These proteins do not exist in monocotyledonous plants, but a qualitatively similar mechanism has been proposed for these (Will and van Bel, 2006).…”

“…Many stylet bundles exude at a slow rate (between (Will and van Bel, 2006), and it is possible that these proteins act to affect exudation rates. These proteins do not exist in monocotyledonous plants, but a qualitatively similar mechanism has been proposed for these (Will and van Bel, 2006). Sap exuded from cut stylet bundles 2.8 times more slowly on resistant compared with susceptible alfalfa varieties, consistent with such partial occlusion by a ST defense system (Girousse and Bourneville, 1994).…”

“…Sampling of phloem sap from individual STs can also be achieved using aphid stylectomy (Fisher and Frame, 1984). Aphids feed exclusively from the phloem (for review, see Will and van Bel, 2006), and a large literature shows that their stylet bundles penetrate and extract phloem sap from an individual ST (Kimmins and Tjallingii, 1985;Tjallingii and Esch, 1993). It is possible to sever the stylets of feeding aphids and collect samples of phloem sap (Unwin, 1978;Pritchard, 1996;Zhu et al, 2005), and studies have confirmed that the samples obtained represent pure ST sap (Tjallingii and Esch, 1993).…”

Plant- and stimulus-specific variations in remote-controlled sieve-tube occlusion

“…PD constriction is reached by Ca 2+ -dependent 9 deposition of β-1,3-glucane polymers (callose) into the apoplast, caused by activation of membrane-associated callose synthase (β-1,3-glucan synthase); PD re-opening is achieved by a callose-degrading membrane-associated β-1,3-glucanase. 10 In complement sieve-tubes are occluded by structural 7,4 or, possibly, water-soluble proteins 11 ( Fig. 1).…”

Molecular sabotage of plant defense by aphid saliva

“…In response to injury in SEs of intact broad bean plants, spindle-like protein bodies (forisomes) disperse, and parietal proteins detach from the plasma membrane and SE reticulum (3), plugging the sieve plates (4), whereas callose deposition constricts the pores in the sieve plates from the apoplast side (7,8). Protein meshworks inside SEs that collapse as a consequence of wounding are described for some dicotyledonous plants (6,9) and water-soluble proteins, which become insoluble after wounding, thereby plugging the sieve plate, are postulated for Poaceae (10). Different combinations of these mechanisms can be observed in various plant families (11) with exception of forisomes that are restricted to the Fabaceae (12,13).…”