Long Distance Transport in Macrocystis integrifolia: III. MOVEMENT OF THO

Movement of THO and tritium-labeled photoassimilate was studied in intact fronds and frond cuttings of Macrocystis integrifolia following labeling of a mature blade by tritiated water. Both THO and tritium-labeled assimilate moved from the source blade to sink areas at velocities comparable to those recorded earlier for ¹⁴C- and ³²P-labeled compounds. In intact fronds and frond cuttings, THO and tritium-labeled assimilate showed a declining gradient with increasing distance from the source. In the exudate collected from the basal cut end of the frond, there was a marked increase in radioactivity with time in the photoassimilate, but no such gradient was evident for THO. These results support the idea that, although both tritium-labeled assimilate and THO move in the sieve elements, THO is rapidly exchanged with water in the tissues surrounding the sieve elements. Finally, it is shown that THO is transported to the sink and there “unloaded”; indeed, it can move out of the plant itself. The data on velocity and directionality of transport as well as unloading of THO at the sink are discussed, along with computations on specific mass transfer, and favor the idea that Münch's pressure-flow hypothesis is applicable in Macrocystis for long distance translocation of photoassimilates.     

Long Distance Transport in Macrocystis integrifolia: II. Tracer Experiments with C and P

Discs from mature regions of Macrocystis blades picked up significantly more [³²P]phosphate from the ambient medium than similar discs from young meristematic regions, and this uptake was higher in light than in darkness. Double-labeling experiments with NaH¹⁴CO₃ and [³²P]phosphate, using intact fronds as well as cut frond segments, indicated that ³²P was translocated from mature blades to sink regions at velocities of 25 to 45 centimeters per hour, velocities comparable to ¹⁴C translocation velocity in the same material. There was a slight delay in transport of ³²P which may be due to a delay in loading or to a high metabolism of ³²P in the transporting channels. Histoautoradiography of stipe segments in the translocation pathway indicated that transport of label occurred in the peripheral parts of medulla. An analysis of ³²P-labeled compounds in the fed blade and in the sieve tube sap, collected from basal cut ends of stipes, indicated major differences in labeling patterns. In the blade, a high proportion of ³²P was recovered as inorganic phosphate and relatively small amounts were found in hexose mono- and diphosphates, UDPG and ATP. In the sieve tube sap, however, only a small amount of ³²P was present as inorganic phosphate, a large proportion was found in hexose mono- and diphosphates, and appreciable amounts were present in ATP and UDPG.     

Long Distance Translocation of Sucrose, Serine, Leucine, Lysine, and Carbon Dioxide Assimilates: II. Oats

To establish whether several amino acids were equally able to enter the phloem of oat (Avena sativa L.) plants and be transported, several (14)C-labeled amino acids were applied individually to an abraded spot on a fully expanded source leaf. The base of an immature sink leaf was monitored with a GM tube for time and rate of arrival of radioactivity. Transport of (14)C-sucrose and (14)CO(2) assimilates was measured for a comparison. The applied l-serine, l-lysine, and l-leucine, as well as sucrose, entered the phloem and were transported to the sink leaf at rates between 1.16 and 1.83 cm/min. Transport velocity for CO(2) assimilates was 1.57 cm/min. A heat girdle near the top of the source leaf sheath blocked most transport, which indicated that transport was primarily through the phloem. Mass transfer rates for amino acids were only 3% as great as that for sucrose, suggesting different mechanisms of entry for sucrose than for amino acids into the phloem. The higher percentage of CO(2) assimilates mobilized to the sink leaf was attributed to the greater surface area of minor veins accessible to loading, as compared to those compounds supplied via an abraded spot. Serine was extensively metabolized in the source leaf, and radioactive products in the sink leaf mirrored those in the source leaf. Most radioactivity of lysine and leucine remained within these compounds in the source, path, and sink tissues. We concluded that there was no barrier to entry of amino acids into the phloem and transport therein. Data do not suggest a specific mechanism for entry of amino acids into the phloem.     

Chromosome Number of Macrocystis integrifolia Bory

Cultures of Macrocystis integrifolia zoospores have been madein sea-water enriched with phosphate and nitrate. It has beenshown that the spores and gametophytes possess nuclei with thehaploid complement of 16 chromosomes while the sporophyte nucleiare diploid with 32 chromosomes. Spores were transported byair from British Columbia to the British Isles. Results arecompared with other Laminariaceae.     

Translocation of Assimilates Within and Between Potato Stems

Three aspects of translocation in potato were examined: (i)translocation within stems (ii) translocation between individualstems of a plant (iii) translocation between tubers followinginjection of ¹⁴C sucrose into a single daughter tuber. Assimilatesexported from single leaves of evenly illuminated potato stemsremained confined to the same side of the stem as the sourceleaf in a pattern consistent with the internal arrangement ofvascular bundles in the stem, and tubers borne on stolons verticallybelow the source leaf contained higher concentrations of ¹⁴Cthan those on the opposite side. Consequently ¹⁴C import intothe tubers bore little relationship to tuber growth rates. However,alteration of source/sink relations by pruning stems to a singlesouce leaf resulted in an even distribution of ¹⁴C throughoutthe vascular bundles of the stem and ¹⁴C import into the tubersbore a stronger relationship to tuber growth rates than to thephyllotactic relationship of the tubers with the source leaf. Labelling one stem of a potato plant resulted in little or nomovement of ¹⁴C into tubers on other unlabelled stems. However,removal of the unlabelled stems at ground level induced a significantmovement of ¹⁴C from the labelled stem to the tubers on unlabelledstems, this movement occurring via the mother tuber. Shadingthe unlabelled stems had less effect than stem removal. ¹⁴C sucrose injected into single daughter tubers was translocatedto other tubers on the same stem and also to tubers on a secondstem at the opposite end of the mother tuber. The sucrose wasconverted to starch in these tubers. The results favour the view that each potato stem functionsas an independent unit with potential for assimilate redistributionwithin a stem but with little or no carbon exchange occurringbetween stems, unless under severely altered source/sink patterns. Assimilates, ¹⁴C, autoradiography, potato (Solanum tuberosum L.), tuber growth     

Repopulation techniques for Macrocystis integrifolia (Phaeophyceae: Laminariales) in Atacama,Chile

The giant kelp Macrocystis (integrifolia) has been intensely harvested in northern Chile for several years. In order to prevent a future disaster, we developed two different techniques for restoration of damaged Macrocystis integrifolia beds in the Atacama region of Chile. (1) Explantation: Laboratory-grown juvenile sporophytes were fixed to different substrata (plastic grids, ceramic plates, or boulders) by elastic bands or fast-drying glue (cyanoacrylate). Explants reached 150–200 cm in length within 5 months (relative growth rate?≈?1.3–1.7 % day^?1), and reproductive maturity in 5–7 months. (2) Seeding of spores: Mature sporophylls were placed at 8 m depth on the sea bottom, supported by cotton gauze sleeves attached to boulders of different origin. Sixty percent of clean boulders collected on the beach produced up to seven recruits per boulder. In contrast, 20 % of the boulders from the sea bottom, colonized by epibionts, showed up to two recruits. Relative growth rates, however, were similar (≈2.4–2.6 % day^?1). Practical applications of our findings are: laboratory-produced juvenile sporophytes fixed to various substrata by elastic bands or cyanoacrylate glue can be used to colonize rocks or artificial reefs. In cases, where laboratory-grown seedlings are unavailable, mature sporophylls from nearby Macrocystis beds can be used to establish new recruits on rocky substrata.     

Cultivation of Macrocystis integrifolia (Laminariales,Phaeophyta) in southeastern Alaskan waters

The artificial culture of Macrocystis integrifolia in southeastern Alaskan waters has been initiated as a first step in a project to augment the existing herring roe-on-kelp fishery in the state. The growing of Macrocystis in Prince William Sound has the potential of considerably enhancing this fishery by eliminating the costly importation of this kelp from southeast Alaska. In an ongoing feasibility study, Macrocystis has been cultured under laboratory conditions through the embryonic sporophyte stage and outplanted in waters near Sitka, Alaska (57° N). Growth of the outplanted kelps has been monitored as a function of the time and depth of the outplanting. Preliminary results suggest that light is limiting for growth in winter and that the optimal depth for outplanting will vary with the season.     

Translocation of C in Macrocystis pyrifera (Giant Kelp)

The pattern of import and export of ¹⁴C-labeled assimilates in Macrocystis pyrifera (L.) C. A. Agardh in southern California was studied by labeling single blades on fronds, in situ, with [¹⁴C]NaHCO₃ for 24 hours. The pattern was found to be similar to that known in dicotyledons: actively growing tissue imported and did not export. As a blade reached maturity it began to export, at first only acropetally to the apex which formed it, later also down the frond to sporophylls and frond initials at the base of the frond, and into the apical regions of juvenile fronds; finally there was a phase of declining export, late in the life of the blade, when transport was only downward. Young fronds imported from older fronds until they were approximately 3 meters long, by which time they had developed mature, upward exporting blades. No translocation was found from a younger frond to an older frond, nor was there transport upward from a blade on a frond lacking the apical region.     

植物病毒长距离转运的分子机理

植物病毒侵入寄主细胞后,其局部侵染和系统侵染的形成涉及病毒在植物体内二种不同的转运模式:经过叶肉细胞胞间连丝来实现的胞间转运(cel-to-cell movement)和经过植物维管系统的韧皮部筛管来实现的长距离转运(long-distance transport)[1].近十年来对胞间转运的大量研究,尤其是对TMV在烟草叶肉细胞间转运机理的出色研究,使人们逐步明晰了病毒胞间转运的一些基本步骤及转运机理,建立起了植物病毒胞间转运机理研究的基本模式[2-5].与此同时,因病毒的长距离转运是其实现系统侵染的关键过程,人们对病毒长距离转运机理的研究也积累了相当多的工作,该方面的研究日益成为植物病毒学研究的一个重要内容.本文拟对病毒长距离转运过程中所涉及的病毒因子、病毒-寄主的互作及病毒进出韧皮部筛分子的可能方式作一概述.     

Hormone-directed Transport of Assimilates in Decapitated Internodes of Phaseolus vulgaris L.

Application of ethylene, indole-3yl-acetic acid (IAA), 6-(benzylamino)-9-(2tetrahydropyranyl)-9-Hpurine (SD8339), or mixtures of IAA, gibberellic acid (GA),and cytokinins, increased the accumulation of ¹⁴C-activity indecapitated internodes of Phaseolus vulgaris seedlings. Differencesbetween treated and untreated tissues with respect to importof labelled assimilate were detected 3 h after application ofa mixture of IAA, GA, and SD8₃₃₉. In longer-term experimentseffects of the growth-regulator mixture on translocation oflabel were greater than those of IAA alone. Inhibitory effectsof abscisic acid on import of assimilate were counteracted bySD8₃₃₉. The ability of internode tissues to import ¹⁴C-photosynthatedeclines with time from decapitation, and a decrease in incorporationof ¹⁴C-leucine into protein was detected after 24 h. There wasan increase in protein and RNA synthesis in internodal tissuesfollowing a 2.5-h pre-treatment of decapitated internodes withIAA, GA, and SD8₃₃₉. Concentrations of 2, 3, 5-triiodobenzoicacid which inhibit ¹⁴C-IAA translocation stimulate protein synthesisin decapitated internodes, and augment the IAA-effect on importof ¹⁴C-photosynthate. ‘Hormone-directed’ assimilatetransport is discussed in relation to confounding effects ofgrowth responses and differential senescence of treated anduntreated tissues. It is suggested that accumulation of labelledassimilate in treated tissues results from effects of growthregulators on synthetic activities at the point of application.     

