Plant hormone response mutants

A variety of plant hormone response mutants has now been described, and is surveyed in this article. In addition to hormone-insensitive mutant phenotypes with defects in hormone-related features, there exist mutants apparently constitutive for the gibberellin responses, and also a mutant hyper-responsive to gibberellin. Although there is still little biochemical evidence on the nature of these mutants, the emerging picture of their genetic dominance relationships has given rise to tentative suggestions of the involvement of represser functions in hormonal control systems.     

Heat treatment of ripening apples: Differential effects on physiology and biochemistry

Apples ( Malus domestica Borkh.) were heated for 4 days at 38°C immediately after harvest and then placed at 20°C for 7–10 days. Protein synthesis, ethylene production and fruit softening were reversibly inhibited by the heat treatment. Fruit respiration, membrane permeability and chlorophyll degradation in the fruit peel were enhanced during the treatment. The heat-treated apples ripened normally but more slowly than untreated apple We hypothesize that heat treatment differentially affects processes which normally increase simultaneously during fruit ripening, by inhibiting those processes which require tie novo protein synthesis and enhancing those that do not.     

山茶科紫茎属和舟柄茶属的系统学研究

本文对山茶科紫茎属和舟柄茶属进行了深入细致的系统学研究,藉助形态学、古植物学、孢粉学,细胞学和解剖学资料澄清了两属的分合问题,证实两属在各方面具有较大相似性,并且各分类特征存在广泛的联系而无法分开,从而赞同H．K．Airy Shaw,J．R．Sealy及S．A.Spongberg的主张,即将这两属合并。在此基础上本文提出了世界范围广义紫茎属下分类系统。属下新系统根据花柱合生程度、花序类型,苞片与萼片的形状以及两者的相对长度等特征,分为两个亚属,五个组,同时对该属种类进行修订。该属共有23种5变种,本文发表新组1个,新名称2个,新组合9个,新异名10个,新种1个,并附有分种检索表。广义的紫茎属为东亚-北美间断分布类型,中国南部和西南部是该属的起源中心和高度分化中心。根据化石资料推断,该属起源于早白垩纪,在第三纪以前于整个劳亚古陆上呈广泛而连续的分布,后因冰川及造山运动的影响,从而形成现在的分布格局。     

Stimulation of root hair elongation in Arabidopsis thaliana by low phosphorus availability

Low phosphorus availability stimulates root hair elongation in many plants, which may have adaptive significance in soil phosphorus acquisition. We investigated the effect of low phosphorus on the elongation of Arabidopsis thaliana root hairs. Arabidopsis thaliana plants were grown in plant culture containing high (1000 mmol m^?3) or low (1 mmol m^?3) phosphorus concentrations, and root hair elongation was analysed by image analysis. After 15d of growth, low-phosphorus plants developed root hairs averaging 0.9 mm in length while high-phosphorus plants of the same age developed root hairs averaging 0.3 mm in length. Increased root hair length in low-phosphorus plants was a result of both increased growth duration and increased growth rate. Root hair length decreased logarithmically in response to increasing phosphorus concentration. Local changes in phosphorus availability influenced root hair growth regardless of the phosphorus status of the plant. Low phosphorus stimulated root hair elongation in the hairless axr2 mutant, exogenously applied IAA stimulated root hair elongation in wild-type high-phosphorus plants and the auxin antagonist CM PA inhibited root hair elongation in low-phosphorus plants. These results indicate that auxin may be involved in the low-phosphorus response in root hairs.     

