Abstract:

Background and Aims Species of Cactaceae are well adapted to arid habitats. Determinate growth of the primary root, which involves early and complete root apical meristem (RAM) exhaustion and differentiation of cells at the root tip, has been reported for some Cactoideae species as a root adaptation to aridity. In this study, the primary root growth patterns of Cactaceae taxa from diverse habitats are classified as being determinate or indeterminate, and the molecular mechanisms underlying RAM maintenance in Cactaceae are explored. Genes that were induced in the primary root of Stenocereus gummosus before RAM exhaustion are identified. Methods Primary root growth was analysed in Cactaceae seedlings cultivated in vertically oriented Petri dishes. Differentially expressed transcripts were identified after reverse northern blots of clones from a suppression subtractive hybridization cDNA library. Key Results All species analysed from six tribes of the Cactoideae subfamily that inhabit arid and semi-arid regions exhibited determinate primary root growth. However, species from the Hylocereeae tribe, which inhabit mesic regions, exhibited mostly indeterminate primary root growth. Preliminary results suggest that seedlings of members of the Opuntioideae subfamily have mostly determinate primary root growth, whereas those of the Maihuenioideae and Pereskioideae subfamilies have mostly indeterminate primary root growth. Seven selected transcripts encoding homologues of heat stress transcription factor B4, histone deacetylase, fibrillarin, phosphoethanolamine methyltransferase, cytochrome P450 and gibberellin-regulated protein were upregulated in S. gummosus root tips during the initial growth phase. Conclusions Primary root growth in Cactoideae species matches their environment. The data imply that determinate growth of the primary root became fixed after separation of the Cactiodeae/Opuntioideae and Maihuenioideae/Pereskioideae lineages, and that the genetic regulation of RAM maintenance and its loss in Cactaceae is orchestrated by genes involved in the regulation of gene expression, signalling, and redox and hormonal responses.

Author affiliation: Shishkova, Svetlana. Universidad Nacional Autónoma de México; México

Author affiliation: Las Peñas, Maria Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Instituto Multidisciplinario de Biología Vegetal (p); Argentina. Universidad Nacional de Córdoba; Argentina

Author affiliation: Napsucialy Mendivil, Selene. Universidad Nacional Autónoma de México; México

Author affiliation: Matvienko, Marta. University of California; Estados Unidos

Author affiliation: Kozik, Alex. University of California; Estados Unidos

Author affiliation: Montiel, Jesús. Universidad Nacional Autónoma de México; México

Author affiliation: Patiño, Anallely. Universidad Nacional Autónoma de México; México

Author affiliation: Dubrovsky, Joseph. Universidad Nacional Autónoma de México; México

Abstract:

Determinate primary root growth in Cactaceae has been interpreted as an adaptation to dry environments. However, little information is available regarding ecological patterns of this process. Our research question was whether primary root length is affected by the determinate growth pattern of the plant or following predictions from resource allocation theories. We analyzed the presence of apical meristem exhaustion and patterns of primary root length (PRL), days until the end of growth (day's post-germination, DPG) and seed mass in Gymnocalycium monvillei and G. quehlianum, which present different elevation distributions and wide elevation ranges. We analyzed five elevation provenances for G. monvillei (878, 1250, 1555, 1940 and 2230 m a.s.l.), and three for G. quehlianum (610, 950 and 1250 m a.s.l.). One hundred seeds per species per altitude were set to germinate in vertical petri dishes. We measured PRL and DPG in each seedling and also seed mass. Both species present determinate growth and PRL varied between species and among populations. PRL was higher in G. quehlianum. DPG was related to differences between species in PRL: roots of G. quehlianum grow for a longer period. In both species we found differences among elevation provenances, with higher PRL at the extremes of the distribution. Among elevation provenances, DPG was significantly related to PRL in G. monvillei, and marginally significantly related in G. quehlianum. Seed size was not related to differences in PRL between species or among elevation provenances. The comparison between species and among elevation provenances suggests that a higher PRL would be related to more extreme environments; this assumption agrees with plant resource allocation theories, which predict a lower shoot : root ratio with increasingly stressful environments.

Author affiliation: Martino, P. A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentina

Author affiliation: Bauk, Karen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentina

Author affiliation: Ferrero, María Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentina

Author affiliation: Gurvich, Diego Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentina

Author affiliation: Las Peñas, Maria Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentina