Biological Research Advancement in Aloe

Review

Biological research advancement in Aloe

Xiaohong Liu*, Jun Li, Yongsi Zhang, Linhui Li and Daowen He

1College of Life Science, China West Normal University, 637002, Nanchong, Sichuan, P. R. China. 2Key Laboratory of Southwest China Wildlife Resources Conservation (Ministry of Education), P. R. China.

Accepted 18 October, 2010

Aloe , a genus belonging to Aloaceae family, is distributed throughout the world and has rich medical ingredients. At present, Aloe has been widely applied in many aspects for human being. In this paper, we introduced briefly its basal biological characteristics, including germplasm resources, growth habit, active ingredients and biological functions, and discussed deeply its research development in cytology and molecular biology. This knowledge stated here is beneficial for understanding and exploring its potential medical and edible values more sufficiently.

Key words: Aloe , medical plant, cytology, molecular biology.

INTRODUCTION

Germplasm resources cold, shady and humidity. It will be frozen and can not grow when environmental temperature is below -10 ℃; if it Aloe , a genus belonging to Aloaceae family grows in ponding soil for long time, its roots and leaves (www.ipni.org), belongs to perennial, evergreen and will be harmed seriously and become necrotic gradually. monocot crassulacean acid metabolism (CAM) plant. It is More interestingly, Aloe shows strong resistance to one of herbaceous or woody plants, and characterized by drought, salt and poor soil, certainly, it can grow better in stemless, large, thick and fleshy leaves showing lance loose and fertile soil than in consolidated and nutrient shaped, a sharp apex and a spiny margin. Aloe is widely deficient soil. Generally, Aloe can blossom after growing distributed in the world (Steenkamp and Stewart, 2007). about 2 to 3 years; nevertheless, its proliferation is mainly In southern Africa and Madagascar islands, it is cultivated accomplished by tillering in root due to pollen abortion (Lv as a popular economic plant (Zhu, 2007). In P. R. China, et al., 2004). it is also planted widely in many provinces including Guangdong, Yunnan, Fujian and Hainan (Xiong, 2002). Aloe originated from Africa, includes at least 300 wild Active ingredients species and over 200 bred varieties according to previous literature (Zheng et al., 2005), however, only Aloe has complex chemical ingredients, from literature, about ten of them are applicable to medicine and less there are over 100 secondary metabolites in leaf (Xiong, than ten can be eaten safely (Xiong, 2002). 2002). The main chemical components in Aloes can be classified into seven compounds, including anthraquinones, carbohydrates, amino acids, organic Growth habit acids, minerals and microelements, active enzymes and vitamins, among which anthraquinones are the most Aloe is fond of warmth and light, even being exposed in important active ingredients and the four matters showing sunshine about two months, it will not die, only presents quite high medical values, including aloin, Aloe emodin, no continuous growing. On the contrary, it is afraid of Aloe bitter and Aloe lectin, belong to anthraquinones (Wang, 2009). In general, the content of active ingredients is determined by variety and ecological condition (Wang et al., 2002; Ye et al., 2005). For *Corresponding author. E-mail: [email protected]. example, in the experiment by Qiao et al. (2009), blue Liu et al. 1047

light was beneficial to the accumulation of economical characters, and stronger resistance to cold anthraquinones. and disease is a typical example (Ren et al., 2007).

