The control of root hair formation: suggested mechanisms

Little is known about the physiological regulation of root hair development. Though the literature on the topic is fragmentary, with many gaps, it has been used to put forward some proposals for a central regulatory mechanism, taking note especially of the strong physiological influence of environmental factors on root hair formation. A hypothesis which implicates ethylene (ET) in this mechanism is proposed. This hypothesis is supported by numerous indications and observations in the literature about the effect of ET on cell wall formation and cell wall properties during the phase of root expansion and hair formation. It is assumed that environmental conditions control the effective ET concentration in epidermal hair-forming cells; they influence root development and ET production, while, through affecting the rhizosphere, they modify gas exchange at the root surface, accelerating removal of ET thereby limiting its function in hair formation. In such a way the effects of various specific factors (e.g. soil temperature, bulk density, gas exchange at the root surface or the effect of nutrients) might be manifestations of a central regulatory mechanism. The hope is that this hypothesis will stimulate further research and some suggestions are made as to the direction such research might take.     

Floral induction in woody angiosperms

The long juvenile period of trees is a severe impediment to study of reproductive biology and genetic inheritance, and is a serious constraint for traditional breeding programs. Very little effort has been directed toward the development of practical methods for inducing early flowering in most woody angiosperms, particularly members of the genus Populus. This review is intended to stimulate interest in, and provide direction for, future research in this area. An emphasis is placed on techniques that can be applied easily and inexpensively. Inductive treatments discussed include: phytohormones (gibberellins, cytokinins, abscisic acid, ethylene and auxin); growth retardants (paclobutrazol, uniconazole, daminozide, chlormequat and cimecthacarb); physical constraints (girdling, root restriction and shoot training); cultural conditions (photoperiod, mineral nutrition, moisture stress and temperature); and grafting. Recent reports on stimulation of flowering by genetic transformation with floral homeotic genes are also described. Several research avenues which appear promising are proposed for near-term study.     

The role of photoprotection in defence of two wheat genotypes against Zymoseptoria tritici

This study provides new insights into the role of photoprotection in preformed and induced defence of two wheat genotypes with contrasting phenotypes to infection by Zymoseptoria tritici. We investigated the mechanisms of the photoprotective response during early infection, including nonphotochemical quenching (NPQ), β-carotene-derived xanthophylls, reactive oxygen species, and the phytohormones abscisic acid (ABA), jasmonic acid (JA), and salicylic acid (SA). Furthermore, we quantified the effects of pathogenesis on photosynthesis, stomatal control, and expression of plant defence molecular markers. The photoprotective mechanism of successful defence involved the qI component of NPQ leading to rapid down-regulation of photosystem II quantum yield and chlorophyll a:b, increased biosynthesis of the xanthophyll neoxanthin and ABA, and the expression of chloroplast-specific enzymes to engage in scavenging of O₂^●−. Elevated ABA in the resistant genotype correlated with preformed leaf defence traits including low stomatal density, increased expression of wax biosynthesis, and lignification. Z. tritici exhibited reduced germination and branching on the resistant host genotype and hijacked stomatal control in both genotypes by enhancing stomatal sensitivity to light. Increased biosynthesis of JA and anthocyanins, in contrast to SA, were quantified in the incompatible interaction. Our results indicate that ABA and JA in antagonistic action to SA were associated with defence in the resistant genotype, Cougar, against Z. tritici.     

干旱胁迫下几种柑桔植物内源激素含量的变化规律

本文研究了干旱胁迫下枳壳、纽荷尔脐橙和沙田柚内源激素含量的变化规律。结果表明:随着失水率增加,三种植物中吲哚乙酸(IAA)含量逐渐减少,脱落酸(ABA)含量逐渐增加,而赤霉酸(GA3)和玉米素(Z)含量变化有些起伏,但当失水率大于40%时,其含量逐渐减少。     

A synopsis of symbiotic nitrogen fixation and other apparently similar host‐microorganism interactions

Physical, physiological and biochemical processes occurring during colonization, infection, and nodule development and maintenance phases of an effective legume‐rhizobia symtiotic nitrogen fixation system are discussed. Limited knowledge of host reactions to invasion by rhizobia which result in failure to establish a symbiotic nitrogen fixation system are related to more thoroughly researched reactions of resistant host plants to invastion by pathogenic organisms. The most common resistant host responses are an increase in the production of phenolic compounds and phenol oxidizing enzymes. Many of the pheolic compounds or their quinones produced by enzymatic oxidation inhibit the action cell wall degrading enzymes and phytohormones, are antibiotic toward pathogenic organisms, and are phytotoxic to host plant cells. It is postulated that similar host responses result with rhizobia invasion and that the magnitude of these responses determine specificity of legume‐rhizobia symbiosis.     

