棉花li突变体生长素极性运输的减弱

陆地棉(Gossypium hirsutum L.)li突变体叶片卷曲,植株扭曲,种子表皮毛明显偏短。通过扫描电子显微镜(SEM)观察发现,li突变体的纤维发育在起始期与野生型植株并无明显差异,但在伸长期开始后,如开花后3d(3 day post anthesis,DPA),纤维伸长受阻;li突变体茎的形成层和韧皮部分化发育不完全,生长素由顶端向基部的极性运输能力下降,仅为野生型植株的大约三分之一。推测棉花li突变体包括纤维发育不良在内的多效性异常表型,与其生长素极性运输能力的下降有关。     

Studies on Auxin Protectors XII. Auxin Protectors and Polyphenol Oxidase in Developing Coffee Fruit

The fruit of the coffee plant (Coffea arabica) was analyzed for auxin protector content. Ripe coffee berries were separated into pit and pulp, ground in buffer, and assayed for auxin protectors. The extracts were then subjected to gel filtration in order to determine the molecular weight of the protector(s). In the pit, a single protector was found with a molecular weight approaching 5000 daltons, while the pulp contained several auxin protectors, the largest of which appeared to be about 1000 daltons. Chromato-graphic studies of various gel filtration fractions showed that protector activity was always associated with spots which exhibited a light blue fluorescence under UV. The changing patterns during coffee fruit development were also investigated. Auxin protector production, and polyphenol oxidase (E.C. 1.10.3.1), an enzyme related to protector metabolism, were assayed at weekly intervals. In the unripe berry, an auxin protector was found with a molecular weight exceeding 200,000 daltons; as the berry ripened the amount of this protector gradually decreased until almost none was present in the ripe berry and the pattern changed to the pattern described above. Polyphenol oxidase content decreased as the berry ripened. Commercially roasted pits, i.e., coffee “beans”, contained very high levels of protector activity. However, gel filtration studies showed this activity to be associated entirely with low molecular weight compounds.     

Metabolism of Auxin in Pine Tissues: Naphthaleneacetic Acid Conjugation

Incubation of sections of various tissues of Pinus pinea L. and Pinus halepensis Mill, with α-naphthaleneacetie acid-1-¹⁴C (NAA) resulted in two metabolites which proved to be l-O-(α-naphthylacetyl)-β-D-glucose (NAGlu) and α-naphthylacetylaspartic acid (NAAsp). NAGlu was purified by means of insoluble polyvinyl-polypyrrolidone (Polyclar AT) column chromatography and preparative thin layer chromatography and identified by its ‘H-nuclear magnetic resonance and mass spectra. NAAsp was partially purified by means of preparative thin-layer chromatography and identified by co-chromatography with a synthetic standard and hydrolysis to the parent compounds. NAA and L-aspartic acid. Needles and shoot bark rapidly converted NAA mainly to NAGlu. In contrast, woody roots and shoot wood showed a much slower rate of conjugation with the formation of both NAGlu and NAAsp. Preincubation of wood sections in NAA increased the formation of NAGlu, whereas the formation of NAAsp was almost unaffected.     

生长素的生物合成、代谢、受体和极性运输1

主要介绍生长素的生物合成、代谢、受体,生长素极性运输和生长素响应基因等方面的研究近况.     

Interactions between Plants and Epiphytic Bacteria Regarding Their Auxin Metabolism

Epiphytic, IAA-producing bacteria strains were fed with ¹⁴C-tryptophan (Try). ¹⁴C-Try absorption and, after transfer to a Try-free medium, ¹⁴C-IAA output were stated. Using 4 different methods, the ¹⁴C-Try containing bacteria were applied to the tips of sterile corn coleoptiles and the ‘diffusible’ auxin collected at the coleoptile bases by means of agar blocks. ¹⁴C-IAA was detected in the agar blocks. Sterile coleoptiles the tips of which were wupplied with ¹⁴C-Try also deliver some ¹⁴C-IAA at their bases, but much less than both sterile coleoptiles supplied with ¹⁴C-Try-containing bacteria and nonsterile supplied with ¹⁴C-Try.     

Interactions between Plants and Epiphytic Bacteria Regarding Their Auxin Metabolism

Homogenates of epicotyls or roots of nonsterile pea plants incubated with tryptophan produce IAA within 1 to 4 hours, which was detected by means of the Avena curvature test and thin layer chromatography. Three results prove this short-term IAA production to be mainly caused by epiphytic bacteria: 1) Homogenates of sterile plant parts catalyze a conversion of tryptophan to IAA, a hundredfold lower. 2) Chloramphenicol or streptomycin very actively reduce the IAA gain obtained with nonsterile homogenates. 3) Washing solutions of nonsterile plant parts which do not contain plant enzymes but only epiphytic bacteria, produce IAA from tryptophan, too. IAA synthesis from tryptophan in vitro by enzymes of the pea plant occurs with lower intensity than hitherto known; possibly it is physiologically unimportant. It is discussed to what extent the hitherto existing research work about the IAA biogenesis in higher plants might be incriminated by disregarding tbe rôle of epiphytic bacteria.     

