A survey of translocation in laminariales (Phaeophyceae)

Marine Biology 36, 207-216 1976) �9 by Springer-Verlag 1976

A Survey of Translocation in Laminariales (Phaeophyceae)

K. Schmitz 1 and C. S. Lobban 2

1 Botanisches Institut der Universit~t zu K61n; K61n, Germany (FRG) and 2Department of Biological Sciences, Simon Fraser University; Burnaby, British Columbia, Canada

Abstract

A survey of translocation of photoassimilates in 13 genera of Laminariales is presented. All showed long-distance transport of 14C-labeled products from mature source tissue to meristematic sinks (haptera and intercalary growing regions). In plants with several laminae forming one frond, older laminae may provide assimilates for the growth of younger ones, and in Macrocystis spp., where fronds of different ages and developmental stage arise from a common holdfast, mature fronds initiate and support new fronds. Translocation velocities vary from species to species but are in the range of 55 to 570 mm/h. The results strongly support the hy- pothesis that Laminariales in general have an effective translocation system, on which their thallus growth depends.

Introduction

Sieve elements I or sieve-element equiv- alent cells have b@en described from all members of the Lam~nariales which have been examined so fir, but depending on the species investigated these cells are rather different in size and cytological organisation (for literature review see Esau, 1969). In recent years, transloca-

cross walls also translocate, and what the physiological characteristics of this transport might be. We have shown long-distance transport of 14C-labeled photoassimilates in Laminaria hyperborea and L. saccharina (LHning et al., 1972; Schmitz et al., 1972) and recently in Alaria mar~nata (Schmitz and Srivastava, 1975). Assimilate transport was in all cases directed very largely to the grow-

tion of organic compounds has been demon- ing regions which act as sinks. In con- strated in a few species. Indirect evi- sideration of these data, one is easily dence for such a transport in Sacrocystis led to conclude that translocation is a pyrifera (L.) C.A. Agardh was presented general phenomenon in the Laminariales. by Sargent and Lantrip (1952), and trans- To confirm this statement, we undertook port has been shown in a more direct way by tracer experiments for M. pyrifera (Parker, 1965, 1966) and Nereocystis luetkeana (Mertens) Postels et Ruprecht (Nicholson and Briggs, 1972), both members of the Lessoniaceae. It is known that in contrast to the Laminariaceae and Alariaceae, these two plants have wide sieve elements and sieve pores (Ziegler, 1963; Parker and Huber, 1965; Schmitz and Srivastava, 1976). The ques- tion therefore, was, whether those Lami- nariales with sieve elements having numerous, but very fine pores in their

to survey translocation in other genera as well. Approximately half the genera of the Laminariales are represented on the west coastj0f British Columbia, Can- ada, and we wege able to examine most of these -- 13 genera in all, including three of the four previously shown to translocate. In this paper we present further evidence in support of the statement that translocation of assimilates from surplus-producing parts of a thallus to sinks, like growing regions, is a general physiological process in the Laminariales.

iWe use the expression sieve elements here, rath- Materials and Methods er than sieve filaments. For a discussion of the terminology, refer to Schmitz and Srivasta- The algae listed in Table I were col- va, 1974b. lected during the spring growing season

208 K. Schmitz and C.S. Lobban: Long-Distance Transport in Laminariales

in or near Barkley Sound, on the west coast of Vancouver Island, Canada. The experiments were conducted in aquaria with running seawater at IOOC under a bank of 10 white fluorescent tubes. The irradiance at the plants was 2230 ~W/cm 2. The distribution of assimilates was fol- lowed by tracer experiments with 14C. The technic to feed radiocarbon had to be adapted to the different morphology of the algae. We therefore used different types of 14C-assimilation chambers and were forced to choose only smooth, intact, mature apical blade areas to attach the chambers. A plastic bag, a Plexiglas chamber, or a glass cylinder with slit rubber-stopper ends was used to expose a part of the thallus to a 2 h pulse of 1OO ~Ci NaH14CO 3 (specific activity: 60.1 mCi/mM). Samples of the tank water were assayed for radioactivity while the experiments were run, to make sure that no radioactivity left the chamber by a leak and contaminated the surface of the thallus.

