RESUMO
Moso bamboo (Phyllostachys heterocycla) is the most important bamboo species in China and is famous for its fast-growing culms. To investigate the possible relationship between internode development and endogenous hormones, the concentrations of indole-3-acetic acid (IAA), zeatin riboside (ZR), gibberellins (GA3), and abscisic acid (ABA) were analyzed in culm samples from plants at different developmental stages during a single growing season and, at the same time, anatomical structure was closely monitored. Cell division was the dominant process in internode development during early development, while cell elongation predominated at later stages. There was a negative correlation between the rates of cell division and cell elongation. The four endogenous hormones (IAA, ZR, GA3, and ABA) displayed fluctuations in their levels at different developmental stages but their peak activities were not synchronous. Cell division rate had a significant positive correlation with ZR concentration. Cell elongation had a significant positive correlation with the ratio of promoting hormones (IAA, GA3, and ZR) to inhibitory hormone (ABA) concentrations. We conclude that hormonal equilibrium might regulate the division and elongation of bamboo culms.
Assuntos
Ácido Abscísico/metabolismo , Giberelinas/metabolismo , Reguladores de Crescimento de Plantas/metabolismo , Poaceae/crescimento & desenvolvimento , Divisão Celular , Tamanho Celular , Isopenteniladenosina/análogos & derivados , Isopenteniladenosina/metabolismo , Feixe Vascular de Plantas/citologia , Feixe Vascular de Plantas/crescimento & desenvolvimento , Feixe Vascular de Plantas/metabolismo , Poaceae/citologia , Poaceae/metabolismoRESUMO
Aluminium (Al) toxicity and drought are two major factors limiting common bean (Phaseolus vulgaris) production in the tropics. Short-term effects of Al toxicity and drought stress on root growth in acid, Al-toxic soil were studied, with special emphasis on Al-drought interaction in the root apex. Root elongation was inhibited by both Al and drought. Combined stresses resulted in a more severe inhibition of root elongation than either stress alone. This result was different from the alleviation of Al toxicity by osmotic stress (-0.60 MPa polyethylene glycol) in hydroponics. However, drought reduced the impact of Al on the root tip, as indicated by the reduction of Al-induced callose formation and MATE expression. Combined Al and drought stress enhanced up-regulation of ACCO expression and synthesis of zeatin riboside, reduced drought-enhanced abscisic acid (ABA) concentration, and expression of NCED involved in ABA biosynthesis and the transcription factors bZIP and MYB, thus affecting the regulation of ABA-dependent genes (SUS, PvLEA18, KS-DHN, and LTP) in root tips. The results provide circumstantial evidence that in soil, drought alleviates Al injury, but Al renders the root apex more drought-sensitive, particularly by impacting the gene regulatory network involved in ABA signal transduction and cross-talk with other phytohormones necessary for maintaining root growth under drought.
Assuntos
Alumínio/toxicidade , Citocininas/biossíntese , Secas , Phaseolus/genética , Phaseolus/fisiologia , Estresse Fisiológico/efeitos dos fármacos , Estresse Fisiológico/genética , Ácido Abscísico/biossíntese , Vias Biossintéticas/efeitos dos fármacos , Vias Biossintéticas/genética , Parede Celular/efeitos dos fármacos , Parede Celular/genética , Colômbia , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Genes de Plantas/genética , Genótipo , Glucanos/metabolismo , Isopenteniladenosina/análogos & derivados , Isopenteniladenosina/metabolismo , Modelos Biológicos , Pressão Osmótica/efeitos dos fármacos , Phaseolus/efeitos dos fármacos , Raízes de Plantas/efeitos dos fármacos , Raízes de Plantas/genética , Raízes de Plantas/crescimento & desenvolvimento , Raízes de Plantas/fisiologia , Plântula/efeitos dos fármacos , Plântula/crescimento & desenvolvimentoRESUMO
This study reports the effects of thidiazuron (TDZ) on the endogenous levels of indoleacetic acid (IAA), zeatin, zeatin riboside ([9R]Z), isopentenyladenine and isopentenyladenosine ([9R]iP) as well as structural changes in the apical meristem of Dendrobium Second Love shoots during flower induction and initial development in vitro. The results revealed that the presence of 1.8microM TDZ had a profound effect on the endogenous cytokinins (CKs) and IAA levels of the explants, when compared to those grown on a TDZ-free medium. A significant increase in CKs (especially [9R]iP and [9R]Z) and IAA in the first samples (taken at day 5) grown on TDZ-enriched medium was associated with flower induction, while a second increase in the level of these hormones after 25d of culture was related to flower development. The histological changes detected in the shoot apical meristem of explants grown in the presence of 1.8microM TDZ during 30d of culture are also described. Based on these findings, it is suggested that both auxin and CKs seem to be involved with the floral transition of Dendrobium Second Love in vitro. However, a possible direct effect of TDZ on flower formation is not discarded.