Interactions between Plants and Epiphytic Bacteria Regarding Their Auxin Metabolism

Proofs of different kind are presented of the existence of highly active bacteria producing IAA from tryptophan on plant surfaces and in plant homogenates. Both homogenates and washing solutions of nonsterile pea plant parts are active in producing IAA from tryptophan. Activity is much enhanced by the addition of glucose or by preincubating the preparations; it is abolished by sterile filtration, by some bactericidic and bacteriostatic substances, by chloramphenicol, streptomycin, and albucid (penicillin being only partly effective). Preparations of sterile plants do not produce IAA from tryptophan within the detection limit of the Salkowski test. The bacteria are even present on seed surfaces, in the air, and in aceton or ammonium sulfate precipitations of homogenates. Main products of the bacterial tryptophan conversion, as demonstrated by paper chromatography, are indolepyruvic acid, indoleacetic acid, indolecarboxaldehyde, and indolecarboxylic acid. In presence of glucose indolepyruvic acid is by far dominating. Many hitherto known results about tryptophan conversion to IAA by higher plants are likely to be falsified by epiphytic bacteria.     

Dependence of Basipetal Polar Transport of Auxin upon Aerobic Metabolism

The movement of IAA-¹⁴C through coleoptile segments of Avena and Zea has been investigated under aerobic and anaerobic conditions. The results are as follows: Zea. Using a 5-mm segment and a 2-hour transport period anaerobic conditions reduced the total uptake of ¹⁴C from an apical donor by 74% and the proportion of the total found in the receiving block by at least 45%. Anaerobic conditions reduced total uptake from a basal donor by 58% but no ¹⁴C reached the apical receiving block in either air or N₂. Uptake from apical and basal donor blocks in N₂ is closely similar.

The presence of ¹⁴C in the basal receiving blocks, and its absence in the apical receiving blocks, in N₂ suggests that even in anaerobic conditions movement of IAA is polarized basipetally, although the movement occurs at only a fraction of the rate found in air.

Anaerobic conditions induced a similar reduction in basipetal movement of IAA in upper and lower 5-mm segments taken from the apical 10 mm of a Zea coleoptile.

Using 10-mm Zea segments no ¹⁴C was recovered in the receiving blocks at the basal end of the segment after 2 and 4 hours in N₂ whereas large amounts were recovered in air.

Avena: Using 5-mm segments and a 2-hour transport period the total uptake of ¹⁴C from an apical donor is reduced by 83%. Movement of ¹⁴C into the basal donor is totally inhibited in N₂. Total uptake of ¹⁴C from a basal donor is reduced by 61% in nitrogen and no ¹⁴C reached the apical receiving blocks regardless of the atmospheric conditions.

A time course for the movement of ¹⁴C into the basal and apical receiving blocks through 5-mm segments showed that in air the amount in the basal receivers increased for 4 hours and then remained approximately uniform. In N₂ no significant ¹⁴C reached the receivers until 6 to 8 hours after the application of donors but even then the amounts were about 12 to 14% of that in aerobic receivers. Movement of ¹⁴C into apical receivers was similar in air and in nitrogen and even after 6 to 8 hours the amount of radioactivity barely reached significant levels.

     

Auxin Transport as Related to Leaf Abscission during Water Stress in Cotton

Plant water deficits reduced the basipetal transport of auxin in cotyledonary petiole sections taken from cotton (Gossypium hirsutum L.) seedings. A pulse-labeling technique was employed to eliminate complications of uptake or exit of ¹⁴C-indoleacetic acid from the tissue. The transport capacity or the relative amount of radioactivity in a 30-minute pulse which was basipetally translocated was approximately 30% per hour in petioles excised from well watered seedlings (plant water potentials of approximately -4 to -8 bars). No cotyledonary leaf abscission took place in well watered seedlings. Plant water potentials from -8 to -12 bars reduced the transport capacity from 30 to 15% per hour, and although the leaves were wilted, cotyledonary abscission did not increase appreciably at these levels of stress. The threshold water potential sufficient to induce leaf abscission was approximately -13 bars and abscission increased with increasing stress while the auxin transport capacity of the petioles remained relatively constant (15% per hour). The basipetal transport capacity of well watered petioles tested under anaerobic conditions and acropetal transport tested under all conditions were typically less than basipetal transport under the most severe stress conditions. Cotyledonary abscission took place during and 24 hours after relief of stress with little or no abscission taking place 48 hours after relief of stress. Although the water potential returned to -4 bars within hours after rewatering the stressed plants, partial recovery of the basipetal transport capacity of the petioles was not apparent until 48 hours after rewatering, and at least 72 hours was required to return the transport capacity to near normal values. These data support the view that decreased levels of auxin reaching the abscission zone from the leaf blade influence the abscission process and further suggest that the length of time that the auxin supply is maximally reduced is more critical than the degree of reduction.     

