THEORY OF REGENERATION BASED ON MASS ACTION

1. The writer''s older experiment, proving that equal masses of isolated sister leaves of Bryophyllum regenerate under equal conditions and in equal time equal masses (in dry weight) of shoots and roots, is confirmed. It is shown that in the dark this regeneration is reduced to a small fraction of that observed in light. 2. The writer''s former observation is confirmed, that when a piece of stem inhibits or diminishes the regeneration in a leaf, the dry weight of the stem increases by as much or more than the weight by which the regeneration in the leaf is diminished. It is shown that this is also true when the axillary bud in the stem is removed or when the regeneration occurs in the dark. 3. These facts show that the regeneration of an isolated leaf of Bryophyllum is determined by the mass of material available or formed in the leaf during the experiment and that such a growth does not occur in a leaf connected with a normal plant for the reason that in the latter case the material available or formed in the leaf flows into the stem where it is consumed for normal growth. 4. It is shown that the sap sent out by a leaf in the descending current of a stem is capable of increasing also the rate of growth of shoots in the basal parts of the leaf when the sap has an opportunity to reach the anlagen for such shoots. 5. The fact that a defoliated piece of stem forms normally no shoots in its basal part therefore demands an explanation of the polar character of regeneration which lays no or less emphasis on the chemical difference between ascending and descending sap than does Sachs'' theory of specific root- or shoot-forming substances (though such substances may in reality exist), but which uses as a basis the general mass relation as expressed in the first three statements of this summary. 6. It is suggested that the polar character of the regeneration in a stem of Bryophyllum is primarily due to the fact that the descending sap reaches normally only the root-forming tissues at the base of the stem, while the ascending sap reaches normally only the shoot-forming anlagen at the apex of the stem. 7. This suggestion is supported by the fact that when the anlagen for shoots and roots are close together as they are in the notch of a leaf, the sap of the leaf causes the growth of both roots and shoots from the same notch and the influence of the sap of the leaf on this growth increases for both roots and shoots in proportion with the mass of the leaf.     

THE LAW CONTROLLING THE QUANTITY OF REGENERATION IN THE STEM OF BRYOPHYLLUM CALYCINUM

1. A method is given which allows us to measure the influence of the mass of a leaf upon the quantity of shoots regenerated in an isolated piece of stem. This method consists in isolating a piece of stem with only two leaves left at the basal node and then splitting the stem lengthwise so that each half has one basal leaf. By leaving one leaf intact while the size of the sister leaf is reduced, the influence of the mass of the leaf upon the quantity of shoots regenerated by the stem can be measured. 2. This method has yielded the result that the mass of shoots regenerated at the apex of such a piece of stem increases under equal conditions and in equal time with the mass of the leaf, and is approximately proportional to the mass of the leaf. 3. Such an influence of the mass of the leaf upon the mass of shoots produced by the stem is only intelligible on the assumption that the growth of the regenerating shoot occurs at the expense of material furnished by the basal leaf. 4. This assumption is supported by two facts: first, that in the dark this influence of the leaf disappears more or less completely; and, second, that a leaf attached to the base of a regenerating stem after some time weighs markedly less than does a sister leaf completely detached from the stem, but otherwise under equal conditions. 5. This latter fact that a leaf when attached to the base of an excised piece of stem wilts more rapidly than when completely isolated is the reason that the proportionality between mass of a basal leaf and mass of shoot regenerated at the apex of an isolated piece of stem cannot always be demonstrated with the same degree of accuracy as the proportionality between the mass of completely isolated leaves and the mass of shoots they produce. 6. The material furnished by the leaf to the stem is not restricted to water but includes also the solutes, since not only the fresh weight but also the dry weight of the shoot regenerated by a piece of stem increases with the mass of the leaf attached to the base of the stem; and since not only the water contents but the dry weight of a leaf attached to the base of an excised piece of stem diminish when compared with the dry weight of a completely detached sister leaf. 7. The mass of shoots produced by an isolated piece of stem without leaf is small and almost negligible compared with the mass of shoots produced by the same piece of stem when a leaf of sufficient mass is attached to the base of the stem.     

