Table 2
Cytosolic protein contamination of cucumber hypocotyl apical or basal segment cell wall extracts. Glucose-6-P-dehydrogenase activity was taken as a cytosolic protein marker. Results are expressed as units of Glucose-6-P-dehydrogenase activity (g DW 1). One unit 1⁄4 nmol of Glucose-6-P min 1. Results are shown as mean S.D. (P < 0.05) obtained from three replicates of 1.2 g each.
It has also been demonstrated in many plant tissues that expansin expression is correlated with growth [39,31]. Acid induced extension is associated with expansin activity [39]. As recently was published that an expansin from the PGPR Bacillus subtilis may be involved in the promotion of bacterial colonization of wheat [25] expansin involvement in other processes in the Azospirillum–plant interaction remains a possibility.
Finally, we analyzed some tightening factors. It has been sug- gested that peroxidase-catalyzed cross-linking between phenolic residues of matrix polysaccharides may partially account for wall stiffening [51]. Peroxidases are widespread in plant tissues and are often particularly abundant in cell walls, to which they are mainly ionically bound. In the classical peroxidase cycle these enzymes use H2O2 as an oxidant in a two step reaction that leads to a cross- linking of wall polysaccharides [21]. These processes have remarkable consequences for wall expansion during growth and differentiation [22,28]. Consistent with this phenomenon is the finding that there is an inverse correlation between peroxidase activity and growth [51,15]. Hydrogen peroxide may be used as oxidative coupling of phenolic moieties in the cell wall [21]. Moreover, NADH oxidase activity may be involved in H2O2 level regulation. A balance between intracellular and wall-localized H2O2 production could control wall stiffening and cell growth rate [7]. A key finding in this context is that H2O2 has been demonstrated to be a limiting factor in wall stiffening in vitro and inhibits IAA-induced elongation of coleoptile segments [56].
Total peroxidase activity was greater in basal segments than in apical ones. Inoculation did not alter this activity (Fig. 4A). As we demonstrated, while apical segments were still actively elongating, basal ones had stopped their elongation growth (Fig. 3). The higher total peroxidase activity detected in the basal region might be indicating that wall-stiffening reactions mediated by peroxidase- catalyzed cross-linking of wall-polymer-phenolic residues are occurring. The absence of differences between Azospirillum treated and non-treated seedlings might be showing a kind of homeostasis process as this total activity is the sum of all peroxidases activities. In fact, ferulic acid peroxidase activity was lower in both apical and basal segments from inoculated seedlings (Fig. 4B). On the other hand, NADH oxidase activity was higher in basal than in apical regions and it also showed lesser values in both regions of inocu- lated seedlings (Fig. 4C). The endogenous H2O2 level can be related to the elongation process. Fry et al. [18] demonstrated that extra- protoplasmic dimerisation of feruloyl groups was limited by H2O2 supply. According to this result, Schopfer [55] found that the apo- plastic H2O2 level in dicotyledons was lower in the hypocotyl elongation zone than in the basal one. Based on the lesser NADH oxidase and ferulic acid peroxidase activities detected in inoculated seedlings in both types of segments, the lower provision of H2O2 in the cell walls could delay stiffening, enabling them to keep on elongating while non-inoculated ones had stopped their growth. Nevertheless, it is worth to note that there are other oxidases present in the cell wall participating in the H2O2 supply [7].
Fig. 4. Cell wall peroxidase activities in control non-inoculated (empty bars) or Azo- spirillum-inoculated (filled bars) cucumber hypocotyl basal or apical segments. (A) Total peroxidase activity assayed with guaiacol as a substrate, (B) ferulic acid peroxi- dase activity assayed against ferulic acid, and (C) NADH oxidase activity. Activities were determined by measuring the initial rate of the decrease of absorbance at corre- sponding maxima. Reactions were followed spectrophotometrically. Total peroxidase activity was measured at 470 nm for 5 min. Blanks were measured without H2O2 added. Results are expressed as units of total peroxidase. g DW 1. One U 1⁄4 mmol of tetraguaiacol min 1. Ferulic acid peroxidase activity w
