Signaling events for photomorphogenic root development.

A germinating seedling incorporates environmental signals such as light into developmental outputs. Light is not only a source of energy, but also a central coordinative signal in plants. Traditionally, most research focuses on aboveground organs' response to light; therefore, our understanding of photomorphogenesis in roots is relatively scarce. However, root development underground is highly responsive to light signals from the shoot and understanding these signaling mechanisms will give a better insight into early seedling development. Here, we review the central light signaling hubs and their role in root growth promotion of Arabidopsis thaliana seedlings.

Germination and initial development in vitro, and acclimatization of Oeceoclades maculata (Orchidaceae), aiming at its reintroduction in natural environments

Oeceoclades maculata is a terrestrial orchid species that has potential for commercial purposes. Taking that into consideration, the present investigation aimed at studying its germination and initial development in vitro as well as its acclimatization. The influence of Murashige and Skoog (MS), Knudson C (KC), and Vacin and Went (VW) media in the presence and absence of 0.3% activated charcoal on in vitro germination and protocorm development were investigated. The effects of different concentrations of BA in combination with 0.5 mg L-1 NAA on seedling multiplication and growth were evaluated. The possibility of using dark-grown stem segments for micropropagation and acclimatization under laboratory and field conditions was also assessed. The results indicated that the most adequate media for germination were full-strength MS enriched with activated charcoal or KC supplemented with 1.5 mg L-1 BA in combination with 0.5 mg L-1 NAA. In terms of protocorm development, KC supplemented with 1.5 mg L-1 BA alone or in combination with 0.5 mg L-1 NAA provided the best results. The addition of 1.5 mg L-1 BA in combination with 0.5 mg L-1 NAA to KC medium favored the best results for seedling multiplication and development. The use of dark-grown stem segments is a viable alternative for the micropropagation of O. maculata. Regarding acclimatization, 100% survival of plants was observed during the initial phases and under field conditions average survival was 53.33%.(AU)

TCP15 interacts with GOLDEN2-LIKE 1 to control cotyledon opening in Arabidopsis.

After germination, exposure to light promotes the opening and expansion of the cotyledons and the development of the photosynthetic apparatus in a process called de-etiolation. This process is crucial for seedling establishment and photoautotrophic growth. TEOSINTE BRANCHED 1, CYCLOIDEA, and PROLIFERATING CELL FACTORS (TCP) transcription factors are important developmental regulators of plant responses to internal and external signals that are grouped into two main classes. In this study, we identified GOLDEN2-LIKE 1 (GLK1), a key transcriptional regulator of photomorphogenesis, as a protein partner of class I TCPs during light-induced cotyledon opening and expansion in Arabidopsis. The class I TCP TCP15 and GLK1 are mutually required for cotyledon opening and the induction of SAUR and EXPANSIN genes, involved in cell expansion. TCP15 also participates in the expression of photosynthesis-associated genes regulated by GLK1, like LHCB1.4 and LHCB2.2. Furthermore, GLK1 and TCP15 bind to the same promoter regions of different target genes containing either GLK or TCP binding motifs and binding of TCP15 is affected in a GLK1-deficient background, suggesting that a complex between TCP15 and GLK1 participates in the induction of these genes. We postulate that GLK1 helps to recruit TCP15 for the modulation of cell expansion genes in cotyledons and that the functional interaction between these transcription factors may serve to coordinate the expression of cell expansion genes with that of genes involved in the development of the photosynthetic apparatus.

A novel strategy to uncover specific GO terms/phosphorylation pathways in phosphoproteomic data in Arabidopsis thaliana.

BACKGROUND: Proteins are the workforce of the cell and their phosphorylation status tailors specific responses efficiently. One of the main challenges of phosphoproteomic approaches is to deconvolute biological processes that specifically respond to an experimental query from a list of phosphoproteins. Comparison of the frequency distribution of GO (Gene Ontology) terms in a given phosphoproteome set with that observed in the genome reference set (GenRS) is the most widely used tool to infer biological significance. Yet, this comparison assumes that GO term distribution between the phosphoproteome and the genome are identical. However, this hypothesis has not been tested due to the lack of a comprehensive phosphoproteome database. RESULTS: In this study, we test this hypothesis by constructing three phosphoproteome databases in Arabidopsis thaliana: one based in experimental data (ExpRS), another based in in silico phosphorylation protein prediction (PredRS) and a third that is the union of both (UnRS). Our results show that the three phosphoproteome reference sets show default enrichment of several GO terms compared to GenRS, indicating that GO term distribution in the phosphoproteomes does not match that of the genome. Moreover, these differences overshadow the identification of GO terms that are specifically enriched in a particular condition. To overcome this limitation, we present an additional comparison of the sample of interest with UnRS to uncover GO terms specifically enriched in a particular phosphoproteome experiment. Using this strategy, we found that mRNA splicing and cytoplasmic microtubule compounds are important processes specifically enriched in the phosphoproteome of dark-grown Arabidopsis seedlings. CONCLUSIONS: This study provides a novel strategy to uncover GO specific terms in phosphoproteome data of Arabidopsis that could be applied to any other organism. We also highlight the importance of specific phosphorylation pathways that take place during dark-grown Arabidopsis development.

