Adventitious root initiation in hypocotyl and epicotyl cuttings of eastern white pine (Pinus strobus) seedlings

The present paper reports results of experiments to develop a system for studying adventitious root initiation in cuttings derived from seedlings. Hypocotyl cuttings of 2-week-old eastern white pine (Pinus strobus L.) seedlings were treated for 5 min with 0, 100, 200, 300, 400, 500 or 600 mg l^?1 (0, 0.54, 1.07, 1.61, 2.15, 2.69 or 3.22 mM) 1-naphthaleneacetic acid (NAA) to determine the effect on root initiation. The number of root primordia per cutting was correlated with NAA concentration and the square of NAA concentration. Thus, the number increased from less than one per cutting in the 0 NAA treatment to approximately 40 per cutting at 300 mg l-1 NAA, above which no substantial further increase was observed. The larger number of root primordia formed in response to increasing concentrations of NAA was due to the formation of primordia over a larger proportion of the hypocotyls. Histological analysis of the timing of root primordium formation in hypocotyl cuttings revealed three discernible stages. Progression through these stages was relatively synchronous among NAA-treated hypocotyl cuttings and within a given cutting, but variation was observed in the portion of different cuttings undergoing root formation. Control-treated hypocotyl cuttings formed root primordia at lower frequencies and more slowly than NAA-treated cuttings, with fewer primordia per cutting. Epicotyl cuttings from 11-week-old seedlings also formed adventitious roots, but more slowly than hypocotyl cuttings. NAA treatment of epicotyl cuttings caused more rapid root initiation and also affected the origin of adventitious roots in comparison with nontreated cuttings. NAA-treated epicotyl cuttings formed roots in a manner analogous to that of the hypocotyl cuttings, directly from preformed vascular tissue, while control-treated epicotyl cuttings first formed a wound or callus tissue and subsequently differentiated root primordia within that tissue. This system of inducing adventitious roots in pine stem cuttings lends itself to studying the molecular and biochemical steps that occur during root initiation and development.     

Mediators,Genes and Signaling in Adventitious Rooting

Adventitious roots are a post-embryonic root which arise from the stem and leaves and from non-pericycle tissues in old roots and it is one of the most important ways of vegetative propagation in plants. Many exogenous and endogenous factors regulate the formation of adventitious roots, such as Ca²⁺, sugars, auxin, polyamines, ethylene, nitric oxide, hydrogen peroxide, carbon monoxide, cGMP, MAPKs and peroxidase, etc. These mediators are thought to function as signaling and mediate auxin signal transduction during the formation of adventitious roots. To date, only a few genes have been identified that are associated with the general process of adventitious rooting, such as ARL1, VvPRP1, VvPRP2, HRGPnt3, LRP1 and RML, etc. Auxin has been shown to be intimately involved in the process of adventitious rooting and function as crucial role in adventitious rooting. Great progress has been made in elucidating the auxin-induced genes and auxin signaling pathway, especially in auxin response Aux/IAA and ARF genes family and the auxin receptor TIR1. Although, some of important aspects of adventitious rooting signaling have been revealed, the intricate signaling network remains poorly understood.     

Roles of leaf in regulation of root and shoot growth from single node softwood cuttings of grape (Vitis vinifera)

The role of leaf in regulation of root and shoot growths in single node softwood cuttings of grape (Vitis vinifera) was characterised. Leafy cuttings showed early rooting, vigorous root growth and subsequent shoot development. Defoliation at planting induced early sprouting, but adversely affected rooting and decreased the survival of cuttings irrespective of pre‐planting treatment with 100 μM indole 3‐acetic acid (IAA). Treatment with IAA did not affect the percent rooting of leafy cuttings but increased root and shoot growth. Leaf weight (wt) and leaf area of the cuttings showed a highly significant correlation to root wt of the new plant at 4 wk after planting, while cutting stem + petiole wt was either not or less significantly correlated to root and shoot weights of the subsequent plant. The greater the area or wt of leaf, the better the root and shoot growths, implying that leaf contributed to adventitious root growth. However, retaining the leaf for just 2 days was enough to stimulate rooting in more than 80% of the cuttings, suggesting that leaf tissue could also induce root formation. Root growth increased with the period of leaf retention but leaf removal before 3 wk triggered sprouting leading to high mortality in rooted cuttings. Bringing the leaf closer to the rooting zone by preparing leaf at base (LAB) cuttings delayed rooting and sprouting compared with the standard leaf at top (LAT) cuttings. An inhibitory effect on rooting and sprouting by the exposed upper internode region in LAB cuttings is suggested.     