QUANTITATIVE LAWS IN REGENERATION : III. THE QUANTITATIVE BASIS OF POLARITY IN REGENERATION.

It is well known that a long defoliated piece of stem of Bryophyllum calycinum forms shoots only at the apical or the two apical nodes, while when such a stem is cut into as many pieces as there are nodes each node produces shoots. It is shown in this paper that the dry weight of shoots produced in the apical nodes of a long piece of stem is approximately equal to the dry weight of shoots the same stem would have produced if it had been cut into as many pieces as it possesses nodes. Hence all the material which can be used for the growth of shoots goes into the most apical part of the stem and this accounts for the polar character of regeneration in this case. It seems that the mass of basal roots produced by a piece of defoliated stem also increases with the mass of the stem.     

QUANTITATIVE LAWS IN REGENERATION. II

This paper contains the results of a reexamination of a law expressed in a previous paper; namely, that when a piece of stem inhibits the growth of shoots and roots in a leaf connected with it the dry weight of the stem increases and that this gain equals approximately the mass of shoots and roots the leaf would have produced if it had been detached from the stem. This has been confirmed and it has been shown that the gain of the stem as a rule even exceeds slightly the mass of shoots and roots the leaf would have produced if it had not been inhibited by the stem. This supports the idea that the inhibitory influence of the stem upon the formation of roots and shoots in the leaf is due to the fact that the material available and required for this process naturally flows into the stem.     

A low watering treatment alters biomass allocation and growth rate but not heteroblastic development in an <Emphasis Type="Italic">Acacia</Emphasis> species

Key message

The Acacia phyllode leaf form is hypothesised to be an adaptation to drought. However, in this experiment, the timing of phyllode development was not related to a low water treatment.

Abstract

Acacia species have markedly different leaf forms known as compound leaves, transitional leaves, and phyllodes, also known as heteroblastic development. The different leaf types are thought to confer an advantage under varying moisture regimes, with phyllodes favoured in drier conditions. The hypothesis that phyllodes develop earlier under low water treatment was tested in this experiment. Three watering level treatments (100, 50, and 25 %) were imposed on seedlings of A. implexa to assess developmental traits (leaf emergence, initial onset of transitional leaves, and phyllodes), biomass allocation patterns (root, stem, compound leaf area/mass, transitional leaf area/mass, and phyllode area/mass), and leaf anatomy traits (epidermis, palisade and spongy mesophyll, and stomatal density). Across watering treatments, there was no difference in the developmental onset of transitional leaves or phyllodes (produced at the 6th and 9th nodes, respectively). Under low watering treatment, there was a decrease in stem height per unit stem diameter, shorter internodes, and greater allocation of biomass to roots. There was no significant difference in leaf anatomy traits. Under the low watering treatment, there was less compound leaf area and mass due to leaf shedding. In this experiment, the low watering treatment did not favour phyllode development at the expense of compound leaf development. Rather, it was found that A. implexa responds to a low water treatment similarly to many other plant species: increased allocation to roots, increased stem area per unit stem height, decrease in leaf area through senescence of older leaves, and lower relative growth rates.

     

THE PHYSIOLOGICAL BASIS OF MORPHOLOGICAL POLARITY IN REGENERATION. II

1. The experiments show that the mass of air roots formed in a stem increases with the mass of the leaf attached to the stem, though it has not been possible to establish an exact mathematical relation between the two masses, owing to unavoidable sources of error. 2. Darkened leaves do not increase the mass of roots formed. 3. In stems suspended horizontally air roots appear on the lower side of the stem, with the exception of the cut end where they usually appear around the whole circumference of the stem. When the lower half of a stem suspended horizontally is cut off, roots are formed on the upper side. It is shown by experiments on leaves suspended horizontally that the more rapidly growing roots and shoots on the lower side inhibit the root and shoot formation in the upper half of such a leaf; and likewise the more rapid formation of roots on the lower side of a horizontally suspended stem seems to account for the inhibition of root formation on the upper side of such a stem. Likewise the more rapid growth of shoots on the upper side of a stem suspended horizontally is likely to inhibit the growth of shoots on the lower side. 4. Each leaf contains in its axil a preformed bud capable of giving rise to a root, which never grows out in the normal stem on account of the inhibitory influence of the normal roots at the base of the plant. These dormant root buds are situated above (apically from) the dormant shoot bud. The apical root buds can be caused to develop into air roots when a piece of stem is cut out from a plant from which the leaves except those in the basal node of the piece are removed. The larger these basal leaves the better the experiments succeed. 5. These apical air roots grow out in a few days, while the roots at the basal end of the stem (which in our experiments dip into water) grow out about a week later. As soon as the basal roots grow out in water they cause the air roots in the more apical region of the stem to dry out and to disappear. 6. In addition to the basal roots, basal nodes have also an inhibitory effect on the growth of the dormant root buds in the apical region of a stem. This is indicated by the fact that a stem with one pair of leaves near the base will form apical air roots more readily when no node is situated on the stem basally from the leaf than if there is a node basally from the leaf.     