Ultra-High-Density QTL Marker Mapping for Seedling Photomorphogenesis Mediating Arabidopsis Establishment in Southern Patagonia.

Arabidopsis thaliana shows a wide range of genetic and trait variation among wild accessions. Because of its unparalleled biological and genomic resources, Arabidopsis has a high potential for the identification of genes underlying ecologically important complex traits, thus providing new insights on genome evolution. Previous research suggested that distinct light responses were crucial for Arabidopsis establishment in a peculiar ecological niche of southern Patagonia. The aim of this study was to explore the genetic basis of contrasting light-associated physiological traits that may have mediated the rapid adaptation to this new environment. From a biparental cross between the photomorphogenic contrasting accessions Patagonia (Pat) and Columbia (Col-0), we generated a novel recombinant inbred line (RIL) population, which was entirely next-generation sequenced to achieve ultra-high-density saturating molecular markers resulting in supreme mapping sensitivity. We validated the quality of the RIL population by quantitative trait loci (QTL) mapping for seedling de-etiolation, finding seven QTLs for hypocotyl length in the dark and continuous blue light (Bc), continuous red light (Rc), and continuous far-red light (FRc). The most relevant QTLs, Rc1 and Bc1, were mapped close together to chromosome V; the former for Rc and Rc/dark, and the latter for Bc, FRc, and dark treatments. The additive effects of both QTLs were confirmed by independent heterogeneous inbred families (HIFs), and we explored TZP and ABA1 as potential candidate genes for Rc1 and Bc1QTLs, respectively. We conclude that the Pat × Col-0 RIL population is a valuable novel genetic resource to explore other adaptive traits in Arabidopsis.

The light and dark sides of nitric oxide: multifaceted roles of nitric oxide in plant responses to light.

Light drives photosynthesis and informs plants about their surroundings. Regarded as a multifunctional signaling molecule in plants, nitric oxide (NO) has been repeatedly demonstrated to interact with light signaling cascades to control plant growth, development and metabolism. During early plant development, light-triggered NO accumulation counteracts negative regulators of photomorphogenesis and modulates the abundance of, and sensitivity to, plant hormones to promote seed germination and de-etiolation. In photosynthetically active tissues, NO is generated at distinct rates under light or dark conditions and acts at multiple target sites within chloroplasts to regulate photosynthetic reactions. Moreover, changes in NO concentrations in response to light stress promote plant defenses against oxidative stress under high light or ultraviolet-B radiation. Here we review the literature on the interaction of NO with the complicated light and hormonal signaling cascades controlling plant photomorphogenesis and light stress responses, focusing on the recently identified molecular partners and action mechanisms of NO in these events. We also discuss the versatile role of NO in regulating both photosynthesis and light-dependent stomatal movements, two key determinants of plant carbon gain. The regulation of nitrate reductase (NR) by light is highlighted as vital to adjust NO production in plants living under natural light conditions.

Strategies for vegetative propagation and viral cleaning of a miniature ornamental pineapple hybrid