Approaching Cellular and Molecular Resolution of Auxin Biosynthesis and Metabolism

There is abundant evidence of multiple biosynthesis pathways for the major naturally occurring auxin in plants, indole-3-acetic acid (IAA), and examples of differential use of two general routes of IAA synthesis, namely Trp-dependent and Trp-independent. Although none of these pathways has been completely defined, we now have examples of specific IAA biosynthetic pathways playing a role in developmental processes by way of localized IAA synthesis, causing us to rethink the interactions between IAA synthesis, transport, and signaling. Recent work also points to some IAA biosynthesis pathways being specific to families within the plant kingdom, whereas others appear to be more ubiquitous. An important advance within the past 5 years is our ability to monitor IAA biosynthesis and metabolism at increasingly higher resolution.The topic of auxin biosynthesis and metabolism in plants was comprehensively reviewed in 2005 (Woodward and Bartel 2005). Since then, more genes involved in IAA biosynthesis and metabolism have been identified. A combination of numerous valuable mutants, the manipulation of IAA synthesis in specific cell types, and direct measurement of IAA levels at tissue and cellular resolution now point to localized IAA biosynthesis and metabolism as playing key roles in specific developmental events (reviewed in Cheng and Zhao 2007; Lau et al. 2008; Zhao 2008; Chandler 2009). With apologies to any authors who were not included because of space constraints, this review summarizes those recent findings that require us to rethink yet again, the role of IAA biosynthesis and metabolism in auxin biology.     

Interactions between Plants and Epiphytic Bacteria Regarding Their Auxin Metabolism

More “diffusible” auxin is received from nonsterile than from sterile corn coleoptile tips. An artificial reinfection of sterile coleoptiles with epiphytic, IAA-producing bacteria strains does, a superinfection of nonsterile coleoptiles does not increase the auxin amount. The difference between sterile and nonsterile tips persists if diffusion from the coleoptile surface is excluded by covering the surface with a paraffin layer. The greater the distance from the apex, the higher becomes the superiority of nonsterile tips. An artificial bacterial contamination of the contact face between tip and receiver agar block, or addition of glucose and tryptophan to the agar block, do not influence the received auxin amount. Consequently the additional, bacteria-produced auxin delivered by the nonsterile tip is not produced at the cut surface or in the agar but is present in the tissues of the coleoptile tip.     

Interactions between Plants and Epiphytic Bacteria Regarding Their Auxin Metabolism

Using hydrocultured pea plants, 109 bacterial strains (42 from shoots) were isolated from shoots, roots, and from the hydroculture medium. 58 different strains (26 from shoots) were able to produce IAA from tryptophan, 15 different strains (7 from shoots) were able lo destroy IAA. (Included are 13 strains possessing both properties.) As far as they could be identified, the IAA-producing and -destroying strains belong to Pseudomonas (by far dominating), Achromobacter, Alcaligenses, Bacillus, and Flavobacterium. The IAA-destroying activity strongly depends on the physiological state of the bacteria and the milieu conditions. Bacterial IAA production (but not IAA-degradation) is supposed to be important for the plant.     

Interactions between Plants and Epiphytic Bacteria Regarding Their Auxin Metabolism

The auxin content (extractable and ‘diffusible’ auxin) of non-sterile corn plants is much more increased by a tryptophan application than the auxin content of sterile plants. This effect is independent of the mode of tryptophan application (spray or supply with the transpiration stream). The epiphytic bacteria settling the shoot surface are responsible for this effect, since in special experiments the rhizosphere was separated from the tryptophan treatment. Sterilized plants which were artificially reinfected with epiphytic IAA-producing bacteria strains behave like non-sterile plants. Non-sterile plants which were superinfected with these bacteria strains have a still higher capacity to convert tryptophan to auxin.     

Relationship between Auxin and Amino Acid Metabolism of Tobacco Protoplast-Derived Cells

Single amino acids were found to be highly toxic to protoplast-derived cells of tobacco (Nicotiana tabacum cv Xanthi) cultured at low density in a culture medium containing a low naphthaleneacetic acid concentration (0.05 micromolar). The cytotoxicities of alanine, aspartic acid, asparagine, glutamic acid, glutamine, glycine, lysine, proline, and valine were reduced when the naphthaleneacetic acid concentration of the culture medium was increased to 1 micromolar. This selective modification of amino acid toxicity by naphthaleneacetic acid could not be correlated with modifications of uptake rates or incorporation of these amino acids into protein or amino acid-auxin conjugates. A mutant clone resistant to high naphthaleneacetic acid concentrations and affected in root morphogenesis did not display, at the cellular level, the naphthaleneacetic acidmediated modification of amino acid cytotoxicity.