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ตารางที่ 2ปนเปื้อนของโปรตีน cytosolic แตงกวา hypocotyl apical หรือฐานส่วนผนังเซลล์สารสกัดจาก กลูโคส-6-P-พร่องกิจกรรมถูกนำมาเป็นเครื่องหมาย cytosolic โปรตีน ผลลัพธ์จะแสดงเป็นหน่วยของกลูโคส-6-P-พร่องกิจกรรม (g DW 1) นาโนโมลว่าหนึ่งหน่วยของกลูโคส-6-P นาที 1 ผลลัพธ์จะแสดงเป็นหมายความว่า เอส (P < 0.05) ได้จากสาม replicates 1.2 กรัมมันมียังได้แสดงให้เห็นในเนื้อเยื่อพืชต่าง ๆ ว่า นิพจน์ expansin มีความสัมพันธ์กับการเจริญเติบโต [39,31] กรดเกิดนามสกุลเกี่ยวข้องกับกิจกรรม expansin [39] ที่เพิ่ง ถูกประกาศว่า เป็น expansin จากเชื้อ PGPR ที่ subtilis อาจมีส่วนส่งเสริมการล่าอาณานิคมแบคทีเรียของข้าวสาลี [25] expansin การมีส่วนร่วมในกระบวนการอื่น ๆ ในการโต้ตอบ Azospirillum – โรงงานยังคงมี ความเป็นไปได้ในที่สุด เราวิเคราะห์ปัจจัยบางขัน แล้ว gested ว่า ฮอสกระบวนการเชื่อมโยงระหว่างฟีนอตกค้างของสารเมทริกซ์อาจบางส่วนบัญชีสำหรับผนังแข็ง [51] sug- อิสระจะแพร่กระจายในเนื้อเยื่อพืช และมักมากโดยเฉพาะอย่างยิ่งในผนังเซลล์ ซึ่งส่วนใหญ่ ionically เลี่ยง ๆ ในวงจรคลาสสิกฮอส เอนไซม์เหล่านี้ใช้ H2O2 เป็นตัวต้านอนุมูลอิสระในปฏิกิริยาขั้นตอนที่สองที่นำไปสู่การข้าม - การเชื่อมโยงของผนังไรด์ [21] กระบวนการเหล่านี้มีผลที่โดดเด่นสำหรับการขยายตัวของผนังในระหว่างการเจริญเติบโตและสร้างความแตกต่าง [22,28] สอดคล้องกับปรากฏการณ์นี้คือการค้นพบว่ามีความสัมพันธ์ผกผันระหว่างกิจกรรมฮอสและเจริญเติบโต [51,15] ไฮโดรเจนเปอร์ออกไซด์อาจจะใช้เป็นข้อต่อออกซิเดชันของฟีนอลิ moieties ในผนังเซลล์ [21] นอกจากนี้ NADH oxidase กิจกรรมอาจจะมีในกฎระเบียบระดับ H2O2 ความสมดุลระหว่างการผลิต H2O2 ภายในเซลล์ และผนังเป็นภาษาท้องถิ่นสามารถควบคุม stiffening ผนังและอัตราการเติบโตของเซลล์ [7] คีย์หาในบริบทนี้คือ H2O2 ได้แสดงให้เห็นจะ เป็นปัจจัยจำกัดใน stiffening ผนังในหลอดทดลอง และยับยั้ง IAA ที่เกิดการยืดตัวของส่วน coleoptile [56]Total peroxidase activity was greater in basal segments than in apical ones. Inoculation did not alter this activity (Fig. 4A). As we demonstrated, while apical segments were still actively elongating, basal ones had stopped their elongation growth (Fig. 3). The higher total peroxidase activity detected in the basal region might be indicating that wall-stiffening reactions mediated by peroxidase- catalyzed cross-linking of wall-polymer-phenolic residues are occurring. The absence of differences between Azospirillum treated and non-treated seedlings might be showing a kind of homeostasis process as this total activity is the sum of all peroxidases activities. In fact, ferulic acid peroxidase activity was lower in both apical and basal segments from inoculated seedlings (Fig. 4B). On the other hand, NADH oxidase activity was higher in basal than in apical regions and it also showed lesser values in both regions of inocu- lated seedlings (Fig. 4C). The endogenous H2O2 level can be related to the elongation process. Fry et al. [18] demonstrated that extra- protoplasmic dimerisation of feruloyl groups was limited by H2O2 supply. According to this result, Schopfer [55] found that the apo- plastic H2O2 level in dicotyledons was lower in the hypocotyl elongation zone than in the basal one. Based on the lesser NADH oxidase and ferulic acid peroxidase activities detected in inoculated seedlings in both types of segments, the lower provision of H2O2 in the cell walls could delay stiffening, enabling them to keep on elongating while non-inoculated ones had stopped their growth. Nevertheless, it is worth to note that there are other oxidases present in the cell wall participating in the H2O2 supply [7].Fig. 4. Cell wall peroxidase activities in control non-inoculated (empty bars) or Azo- spirillum-inoculated (filled bars) cucumber hypocotyl basal or apical segments. (A) Total peroxidase activity assayed with guaiacol as a substrate, (B) ferulic acid peroxi- dase activity assayed against ferulic acid, and (C) NADH oxidase activity. Activities were determined by measuring the initial rate of the decrease of absorbance at corre- sponding maxima. Reactions were followed spectrophotometrically. Total peroxidase activity was measured at 470 nm for 5 min. Blanks were measured without H2O2 added. Results are expressed as units of total peroxidase. g DW 1. One U 1⁄4 mmol of tetraguaiacol min 1. Ferulic acid peroxidase activity w
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