N,N′-bis-(2,3-Methylenedioxyphenyl)urea and N,N′-bis-(3,4-methylenedioxyphenyl)urea enhance adventitious rooting in Pinus radiata and affect expression of genes induced during adventitious rooting in the presence of exogenous auxin

We have analyzed the effect of N,N′-bis-(2,3-methylenedioxyphenyl)urea (2,3-MDPU) and N,N′-bis-(3,4-methylenedioxyphenyl)urea (3,4-MDPU), two symmetrically substituted diphenylurea derivatives with no auxin or cytokinin-like activity, on the rooting capacity of Pinus radiata stem cuttings. Results indicate that both diphenylurea derivatives enhance adventitious rooting in the presence of exogenous auxin (indole-3-butyric acid, IBA), even at low auxin concentration, in rooting-competent cuttings, but have no effect on the adventitious rooting of low or null competent-to-root cuttings. Histological analyses show that, in the simultaneous presence of MDPUs and low concentration of exogenous auxin, adventitious root formation is induced in the cell types that retain intrinsic competence to form adventitious roots in response to auxin. The time course of cellular events leading to root formation and the time of root emergence are closely similar to that observed in cuttings treated only with higher auxin concentration. In addition, the mRNA level of a P. radiata SCARECROW-LIKE gene, which is significantly induced in the presence of the optimal concentration (10 μM) of exogenous auxin needed for cuttings to root, is increased in the presence of MDPUs and low concentration of exogenous auxin (1 μM). The expression of a P. radiata SHORT-ROOT gene in rooting-competent cuttings during adventitious rooting is also affected by the presence of MDPUs when combined with auxin. As MDPUs do not affect the expression of either gene in the absence of exogenous auxin, but only in its presence, we suggest that MDPUs could interact, directly or indirectly, with the auxin-signalling pathways in rooting-competent cuttings during adventitious rooting.     

Adventitious Root Formation in Veronica Spp.

Species of the genus Veronica differ in habitat preferences,growth form and in adventitious root production. The annualspecies rarely or never produce adventitious roots in intactplants in the field but some, for example V. persica and V.arvensis will root vigorously from single node stem segmentsin culture. Others, such as V. agrestis require the presenceof IAA for substantial levels of root formation to occur incultured stem segments. Veronica hederifolia cuttings rarelyproduce roots. Stem cuttings of the perennial species, in general,rooted more vigorously than those of annual plants. Both V.fihiformis and V. serpyllifolia root very strongly. The position of root production from the stem cuttings differedfrom species to species. Roots arose either from the node, theregion of the base or at some intermediate point. Veronica arvensis,V. chamaedrys and V. persica rooted mainly from the basal regionwhereas V. filiformis rooted mainly from the node. Veronicaserpyllifolia cuttings rooted at both of these locations. Veronica filiformis, a perennial species that is infertile inBritain, produces root primordia in intact plants at nodes whichare close to the shoot apex. Thus, even very young stem segmentshave ‘preformed’ root primordia. For this reason,detached stem segments of V. filiformis root very rapidly andthis probably has been of great significance in its successfulinvasion and spread in lawns and short turf areas. Veronica spp., adventitious roots, indol-3-ylacetic acid, root primordia, vegetative reproduction     

Residual phosphorus and long-term management strategies for an Ultisol

Due to their extensive growth potential, transgenic root systems arising from inoculation withAgrobacterium rhizogenes became popular in the last decade as model systems in domains as diverse as production of secondary metabolites, interactions with pathogens and symbionts, examination of gene importance in control of root development or in regulation of gene expression in roots. Wild-type bacterial strains have also been considered as useful tools to stimulate rooting on recalcitrant cuttings or microcuttings as they cause abundant root initiation at the site of inoculation.Root initiation and the in vitro growth characteristics of transformed roots result from the transfer of genes located on the root-inducing plasmid (Ri) to plant cells and their expression therein. Two sets of pRi genes are involved in the root induction process: therol (rootloci) genes located in the TL region and theaux genes of the TR region. Some of these genes being able to interact, the system appears also as a new tool to study the role of auxin in the process of root initiation. The distinctive phenotype of the transformed roots which are capable of hormone autonomous growth seems to be controlled mainly by therol genes. Theserol genes, i.e. the geneticloci rol A, rol B, rol C androl D correspond to open reading frames ORFs 10, 11, 12 and 15. In vitro experiments determined the functions of the Rol B and Rol C proteins but the functions of Rol A and Rol D are still unknown. Altered metabolism of developmental regulators or modified sensitivity to auxin have been suspected to mediate root induction and morphological abnormalities of transformed roots and plants.The target cells for transformation and the cells which are competent for root initiation will be characterized as well as the subsequent development of transgenic roots provided with various constructs from the whole T-DNA to singlerol genes. Results dealing with auxin contents in relation with root growth kinetics, phenotype and structure, will also be presented and discussed with the potential use of therol genes to control root biomass. F J de Bruijn Section editor     

