Photosynthetic carbon acquisition in <Emphasis Type="Italic">Sargassum henslowianum</Emphasis> (Fucales,Phaeophyta), with special reference to the comparison between the vegetative and reproductive tissues

The photosynthetic oxygen evolution characteristics were examined in both vegetative (blade) and sexual reproductive (receptacle) tissues of Sargassum henslowianum (Fucales, Phaeophyta) from the Shenao bay of Nanao Island, China, to establish the mechanism of photosynthetic acquisition of inorganic carbon (Ci) in this species. In natural seawater (pH 8.1, ca. 2.2 mM Ci), irradiance-saturated net photosynthetic rate (NPR) was greater by 25.3% in blade than receptacle, whereas dark respiratory rate (DR) was 2-fold higher in receptacle than blade. NPR at pH 8.1 was nearly saturated with the 2.2 mM Ci for both blade and receptacle. However, the values of the half-saturation constant for Ci were sharply increased at pH 9.0. NPR was significantly affected, but DR was remained unchanged, with the variation of the pH values in seawater. The data from the final pH value derived from the pH-drift experiments and the comparison between the measured and theoretically estimated photosynthetic rates suggested that both blade and receptacle were capable of acquiring HCO₃ ⁻ in seawater. The inhibitors experiments showed that a HCO₃ ⁻ dehydration mechanism mediated by external carbonic anhydrase activity occurred in both the blade and receptacle tissues of S. henslowianum. The proton buffer TRIS had no inhibitory effect on NPR at normal pH value in natural seawater (pH 8.1), but it significantly depressed NPR at pH 9.0. This suggested that proton transport occurred at the outside of the plasma membrane facilitated the operation of the carbon acquisition at pH 9.0. It was proposed that the strategy of photosynthetic carbon acquisition at higher pH would prevent the alga from the damage of over-excitation and photoinhibition in case of sunshine and calm water. We concluded that the blade and receptacle tissues of S. henslowianum have similar mechanism of acquisition of exogenous Ci from seawater to drive photosynthesis; yet they are differentiated more or less with the photosynthetic properties.     

PHYSIOLOGICAL INVESTIGATIONS ON ALARM ESCULENTA (LAMINARIALES. PHAEOPHYCEAE). IV. INORGANIC AND ORGANIC NITROGEN IN THE BLADE1,2

Seasonal variations in nitrate and organic nitrogen content along the wing and midrib of Alaria esculenta (L.) Grev. lamina have been compared with the NO₃^- cycle in the sea and yearly growth pattern of the blade. Throughout the year, organic N is highest in blade meristem, while NO₃^- distribution is less consistent. NO₃^-in blades reaches a peak in March (ca. 25–28 μM), whereas maximum relative accumulation, 3,300X ambient seawater level, occurs in October. Content of NO₃^- and organic N in the blade decreases in concert with the decline of seawater NO₃^- in April. The three periods of rapid blade growth are not correlated with a specific organic N content in the blade meristem. Laboratory experiments suggest that low NO₃^- and elevated seawater temperature are not the major factors retarding Alaria blade growth during summer and early fall in nature.     

Breeding of an elite <Emphasis Type="Italic">Laminaria</Emphasis> variety 90-1 through inter-specific gametophyte crossing