Effect of 2,4-dichlorophenoxyacetic acid on the dark- and light-induced pulvinar movements in Cassia fasciculata Michx

2,4-dichlorophenoxyacetic (2,4-D) applied to excised leaves of Cassia fasciculata modified the dark-induced (scotonasty) and light-induced (photonasty) leaflet movements, showing that this compound acts on rapid turgor variation and the concomitant ion migrations, in particular K⁺. 2,4-D inhibited the scotonastic closure in a dose-dependent manner from 10^–8 M to 10^–5 M and promoted the photonastic opening in the same range of concentrations. The compound acted rapidly since a treatment as short as 5 min gave an obvious effect on the motile reaction; however, a lag period of 45–60 min was needed to observe its effect. Although 2,4-D is a weak acid, its greatest physiological efficiency was obtained with pH values close to neutrality. The physiological results are discussed in relation to the chemical properties and the characteristics of transport of the molecule.Abbreviations ABA abscisic acid - 6-BAP 6-benzylaminopurine - 2,4-D 2,4 dichlorophenoxyacetic acid - GA₃ gibberellic acid - HEPES N-[2-hydroxyethyl] piperazine-N-[2-ethanesulphonic acid] - IAA indole-3-acetic acid - NAA 1-naphthaleneacetic acid - MES 2-(N-morpholino)-ethanesulphonic acid     

Differential IAA dose response relations of the axr1 and axr2 mutants of Arabidopsis

In comparison to wild type Arabidopsis thaliana, the auxin resistant mutants axr1 and axr2 exhibit reduced inhibition of root elongation in response to auxins. Several auxin-regulated physiological processes are also altered in the mutant plants. When wild-type, axr1 and axr2 seedlings were grown in darkness on media containing indoleacetic acid (IAA), promotion of root growth was observed at low concentrations of IAA (10^?11 to 10^?7M) in 5-day-old axr2 seedlings, but not in axr1 or wild-type seedlings. In axr1 there was little or no measurable root growth response over the same concentration range. In wild type, root growth was inhibited at concentrations greater than 10^?10M and no detectable root growth response was observed at lower concentrations. In addition, production of lateral roots in response to IAA increased in axr2 seedlings and decreased in axr1 seedlings relative to wild type. Promotion of root elongation and initiation of lateral roots in axr2 seedlings in response to auxin indicate that axr2 seedlings are able to perceive and respond to IAA.     

Colchicine-mediated chromosome doubling during anther culture of maize (Zea mays L.)

Efficient methods of chromosome doubling are critical for the production of microspore-derived, doubled-haploid (=DH) plants, especially if, as in maize anther culture, spontaneous chromosome doubling occurs infrequently. In the present study, colchicine (5–1000 mg/l) was added to the induction medium and maize anthers were incubated in the colchicine-containing medium for different durations (1–7 days). In order to improve overall anther culture response, the culture temperature was adjusted to 14°C during the first 7 days. Colchicine applied at low concentration, i.e. 5 mg/l (7 days), or for short duration, i.e. 1–3 days (250 mg/l), showed beneficial effects on the formation of embryolike structures (=ES) and thus led to increased plant production, but was comparatively ineffective regarding chromosome doubling. Optimal doubling effects were observed when anthers had been exposed to culture medium containing 250 and 1000 mg/l of colchicine (7 days); in these treatments the doubling index (=DI), defined as the quotient of the number of DH plants and the number of totally regenerated plants in a specific treatment, rose to 0.56 and 0.53, respectively, compared to 0.20 in the untreated control. However, colchicine administered at concentrations higher than 250 mg/l seemed to be detrimental to general plant production; thus, in spite of a high DI, the overall DH plant production was even lower than in the control treatment. Maximum DH plant production for three different genotypes was accomplished with culture medium containing 250 mg/l of colchicine (7 days). With the best-responding genotype (ETH-M 36) a DH plant production of 9.9 DH plants/100 anthers was accomplished, i.e. a 7-fold increase compared to the non-treated anthers. This is the first report on efficient chromosome doubling in anther culture by subjecting anthers to colchicinecontaining induction medium during a post-plating cold treatment. Chromosome doubling as described here becomes an integral part of the maize anther culture protocol and thus represents a rapid and economical way to produce DH plants.     