Plant growth regulators and adventitious root development in relation to auxin

Adventitious root formation in stem cuttings of mung bean was enhanced by ethrel, which had an additive effect when employed simultaneously with indolebutyric acid (IBA). Abscisic acid (ABA) did not influence the number of roots per cutting whereas gibberellic acid (GA₃) and kinetin were without effect on rooting at lower concentrations but were inhibitory at higher concentrations. Nevertheless, all three of these chemicals showed synergistic interactions with IBA and/or indol-3-ylacetic acid (IAA) and thereby significantly promoted root formation. A localised application of morphactin to the epicotyl of cuttings totally inhibited root production irrespective of which of the foregoing growth regulators were suppliedvia the hypocotyl. Morphactin application also prevented root formation in cuttings treated with vitamin D₂. The various growth regulators employed had differing effects on growth of roots but there was no simple relationship between their effects on root formation and subsequent root growth.     

Effect of maleic hydrazide on peroxidase isoenzymes in relation to rooting hypocotyl cuttings ofPhaseolus mungo

A time course study of changes in the pattern of peroxidase isoenzymes shows that two new isoenzymesa andb appeared in hypocotyl cuttings cultured either in indolyl-3 acetic acid (IAA) + sucrose or in water but not in maleic hydrazide (MH). Roots were also initiated in the former two cases but not in the last case. That these isoenzymes may be associated with root initiation is also evident from the fact that these appeared when hypocotyl cuttings were transferred from MH to IAA + sucrose. The time of appearance of these isoenzymes in different cultures also synchronized with the time of microscopic root initiation. While the isoenzymea disappeared,b persisted in cuttings transferred from IAA + sucrose to MH. The number of roots produced on cuttings transferred to MH was very low, though their development was normal. It is suggested that isoenzymesa andb may be associated with root initiation andc andd with root development.     

Metabolic changes during rooting in stem cuttings of five mangrove species

Vegetative propagation through rooting in stem cuttings in five tree mangroves namely Bruguiera parviflora, Cynometra iripa, Excoecaria agallocha, Heritiera fomes, and Thespesia populnea using IAA, IBA and NAA was reported. Spectacular increase in the root number was noted in the cuttings of H. fomes and C. iripa treated together with IBA (5000 ppm) and NAA (2500 ppm). The highest number of roots was obtained with IBA (2500 ppm) and NAA (500 ppm) in E. agallocha. B. parviflora and T. populnea responded better to IAA and IBA treatment. The species specific variation in the rooting response to exogenous application of auxins was reflected in the metabolic changes during initiation and development of roots in cuttings. Biochemical analysis showed increase of reducing sugar in the above-girdled tissues at initiation as well as subsequent development of roots which was further enhanced by the use of auxins. Decreases in the total sugar, total carbohydrate and polyphenols and increase in total nitrogen were recorded in the girdled tissues and the high C/N ratio at the initial stage helped in initiation of roots in all the species. Interaction of IBA and NAA promoted starch hydrolysis better than IAA and IBA during root development and subsequently reduced the C/N ratio and increased the protein-nitrogen activity during root development which suggest the auxin influenced mobilization of nitrogen to the rooting zone.Abbreviations IAA Indole-3-acetic acid - IBA Indole-butyric acid - NAA A-naphthalene acetic acid     

A role for ALF4 during gall and giant cell development in the biotic interaction between Arabidopsis and Meloidogyne spp.

Root‐knot nematodes (RKNs; Meloidogyne spp.) are a major pest for the agriculture worldwide. RKNs induce specialized feeding cells (giant cells, GCs) inside galls which are de novo formed pseudo‐organs in the roots that share similarities with other developmental processes as lateral root (LR) and callus formation or grafting involving new vascular development or pericycle proliferation. Hence, it is pertinent to study the molecular mechanisms directing the plant‐nematode interaction. In this respect, ALF4 is a key gene during LR formation, vascular vessels reconnection in grafting, hormone‐induced callus formation or de novo root organogenesis from leaf explants. Our results show that ALF4 is also induced in galls at early infection stages in an auxin‐independent way. Furthermore, ALF4 activity is necessary for the formation of proper galls and GCs, as the mutant alf4‐1 presents aberrant galls and GCs with severe structural abnormalities leading to a dramatic reduction in the nematode egg production. However, a low‐reproduction rate is maintained, that might be explained by the local auxin maximum build by the nematodes in galls, partially rescuing alf4‐1 phenotype. This would be similar to the partial rescue described for LR formation with exogenous auxins and also agrees with the LR emergence from alf4‐1 galls but not from uninfected roots. In addition, ALF4 is also induced in syncytia formed by cyst nematodes. All these data support a pivotal role for ALF4 during de novo organogenesis processes induced by endoparasitic nematodes, in addition to its role in LR formation, callus development or vessel reconnection during grafting.     