This study assessed and compared different methods for vegetative propagation of a miniature ornamental pineapple hybrid (ORN-MUT), seeking to determine the best method for production of plantlets, as well as for removal of the PMWaV viral complex from plants cultured in vitro, for production of healthy parent plants. Pineapple wilt is a disease that can cause large economic and is caused by a viral complex called Pineapple mealybug wilt-associated virus (PMWaV). For this, four propagation methods were evaluated (conventional, stem sectioning, micropropagation and etiolation of nodal segments). The time necessary for each method and the number of plants formed were assessed. Stem tips (0.5 mm) were cultured and indexed for three PMWaV types. Conventional propagation produced 17 plantlets per plant in 566 days, stem sectioning produced 2.3 plantlets per stem in 591 days, while the conventional micropropagation technique produced 1,284 plants after four subcultures in 778 days. Stems etiolated for 60 days showed peak production in the second subculture, with 1,224 plants. This method required 883 days to obtain plants with ideal size for transplantation to the field. In turn, stems etiolated for 120 days produced 935 plants at the end of four subcultures, with peak output in the third subculture, in which the plants could be cultivated in the field after 943 days. Conventional micropropagation and etiolation for 60 days were the best methods for production of plantlets of the ORN-MUT hybrid. The results of this work showed that the cultivation of shoot tips is an efficient strategy to remove the PMWaV complex and obtain healthy mother plants and can be a useful tool for other varieties of pineapple.(AU)

Strategies for vegetative propagation and viral cleaning of a miniature ornamental pineapple hybrid

This study assessed and compared different methods for vegetative propagation of a miniature ornamental pineapple hybrid (ORN-MUT), seeking to determine the best method for production of plantlets, as well as for removal of the PMWaV viral complex from plants cultured in vitro, for production of healthy parent plants. Pineapple wilt is a disease that can cause large economic and is caused by a viral complex called Pineapple mealybug wilt-associated virus (PMWaV). For this, four propagation methods were evaluated (conventional, stem sectioning, micropropagation and etiolation of nodal segments). The time necessary for each method and the number of plants formed were assessed. Stem tips (0.5 mm) were cultured and indexed for three PMWaV types. Conventional propagation produced 17 plantlets per plant in 566 days, stem sectioning produced 2.3 plantlets per stem in 591 days, while the conventional micropropagation technique produced 1,284 plants after four subcultures in 778 days. Stems etiolated for 60 days showed peak production in the second subculture, with 1,224 plants. This method required 883 days to obtain plants with ideal size for transplantation to the field. In turn, stems etiolated for 120 days produced 935 plants at the end of four subcultures, with peak output in the third subculture, in which the plants could be cultivated in the field after 943 days. Conventional micropropagation and etiolation for 60 days were the best methods for production of plantlets of the ORN-MUT hybrid. The results of this work showed that the cultivation of shoot tips is an efficient strategy to remove the PMWaV complex and obtain healthy mother plants and can be a useful tool for other varieties of pineapple.

A single haplotype hyposensitive to light and requiring strong vernalization dominates Arabidopsis thaliana populations in Patagonia, Argentina.

The growing collection of sequenced or genotyped Arabidopsis thaliana accessions includes mostly individuals from the native Eurasian and N. African range and introduced North American populations. Here, we describe the genetic and phenotypic diversity, along with habitats and life history, of A. thaliana plants collected at the southernmost end of its worldwide distribution. Seed samples were harvested from plants growing in four sites within a ~3500-km2 -area in Patagonia, Argentina, and represent the first germplasm to be collected in South America for this species. Whole-genome resequencing revealed that plants from the four sites and a Patagonia herbarium specimen collected in 1967 formed a single haplogroup (Pat), indicating that the phenotypic variation observed in the field reflected plastic responses to the environment. admixture and principal components analyses suggest that the ancestor of the Pat haplogroup either came from Italy or the Balkan/Caucasus regions of Eurasia. In the laboratory, plants from the Pat haplogroup were hyposensitive to continuous red (Rc) and shade light, with corresponding changes in the expression of phytochrome signalling genes. Pat had higher PIF3 and PIF5 and lower HY5 expression under Rc light; and lower expression of PIL1, ATHB2 and HFR1 under shade compared to Col-0. In addition, Pat plants had a strong vernalization requirement associated with high levels of FLC expression. We conclude that including Pat in studies of natural variation and in comparison with other introduced populations will provide additional information for association studies and allow for a more detailed assessment of the demographic events following colonization.

Phytochrome A antagonizes PHYTOCHROME INTERACTING FACTOR 1 to prevent over-activation of photomorphogenesis.