After labeling, the radioactivity was replaced by a continuous seawater flow through the chamber. The experimental time varied between 3 and 12 h. At the end of an experiment, the 14C-exposed area was cut off and tissue samples 20 x 60 mm were taken at varying distances from the assimilation chamber towards both the apex and the base of the plant. Due to the different morphology of the species investigated, the size and spacing of these samples were not uniform throughout. It was not the in- tent of this study to obtain quantitative data on translocation rates, or exact data on translocation velocity, but to determine whether translocation of organics took place or not. The tissue samples were chopped and repeatedly ex- tracted with ethanol (ethanol 80% boil-

Table I. List of algal species investigated

Laminariaceae Laminaria setchellii Silva Laminaria sinclairii (Harvey ex Hooker et Har-

vey) Farlow, Anderson et Eaton Pleurophycus gardneri Setchell et Saunders Cymathere triplicata (Poste!s et Ruprecht) J.

Agardh Costaria costata (Turner) Saunders Agarum fimbriatum Harvey Hedophyllum sessile (C. Agardh) Setchell

Lessoniaceae Postelsia palmaeformis Ruprecht Nereocystis luetkeana (Mertens) Postels et

Ruprecht Macrocystis integrifolia Bory Macrocystis pyrifera (Linnaeus) C. Ag. Lessoniopsis littoralis (Farlow et Setchell)

Reinke

Alariaceae Pterygophora californica Ruprecht Alaria marginata Postels et Ruprecht Egregia laevigata Setchell Egregia menziesii (Turner) Areschoug Eisenia arborea Areschoug

Individual lateral blades of Egregia menziesii (Turner) Areschoug were too small to enclose in any of our chambers, and labeling the terminal part of the stipe, with many laterals, showed no translocation. We therefore took an op- portunity to study E. lae~gata Setchell in California, USA. Single lateral blades were enclosed for 3 and 6 h in a small plastic bag with 100 ~Ci 14C, under clear skies outdoors.

The data presented below on Macrocystis integrifolia Bory and M. pyrifera are a pre- liminary summary of work by C. Lobban (in preparation). Experiments consisted of labeling a whole blade on a mature

ing, ethanol 80% cold, ethanol 50% cold), frond for 24 h in situ with 250 ~Ci The extracts were combined and an ali- NaH14CO 3. The fronds were dried after quot was assayed for radioactivity by liquid scintillation counting.

The different morphology of the plants necessitated our using different labeling methods, but whenever possible a small Plexiglas chamber was attached to the lamina as described earlier (Schmitz et al., 1972). This chamber of- ten had to be attached over the smooth midrib because of holes in, irregularity of, and fragility of the rest of the lamina. The position of the 14C-exposed thallus areas is outlined in the corre- sponding figures.

Blades of Postelsia palmaeformis Ruprecht were too narrow for the chamber and were enclosed in a plastic bag secured with rubber bands around the upper end of the stipe.

harvest, and 25 mg samples of the meristematic (proximal) regions of the blades digested in perchloric-peroxide (Lobban, 1974) for liquid scintillation counting. This same method was also used to determine the translocated radioactivity in Egre~a laevigata.

Autoradiographs of Macrocystis integrifolia were prepared by placing X-ray film in contact with plant material dried on- to herbarium sheets. The film was exposed for 12 days.

Results

For convenience, the algae listed in Ta- ble I and studied here are divided into 3 morphological groups: (a) plants with

K. Schmitz and C.S. Lobban: Long-Distance Transport in Laminariales 209

310

t 380

1411

T 600 (6h)

800 (12h)

1

900(6h)

905112h)

'M/SAMPLE

12h

836

3536

1886

2115

. . . . . . . . . . . . . . . . . . . . . 114

,147

1 0 0 ~

30265

3215

1447

1300

1209

1304

1230

1198

334

- . . . . . 281

0

DPM/SAMPLE

6h 12h

t i 83

1647 3506

3235 12535

4000

2132

2225

2808

11133

8717

3018

1198

150(6h) I

400 (12h)

470(6h)

I 750(12h)