Biological functions Karyotype and band pattern

Aloe has important applications for human being in many Although, most Aloe has same chromosome number, fields, including medicine, food, cosmetic, health care different species display differences in karyotype. The and horticulture. Take medical value as an example, karyotype of Aloe consists of near-to-terminal and near- generally speaking, it plays important roles in many to-middle centromere chromosomes (Ji et al., 2002; aspects (Grindlay and Reynolds, 1986), such as Zheng et al., 2005). According to the classification bacteriostasis, reducing blood lipid, resistance to life criterion reported by Stebbins (1971), the karyotypes of ageing and tumor forming. More specifically, it can Aloe belong to ‘3B’, ‘4B’, ‘3C’ or ‘4C’ (Zheng et al., 2005). provide curative effects to some extent in constipation, For example, K(2n) = 4sm + 10st of Aloe ferox Miller and tuberculosis, skin disease, heart disease, diabetes and K(2n) = 4sm + 10st of Aloe arborescens were belonged so on (Reynolds and Dweck, 1999; Kambizi and to 4C and 3B, respectively (Liang and Bo, 2001). At Afolayan, 2008). With the development of modern present, the studies on chromosome band pattern of Aloe science and technology, many unknown functions in Aloe were hardly ever reported, only Aloe yuanjianggensis were gradually revealed. Owing to unique effective from P. R. China was analyzed by Li et al. (2003), which gradients and special functions, Aloe gained many pattern formula is 2n = 14 = 4st + 6sm + 4m, and the reputations, such as these bynames “the champion result obtained by Giemsa C-bands showed that the short among health care medicines”, “the best heath food in arms of chromosomes 3 and 4 presented whole bands, 21st century” and “new star in plant”. In Japan, it is known while the other chromosomes just displayed centromeric as “all-day service” and “doctor away”. Because of the bands. ability of curing large number of diseases, Aloe is also reputed as “the standby medicine-chest”. In addition, it is named “raw cosmetic materials” and “natural beautician”, Meiosis and pollen abortion due to the important effect on face-painting. Furthermore, Aloe is also “air pollution detector” because the pollution As is well-known, Aloe shares a conserved bimodal extent of air is related to its growing status (Yang and Ma, karyotype with a basic genome of four large and three 2000). small submetacentric or acrocentric chromosomes. But due to deviant chromosomal conjugating of pollen mother cells, the genetic materials of their daughter cells behave heterogeneous frequently (Brandham, 1990). In addition, CYTOLOGICAL RESEARCHES some abnormal phenomena can be found during meiosis for pollen mother cells, such as univalent, multivalent,

Chromosome chromosome bridge, lagged chromosome and micronuclei (Lv et al., 2005). And thus, the pollens Many studies showed that the chromosome number for descended from pollen mother cells are often sterile somatic cell of most Aloe is 2n = 14, and the haploid set (Spare, 1975), this can explain high self-incompatibility of genome consists of three short chromosomes and four Aloe . But interestingly, its stigmas located on the top of long ones (Brandham and Doherty, 1998 ；Ji et al., 2002; gynoecia have high receptivity ability in pollination (Tie et Alam and Khanam, 2005). Many studies demonstrated al., 2004). that most plants have Arabidopsis -type telomeres consisting of many repeat copies of the sequence 5’- TTTAGGG-3’ (Adams et al., 2000a), nevertheless, this Tissue culture kind of telomeres are not found in Aloe , similar to Allium , Nothoscordum and Tulbaghia . Aloe lacks Arabidopsis - Aloe will bloom and fruit after planting for years, type telomeric repeats, but it has vertebrate-like telomeric nevertheless, its seeds is often lacking due to great sequences (T 2AG 3) n according to the report by Weiss interval between male and female flowering time and and Scherthan (2002). Tetraploid and hexaploid A loe can high-frequency pollen sterileness. Therefore, natural and be induced from diploid Aloe (Ren et al., 2007). In the artificial propagation are mainly depended on tillering in report by Wang et al. (2001), the highest induction rate root and cuttage, respectively. Comparatively, tissue was up to 50% after treatment with 0.06% colchicines for culture can accelerate propagating of Aloe and improve 12 h. Compared to diploid, polyploid Aloe displayed its partial economic traits (Qin and Luo, 2003; Bedini et thicker, larger and darker leaves, besides, this kind of al., 2009). At present, there are many studies on Aloe Aloe presented more excellent physiological and tissue culture in literature (Qu et al., 2004; Hashemabadi 1048 J. Med. Plant. Res.