Phytochrome A (phyA) is crucial to initiate the early steps of the transition between skoto- and photomorphogenesis upon light exposure and to complete this process under far-red light (typical of dense vegetation canopies). However, under prolonged red or white light, phyA mutants are hyper-photomorphogenic in many respects. To investigate this issue, we analyzed the late response of the transcriptome of the phyA mutant to red light. Compared to the wild-type (WT), hyper-responsive genes outnumbered the genes showing reduced response to red light in phyA. A network analysis revealed the co-expression of PHYTOCHROME INTERACTING FACTOR 1 (PIF1) with those genes showing hyper-promotion by red light in phyA. The enhanced responses of gene expression, cotyledon unfolding, hypocotyl growth, and greening observed in the phyA mutant compared to the WT were absent in the phyA pif1 double mutant compared to pif1, indicating that the hyper-photomorphogenic phenotype of phyA requires PIF1. PIF1 directly binds to gene promoters that displayed PIF1-mediated enhanced response to red light. Expression of mutant PIF1 deficient in interactions with phyA and phyB enhanced the long-term growth response to red light but reduced the expression of selected genes in response to red light. We propose that phytochrome-mediated degradation of PIF1 prevents over-activation of photomorphogenesis during early seedling development.

Estratégias para produção de mudas de tomateiro utilizando paclobutrazol / Strategies for tomato seedlings production using paclobutrazol

A tomaticultura moderna, de mesa ou para processamento industrial, demanda mudas de qualidade, capazes de resistir às adversidades ambientais após o plantio e que mantenham o padrão produtivo do genótipo. O objetivo deste trabalho foi avaliar o efeito de três concentrações de PBZ (0, 50 e 100 mg L-1) e dois métodos de aplicação (tratamento de sementes e rega de plântulas) na emergência de plântulas e produção de mudas de tomateiro de crescimento indeterminado. Adotou-se o delineamento inteiramente casualizado, em esquema fatorial 2x3, com quatro repetições. Foi avaliada a emergência de plântulas, o índice de velocidade de emergência, altura de plântulas e diâmetro do caulículo e suas respectivas taxas de crescimento absoluto (TCA), área foliar, massa de matéria seca da parte aérea, das raízes e total, e razão de área foliar (RAF). Os dados foram submetidos a analise de variância e as médias dos níveis do fator “métodos de aplicação” comparadas pelo teste de Tukey, a 5% e as médias dos níveis do fator “concentrações” submetidas à análise de regressão. A aplicação de paclobutrazol via rega de plântulas não comprometeu a emergência de plântulas, reduziu significativamente a taxa de crescimento das plântulas e, conseqüentemente, o porte das mudas, sem afetar o diâmetro do caulículo, além de permitir acúmulo de matéria seca de raízes. A concentração de 50 mg L-1 mostrou-se suficiente para obtenção de plântulas mais compactas, sem prejuízo à área foliar, na aplicação via rega, além de permitir um incremento de cerca de 37% na massa de matéria seca de raízes.(AU)

The modern tomato production, either for fruit table production or for processing, has required quality seedlings, able to withstand environmental adversities after planting and maintaining the standard genotype productive. The aim of this study was to evaluate the effect of three concentrations of PBZ (0, 50 and 100 mg L-1) and two methods of application (seed treatment and watering seedlings) on seedling emergence and seedling production of tomato growth indeterminate. We adopted a completely randomized in a 2x3 factorial scheme with four replications. We evaluated the seedling emergence, the rate of speed of emergence, seedling height and diameter of hypocotyl and their absolute growth rate (TCA), leaf area, dry weight of shoots, roots and total, and reason leaf area (RAF). Results were subjected to analysis of variance and the mean levels of the factor “methods of application” comparedby Tukey test at 5% and the mean levels of the factor “concentrations” subjected to regression analysis. The application of paclobutrazol via seedlings watering did not affect seedling emergence, significantly reduced the rate of seedling growth and, consequently, the size of the seedlings without affecting the diameter of hypocotyl, plus allow accumulation of dry roots. A concentration of 50 mg L-1 was shown to be sufficient to obtain seedlings more compact, subject to leaf area, the application via watering, beyond allowing an increase of about 37% in dry weight of roots.(AU)

Estratégias para produção de mudas de tomateiro utilizando paclobutrazol / Strategies for tomato seedlings production using paclobutrazol