Developmental and genotypic differences in the response of pea stem segments to auxin

The objective of this investigation was to examine the response to exogenous auxin (indole-3-acetic acid; IAA)of stem segments at two developmental stages. The standard auxin response of excised stem segments and intact plants consists of an initial growth response and a prolonged growth response. We found that this biphasic response does not occur in internodes at very early stages. Stem segments of light grown pea of various genotypes were cut when the fourth internode was at 6–13% of full expansion (early-expansion) or at 18–25% of full expansion (mid-expansion). Length measurements of excised segments were made after 48 hours of incubation on buffer with or without auxin. An angular position transducer linked to a computerized data collection system provided high-resolution measurement of growth of stacks of segments incubated in buffer over 20 hours. Early-expansion segments of all genotypes deviated from the standard auxin response, while mid-expansion segments responded in a manner consistent with previous reports. Early-expansion segments of tall, light-grown plants were unique in showing an auxin-induced inhibition of growth. The auxin-induced inhibition correlated with high endogenous auxin content, as determined by HPLC and GC/MS, across genotypes and between early-expansion and mid-expansion segments of tall plants. Measurement of ethylene evolved from stem segments in response to auxin, and treatment of segments with the ethylene action inhibitor, norbornadiene, showed the inhibition to be mediated in part by heightened ethylene sensitivity. Growth of early-expansion segments of dwarf and severe dwarf plants was stimulated by exogenous auxin, but the growth rate increase was delayed compared to that in mid-expansion segments. This is the first time that such a growth response, termed the delayed growth response has been emonstrated. It is concluded that developmental stage and endogenous hormone content affect tissue response to exogenous auxin.     

Changes in IAA responsiveness in the elongation region of graviresponding mung bean roots

IAA responsiveness of sections of root tissue taken from the top and bottom of mung bean roots was assessed prior to and at varying times following gravistimulation. Prior to gravistimulation, root tissue sections from the sides of the elongation zone responded similarly to IAA. After gravistimulation (within 5 min), root sections from the bottom of the elongation zone became more responsive to IAA than sections collected from the upper side of the elongation zone. The change in IAA responsiveness of these tissue sections was transient with root sections from both the top and bottom of the elongation zone again exhibiting similar responsiveness to IAA following 15 minutes of gravistimulation.These studies also examined if the root tip is required for the gravity-induced shift in IAA responsiveness in the tissues of the elongation zone. The IAA responsiveness of top and bottom sections of the elongation zone from decapped mung bean roots was assessed at varying times following gravistimulation. The responsiveness to IAA of top and bottom sections changed rapidly in decapped roots, just as had been previously found for intact roots. Although the alteration in responsiveness was transient in decapped roots (just as intact roots), the time it took for the sections to recover previous responsiveness to IAA was extended.These results suggest that the initial growth response of graviresponding roots may be due to a change in the IAA responsiveness of tissues in the elongation zone and not an asymmetric accumulation of IAA on the lower side of the elongation zone. The results also indicate that the gravity-induced shift in IAA responsiveness in the elongation zone occurs independently of the root cap, suggesting that the cells in the elongation region can perceive and respond to gravity independently of the root cap during the intial phases of the gravity response.     

Keratinolytic fungi in sewage sludge

Sewage sludge from the Upper Silesia Region of Poland were surveyed for keratinolytic fungi. Out of 100 Petri dishes examined, 89 were positive for these micro-organisms. Altogether, 185 fungal appearances belonging to 10 species were observed. Trichophyton terrestre with its teleomorph Arthroderma quadrifidum, T. ajelloi with A. uncinatum, Microsporum gypseum with Arthroderma sp., and Chrysosporium keratinophilum with Aphanoascus keratinophilus prevailed in the sludges. The sewage treatment technologies together with the sludge structure, humidity and pH were found to be critical factors determining the occurrence of keratinolytic fungi in the sludge environment. The qualitative and quantitative composition of keratinolytic fungi could be a useful tool in evaluation of sludge treatment processes.