Changes in xyloglucan endotransglycosylase (XET) activity during hormone-induced growth in lettuce and cucumber hypocotyls and spinach veil suspension cultures

Abstract

The promotion of stem elongation in dwarf pea plants by GA3 has been correlated with an increase in extractable xyloglucan endotransglycosylase (XET) activity (Potter and Fry, 1993). Doses of auxin that caused either elongation or lateral swelling in pea stems have not been found to increase XET activity (Fry et al., 1992). We therefore explored the generality of the association between GA3 action and XET activity by testing three other bioassay systems. A similar correlation was found in the hypocotyls of intact lettuce seedlings, where GA3 strongly promoted elongation and doubled the extractable XET activity per unit fresh weight. In the hypocotyls of intact cucumber seedlings, GA3 evoked a prolonged promotion of elongation for at least 96 h; this was correlated with only a small increase in XET activity per unit fresh weight of tissue. IAA promoted elongation for only 48 h, but this effect was correlated with a larger increase in XET activity per unit fresh weight than that due to GA3. In cell suspension cultures of spinach, much of the XET activity was present in solution in the culture medium. GA3 had little effect on this fraction for the first 9 d, but thereafter the hormone suppressed a sudden burst in soluble extracellular XET activity that occurred in the untreated controls. A further proportion of the XET activity was ionically wall-bound; this fraction was enhanced by GA3 in the early phase of the growth cycle of the culture and inhibited in later phases. Pre-adaptation of the culture by growth for 6 years in the presence of 10−7 M GA3 intensified the response of the cells to re-addition of GA3. We conclude that there is no simple or unique relationship between total extractable XET activity and GA3 action. Nevertheless, we have extended the evidence that XET is often subject to the effects of GA3 in systems where this hormone influences growth.

A xyloglucan oligosaccharide‐active, transglycosylating‐D‐glucosidase from the cotyledons of nasturtium (Tropaeolum majus L) seedlings – purification, properties and characterization of a cDNA clone

“…It is becoming increasingly clear that related enzymes are associated with xyloglucan metabolism in primary cell walls. XETs are involved in developmentally regulated xyloglucan metabolism (Nishitani and Tominaga, 1992;Potter and Fry, 1994;Redgwell and Fry, 1993;Schroder et al, 1998;de Silva et al, 1994), and a xyloglucan oligosaccharide-specific α-xylosidase is associated with xyloglucan turnover in elongation growth (Koyama et al, 1983;O'Neil et al, 1989).…”

In Vivo Colocalization of Xyloglucan Endotransglycosylase Activity and Its Donor Substrate in the Elongation Zone of Arabidopsis Roots

“…XET activity is often correlated with growth rate (Fry et al, 1992;Hetherington and Fry, 1993;Pritchard et al, 1993;Potter and Fry, 1994;Xu et al, 1995;Palmer and Davies, 1996; Antosiewicz et al, 1997; Catalá et al, 1997). Xyloglucan turnover is correlated with auxin-induced elongation (Labavitch and Ray, 1974;Nishitani and Masuda, 1982), and in dicots, both auxin-induced elongation and xyloglucan breakdown are inhibited by lectins and by antibodies that bind xyloglucans and thereby presumably shield them from enzymic attack (Hoson and Masuda, 1991; Hoson et al, 1991).…”

Application of brassinosteroid to Tabebuia alba (Bignoniaceae) plants

“…They also observed that GA 3 , benzyladenine (cytokinin), and 1-aminocyclopropane-1-carboxylic acid (ACC) had no detectable effect on TCH4 expression. However, Potter and Fry (1994) and Smith et al (1996) observed a GA-stimulated growth and XET activity in many tissues. Xu et al (1995) suggested that no relationship was seen between the effects of auxins on cell elongation and XET activity, but endogenous IAA (3-indoleacetic acid) stimulated TCH4 gene expression.…”