Laminaria longissima and Zaohoucheng No.1 (a commercial variety selected from Laminaria japonica) differ to a certain extent in their morphological characteristics and biological habits. It was assumed that varieties bred through their hybridization should exhibit high yield potential and tolerate relatively high seawater temperatures. Female gametophyte clones isolated from L. longissima were crossed with male clones isolated from Zaohoucheng No.1. Laminaria variety 90-1 was obtained after gametophyte crossing, continuous self-crossing and selection. This variety was genetically homozygous; the indices of variation of blade length, width and thickness of the final two selection cycles were 7–8%; i.e., not different significantly. Variety 90-1 grew faster, lost less tissue and had higher yield potential than two widely used commercial varieties of L. japonica (all commercial varieties currently used in China originate from this latter species). The blade of variety 90-1 increased 3.71 cm day⁻¹ on average during the whole period of cultivation, almost two-fold that of two controls, and growth was maintained even when seawater temperature was higher than 18°C–3°C higher than the temperature tolerated by other Laminaria varieties. Variety 90-1 increased yield by more than 70% over two controls and also synthesized desirable amounts of iodine, mannitol and algin. In blade length, variety 90-1 was more similar to L. longissima than to L. japonica, but more similar to L. japonica in blade width and thickness. Since the adoption of variety 90-1 in 1999, its culturing area has increased each year to reach its current area of 7,000 ha, i.e., almost one-third of the total cultivation acreage of Laminaria in China. Breeding of variety 90-1 has demonstrated that it is feasible to develop elite Laminaria varieties by crossing gametophytes from different Laminaria species in combination with successive self-crossing and selection.     

Leaf development and phloem transport in Cucurbita pepo: Transition from import to export

Summary The capacity of a growing leaf blade of Cucurbita pepo L. to import ¹⁴C-labelled photoassimilate is lost in a basipetal direction. Import into the lamina tip stops when the blade is 10% expanded. Development of the leaf progresses linearly with time and the lamina base stops importing when the blade is 45% expanded. Export capacity also develops basipetally and follows immediately the loss of import capacity, at least in the lamina base. The small amount of material initially exported from the leaf tip is redistributed to the still-importing leaf base, delaying export from the lamina until the blade is 35% expanded. Loss of import capacity by the petiole is both basipetal and dorsoventral. The proximal, adaxial portion of the petiole is the last region to cease importing ¹⁴C. Leaves of Beta vulgaris L. and Nicotiana tabacum L. also lose import capacity in a basipetal direction.     

PHYSIOLOGICAL INVESTIGATIONS ON ALARIA ESCULENTA (L.) GREV. (LAMINARIALES). I. ELONGATION OF THE BLADE1,2,3

A seasonal rhythm in blade elongation rate was observed in Alaria esculenta. Maximum (3.0–3.6 cm/week) and minimum (0.5–1.0 cm/week) rates were recorded in June and September, respectively. Translocation of growth-promoting metabolites occurs within the main blade and between the sporophylls and blade. Bidirectional flow of growth-promoting metabolities within the stipe was demonstrated. Seasonal effects of nutrients (NO₃- and PO₄^3-) and photoperiod on blade elongation were shown in long-term laboratory experiments. Control of seasonal blade growth by exogenous and endogenous factors is discussed.     

Prediction of the heterosis of <Emphasis Type="Italic">Laminaria</Emphasis> hybrids with the genetic distance between their parental gametophyte clones

Eighteen microsatellite markers were used to determine the genetic distances between the parental gametophyte clones of 14 Laminaria hybrids, which were then used to establish a linear relationship with the heterosis (hybrid vigor) of economic traits including yield, mean blade try weight, mean blade fresh weight, blade length, blade width and mean blade thickness using regression analysis. Significant regression was found between the genetic distance (x) and the heterosis (y) of yield (y = 115.10x − 77.97, r = 0.8151, p = 0.00038), mean blade dry weight (y = 115.23x  −77.97, r = 0.8154, p = 0.00038), mean blade fresh weight (y = 100.08x − 57.85, r = 0.7306, p = 0.0030) and blade length (y = 204.11x − 46.77, r = 0.6963, p = 0.00566). The prediction of the heterosis of Laminaria hybrids with the genetic distance between parental gametophyte clones will facilitate the selection of elite Laminaria hybrids by avoiding the time-consuming and labor-intensive trait evaluation of a large number of hybridization combinations.     

First estimates of productivity in Lessonia trabeculata and Lessonia nigrescens (Phaeophyceae, Laminariales) from the southeast Pacific

Lessonia is the main Laminariales found along the southeast Pacific coast. Lessonia nigrescens Bory de Saint‐Vincent in the intertidal and Lessonia trabeculata Villouta et Santelices in the subtidal, are the most important habitat constructors in rocky coastal communities in northern and central Chile. In both species, the seasonal production and erosion of distal tissue were estimated in biomass units using the Area of Constant Biomass Model that combined the individual blade elongation, obtained with the traditional hole‐punching method, with the blade length and biomass distribution along the blade. In austral late spring (December 96) and autumn (May 97), blade production and erosion were transformed to the level of population from standing stock measurements (number and biomass of blades and plants per substrate area), considering that previous blade weight analysis showed the highest and lowest values at these times, as well as the population parameter extremes that were expected to occur. Both species displayed a seasonal pattern, with a production increase in later winter and spring and decrease towards the end of summer that coincided with higher distal tissue erosion. At the level of individual blades, Lessonia trabeculata showed higher mean production (0.026 g dw d⁻¹) and erosion (0.01 g dw d⁻¹) than L. nigrescens (production 0.01 g dw d⁻¹ and loss 0.002 g dw d⁻¹). The standing stocks, with respect to density and biomass, were similar in spring and autumn for both populations. Nevertheless, the net productivity (production minus erosion) of the intertidal L. nigrescens showed greater values due to the greater density of blades (2112 ± 1360 (SE) blades m⁻²) compared with the subtidal L. trabeculata (527 ± 151 (SE) blades m⁻²). Spring net productivities of 42 g dw m⁻²d⁻¹ (254 g ww m⁻²d⁻¹; 11.46 gC m⁻²d⁻¹) for L. nigrescens and 11 g dw m⁻² d⁻¹ (64 g ww m⁻² d⁻¹; 2.46 gC m⁻²d⁻¹) for L. trabeculata were estimated. A preliminary model of production and biomass fate for Lessonia populations is proposed.     

SEASONAL PHOTOSYNTHETIC PERFORMANCE OF MACROCYSTIS INTEGRIFOLIA (PHAEOPHYCEAE)1

The seasonal photosynthetic performances of three age classes of blades of Macrocystis integrifolia Bory were estimated by studying their photosynthetic rate vs. irradiance curves and pigment contents for 15 months. All blade types were irradiance-saturated between 25 and 70 μE · m^?2· S^?1. Young and mature blade tissues had higher photosynthetic maxima and initial slopes on an area basis than older blade tissue. The latter, however, had pigment concentrations similar to those in mature blade tissues. All these parameters varied on a seasonal basis. The photosynthetic maxima ranged from 0.1–0.8 μmol · C · cm^?2· h^?t and showed two peaks, one in late summer-early fall and the other in late winter. Changes in initial slope and pigment concentrations in the blade tissues suggest that, changes in the size or efficiency of electron transfer in the photosynthetic unit occur. These data are discussed in relation to changes in seawater temperature and nitrate concentrations.     

Selection of age classes of<Emphasis Type="Italic"> Sasa</Emphasis> leaves by caterpillars of the skipper butterfly<Emphasis Type="Italic"> Thoressa varia</Emphasis> using albo-margination of overwintered leaves

A blade of the bamboo grass Sasa veitchii var. hirsuta (Koidzumi) typically has a lifespan of 2–4 years. After winter, the edge of the blade dies and a white margin is drawn on the blade. Such an albo-marginated blade is thought to be of relatively low quality as food for insects. Caterpillars of the skipper butterfly Thoressa varia (Murray) (Lepidoptera: Hesperiidae) that fed on blades of S. veitchii almost always utilized current-year blades. The mechanism by which they discriminate between age classes of blades was studied. The caterpillars did not choose albo-marginated blades, but they chose overwintered blades whose margins had been removed. This indicates that they use albo-margination as evidence of the age of a blade.     