190(3h) 300(6h) 30(3(12h)

380(3h) I

350 (6h)

I 920(12h)

240 - 270 ~I

7::7 - 684

~ __ 958

~ ~ . 874

~ - - - 836

168

DPM/SAMPLE

6h 2h

.~1:

z9;

735 30

1349 79

677 14

533 '5~

416 i8~

2C

274 6(

329 2(

151 O

43 0

(Z)

DPM/SAMPLE

160:8 12h

1414

!1841

550(

328(

342,2

318C

1484

55O

|

Fig. i. Distribution (disintegrations/min/sample) of 14C after 3, 6, or 12 h of translocation in

plants with a single lamina. Sample size was 20 x 60 mm where the shape of the thallus would allow, otherwise somewhat smaller samples were taken. The shaded areas were pulse-labeled for 2 h under a

Plexiglas chamber. The size of the plants used in different experiments is indicated on the left ordinate (mm). i: Laminaria setchellii; 2: Pleurophycus gardneri; 3: Cymathere triplicata; 4: Co- staria costata


a single lamina; (b) plants with several laminae forming one frond; (c) plants with ~ore than one frond arising from a common holdfast.

Plants with a Single Lamina

This group includes all theLaminariaceae listed in Table I with the exception of Laminaria sinclairii, Egregia spp. and Eisenia arborea. In all species examined, 14C- labeled assimilate was translocated over considerable distances at a velocity greatly exceeding that of diffusion. The main direction of transport was from the non-growing area of the lamina towards the intercalary growing region and out- growing haptera. This confirm~ the pattern of assimilate transport established for L. hyperborea and L. saccharina earlier (L~ning et al., 1972 ; Schmitz et al., 1972).

Laminaria setchellii Silva (Fig. 1:1). In a 12-h experiment, radiocarbon reached the base of the stipe 690 mm away from the 14C-exposed area of the lamina. Translo- cation velocity was at least 55 mm/h, which is in the range of translocation

Costaria costata (Turner) Saunders (Fig. 1:4), Agarum fimbriatum Harvey (Fig. 2) and Hedophyl- lum sessile (C. Agardh) Setchell (Fig. 3). Three sets of experiments (3, 6, and 12 h) were performed to investigate assimilate transport in these species. The presented data prove that long-distance transport of 14C occurs in all three species. The data also confirm our previous statement, that the main direction of translocation is towards the intercalary growing region and the holdfast. The 14C export acropetally into older non-growing areas of a lamina is less signifi- cant.

Hedophyllum sessile is an atypical member of the Laminariaceae with respect to its morphology. It has no stipe and is char- acterized by a lobed, irregular lamina which gives it a cabbage-like appearance. As seen from Fig. 3b and c, ]4C was not only translocated towards the basal growing region of the labeled lamina-lobe, but was also translocated laterally into neighboring lobes, as reported for Lami- naria setchellii.

Alaria marginata Postels et Ruprecht. A. marginata has been studied in more detail, and results on the physiology of assim-

velocities reported for s hyperborea and ilate transport and the fine structure L. saccharina (Schmitz et al., 1972). Trans- of sieve elements has been reported sep- locate was also found in the basal arately (Schmitz and Srivastava, 1975).

parts of neighboring lobes of the lamina, but this is not surprising since it has been shown for L. groenlandica (Schmitz and Srivastava, 1974b) that sieve tubes are cross-connected and traverse the whole thallus as a continuous network.

Pleurophycus gardneri Setchell et Saunders (Fig. 1:2). Experiments were run for 6 and 12 h. Although export was very largely basipetal, some radioactivity was detected in the distal part of the lamina. 14C reached the base of the stipe at a distance of 470 mm within 6 h, indicat- ing a velocity of nearly 80 mm/h.

Cymathere triplicata (Postels et Ruprecht) J. Agardh (Fig. 1:3). The thallus of c. triplicata has characteristic folds which run the length of the lamina. The assimilation chamber therefore, had to be pl'aced to one side. Photoassimilated 14C traveled mainly in a basipetal direction, with a velocity of at least 150 mm/h since it reached the holdfast at a distance of 900 mm in less than 6 h. The data for a 12-h experiment show a slight but distinct accumulation of radioactivity in the intercalary growing region.