and Kaviani, 2008). With respect to the effects of pant subtractive hybridization and Zhang et al. (2007) obtained regulators on tissue culture in Aloe , You (2001) reported some expressed sequence tags derived from the sixth 6-BA (6-Benzylaminopurine) was the most important chromosome of Aloe . phytohormone for callus induction on MS basal media, followed by IBA (indole-4-butyric acid), then 2,4-D (2,4- dichlorophenoxyacetic acid), and NAA (1-naphthlcetic Genetic transformation acid) was the worst. Additionally, Xiao et al. (2006) reported the perfect combination of plant growth Although, Aloe has strong resistance to drought and regulators for callus induction was “4.0 mg/L 6-BA + 0.25 many pathogens in plant, it is afraid of cold (Zhang et al., mg/L NAA + 3.0 mg/L 2, 4-D + 0.5 mg/L IBA”. As for Aloe 2009b), and thus, particular attentions in transgenic study tissue culture, different parts of plant possess different have been focused on cold stress. In order to improve the callus induction rate and regeneration ability, and stem resistance to cold stress of Aloe plant, Chen et al. (2005) segment is considered as the best explant (Long et al., first introduced otsA gene into its genome via 2007). For example, in the result as described by Yuan et microprojectile bombardment, and obtained some al. (2001), the stems of Aloe barbadensis Mill could be transgenic plants. Subsequently, Chen et al. (2007) induced by callus and differentiated into plantlets, but transformed Aloe with otsA gene mediated by under same experimental condition, the leaf can hardly Agrobacterium , and the transgenic plants presented more be differentiated. content of trehalose than untransformed plants as control. Lately, Zhao et al. (2009) introduced TaDREB gene isolated from wheat into Aloe by Agrobacterium , MOLECULAR RESEARCH and the results demonstrated that this transformation could improve the resistant ability of Aloe to low Gene cloning and expression temperature. As for the influence factors on Aloe transformation, Aloe is a CAM plant which possesses many experimental results showed that acetosyringone phosphoenolpyruvate carboxylase (PEPCase) and was necessary in improving transformation rate mediated NADP-malic enzyme (NADP-ME). Till date, both of the by Agrobacterium (Chen et al., 2004; Pan et al., 2005). In two enzyme genes had successfully been cloned from addition, Pan et al. (2005) reported pretreatment time of Aloe (Honda et al., 1996; Houda et al., 2000). According the Agrobacterium liquid and the pH value could to the report by Honda (1996), the circadian rhythm for significantly influence genetic transformation. The PEPCase activity may be regulated at post-translation optimum infection time was 12 to 18 min, and the best level. As for Aloe NADP-ME, Honda et temperature and cocultivation time were 25 °C and 5 al. （2000 ）reported three major isoforms, including 65 days, respectively. With respect to host bacteria, EHA105 kDa protein with a pI of 5.5 in leaf, 65 kDa protein with a was more efficient than LBA4404, AGL1 and C58C1 in pI of 5.6 in roots, and 72 kDa protein in leaf and roof the genetic transformation (Pan et al., 2005; He et al., simultaneously. Further, Sun et al. (2003a) pointed out 2007). As for antibiotics, Chen (2004) pointed out that the expression of NADP-ME gene can be induced by untransformed Aloe was resistant to cefotaxime and high salt, dehydration, and exogenous plant regulator carbenicillin, while susceptible to kanamycin and abscisic acid, but not by cold treatment, and the further hygromycin. As far as concrete procedure of experiment indicated that its protein expression level microprojectile bombardment transformation, Chen would gradually increase with the prolonging of treat time. (2005) talked about that pre-culture, hypertonicity Additionally, some resistance genes to environmental treatment and postponing screening could contribute to stress were also cloned from Aloe . A new cold-induced successful transformation. dehydration-responsive element-binding (DREB) gene was cloned by Wang and He (2007), named Aloe DREB1 and encoding an AP2/ethylene response element binding Genetic diversity protein transcription factor. Afterwards, another gene encoding DREB protein was isolated by Zhang et al. To this day, only few studies on genetic diversity of Aloe (2009a), the gene named AlDREB2 is an active regulator species were reported in literature, Adams et al. (2000b) and its expression is involved in dehydration tolerance constructed a phylogenetic tree using 28 Aloe species by and cold acclimation in Aloe . Besides, some other genes sequence analysis of the internal transcribed spacer were successfully also isolated from Aloe , including a (ITS) of 18S-5.8S-26S rDNA, and found the distribution of novel aldo-keto reductase gene by Mortita et al. (2007) 18S-5.8S-26S rDNA was variable in number, location and and three novel type III polyketide synthase genes size in different Aloe species. Afterwards, Hou et al. (PKS3 , PKS4 and PKS5 ) by Mizuuchi et al. (2009). (2001); Li et al. (2002); Shioda et al. (2003) investigated Besides these, Sun et al. (2003b) constructed a cDNA the phylogenetic relationship for different varieties of Aloe subtractive library by the method of suppression using random amplified polymorphic DNA technology. Liu et al. 1049

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