The<Emphasis Type="Italic"> Arabidopsis thaliana rlp</Emphasis> mutations revert the ectopic leaf blade formation conferred by activation tagging of the<Emphasis Type="Italic"> LEP</Emphasis> gene

Activation tagging of the gene LEAFY PETIOLE ( LEP) with a T-DNA construct induces ectopic leaf blade formation in Arabidopsis, which results in a leafy petiole phenotype. In addition, the number of rosette leaves produced prior to the onset of bolting is reduced, and the rate of leaf initiation is retarded by the activation tagged LEP gene. The ectopic leaf blade results from an invasion of the petiole region by the wild-type leaf blade. In order to isolate mutants that are specifically disturbed in the outgrowth of the leaf blade, second site mutagenesis was performed using ethane methanesulphonate (EMS) on a transgenic line that harbours the activation-tagged LEP gene and exhibits the leafy petiole phenotype. A collection of revertant for leafy petiole ( rlp) lines was isolated that form petiolated rosette leaves in the presence of the activated LEP gene, and could be classified into three groups. The class III rlp lines also display altered leaf development in a wild-type (non-transgenic) background, and are probably mutated in genes that affect shoot or leaf development. The rlp lines of classes I and II, which represent the majority of revertants, do not affect leaf blade outgrowth in a wild-type (non-transgenic) background. This indicates that LEP regulates a subset of the genes involved in the process of leaf blade outgrowth, and that genetic and/or functional redundancy in this process compensates for the loss of RLP function during the formation of the wild-type leaf blade. More detailed genetic and morphological analyses were performed on a selection of the rlp lines. Of these, the dominant rlp lines display complete reversion of (1) the leafy petiole phenotype, (2) the reduction in the number of rosette leaves and (3) the slower leaf initiation rate caused by the activation-tagged LEP gene. Therefore, these lines are potentially mutated in genes for interacting partners of LEP or in downstream regulatory genes. In contrast, the recessive rlp lines exhibit a specific reversion of the leafy petiole phenotype. Thus, these lines are most probably mutated in genes specific for the outgrowth of the leaf blade. Further functional analysis of the rlp mutations will contribute to the dissection of the complex pathways underlying leaf blade outgrowth.Communicated by G. Jürgens     

Development of a shoot regeneration protocol for genetic transformation in <Emphasis Type="Italic">Pelargonium zonale</Emphasis> and <Emphasis Type="Italic">Pelargonium peltatum</Emphasis> hybrids

The attempts of this investigation were to develop a system for plant regeneration from explants of adult plants and its use for genetic transformation of important commercial Pelargonium zonale hybrid and P. peltatum hybrid cultivars. To this aim, leaf blade and petiole explants of eight cultivars were cultured on modified MS (Murashige and Skoog, 1962) medium with two concentrations of TDZ, BA, and zeatin (5 and 20 M). Petiole explants showed a higher regeneration response than leaf blade explants and TDZ was the most effective cytokinin. Petioles of 16 cultivars were incubated on medium containing 5, 10, 15, and 20 M TDZ, respectively, in order to identify the most effective TDZ concentration. For the majority of genotypes 10 M TDZ resulted in the best regeneration response. Cefotaxim at 500 mg l ^–1 had no effect on shoot regeneration and did not show interaction with glufosinate. For selection of transgenic cells, a concentration of 2.5 M glufosinate was shown to be appropriate. LBA4404 and EHA101 Agrobacterium strains carrying pIBGUS vector with pat gene as selectable marker gene and GUS gene as reporter gene were compared in transformation studies. With regard to GUS expression in petiole explants 16 days after coculture, better results were obtained with EHA 101 than with LBA 4404.     