Transport of photoassimilates, mainly mannitol and a variety of free amino acids, occurred from the apical part of the lamina to the intercalary growing region and growing haptera. The midrib was the preferential pathway of translocation. Transport velocities were in the range of 250 to 400 mm/h.

Pterygophora californica Ruprecht. This is a second member of the Alariaceae belong- ing to the first morphological group which was examined here. The sporophytes of P. californica which we used were several years old and 1.40 to 2.00 m long, each with a number of sporophylls. In different experiments we labeled both the terminal blade and sporophylls, and in each experiment -- after 6 and 12 h -- there was transport of 14C from the fed area both distally and proximally. When the blade was labeled, some activity was also found in the rachis and in the bases of some sporophylls.

Plants with Several Laminae

Postelsia palmaeformis Ruprecht (Fig. 4). Three experiments in which 14C was fed continuously for 1, 3 or 6 h to all the


:4 500- 700 ~

570(3h) i

360(6h) i

440(12h)

530(3h) I

355(6h) t

630(12h)

DPM/SAMPLE

3h 6h 12h

87 890 180

122 ~230 229

1193 ~30~ '783

115 .32C

89 638 456

80 499 205

59 207 56 0 44 4 0 43 0

Fig. 2. Agarum fimbriatum. Distribution of radioactivity (dpm/sample) in thalli after 3, 6, and 12 h; shaded area pulse-labeled for 2 h

blades of younger plants are shown. A considerable amount of 14C was translocated along the hollow stipe into the actively growing haptera. The amount of activity detectable in the stipe tissue and the holdfast increased with time.

Nereocystis luetkeana (Mertens) Postels et Ruprecht (Fig. 5). Long-distance transport of 14C-labeled photoassimilates in N. luetkeana has been reported by Nicholson and Briggs (1972), who showed that 14C which was exported from the apical parts of the blades and translocated the length of the plant could be traced in medulla-exudate from the lower stipe. They reported a translocation velocity of 370 mm/h in the blades.

We reexamined Nereocystis luetkeana, and exposed the apical part of Younger blades which were about 300 to 500 mm long to 14C for different periods between I and 6 h. The distribution of radioactivity within the rest of the blades is shown in Fig. 5. The profiles show an increasing level of 14C along the transport path with increasing time. In the 6-h experiment there is already a distinct accumulation of radioactivity in the growing region at the base of the lamina, whereas the 1-h profile shows a logarithmic decline of radiocarbon towards the growing region. Extrapolation to zero-DPM in the 1-h experiment indi- cates that the front of radioactivity might have reached 2OO mm. Data on translocation velocity derived from other experiments with plants of different age are in the range of 110 to 180 mm/h, with an average of 170 mm/h. When only

a

170

130

170 ~]

230

I C :~ 180 ~ 240 m;

Fig. 3. Hedophyllum sessile. Distribution of 14C (dpm/sample) from the chamber (hatched) in thalli, showing transport into adjacent lobes of the lamina. (a) After 3 h; (b) after 6 h; (c) after 12 h

120

DPM/SAMPLE

5314

lh 3h

2580 86286

008 68068

600 71040

585 69551

74120

6h

272979

222948

263337

276520

589380

Fig. 4. Postelsia palmaeformis. Distribution

(dpm/sample) of 14C. All the blades were en-

closed in a plastic bag for continuous labeling

for i, 3, or 6 h. Samples from the stipe were

20 mm in length

5xlO 4 I I I 1 I I f I I I I I

Z ,,t

~9 09

E lx lO a E

5 x l O 2 O_ D

lxlO 4 / o f , 6 h

�9 o

\ .