A tomaticultura moderna, de mesa ou para processamento industrial, demanda mudas de qualidade, capazes de resistir às adversidades ambientais após o plantio e que mantenham o padrão produtivo do genótipo. O objetivo deste trabalho foi avaliar o efeito de três concentrações de PBZ (0, 50 e 100 mg L-1) e dois métodos de aplicação (tratamento de sementes e rega de plântulas) na emergência de plântulas e produção de mudas de tomateiro de crescimento indeterminado. Adotou-se o delineamento inteiramente casualizado, em esquema fatorial 2x3, com quatro repetições. Foi avaliada a emergência de plântulas, o índice de velocidade de emergência, altura de plântulas e diâmetro do caulículo e suas respectivas taxas de crescimento absoluto (TCA), área foliar, massa de matéria seca da parte aérea, das raízes e total, e razão de área foliar (RAF). Os dados foram submetidos a analise de variância e as médias dos níveis do fator “métodos de aplicação” comparadas pelo teste de Tukey, a 5% e as médias dos níveis do fator “concentrações” submetidas à análise de regressão. A aplicação de paclobutrazol via rega de plântulas não comprometeu a emergência de plântulas, reduziu significativamente a taxa de crescimento das plântulas e, conseqüentemente, o porte das mudas, sem afetar o diâmetro do caulículo, além de permitir acúmulo de matéria seca de raízes. A concentração de 50 mg L-1 mostrou-se suficiente para obtenção de plântulas mais compactas, sem prejuízo à área foliar, na aplicação via rega, além de permitir um incremento de cerca de 37% na massa de matéria seca de raízes.

The modern tomato production, either for fruit table production or for processing, has required quality seedlings, able to withstand environmental adversities after planting and maintaining the standard genotype productive. The aim of this study was to evaluate the effect of three concentrations of PBZ (0, 50 and 100 mg L-1) and two methods of application (seed treatment and watering seedlings) on seedling emergence and seedling production of tomato growth indeterminate. We adopted a completely randomized in a 2x3 factorial scheme with four replications. We evaluated the seedling emergence, the rate of speed of emergence, seedling height and diameter of hypocotyl and their absolute growth rate (TCA), leaf area, dry weight of shoots, roots and total, and reason leaf area (RAF). Results were subjected to analysis of variance and the mean levels of the factor “methods of application” comparedby Tukey test at 5% and the mean levels of the factor “concentrations” subjected to regression analysis. The application of paclobutrazol via seedlings watering did not affect seedling emergence, significantly reduced the rate of seedling growth and, consequently, the size of the seedlings without affecting the diameter of hypocotyl, plus allow accumulation of dry roots. A concentration of 50 mg L-1 was shown to be sufficient to obtain seedlings more compact, subject to leaf area, the application via watering, beyond allowing an increase of about 37% in dry weight of roots.

Emprego do estiolamento na propagação de plantas / Etiolation to clonal plant propagation

O estiolamento tem sido utilizado com sucesso no enraizamento de diversas espécies frutíferas e ornamentais lenhosas. Os resultados geralmente são melhores combinando esta técnica com o andamento ou aplicação de reguladores de crescimento. O estiolamento pode ser utilizado de diversas formas, em plantas à campo ou em casa de vegetação. O enraizamento pode ocorrer com os ramos ainda ligados a planta-matriz, realizando-se uma mergulhia, ou então destacados, realizando-se uma estaquia. Neste último caso, após o crescimento do ramo estiolado, ele é novamente exposto à luz, mas com um revestimento opaco em sua base, para que o resto do ramo torne-se verde, mas a base, onde ocorrerá o enraizamento, continue estiolada. O fenômeno ainda não está totalmente conhecido, mas sabe-se que o estiolamento provoca alterações anatômicas e fisiológicas nos tecidos que estão correlacionadas com o melhor enraizamento. Ocorrem reduções na lignificação e suberificação dos tecidos, aumento de tecidos parenquimáticos indiferenciados e redução na espessura das paredes celulares. Também é alterado o controle da luz sobre o metabolismo de auxinas, causando alterações no conteúdo de compostos fenólicos e na atividade do AIA-oxidase e de cofatores do enraizamento.

Etiolation has been used successfully to improve rooting in cuttings of woody fruit-tree and ornamental species. The cuttings rooting is usually better when etiolation is used together with ringbarking or hormone application. Etiolation can be achieved through different forms by covering the stock plants in the field or in the greenhouse. The shoots can be rooted while they are still attached to the stock plant, by stooling or they are removed like cuttings. In this case, after the etiolated shoots have elongated enough, the shading is gradually reduced and an opaque band is wrapped around the base of the new shoot, thereby retaining its etiolated condition while the rest of the shoot turns green in the light. The process is not well understood, although is known that etiolation promove anatomical and physiological tissue changes which are correlated with ease of rooting. The changes include decreased of lignification and suberization of stem tissues, increased of undifferentiated parenchyma and decreased cell wall thickness. The light control of auxin metabolism is also changed, causing changes in phenolic substances content and in the activity of IAA-oxidase and rooting cofactors.