EFFECTS OF PHYTOHORMONES ON PROLINE CONTENT AND ANTIOXIDANT ENZYMES OF VARIOUS WHEAT CULTIVARS UNDER SALINITY STRESS

Salinity stress is one of the important agricultural problems in the world. A factorial experiment based on completely randomized design with four replications was conducted to evaluate the effects of phytohormones (gibberellic acid and abscisic acid) on the activity of antioxidant enzymes (peroxidase, superoxide dismutase and catalase), rubisco activity and content, and proline in three wheat cultivars (Gascogen, Zagros, and Kuhdasht) under control and salinity stress (3.5 and 7 dS m^?1). The results showed that salinity stress (3.5 and 7 dS m^?1) decreased the activity of catalase, rubisco, carboxylase, but increased peroxidase, superoxide dismutase activity and proline content. Gibberellic acid caused 58.03% increased in rubisco carboxylase activity in Zagros at 7 dS m^?1 in comparison with abscisic acid under salinity stress compared with the control plants in Kuhdasht. Activity of superoxide dismutase in Kuhdasht cultivar at 7 dS m^?1 salinity level showed 76.43% increased in Gascogen under salinity stress compared with the control plants with gibberellic acid application. The highest proline content as an osmolyte was found in Zagros at 7 dS m^?1 salinity level with abscisic acid (194 μmol g^?1 DM) application. Peroxidase activity increased 83.31% and catalase activity decreased 61.27% compared with the control plants in Zagros. Gibberellic acid application significantly prevented reduction in rubisco content under salinity stress. In conclusion, increased in peroxidase and superoxide dismutase activity and proline content decreased the adverse effects of salinity stress on studied cultivars. Also, the foliage spray of gibberellic acid enhanced and improved the growth condition. In this experiment, Zagros cultivar showed more tolerance to salinity stress than the other two cultivars.     

不同品种玫瑰扦插技术研究

以‘珲春’、‘牟平’、‘唐红’、‘紫枝’4个玫瑰品种的插穗为试材,研究激素、基质、扦插方式等因素对其扦插成活率的影响。结果表明:利用间歇喷雾设备进行玫瑰嫩枝扦插的生根率远远高于普通硬枝扦插,生根率最高的组合是50mg/L ABT1+处理1h+蛭石;混合基质扦插的成活率高于单一基质;4个品种中‘紫枝’生根率最高。     

花烛愈伤组织不同继代培养的再分化差异

 对花烛( Anthurium andraeanum) ‘Jolanba’无菌苗叶片诱导产生的愈伤组织进行3 种不同的培养处理, 观察其再分化表现, 并探讨了3 种继代培养愈伤组织的生理生化特点。结果表明, 适当降低基本培养基浓度、减少继代次数和延长继代周期培养的愈伤组织分化的芽较多、较壮; 再生芽的分化需要较高水平的可溶性蛋白质, 其生长需要较高水平的可溶性糖; POD 和SOD 活性与分化的芽数呈正相关; GA_{1 + 3}/ABA、ZR_s/ ABA 的高比例与再生芽的高度呈显著正相关; IAA/ ABA 及IAA 的高水平与花烛离体根的发生呈正相关。重新诱导培养和延长愈伤组织继代周期以提高再生芽生长势的主要生理生化基础之一是维持较高的可溶性糖水平和有利的激素平衡。     

马铃薯试管薯形成过程中几种内源激素的变化

 以马铃薯早熟品种‘费乌瑞它’脱毒试管苗为材料, 在试管薯形成过程中, 研究其GA₃、IAA、6- 呋喃氨基嘌呤( KT) 、6- 苄氨基嘌呤( BAP) 、ABA 含量的变化。结果表明: 无论是换入试管薯诱导培养基前的试管苗, 还是试管薯诱导形成过程中的母株试管苗, 根内各种内源激素含量始终高于茎叶。随着诱导环境的改变, 以及匍匐茎、试管薯的形成和发育, 各种内源激素含量发生明显变化。转入诱导培养基后的试管苗在光照培养条件下, 茎叶内GA3、IAA、KT、BAP 和根内ABA 含量均有不同程度的增加;黑暗培养3 d 匍匐茎形成时, GA₃、KT、BAP 及茎叶内IAA 含量下降; 黑暗培养7 d 匍匐茎顶端开始膨大时, 茎叶内GA₃、KT、BAP 含量再次增高, 而根内GA₃、BA 含量继续下降, IAA、ABA 含量无明显变化; 黑暗培养14 d 试管块茎基本形成时, IAA、BAP 含量缓慢上升, 根内GA₃ 含量下降, 茎叶GA₃ 含量处于相对稳定状态。