.. 2 lx102 lh " ~ 3:h

5xlO ] "\ \ ,,,,

\

1 0 i i i I I i \I i I I I I

O 30 60 90 120 150 180 210 240 270 300 330 360

DISTANCE FROM '4C EXPOSED AREA 0F THE BLADE [mm] Fig. 5. Nereocystis luetkeana. Profile of 14C

along single blades. Distal region of the blade

was exposed to radioactivity for i to 6 h

Fig. 6. Egregia laevigata. Part of a branched

frond with many lateral blades after a 6 h trans-

location experiment. Activity is given in dpm/ iO mg dry weight. Shaded lateral blade was exposed to 14C during entire experiment. There was

no activity in the other branches of the thallus

2.5m

SECONDARY

I : F R ~ 1 7 6 ~t~

I 0.55m ~ r,4

HOLDFAST

APEX DAMAGED ~}

52~

PRIMARY FROND

258

151 S E C O N D A R Y

FROND

<:S~e8 <~71

: : ~ 1 5 9 TERTIARY AND QUATERNARY FRONDS

k..OTHER PRIMARY FROND MISSING

Fig. 7. Macrocystis integrifolia. Diagram of

plant composed of several fronds interconnected by a common holdfast, showing distribution of radioactivity after 24 h continuous exposure to

14C on the iOth free blade of the primary frond, in situ. 14C was translocated towards damaged

apex of the primary frond, and also via the holdfast into the secondary fronds


part of one or two blades was labeled with 14C there was also a slight import of radioactivity into growing regions of neighboring blades via lateral transport, but we did not obtain undoubtedly posi- tive results for transport along the stipe in such experiments. However, if we exposed all the blades of a plant to 14C for 2.5 h, radioactivity was clearly detectable in ethanol extracts of stipe segments. The front of radioactivity reached the holdfast at a distance of 1.42 m from the 14C-assimilation chamber in less than 2.5 h. Translocation velocity, therefore, can be calculated as 570 mm/h.

Egregia laevigata Setchell and E. menziesii (Turner) Areschoug. In E. laevigata (Fig. 6), there was transport from the source blade both distally and proximally along the frond after 6 h, but radioactivity could not be detected in other branches of the thallus at that time. As in E. menziesii, the tip of the frond did not export. The reason for this is not appar- ent.

Fig. 8. Macrocystis integrifolia. Autoradiograph of apex of the secondary frond of specimen shown on left in Fig. 7. The outline of the non-radio- active part of the apical scimitar has been drawn in. Radioactivity is confined to the meristematic regions

Lessoniopsis littoralis (Farlow et Setchell) Reinke and Eisenia arborea Areschoug. These species also showed transport of 14C. In both cases a single lamina which was labeled for 6 to 12 h exported radiocarbon into neighboring blades and along the stipe.

2

451265

Fig. 9. Laminaria sinclairii. A representative experiment, showing export of 14C (dpm/sample) from the shaded blade to all other blades

Plants with More Than One Frond

Macrocystis spp. These species consist of a complex of sinks intercompeting for assimilates from many sources. Parker (1966) showed that radioactivity was exported to the apex of the labeled frond of M. pyrifera as well as basipetally from a source blade. Experiments with M. integrifolia and M. pyrifera show that juvenile, subsurface fronds are supported by the mature fronds that initiated them (Fig. 7), as had been speculated by Sargent and Lantrip (1952). Mature blades act as sources, and export is both acropetal and basipetal to the sinks: the apical meristem at the base of the apical keel, and the meristems of the juvenile free blades of both the labeled frond and its juvenile (Fig. 8) and the sporophylls and growing haptera. Particularly in M. pyrifera, there is a pattern of export from developing blades analogous to that typical of vascular plants: at first export is only acropetal, but later it becomes basipetal as well. There is normally no exchange of


assimilates between primary fronds, but if the apex of a labeled primary is damaged or lost (cf. Fig. 7), there is some export into juveniles of other frond groups, as well as an increase in export to the labeled frond's juveniles. This response to cutting is particularly pronounced in M. pyrifera. Without the strong apical sinks to "pull" assimilates up the frond, the blades above the source receive very little. Similarly, if the secondary frond lacks an apex, there is little or no transport into it.

Laminaria sinclairii (Harvey ex Hooker et Harvey) Farlow, Anderson et Eaton {Fig. 9).

tercalated between tissues or organs that produce and those that consume assimilates, is the same in vascular plants and the Laminariales, and thus the directionality of transport which is determined by the source-sink polarity is basically also the same. The pattern of translocation is rather simple in Laminariales having a single,lamina frond, but is more complicated in those plants having one frond with several laminae or even several fronds arising fro~ one common holdfast. The complex morphology of such plants implies numerous sink areas intercompeting for assimilates from many sources.