THE NATURE OF THE DIRECTIVE INFLUENCE OF GRAVITY ON THE ARRANGEMENT OF ORGANS IN REGENERATION

1. When leaves of Bryophyllum calycinum are suspended in moist air in a vertical plane and sidewise, roots and shoots are formed exclusively or predominate in the notches on the lower side of the leaves. When pieces of stems of the same plant are suspended horizontally in moist air, roots develop on the lower side of the stem, with the exception of the extreme basal end where they may develop on both sides. 2. The writer has suggested in a preceding paper that this directive influence of gravity on the arrangement of the regenerating organs may be due to the combination of two factors. The first factor is gravity, which causes a slightly greater collection of sap on the lower side of these organs, and as a consequence roots develop a little more quickly on the lower than on the upper side. The second factor is of an inhibitory character inasmuch as quite generally organs which grow out first, or which grow quickly, have a tendency to retard or inhibit the growth of similar organs in other places. 3. The writer was able to prove the action of this inhibitory factor by cutting off the lower edges of leaves suspended sidewise in a vertical plane or the lower halves of stems suspended in a horizontal plane (in moist air). In this case roots developed as abundantly on the upper side of these organs as they otherwise would have developed on the lower side. 4. It was, however, still necessary to prove the idea that gravity causes sap to collect in larger quantity in the lower parts of organs. This gap is filled by the present paper in which it is shown, first, that in the leaves suspended in moist air a red pigment is formed which has a tendency to collect gradually in the lowest parts of the leaf when the latter is suspended in a vertical plane. This red pigment serves as an indicator for the distribution of sap in the leaf and thus shows directly the tendency of the sap to collect in greater abundance on the lower edge of a leaf suspended in a vertical plane. Second, it is shown that when leaves or stems of Bryophyllum are suspended, in the way described, under water instead of in moist air, roots develop on the upper side as well as on the lower side. The directive effect of gravity upon the arrangement of organs disappears in this case since the abundance of the outside water makes the effect of a slight difference in the distribution of sap between the upper and lower side a negligible factor. Third, it is shown that the dry weight of the lower half of leaves suspended sidewise for several weeks in moist air in a vertical plane is greater than that of the upper half when roots and shoots are formed on the lower side only. This indicates that material from the upper half flows into the growing organs of the lower half. No such difference between upper and lower half of leaf is found when the leaves are suspended in the same way in water and roots and shoots are formed on both sides of the leaf. 5. It is shown that when a leaf connected with a piece of stem is suspended in moist air the red pigment goes into the stem instead of collecting in the lower part of the leaf, thus supporting the view expressed in a preceding paper that the inhibitory action of the stem on the root and shoot formation in a leaf of Bryophyllum is due to the fact that the material available in the leaf for organ formation is naturally sent into the stem.     