Utilization of holdfast fragments for vegetative propagation of Macrocystis integrifolia in Atacama, Northern Chile

We attempted to propagate Macrocystis integrifolia (giant kelp) by fragmentation and regeneration of holdfasts, which consist of creeping stolons with lateral haptera. Stolons from a natural kelp population in Bahia Chasco (Atacama, North Chile) were cut into fragments, each containing one or more lateral stipe and frond initials. Fragments were attached to longlines with elastic bands. We used two additional types of inoculants as controls: (1) natural recruits from the local parent population and (2) laboratory-cultured young sporophytes. Length, reproductive phenology, and mortality were determined monthly. Our results confirmed the feasibility of M. integrifolia propagation by reattachment of stolon fragments, and we obtained up to eight new individuals from one parent holdfast. Individuals from holdfast regeneration formed sporangial sori 3 months earlier than control specimens from recruits and laboratory culture, while all three types gave similar values for mortality. Holdfast morphology of regenerates differed strongly depending on their origin: stolon fragments continued growth and developed new haptera except in the cut surfaces, natural recruits formed typical M. integrifolia holdfast morphs, and sporophytes originating from laboratory culture produced minor stolons with many haptera. Implications of our results on ecology, repopulation, and aquaculture are discussed.     

Effects of kelp (Macrocystis integrifolia) on soil chemical properties and crop response

In 1981 a two-year field plot experiment was established to assess the effects of quantities (0, 7.5, 15, 30, 60 and 120 t ha⁻¹) of fresh kelp (Macrocystis integrifolia) on crop growth and nutritional response and chemical properties of a fine-textured soil. Soil was analyzed for NO₃−N, NH₄−N, electrical conductivity, pH, Cl and exchangeable cations (K, Mg, Ca, Mn and Na). The plots were planted to beans (Phaseolus vulgaris) in the first year and peas (Pisum sativum) in the second year. Marketable bean yields increased in the first year with kelp applications up to 60 t ha⁻¹, with yields, emergence and flowering being reduced by the 120 t ha⁻¹ application. Soluble salts (EC) and Cl concentrations in the soil eight days after application increased linearly and sharply with increasing quantities of kelp. Increased K concentration and moisture content, characteristics of plants growing in a salt-stressed soil environment, were measured. A subsequent companion greenhouse experiment confirmed that the reduced bean emergence and growth with 120 t ha⁻¹ applications of kelp were primarily due to soluble salts. The only growth effects upon peas in the second year was a slight reduction in leaf plus stem yields with increasing applications of kelp.     

Effects of kelp (Macrocystis integrifolia andEcklonia maxima) foliar applications on bean crop growth

In 1983 and 1984 field plot experiments were established to assess the effects of a foliar applied (2 or 4L ha^–1×four applications per season) kelpMacrocystis integrifolia, concentrate on growth and nutrition of bean,Phaseolus vulgaris. A commerical kelp concentrate, prepared fromEcklonia maxima, was also used as a test comparison. In the first year a phytohormonal extract of theM. integrifolia concentrate, designed to extract the cytokinin, auxin and gibberellin phytohormones, was also applied to the crop to test the thesis that these phytohormones are active constitutents. In each of the two field seasons the kelp concentrates increased harvestable bean yields on average by 24%. The phytohormonal extract also increased yields, but was less effective than the kelp concentrate itself. Bioassay results demonstrated the presence of phytohormone-like substances in this crude extract.     

Long Distance Transport of Abscisic Acid in NaCI-Treated Intact Plants of Lupinus albus