Our observations were made during the This species provided an interesting com- growth period of the algae, chiefly in parison to Macrocystis spp. The creeping rhizomatous holdfast of this plant sends up numerous small, unilaminate fronds, which individually resemble other Lamina- ria species. The stipes are short (100 to 200 mm), and there is thus not the surface-subsurface frond division as in Macrocystis species. To judge by the color of the stipes (Markham, 1969), all the fronds were more than I year old, and had thus regenerated their lamina at least once. Five experiments were done on random groups of 2 to 5 fronds, and there was transport from the source lamina into all the other laminae in all cases. As there was no difference in

May and June, at which time we identi- fied the meristematic rapid-growth regions as sinks. These regions are the transition zone between stipe and lamina and (especially in postelsia palmaeformis) the growing haptera. However, in view of the findings of L~ning (1970), we antic- ipate that there may be a different translocation pattern in the fall. At that time, assimilates may be trans- ported to storage in the perennating part of the thallus. In Laminaria hyperbo- tea the lamina overwinters, and this organ, rather than the stipe, appears to be the storage organ (L~ning et ai.,1973); in other species of the Laminariales,

size, age, or morphology between the lam- e.g. Pterygophora californica and Eisenia ar- ina exposed to 14C and the other laminae borea, only the holdfast and stipe remain. linked to it by their common holdfast, the data suggest mutual support. The blades seem to be able to export and import at the same time.

Discussion

The data presented here, and earlier studies (Parker, 1965; Nicholson and Briggs, 1972; Schmitz et ai.,1972; Schmitz and Srivastava, 1975), demon- strate that long-distance transport of assimilates is a general phenomenon in the Laminariales. In addition, some evidence has also been presented for assimilate transport in sargassum pallidum (Fu- cales) (Titlyanov and Peshekhodko, 1973) and the red algae Delesseria sanguinea and Cystoclonium purpureum (Hartmann and Esch- rich, 1969). The pattern of transloca-

The low level of transport from blades of P. californica and E. arborea in spring may indicate that the bulk of transport is carrying stored assimilates from the stipe into the blades.

With increasing time, 14C is accumu- lated at the growing region. This has previously also been demonstrated for Nereocystis luetkeana (Nicholson and Briggs, 1972), Laminaria hyperborea, L. saccharina (L~ning et al., 1972, 1973; Schmitz et al., 1972), and Alaria marginata (Schmitz and Srivastava, 1975). The translocate, mainly mannitol and a variety of amino acids (Schmitz et al., 1972) are rapidly metab- olized and incorporated at the growing region into polysaccharides and proteins (unpublished results of our laboratory).

The occurrence of sieve elements in the medulla of Laminariales, their anat- omy, and the fact that exudate which can

tion in the Laminariales is consistently be collected from the medulla of Macro-

from source to sink, i.e., from more or less mature frond areas, which produce a surplus of photoassimilates, to assimilate deficient parts of the thallus, mainly the growing regions. There is hardly any transport towards distal mature thallus tissue. The basic fact, that assimilate transport is always in-

cystis spp. stipes arises abundantly from the sieve tube region (Crafts and Crisp, 1971; Schmitz and Srivastava, 1974a) is indirect evidence that conduction occurs in the medulla via sieve elements. Di- rect determination of the conducting tissue was achieved by girdle preparations in Nereocystis luetkeana (Nicholson and


Briggs, 1972), and a cellular localisa- tion of the conducting pathway resulted from a histoautoradiographic study of Laminaria hyperborea (SteinbiB and Schmitz, 1973). In fact, Parker (1965) reported earlier that the vital dye fluorescein was translocated through the sieve tubes of M. pyrifera, but although this dye is an excellent tool to study phloem transport in higher vascular plants (Schu- macher, 1933), its use in brown algae seems doubtful as its translocation velocity rarely exceeds I cm/h whereas 14C-labeled assimilates reach 65 to 78 cm/h.