TRANSLOCATION OF 14C IN MACROCYSTIS INTEGRIFOLIA (PHAEOPHYCEAE)1,2

Translocation patterns in the giant kelp, Macrocystis integrifolia Bory, were investigated in situ using ¹⁴C tracer; sources and sinks were identified. Export was first detected after 4 h of labeling; experiments were routinely 24 h continuous ¹⁴C application. Mature blades exported ¹⁴C to young blades on the same frond and on younger fronds, as well as to sporophylls and frond initials at the bases of the fronds. Blades <0.3 m from the apex imported and did not export; this distance did not change seasonally. In spring export from blades 0.3–1.25 m from the apex was exclusively upwards; older blades also exported downwards. In fall downward export began 0.5 m from the apex, and blades >2 m from the apex exported exclusively downwards. Carbon imported by frond initials, young fronds, and sporophylls in fall may partly be stored for growth in early spring. No translocation was seen in very young plants until one blade (secondary frond initial) bad been freed from the apical blade; this blade exported to the apical blade for a time, but imported when it began to develop into a frond. The second and third formed blades on the primary fronds (sporophylls also exported when <0.3 m from the apex, and later stopped. Frond initials and sporophylls on later-formed fronds did not export at all. The translocation pattern in M. integrifolia differs from that previously reported in M. pyrifera in seasonal change and in distances from the apex at which the changes take place.     

Relationship between expression of the PM H<Superscript>+</Superscript>-ATPase,growth and ion partitioning in the leaves of salt-treated <Emphasis Type="Italic">Medicago</Emphasis> species

The role of the plasma membrane (PM) H⁺-ATPase (E.C. 3.6.1.3) in the plants response to salt stress was studied in the perennial leguminosae forage Medicago arborea L. and its close relative Medicago citrina (Font-Quer) Greuter, a species exposed to saline conditions in its original habitat. Plants were solution cultured for 8 days in 1 or 100 mM NaCl. Leaf growth and CO₂ assimilation were more inhibited by salt in M. arborea than in M. citrina. Both species were able to osmoregulate, and salt-treated plants maintained turgor potentials, with no differences between species. Contrasting ion distribution patterns showed that M. citrina was able to exclude Na⁺ from the leaves more selectively, while M. arborea had a greater buildup of leaf blade Na⁺. Isolation of purified PM and quantification of H⁺-ATPase protein by Western blot analysis against the 46E5B11D5 or AHA3 antibodies showed an increase in response to salt stress in the expanding (92%) and expanded leaves (87%) of M. citrina, while no differences were found in the corresponding leaves of M. arborea. The assay of H⁺-ATPase specific activity of the two leaf types in salinized M. citrina confirmed this increase, as activities increased with 55% and 104% for the expanded and expanding leaves, respectively, while no significant differences were found for either leaf type of salinized M. arborea. A possible role of the increased expression of the PM H⁺-ATPase for leaf expansion and ion exclusion in salt-stressed plants is discussed.     

TRANSLOCATION OF IODINE IN LAMINARIA SACCHARINA(PHAEOPHYTA)1

Long-distance translocation of ¹²⁵I in Laminaria saccharina (L.) Lamour. followed a “source to sink” pattern. When the source of ¹²⁵I was placed on the distal mature part of the blade, the translocation was unidirectional, basipetal and directed towards the meristematic region at the blade-stipe junction. When the source was placed directly at the meristem there was no movement of label distal to the meristem. The velocity of¹²⁵I transport ranged from 2 to 3.5 cm · h^?1. The anion I^? seemed to be the only species of¹²⁵I transported. An assay of iodine content in different parts of L. saccharina plant showed much higher levels of iodine in the meristem, stipe and holdfast than in the blade. This distribution concurs well with the pattern of I^? translocation.     