Plants of Lupinus albus were grown for 51 d under control (1.1mol m^–3 NaCl) and saline (40 mol m^–3 NaCl) conditions.Plants were harvested and changes of carbon, nitrogen and abscisicacid (ABA) contents of individual organs were determined 41d and 51 d after germination. In the period between the twoharvests xylem and phloem saps were collected and respirationand photosynthesis of individual organs were measured. Usingflows of carbon, C/ABA ratios and increments of ABA flows ofABA in phloem and xylem and rates of biosynthesis and degradationof ABA were calculated. Both under control and saline conditionsnet biosynthesis occurred in the root, the basal strata of leavesand in the inflorescence. Metabolic degradation of ABA tookplace in the stem internodes and apical leaf strata. Salt stress increased xylem transport of ABA up to 10-fold andphloem transport to the root up to 5-fold relative to that ofthe controls. A considerable amount of ABA in the xylem saporiginated from biosynthesis in the roots, i.e. 55% in salt-treatedand smaller than 28% in control plants. The remaining part ofABA in the xylem sap originated from the shoot: it was translocatedin the phloem from fully differentiated leaves towards the rootand from there it was recirculated back to the aerial partsof the plant. The data suggest that ABA may serve as a hormonalstress signal from the root system. Key words: Lupinus albus, salt stress, abscisic acid, long distance transport     

Movement of C-labeled Assimilates into Kernels of Zea mays L: III. AN ANATOMICAL EXAMINATION AND MICROAUTORADIOGRAPHIC STUDY OF ASSIMILATE TRANSFER

Basal tissue of developing maize kernels was examined by light micros-copy and by scanning and transmission electron microscopy. Plasmodesmata occur in pedicel and endosperm parenchyma but were not seen between the placento-chalazal cells and basal endosperm transfer cells. A layer of noncellular material separates the transfer cells from the placentochalazal cells. Microautoradiography of ¹⁴C-labeled assimilates entering the kernels revealed that incoming sugars are not confined to the apoplast, but rather are present in the cytoplasm and vacuoles of pedicel and endosperm cells. No specific accumulation of radioactivity was seen in any particular tissue, although at later sampling times, a higher grain density in the pedicel than the endosperm indicated a general buildup of sugars in the pedicel. A possible model for sugar movement into developing kernels is discussed.     

Vascular Regeneration and Long Distance Transport of Indole-3-acetic Acid in Coleus Stems

Excision of all leaves and buds of Coleus blumei Benth. plants reduced xylem cell and sieve tube regeneration a highly significant amount around a wound in internode number 5 when compared with regeneration in intact (wounded) plants. Application of indoleacetic acid (IAA-¹⁴C) to the cut surface of internode number 2 restores regenerative activity around the wound in internode number 5. Radioactivity applied as IAA-¹⁴C reaches the wound area when applied at the cut surface of inter-node number 2 showing a logarithmic decrease with distance from the point of application. Chromatography showed that radioactivity was located close to the R_F of IAA as well as near the solvent front.     

Giant kelp (Macrocystis) fishery in Atacama (Northern Chile): biological basis for management of the integrifolia morph

In Bahia Chasco, Atacama, the integrifolia morph of Macrocystis forms one of the most important kelp forests in northern Chile. In order to determine effects of local harvesting policies, we evaluated the population dynamics of this resource in intact, frequently disturbed, and permanently and completely harvested areas. Recruitment, frond length, reproductive phenology and standing crop were assessed monthly. In intact areas, frond length and ratio of reproductive individuals were higher, but recruitment was poorly stimulated. On the other hand, complete harvest had an important effect on Macrocystis population dynamics. Whereas recruitment and growth were much higher after harvest events, reproductive phenology was lower. The harvest techniques with different frequencies practiced by Bahia Chasco fishermen were less harmful than complete harvest, and we conclude that current exploitation techniques applied in this location are not deleterious for the giant kelp beds. They even have favorable effects by renewing the population through stimulation of sexual reproduction, recruitment and growth of young individuals.     

The short-term effects of fresh kelp (Macrocystis integrifolia) on physical properties of a fine-textured soil

In a two year field investigation fresh kelp (M. integrifolia) was broadcast and incorporated into plots of silty clay loam soil in the lower Fraser Valley of British Columbia. The effects of this amendment on bulk density, particle density, total porosity and aeration (volume of pores occupied by air after a saturated core was allowed to freely drain for 12 h at a soil water potential of −0.60 m) were measured. Soil aeration was increased in the first year with 30 and 60 t ha^-1 kelp application but decreased with the 120 t ha^-1 application. This soil aeration effect did not persist into the second year. Soil bulk density, particle density and total porosity were not significantly affected.