Nereocystis luetkeana has also been re-

cholson and Briggs, 1972; Schmitz et al., 1972; Schmitz and Srivastava, 1975). This is much faster than diffusion, and compares with velocities of phloem transport in vascular plants. Translocation velocity may be different in the blades and the stipe of Nereocystis luetkeana. It ranges between 110 and 180 mm/h in the blades, and reaches 570 mm/h in the stipe. There is some discrepancy between the data presented here and those pub- lished by Nicholson and Briggs (1972), who measured a somewhat higher velocity of 200 to 400 mm/h in the blades. Al- though the velocity of transport is cer- tainly influenced by a variety of inter-

ported to release exudate from the medul- nal and external factors and varies from la of the cut stipe (Nicholson and Briggs, 1972). We tried to collect such exudate in order to follow 14C-transport along the stipe, but did not succeed in obtaining appreciable amounts of it, neither with plants of different age and size nor at different times of the year. It is reasonable to suppose that also in the experiments presented here, transport of 14C was via sieve elements in the medulla, although no further evidence is presented.

The conducting system of Laminariales is not organized in discrete bundles as in higher plants, but forms a reticulum in the medulla of the entire thallus (Schmitz and Srivastava, 1974b, 1975, 1976). This does not rule out the exis- tence of functional subunits in this system, for Parker (1965) observed that fluorescein which was fed via the surface of one blade entered the stipe and traveled through a bundle of sieve tubes only. Our observation that mature laminae of Laminaria sinclairii and Macrocystis spp. import and export at the same time favours the idea of a functionally dif- ferentiated transport system, but this has to be investigated in more detail. As a rule, movement of 14C shows a rather strict longitudinal confinement. This has been shown by autoradiography in L. hyperborea (L~ning et al., 1972; SteinbiB and Schmitz, 1973), but there is on the other hand some lateral transport of assimilates into neighboring blades or in- to lobes of the same lamina as reported for L. setchellii (Fig. I:1), Hedophyllum sessile (Fig. 3), and Nereocystis luetkeana. This is possible because of the network- like organisation of the translocation system, where longitudinally arranged sieve elements are frequently Cross- connected by transverse-oriented sieve elements (Schmitz and Srivastava, 1974b).

Translocation velocities in Laminar- iales, as calculated from our experimental data and reported by others, range from 50 to 780 mm/h (Parker, 1965; Ni-

plant to plant and even from one part of a plant to another (Crafts and Crisp, 1971), its difference here may be due to the different size of sieve elements and sieve area pores in the blades and in the stipe of N~ luetkeana (Schmitz and Srivastava, 1976).

Our experiments were not designed to obtain exact data on translocation velocity, but the results we obtained can be used as a rough estimate. It undoubtedly must be the aim for the future, to set up experiments in such a way that more quantitative data of transport physiology will result.

Current evidence suggests (Pickett- Heaps, 1975) that among algae, only a small group of the Chlorphyceae is re- lated to vascular plants. The Laminar- iales developed their highly differenti- ated cormus-like thallus, including the translocation system, parallel to the evolutionary development of the cormophy- ta. This means that the algal sieve- element system is not a primitive form of phloem, and thus the transport mecha- nism in Laminariales must not be the same as in higher vascular plants. Both systems are analogous, but by no means homologous.

Acknowledgements. The authors are pleased to acknowledge the assistance of Mrs. A. Jonson and Mr. D. Morley. The work on which this publica- tion is based was supported by grants from the Deutsche Forschungsgemeinschaft to K.S. and from the National Research Council of Canada to Dr. L.M. Srivastava and Dr. L.D. Druehl. The experiments on Egregia laevigata were carried out at the Kerckhoff Marine Laboratory of the Califor- nia Institute of Technology, thanks to Dr. W.Jo North.

Literature Cited

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Dr. Klaus Schmitz

Botanisches Institut der Universit~t GyrhofstraBe 15 D-5OOO KSln 41 Germany (FRG)

Date of final manuscript acceptance: March 26, 1976. Communicated by O. Kinne, Hamburg

Documents

A survey of translocation in laminariales (Phaeophyceae)