Effect of water flow velocity on growth and morphology of cultured <Emphasis Type="Italic">Undaria pinnatifida</Emphasis> sporophytes (Laminariales,Phaeophyceae) in Okirai Bay on the Sanriku coast,Northeast Japan

Undaria pinnatifida sporophytes, originating from the same strain, were cultured at the commercial cultivation site exposed to wave action and the uncultivated site protected from water action of Okirai Bay, Northeast Japan, from January to April 2007; simultaneously, water flow velocity, water temperature, salinity, NO₃ + NO₂, and chlorophyll a were monitored to investigate the effect of water environment on their growth and morphology. Water temperature and salinity fluctuated within the optimal range for their growth whereas water flow velocity at the cultivation site was greatly fast compared with that at the uncultivated site. Successive chlorophyll a increases synchronized with NO₃ + NO₂ decreases were observed only at the uncultivated site for over a month; indicating developments of phytoplankton blooms and their nutrient consumption under the low-flow condition. Meanwhile, blade growth rate of cultured sporophytes was higher at the cultivation site than at the uncultivated site. Their thallus size expressed by six morphological characters (blade length, stipe length, blade wet weight, stipe wet weight, blade width, and undivided blade width) at the cultivation site became large in comparison with that at the uncultivated site. Their three morphological correlations (correlations between blade length and thallus length; blade wet weight and thallus wet weight; and undivided blade width and blade width) differed between the sites. They produced a thick and flat blade at the cultivation site but formed a thin and wrinkled blade at the uncultivated site. These results show the significant impact of water flow velocity on their growth and morphology.     

Offshore cultivation methods affects blade features of the edible seaweed <Emphasis Type="Italic">Saccharina latissima</Emphasis> in a bay of Galicia,Northwest Spain

Variation in blade morphology of Saccharina latissima may be of importance for its commercial cultivation. Blade features were compared between offshore cultivation on horizontal ropes versus hanging ropes during its reproduction period (early autumn and early spring of the following year). Cultivation experiments were conducted in February 2002 in a sheltered coastal area of a bay of Galicia (Northwest Spain). Significant differences were found between methods in blade area, which in turn affected blade biomass. However, the differences were only significant during the reproduction period in early spring. The cultivation method also significantly affected the “substantiality value”, which is an index that expresses the blade quality for human consumption. The observed variations in morphological features of S. latissima blades likely were caused by the different hydrodynamics of the two cultivation methods.     

Primary production of the kelp Lessonia corrugata varies with season and water motion: Implications for coastal carbon cycling

Kelp forests provide vital ecosystem services such as carbon storage and cycling, and understanding primary production dynamics regarding seasonal and spatial variations is essential. We conducted surveys at three sites in southeast Tasmania, Australia, that had different levels of water motion, across four seasons to determine seasonal primary production and carbon storage as living biomass for kelp beds of Lessonia corrugata (Order Laminariales). We quantified blade growth, erosion rates, and the variation in population density and estimated both the net biomass accumulation (NBA) per square meter and the carbon standing stock. We observed a significant difference in blade growth and erosion rates between seasons and sites. Spring had the highest growth rate (0.02 g C · blade⁻¹ · d⁻¹) and NBA (1.62 g C · m⁻² · d⁻¹), while summer had the highest blade erosion (0.01 g C · blade⁻¹ · d⁻¹), with a negative NBA (−1.18 g C · m⁻² · d⁻¹). Sites exhibiting lower blade erosion rates demonstrated notably greater NBA than sites with elevated erosion rates. The sites with the highest water motion had the slowest erosion rates. Moreover, the most wave-exposed site had the densest populations, resulting in the highest NBA and a greater standing stock. Our results reveal a strong seasonal and water motion influence on carbon dynamics in L. corrugata populations. This knowledge is important for understanding the dynamics of the carbon cycle in coastal regions.     

