192:) When auxin level raise to a certain concentration, auxin will interact with F-Box protein and stimulate the auxin transcriptional repressors. This leads to degradation of auxin protein. Nevertheless, transcriptional response does not only regulate auxin itself but also mediate the gene expression for protein encoded for cell-wall modification (cell wall-remodelling agents). It was found that when treated plant with exogenous auxin, the expression of pectin methylesterases,
152:. Expansin is a pH-dependent hormone that could cause irreversible wall extension and wall stress relaxation without displaying any enzymatic activity. It is activated after detecting the acidification in cell wall solution, consequently breaking down hydrogen bonds or covalent bonds in the cell wall to allow
255:
species to more ancient members within the plant family tree is undeniable. Latter observations on different plant species could help identify conserved hormones and genes, or underlying mechanisms that support the theory, with the confirmation of SAUR19's role in auxin-induced hypocotyl elongation
231:
pH sensors, there is a lack of reliable method in quantifying the absolute apoplast pH value in plants. For instance, scientists made use of whole-organ resolution as part of their apoplastic pH measurement. However, such research methods on the cellular level wouldn't establish equivalent validity
210:
This acid-growth model has been updated to account for new mechanistic understanding. The decrease in apoplast pH value leads to cell-wall modification; the resulting increased extensibility of cell wall results in cell growth. The reduction in apoplastic pH is mediated by auxin-induced mechanisms.
126:
Within the 20-year timespan, many scientists have actively contributed to examining and reevaluating Hager's acid-growth hypothesis. Despite the accumulation of observations that evidently identify the final target of the auxin-induced action to be H-ATPase, which excretes H protons to the apoplast
239:
Limitations on particular plant organs: Most of the research has been limited to the aerial organs of plants. Instead of studying the growth-promoting effect that auxin brings to the aerial organs, David
Pacheco Villalobos discovers the inhibitory effect auxin has on root
73:
Auxin was known to be a growth stimulant, but it was not until the year 1971 that Hager and
Cleland proposed the "acid-growth hypothesis," which primarily suggested the correlation between auxin and apoplast acidification. The hypothesis states that susceptible
55:(SAUR) proteins, which in turn regulate protein phosphatases that modulate proton-pump activity. Acid growth is responsible for short-term (seconds to minutes) variation in growth rate, but many other mechanisms influence longer-term growth.
46:
then activates a range of enzymatic reactions which modifies the extensibility of plant cell walls. Since its formulation in 1971, the hypothesis has stimulated much research and debate. Most debates have concerned the signalling role of
82:
value. The following precise natural mechanism of the wall-loosening process; however, remained unknown at the time. With reference to auxin-induced elongation regarded as "acid-growth," Hager based his experiment on plasmolyzed
175:
Transcriptional modification is crucial in the growth and development of cells When a plant is treated with auxin treatment, auxin-induced transcriptional changes occurs within minutes, which indicates that both
78:
cells expel H protons through membrane-bound proton pumps into the apoplast (space between plant cell wall and cytoplasm) at an accelerated pace, causing a decrease in the apoplastic
144:
through possible hydrolysis of bonds. Back in the year 1971, Hager anticipated the possible existence of enzymes from his experiment which involves heat-killing and denaturation of
243:
Narrow coverage of plant species: Data that supported the early development of the theory initially originated from coleoptiles, epicotyls, and hypocotyls of a wide range of
494:
Hager A, Debus G, Edel HG, Stransky H, Serrano R (November 1991). "Auxin induces exocytosis and the rapid synthesis of a high-turnover pool of plasma-membrane H(+)-ATPase".
993:
Pacheco-Villalobos D, Díaz-Moreno SM, van der
Schuren A, Tamaki T, Kang YH, Gujas B, Novak O, Jaspert N, Li Z, Wolf S, Oecking C, Ljung K, Bulone V, Hardtke CS (May 2016).
101:
In auxin-treated coleoptile and stem (hypocotyl) sections, auxin induces proton extrusion into the apoplast, which could decrease the pH value by as much as one full unit.
