A Developmentally Based Categorization of Branching in Trifolium repens L.: Influence of Nodal Roots

Thomas, R. G.; Hay, M. J. M.; Newton, P. C. D.

doi:10.1093/aob/mcf200

Cited by 17 publications

(39 citation statements)

References 18 publications

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“…With the exception of Acaena, the growth of the secondary branches on the lateral branch at phytomer X was closely similar to that of the branches formed on the primary stem distal to X. In Acaena, instead, the lateral branch at phytomer X formed distinct short shoots with well developed small leaves separated by very short internodes at their non-branched nodes, morphologically similar to those previously described for Trifolium repens (Thomas et al, 2002).…”

Section: Development Of the Nodal Root System At The Start Of Phase IIsupporting

confidence: 82%

“…These treatments were selected, on the basis of our previous experience, to assess whether the mechanisms of control of shoot branching are similar to those we have described for T. repens (Thomas et al, 2002(Thomas et al, , 2003a.…”

Section: Experimental Designmentioning

confidence: 99%

“…For comparison, data for Trifolium repens are included from Thomas et al (2002). No branching occurred at the equivalent phytomers on control plants in treatment 1 over this same period.…”

Section: Development Of the Nodal Root System At The Start Of Phase IImentioning

confidence: 99%

“…To a large extent, current understanding of the outgrowth of axillary buds depends upon the long-standing observations that control is to a greater or lesser degree determined by the stem apex (Phillips, 1975). We have recently found, however, that in the nodally rooting prostrate clonal herb, Trifolium repens, the role of the apical bud is secondary to that of the root system and to that of the actively growing branches (Thomas et al, 2002(Thomas et al, , 2003a. T. repens is one of a group of clonal herb species that have prostrate (plagiotropic) stems and are capable of forming root systems from primordia sited at each node along their plagiotropic stems (Klimes et al, 1997).…”

Section: Introductionmentioning

confidence: 99%

“…We therefore predict that, under conditions preventing the formation of new nodal roots in plagiotropic species, natural selection would similarly have favoured optimal allocation of dwindling root-supplied resources to the exploration for favourable rooting micro-sites by tight regulation of shoot growth. This appears to have been achieved in the absence of nodal roots in T. repens by the maintenance of near maximal internode extension in the primary stem in conjunction with restricted outgrowth of branches from many of the axillary buds along it (Thomas et al, 2002(Thomas et al, , 2003a. We have found the mechanism of regulation of axillary bud outgrowth in this species to be dominated by the allocation of limited quantities of root-supplied resource(s) (RSR) essential for branching (Thomas et al, loc.…”

Section: Introductionmentioning

confidence: 99%

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Evidence suggests plagiotropic clonal species have evolved a branching physiology emphasizing regulation by nodal roots

Thomas

Hay

2004

Evol Ecol

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In the plagiotropic nodally rooting clonal herb, Trifolium repens, the development of branches on stems is primarily controlled by the presence of nodal roots, and apical dominance is of secondary importance; only six to ten branches form distal to the youngest nodal root on a horizontal stem. We assessed the hypothesis that this phenomenon is general for clonal herbs with prostrate nodally rooting stems, and that they all have the same physiological system regulating branching, by testing a selection of species from diverse angiosperm families that exhibit either 'phalanx' (Leptinella (Asteraceae), Hydrocotyle (Apiaceae), Acaena (Rosaceae)) or 'guerilla' (Vinca (Apocynaceae), Glechoma and Lamiastrum (Lamiaceae)) growth strategies. In all these species the establishment of a single nodal root on a prostrate stem, otherwise prevented from nodally rooting, induced the outgrowth of a limited number of axillary buds (the number of which was species specific) at the nodes immediately distal to the newly established root, thereby indicating a phenotypic response similar to that in T. repens. Furthermore, their branching responses to manipulative treatments were also similar to those of T. repens, indicating that their regulatory physiology of axillary bud outgrowth from their prostrate stems is similar. We conclude that, for the group of prostrate nodally rooting clonal herbs as a whole, the apical dominance phenotype arises predominantly from variation in the supply of resources from nodal roots rather than from repression of axillary buds by apical tissues (apical dominance). We suggest that evolution of such a physiological mechanism enhances the exploration for patchily distributed favourable nodal rooting sites by regulating shoot development so as to efficiently utilise the diminishing intra-plant availability of root-supplied resources. For the species examined, inter-specific variation in intensity of branching response to a nodal root is shown to be linked to a trade off in foraging strategy, with the allocation of resources primarily to explorative growth (long internodes, few branches) in 'guerilla' species or to exploitive growth (short internodes, many branches) in 'phalanx' species.

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Section: Development Of the Nodal Root System At The Start Of Phase IIsupporting

confidence: 82%

Section: Experimental Designmentioning

confidence: 99%

“…For comparison, data for Trifolium repens are included from Thomas et al (2002). No branching occurred at the equivalent phytomers on control plants in treatment 1 over this same period.…”

Section: Development Of the Nodal Root System At The Start Of Phase IImentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Evidence suggests plagiotropic clonal species have evolved a branching physiology emphasizing regulation by nodal roots

Thomas

Hay

2004

Evol Ecol

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Resource allocation in clonal plants

Lötscher

Progress in Botany

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The role of nodal roots in prostrate clonal herbs: ‘phalanx’ versus ‘guerrilla’

Thomas

Hay

2010

Evol Ecol

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The influence of nodal rooting on branching was studied in three evolutionarily and morphologically diverse species of prostrate clonal herbs: Tradescantia fluminensis (a monocotyledonous extreme 'phalanx' species), Calystegia silvatica (a dicotyledonous extreme 'guerrilla' species) and Trifolium repens (a dicotyledonous intermediate species). In all three, branch development from axillary buds is regulated by a positive signal produced by roots together with inhibitory influences from both pre-existing branches and shoot apical buds (apical dominance). Responses to nodal roots are cumulative and increased root activity leads to more vigorous bud outgrowth. In the absence of nodal roots, a single basal root system is unable to maintain continued extension growth of the shoot. We suggest that as individual nodal roots and stem internodes are both short-lived in these nodally-rooting clonal species, the plants' investment in them is minimal. Thus, in contrast to perennial species lacking nodal roots, individual root systems in prostrate clonal herbs are small and stems have little secondary thickening and development of long-distance transport tissues. Hence the decline in extension growth of the shoot in the absence of nodal roots could be linked to the weak development of long-distance transport tissues in their relatively thin horizontal stems and to resource sharing between primary stems and lateral branches (as suggested by the greater retardation of primary stem growth in the more profusely branched 'phalanx' species (Trifolium and Tradescantia) than in the weakly branched 'guerrilla' species, Calystegia). These findings are consistent with the view that the long-term persistence of genotypes of nodally-rooting prostrate species is dependent upon them encountering the moist conditions required to facilitate the continual development of new young nodal root systems.

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A Developmentally Based Categorization of Branching in Trifolium repens L.: Influence of Nodal Roots

Cited by 17 publications

References 18 publications

Evidence suggests plagiotropic clonal species have evolved a branching physiology emphasizing regulation by nodal roots

Evidence suggests plagiotropic clonal species have evolved a branching physiology emphasizing regulation by nodal roots

Resource allocation in clonal plants

The role of nodal roots in prostrate clonal herbs: ‘phalanx’ versus ‘guerrilla’

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