Leaf development and phloem transport in Cucurbita pepo: Carbon economy

Summary Net photosynthesis, dark respiration and growth for leaf 5 of Cucurbita pepo L. plants grown under controlled conditions were measured and the data used for an assessment of the changes in carbon balance during growth of the leaf through expansion to maturity. The blade is first capable of net CO₂ fixation when ca. 8% expanded but the initial rapid growth during this period is sustained almost entirely through imported nutrients. When the growth rate starts to decline rapidly the net photosynthetic capacity of the blade begins to increase. This increase is accompanied by an expansion of the intercellular spaces and by decreasing dark respiration measured at night and in dark periods during the day. The blade becomes completely independent of phloem imported nutrients and begins to export excess photosynthate when the phase of rapid decrease in relative growth rate is almost complete at about 45% expansion. Maximum net photosynthesis of ca. 11 mg CO₂ h^-1 dm^-2 is achieved at 70% expansion. The first detectable synthesis of the transport sugars stachyose and raffinose in the blade coincides with the beginning of intralaminar phloem transport from the tip to the base of the leaf. The synthesis of sucrose, the other major transport sugar, is detectable at all stages of leaf development.     

FLOW‐INDUCED MORPHOLOGICAL VARIATIONS AFFECT DIFFUSION BOUNDARY‐LAYER THICKNESS OF MACROCYSTIS PYRIFERA (HETEROKONTOPHYTA,LAMINARIALES)1

In slow mainstream flows (<4–6 cm · s^?1), the transport of dissolved nutrients to seaweed blade surfaces is reduced due to the formation of thicker diffusion boundary layers (DBLs). The blade morphology of Macrocystis pyrifera (L.) C. Agardh varies with the hydrodynamic environment in which it grows; wave‐exposed blades are narrow and thick with small surface corrugations (1 mm tall), whereas wave‐sheltered blades are wider and thinner with large (2–5 cm) edge undulations. Within the surface corrugations of wave‐exposed blades, the DBL thickness, measured using an O₂ micro‐optode, ranged from 0.67 to 0.80 mm and did not vary with mainstream velocities between 0.8 and 4.5 cm · s^?1. At the corrugation apex, DBL thickness decreased with increasing seawater velocity, from 0.4 mm at 0.8 cm · s^?1 to being undetectable at 4.5 cm · s^?1. Results show how the wave‐exposed blades trap fluid within the corrugations at their surface. For wave‐sheltered blades at 0.8 cm · s^?1, a DBL thickness of 0.73 ± 0.31 mm within the edge undulation was 10‐fold greater than at the undulation apex, while at 2.1 cm · s^?1, DBL thicknesses were similar at <0.07 mm. Relative turbulence intensity was measured using an acoustic Doppler velocimeter (ADV), and overall, there was little evidence to support our hypothesis that the edge undulations of wave‐sheltered blades increased turbulence intensity compared to wave‐exposed blades. We discuss the positive and negative effects of thick DBLs at seaweed surfaces.     

Changes of growth characteristics and free amino acid content of cultivated <Emphasis Type="Italic">Porphyra yezoensis</Emphasis> Ueda (Bangiales Rhodophyta) blades with the progression of the number of harvests in a nori farm

It is essential for successful Porphyra breeding to understand the growth characteristics and the quantitative aspect of the taste of gametophytic blades. However, there have been only a few studies on such characteristics with the progression of the number of harvests in nori farms. In this study we examined the changes of blade shape, blade thickness and free amino acid (FAA) content of two P. yezoensis f. narawaensis pure lines (HG-4 and HG-5) with the progression of the number of harvests in a nori farm. With the progression of the number of harvests, the blade length-to-width ratio of both pure lines decreased, while the blade thickness increased. From the results, it is suggested that the increase of blade length is significantly higher in HG-4 than in HG-5, and that the blade is thicker in HG-5 than in HG-4. Total FAA contents between the two lines were not significantly different throughout the investigation period. Among the major four FAA (aspartic acid, glutamic acid, alanine and taurine), only glutamic acid content decreased with the progression of the number of harvests in both pure lines. These results suggest that the superior taste of dried nori sheets made of the first harvest of blades is due to thinner blades and higher content of glutamic acid.