140:
With H protons being excreted to the apoplast as one of the wall-loosening factors (WLF), scientists believed that the mechanism involves activation of
127:
and take in K ions through its rectifying K channel in the following years, the controversy has been carried over till today as an ongoing debate.
97:
for further re-examination. By 1900s, four core pieces of qualitative evidences solidified the core concept of the theory, as summarized below:
211:
With auxin acting as the primary signalling tool, it initiates apoplastic acidification via two mechanisms. Auxin stimulates the activity of the
215:(H-ATPase), acidifying the wall. Auxin changes the cell wall's composition directly by increasing the transcription of wall-modifying agents.
868:
Prat R, Gueissaz MB, Goldberg R (1984-12-01). "Effects of Ca2+ and Mg2+ on
Elongation and H+ Secretion of Vigna radiata Hypocotyl Sections".
148:. However, it wasn't until 1992 when Simon McQueen-Mason and his collaborators discovered the most pH-responsive substance in the apoplast-
156:
slipping- a mechanism that allows microfibrils to slip into the cell wall matrix without extension. Meanwhile, it could also loosen the
117:(Fc) could also induce rapid cell elongation and growth, despite its primary role in promoting extensive acidification of the apoplast.
34:. It was originally proposed by Achim Hager and Robert Cleland in 1971. They hypothesized that the naturally occurring plant hormone,
111:
Acidic buffers of pH 5.0 could accelerate cell elongation at the same or even greater rate in comparison to that induced by auxin.
599:
Hager A (December 2003). "Role of the plasma membrane H+-ATPase in auxin-induced elongation growth: historical and new aspects".
1044:"Constitutive Expression of Arabidopsis SMALL AUXIN UP RNA19 (SAUR19) in Tomato Confers Auxin-Independent Hypocotyl Elongation"
459:
Durand H, Rayle DL (June 1973). "Physiological evidence for auxin-induced hydrogen-ion secretion and the epidermal paradox".
251:
species. To note, it all began with observations from sunflower. The importance to expand the research territory beyond
212:
184:
is necessary for auxin-induced growth. One of the major mechanisms for auxin control in plant is the transport
93:). Subsequently, the wall-acidification model initiated continual controversy among scientists, and act as the
731:"Crystal structure and activities of EXPB1 (Zea m 1), a beta-expansin and group-1 pollen allergen from maize"
946:"Live imaging of intra- and extracellular pH in plants using pHusion, a novel genetically encoded biosensor"
177:
529:
Rayle DL (March 1973). "Auxin-induced hydrogen-ion secretion in Avena coleoptiles and its implications".
181:
695:
227:
Measurement of pH value: Despite optimal high-sensitivity detection brought by the implementation of
1090:
233:
51:
and the molecular nature of cell wall modification. The current version holds that auxin activates
189:
185:
141:
1042:
Spartz AK, Lor VS, Ren H, Olszewski NE, Miller ND, Wu G, Spalding EP, Gray WM (February 2017).
1073:
1024:
975:
926:
850:
801:
760:
711:
668:
616:
581:
546:
511:
476:
441:
390:
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276:
89:
1063:
1055:
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742:
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382:
355:
317:
145:
1108:
252:
105:
27:
699:
386:
359:
163:
within the cell wall to enable the cell to take in more water and expand via turgor and
1068:
1043:
1019:
995:"The Effects of High Steady State Auxin Levels on Root Cell Elongation in Brachypodium"
994:
970:
945:
921:
896:
881:
845:
820:
755:
730:
23:
663:
638:
577:
436:
409:
1102:
281:
244:
228:
564:
Rayle DL, Cleland R (1977). "Control of plant cell enlargement by hydrogen ions".
373:
Du M, Spalding EP, Gray WM (2020-03-04). "Rapid Auxin-Mediated Cell
Expansion".