Emprego do estiolamento na propagação de plantas

Etiolation has been used successfully to improve rooting in cuttings of woody fruit-tree and ornamental species. The cuttings rooting is usually better when etiolation is used together with ringbarking or hormone application. Etiolation can be achieved through different forms by covering the stock plants in the field or in the greenhouse. The shoots can be rooted while they are still attached to the stock plant, by stooling or they are removed like cuttings. In this case, after the etiolated shoots have elongated enough, the shading is gradually reduced and an opaque band is wrapped around the base of the new shoot, thereby retaining its etiolated condition while the rest of the shoot turns green in the light. The process is not well understood, although is known that etiolation promove anatomical and physiological tissue changes which are correlated with ease of rooting. The changes include decreased of lignification and suberization of stem tissues, increased of undifferentiated parenchyma and decreased cell wall thickness. The light control of auxin metabolism is also changed, causing changes in phenolic substances content and in the activity of IAA-oxidase and rooting cofactors.

O estiolamento tem sido utilizado com sucesso no enraizamento de diversas espécies frutíferas e ornamentais lenhosas. Os resultados geralmente são melhores combinando esta técnica com o andamento ou aplicação de reguladores de crescimento. O estiolamento pode ser utilizado de diversas formas, em plantas à campo ou em casa de vegetação. O enraizamento pode ocorrer com os ramos ainda ligados a planta-matriz, realizando-se uma mergulhia, ou então destacados, realizando-se uma estaquia. Neste último caso, após o crescimento do ramo estiolado, ele é novamente exposto à luz, mas com um revestimento opaco em sua base, para que o resto do ramo torne-se verde, mas a base, onde ocorrerá o enraizamento, continue estiolada. O fenômeno ainda não está totalmente conhecido, mas sabe-se que o estiolamento provoca alterações anatômicas e fisiológicas nos tecidos que estão correlacionadas com o melhor enraizamento. Ocorrem reduções na lignificação e suberificação dos tecidos, aumento de tecidos parenquimáticos indiferenciados e redução na espessura das paredes celulares. Também é alterado o controle da luz sobre o metabolismo de auxinas, causando alterações no conteúdo de compostos fenólicos e na atividade do AIA-oxidase e de cofatores do enraizamento.

Emprego do estiolamento na propagação de plantas

Etiolation has been used successfully to improve rooting in cuttings of woody fruit-tree and ornamental species. The cuttings rooting is usually better when etiolation is used together with ringbarking or hormone application. Etiolation can be achieved through different forms by covering the stock plants in the field or in the greenhouse. The shoots can be rooted while they are still attached to the stock plant, by stooling or they are removed like cuttings. In this case, after the etiolated shoots have elongated enough, the shading is gradually reduced and an opaque band is wrapped around the base of the new shoot, thereby retaining its etiolated condition while the rest of the shoot turns green in the light. The process is not well understood, although is known that etiolation promove anatomical and physiological tissue changes which are correlated with ease of rooting. The changes include decreased of lignification and suberization of stem tissues, increased of undifferentiated parenchyma and decreased cell wall thickness. The light control of auxin metabolism is also changed, causing changes in phenolic substances content and in the activity of IAA-oxidase and rooting cofactors.

O estiolamento tem sido utilizado com sucesso no enraizamento de diversas espécies frutíferas e ornamentais lenhosas. Os resultados geralmente são melhores combinando esta técnica com o andamento ou aplicação de reguladores de crescimento. O estiolamento pode ser utilizado de diversas formas, em plantas à campo ou em casa de vegetação. O enraizamento pode ocorrer com os ramos ainda ligados a planta-matriz, realizando-se uma mergulhia, ou então destacados, realizando-se uma estaquia. Neste último caso, após o crescimento do ramo estiolado, ele é novamente exposto à luz, mas com um revestimento opaco em sua base, para que o resto do ramo torne-se verde, mas a base, onde ocorrerá o enraizamento, continue estiolada. O fenômeno ainda não está totalmente conhecido, mas sabe-se que o estiolamento provoca alterações anatômicas e fisiológicas nos tecidos que estão correlacionadas com o melhor enraizamento. Ocorrem reduções na lignificação e suberificação dos tecidos, aumento de tecidos parenquimáticos indiferenciados e redução na espessura das paredes celulares. Também é alterado o controle da luz sobre o metabolismo de auxinas, causando alterações no conteúdo de compostos fenólicos e na atividade do AIA-oxidase e de cofatores do enraizamento.