Causes of Centrifugal Root Promotion

Role of water in centrifugal root promotion, effect of centrifugation on ethylene concentration of cuttings, and effect of ethylene on root formation were investigated using Salix jragilis softwood cuttings. When cuttings were centrifuged with water, more roots formed with increasing water depth. Soaking of cuttings upright in water for 24 h stimulated root formation and produced more roots as the depth of water was increased, with submerged cuttings producing the highest number of roots. Soaking of cuttings upright in hot water for 1 h also stimulated root formation with the best root formation occurring at 40°C. Submerging in, or centrifuging with water increased ethylene concentration in cuttings. Ethylene gas and Ethrel treatments stimulated root formation. It is suggested that submerging in water increases the ethylene concentration in Salix fragilis softwood cuttings which in turn stimulates root formation of the cuttings. Centrifuging cuttings with water increased water content of the cuttings. It is suggested that this increase in water content plays a role similar to the submersion of cuttings as described above.     

葡萄醛酮还原酶(AKR)基因家族的鉴定与表达分析

为明确AKR基因在葡萄非生物胁迫中的作用,利用生物信息学方法对葡萄AKR基因家族(VvAKRs)进行了全基因组鉴定,并验证其在非生物胁迫下的表达规律。结果表明：(1)该基因家族在葡萄基因组中有9个成员,主要分布在5条染色体上;氨基酸残基在275~2 686 aa之间,理论等电点在5.1~9.1之间。(2)系统进化分析表明,该基因家族分为6个亚族,第6亚族VvAKR家族成员最多。(3)密码子偏好性分析结果表明,葡萄AKR基因家族密码子偏好性较弱。(4)共线性分析表明,葡萄9个AKR基因中只有VvAKR8和VvAKR9之间存在共线性关系。(5)qRT PCR分析结果显示,葡萄AKR家族基因在根、茎、叶不同组织中对激素和非生物胁迫的响应程度有差异。非生物胁迫下,VvAKR1、VvAKR3、VvAKR8和VvAKR9基因在葡萄根、茎、叶组织中表达量较高;激素处理下,根组织中VvAKR3、VvAKR6和VvAKR8基因在ABA、MeJA、SA处理下表达量较高;茎组织中VvAKR3基因在NAA、GA₃处理下表达量较高;叶组织中VvAKR1基因在各激素处理下表达量都较高。研究认为,葡萄AKR基因家族在响应葡萄非生物胁迫时发挥着不同的作用,为葡萄抗逆性研究提供了一定的理论依据。     

Early steps of adventitious rooting: morphology,hormonal profiling and carbohydrate turnover in carnation stem cuttings

The rooting of stem cuttings is a common vegetative propagation practice in many ornamental species. A detailed analysis of the morphological changes occurring in the basal region of cultivated carnation cuttings during the early stages of adventitious rooting was carried out and the physiological modifications induced by exogenous auxin application were studied. To this end, the endogenous concentrations of five major classes of plant hormones [auxin, cytokinin (CK), abscisic acid, salicylic acid (SA) and jasmonic acid] and the ethylene precursor 1‐aminocyclopropane‐1‐carboxylic acid were analyzed at the base of stem cuttings and at different stages of adventitious root formation. We found that the stimulus triggering the initiation of adventitious root formation occurred during the first hours after their excision from the donor plant, due to the breakdown of the vascular continuum that induces auxin accumulation near the wounding. Although this stimulus was independent of exogenously applied auxin, it was observed that the auxin treatment accelerated cell division in the cambium and increased the sucrolytic activities at the base of the stem, both of which contributed to the establishment of the new root primordia at the stem base. Further, several genes involved in auxin transport were upregulated in the stem base either with or without auxin application, while endogenous CK and SA concentrations were specially affected by exogenous auxin application. Taken together our results indicate significant crosstalk between auxin levels, stress hormone homeostasis and sugar availability in the base of the stem cuttings in carnation during the initial steps of adventitious rooting.     

Factors Influencing Adventitious Root Production in Cuttings of Griselinia littoralis and Griselinia lucida

Griselinia littoralis roots quickly and vigorously from cuttingsof seedlings and mature plants and also forms roots on detachedleaves. Cuttings root in the dark but leaves must be present.In contrast G. lucida roots vigorously only from cuttings takenfrom seedlings. Light is essential for root formation on oldermaterial. Detached leaves will not root. Although callus formationat the cut base commonly occurs in both species it is not directlyassociated with root formation. Griselinia littoralis Raoul Choix, Griselinia lucida Forst. f. Prodr., adventitious roots, stem cuttings, leaf cuttings, woody plants