248:
223:
There are several aspects of the theory that remain contentious. These include:
205:
160:
897:"Rapid apoplastic pH measurement in Arabidopsis leaves using a fluorescent dye"
735:
Proceedings of the
National Academy of Sciences of the United States of America
612:
271:
232:
at the quantitative level due to the plausible leaking of the signal from the
153:
114:
75:
746:
686:
Cosgrove DJ (September 2000). "Loosening of plant cell walls by expansins".
157:
94:
84:
1077:
1028:
979:
930:
854:
836:
805:
764:
715:
672:
620:
550:
515:
480:
445:
394:
329:
108:(pH~7) into the apoplast could inhibit auxin-induced elongation and growth.
654:
1010:
961:
796:
779:
729:
Yennawar NH, Li LC, Dudzinski DM, Tabuchi A, Cosgrove DJ (October 2006).
266:
193:
149:
39:
1059:
585:
426:
542:
507:
472:
321:
164:
912:
707:
639:"Two endogenous proteins that induce cell wall extension in plants"
48:
35:
31:
38:(indole-3-acetic acid, IAA), induces H proton extrusion into the
410:"Enhancement of wall loosening and elongation by acid solutions"
43:
821:"Pectin methylesterases and pectin dynamics in pollen tubes"
637:
McQueen-Mason S, Durachko DM, Cosgrove DJ (November 1992).
196:
and other protein that changes cell wall's shape and size.
79:
944:
Gjetting KS, Ytting CK, Schulz A, Fuglsang AT (May 2012).
256:
in tomatoes being one of the more recent discoveries.
22:
is a theory that explains the expansion dynamics of
346:Cleland R (1971-06-01). "Cell Wall Extension".
308:Hager A, Menzel H, Krauss A (March 1971). "".
8:
778:Arsuffi G, Braybrook SA (5 January 2018).
1067:
1018:
969:
920:
844:
795:
754:
662:
435:
425:
236:into those originating from the apoplast.
566:Current Topics in Developmental Biology
293:
188:response through singling from F-box (
632:
630:
59:History and development of the theory
7:
895:Villiers F, Kwak JM (January 2013).
819:Bosch M, Hepler PK (December 2005).
341:
339:
303:
301:
299:
297:
387:10.1146/annurev.pp.22.060171.001213
360:10.1146/annurev.pp.22.060171.001213
882:10.1093/oxfordjournals.pcp.a076858
14:
375:Annual Review of Plant Physiology
348:Annual Review of Plant Physiology
950:Journal of Experimental Botany
901:Plant Signaling & Behavior
784:Journal of Experimental Botany
780:"Acid growth: an ongoing trip"
136:Discovery of hydrolytic enzyme
122:Constraints and interpretation
1:
578:10.1016/S0070-2153(08)60746-2
408:Rayle DL, Cleland R (1970).
213:plasma-membrane proton pump
1125:
203:
42:. Such derived apoplastic
870:Plant and Cell Physiology
613:10.1007/s10265-003-0110-x
601:Journal of Plant Research
104:Infiltration of neutral
747:10.1073/pnas.0605979103
171:Transcriptional control
837:10.1105/tpc.105.037473
20:acid-growth hypothesis
655:10.1105/tpc.4.11.1425
200:Modern interpretation
1011:10.1105/tpc.15.01057
1060:10.1104/pp.16.01514
700:2000Natur.407..321C
427:10.1104/pp.46.2.250
234:endomembrane system
131:Ongoing development
69:Emergence of theory
962:10.1093/jxb/ers040
797:10.1093/jxb/erx390
543:10.1007/BF00390285
508:10.1007/BF00202963
473:10.1007/BF00387475
322:10.1007/BF00386886
219:Unsolved questions
190:regulatory protein
142:hydrolytic enzymes
53:small auxin-up RNA
913:10.4161/psb.22587
277:Plant development
146:enzyme inhibitors
90:Helianthus annuus
64:Early development
1116:
1093:
1088:
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1081:
1071:
1054:(2): 1453–1462.
1048:Plant Physiology
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990:
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876:(8): 1459–1467.
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741:(40): 14664–71.
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87:from sunflower (
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831:(12): 3219–26.
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723:
694:(6802): 321–6.
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1005:(5): 1009–24.
999:The Plant Cell
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956:(8): 3207–18.
936:
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825:The Plant Cell
811:
790:(2): 137–146.
770:
721:
678:
643:The Plant Cell
626:
607:(6): 483–505.
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521:
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451:
420:(2): 250–253.
400:
365:
354:(1): 197–222.
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282:Plant hormones
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414:Plant Physiol
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178:transcription
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54:
50:
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44:acidification
41:
37:
33:
29:
25:
21:
16:
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1047:
1037:
1002:
998:
988:
953:
949:
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569:
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537:(1): 63–73.
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417:
413:
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378:
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351:
347:
316:(1): 47–75.
313:
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222:
209:
174:
161:microfibrils
139:
125:
88:
72:
52:
19:
17:
15:
572:: 187–214.
381:: 379–402.
240:elongation.
229:fluorescent
206:Acid growth
182:translation
115:Fusiococcin
288:References
272:Plant cell
253:angiosperm
154:xyloglucan
85:hypocotyls
76:coleoptile
194:expansins
186:inhibitor
158:cellulose
95:blueprint
1103:Category
1078:27999086
1029:27169463
980:22407646
931:23221761
855:16322606
806:29211894
765:16984999
716:11014181
673:11538167
621:12937999
551:24458665
516:24186531
481:24458722
446:16657445
395:32131604
330:24488103
267:Meristem
261:See also
150:expansin
40:apoplast
1091:Table 1
1069:5291034
1020:4904674
971:3350929
922:3745564
846:1315365
756:1595409
696:Bibcode
245:monocot
165:osmosis
1109:Auxins
1076:
1066:
1027:
1017:
978:
968:
929:
919:
853:
843:
804:
763:
753:
714:
688:Nature
671:
664:160229
661:
619:
584:
549:
531:Planta
514:
496:Planta
479:
461:Planta
444:
437:396573
434:
393:
328:
310:Planta
106:buffer
32:plants
28:organs
586:20280
249:dicot
49:auxin
36:auxin
24:cells
1074:PMID
1025:PMID
976:PMID
927:PMID
851:PMID
802:PMID
761:PMID
712:PMID
669:PMID
617:PMID
582:PMID
547:PMID
512:PMID
477:PMID
442:PMID
391:PMID
326:PMID
247:and
180:and
26:and
18:The
1064:PMC
1056:doi
1052:173
1015:PMC
1007:doi
966:PMC
958:doi
917:PMC
909:doi
878:doi
841:PMC
833:doi
792:doi
751:PMC
743:doi
739:103
704:doi
692:407
659:PMC
651:doi
609:doi
605:116
574:doi
539:doi
535:114
504:doi
500:185
469:doi
465:114
432:PMC
422:doi
383:doi
356:doi
318:doi
314:100
30:in
1105::
1072:.
1062:.
1050:.
1046:.
1023:.
1013:.
1003:28
1001:.
997:.
974:.
964:.
954:63
952:.
948:.
925:.
915:.
903:.
899:.
874:25
872:.
849:.
839:.
829:17
827:.
823:.
800:.
788:69
786:.
782:.
759:.
749:.
737:.
733:.
710:.
702:.
690:.
667:.
657:.
645:.
641:.
629:^
615:.
603:.
580:.
570:11
568:.
545:.
533:.
510:.
498:.
475:.
463:.
440:.
430:.
418:46
416:.
412:.
389:.
379:71
377:.
352:22
350:.
338:^
324:.
312:.
296:^
167:.
80:pH
1080:.
1058::
1031:.
1009::
982:.
960::
933:.
911::
905:8
884:.
880::
857:.
835::
808:.
794::
767:.
745::
718:.
706::
698::
675:.
653::
647:4
623:.
611::
588:.
576::
553:.
541::
518:.
506::
483:.
471::
448:.
424::
397:.
385::
362:.
358::
332:.
320::
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