Influence of cold temperatures on leaf lipids of Hibiscus rosa-sinensis

Triaclyglycerols (TAG) accounted for 15% of the leaf acyl lipids in a Hibiscus rosa-sinensis plant that survived the January 1986 freeze in Florida, U.S.A. This high TAG level suggested that the plant had cold hardened. The TAG concentration in leaves on new shoots from this plant was greater than that in new leaves on new shoots from five plants frozen to the roots during the freeze. However, five months later, the amounts of TAG in the six Hibiscus plants were nearly the same. The minor differences in TAG levels, however, related to the survival rate of these six plants during subsequent freezes. In addition to linoleic acid, two cyclopropene fatty acids, malvalic and sterculic, were major constituents of the leaf TAG. Hibiscus plants placed in environmental chambers under control and cold-hardening regimes optimized for Citrus showed TAG concentrations of 7% in control and 20% in hardened plants. A survey of neutral lipids in Hibiscus and other plants showed that plastoquinone A (B) and α-tocopherol decreased and plastoquinone C increased under cold-hardening conditions. Polyprenols, a major component of Hibiscus leaves under normal conditions, declined greatly under cold-hardening regimes.     

1-Aminocyclopropane-1-Carboxylic Acid Transported from Roots to Shoots Promotes Leaf Abscission in Cleopatra Mandarin (Citrus reshni Hort. ex Tan.) Seedlings Rehydrated after Water Stress

The effect of water stress and subsequent rehydration on 1-aminocyclopropane-1-carboxylic acid (ACC) content, ACC synthase activity, ethylene production, and leaf abscission was studied in Cleopatra mandarin (Citrus reshni Hort. ex Tan.) seedlings. Leaf abscission occurred when drought-stressed plants were allowed to rehydrate, whereas no abscission was observed in plants under water stress conditions. In roots of water-stressed plants, a high ACC accumulation and an increase in ACC synthase activity were observed. Neither increase in ACC content nor significant ethylene production were detected in leaves of water-stressed plants. After rehydration, a sharp rise in ACC content and ethylene production was observed in leaves of water-stressed plants. Content of ACC in xylem fluid was 10-fold higher in plants rehydrated for 2 h after water stress than in nonstressed plants. Leaf abscission induced by rehydration after drought stress was inhibited when roots or shoots were treated before water stress with aminooxyacetic acid (AOA, inhibitor of ACC synthase) or cobalt ion (inhibitor of ethylene-forming enzyme), respectively. However, AOA treatments to shoots did not suppress leaf abscission. The data indicate that water stress promotes ACC synthesis in roots of Cleopatra mandarin seedlings. Rehydration of plants results in ACC transport to the shoots, where it is oxidized to ethylene. Subsequently, this ethylene induces leaf abscission.     

In vitro regeneration of Gaillardia pulchella Foug.

Young leaf and internodal stem segments of Gaillardia pulchella, collected from wild species re-established in the greenhouse, were used to initiate callus on Murashige & Skoog medium supplemented with NAA (2.0 mgl⁻¹) and BA (0.4 mgl⁻¹). Callus formed after 10 to 14 days in the dark. Cultures were transferred to fresh medium and placed under lighted conditions where shoot formation occurred approximately 14 to 30 days after initiation. Callus sub-cultured at 14 to 21-day intervals continued to produce primordia for several weeks. Flowers were produced by regenerated shoots maintained on MS medium, but roots did not develop until the plantlets were transferred to soil conditions.     

The Export and Distribution of 14C-labelled Assimilates from each Leaf on the Shoot of Lolium temulentum during Reproductive and Vegetative Growth

In both reproductive and vegetative plants of Lolium temulentumL., the export of ¹⁴C-labelled assimilates from each healthyleaf on the main shoot to terminal meristem, stem, tillers,and roots was measured each time a new leaf was expanded, fora period of 5 to 6 weeks. Some labelled assimilates moved fromeach leaf on the main shoot to every meristem in the same shoot,as well as to the tops and roots of adjacent organically attachedtillers. The terminal meristem of the reproductive shoot, which includedthe developing inflorescence, received 70–80 per centof the carbon assimilated by the emerged portion of the growingleaf, 15–25 per cent of the carbon assimilated by thetwo youngest expanded leaves, and 5–10 per cent of thatfrom each of the older leaves. A similar pattern of carbon supplyto the terminal meristem was found in vegetative shoots, exceptthat older leaves on young vegetative shoots supplied even lessof their carbon to the terminal meristem. The general conclusionis that developing leaves at the tip of the shoot receive aboutthe same proportion of carbon from each leaf as does a developinginflorescence. Young expanded leaves provided most labelled assimilates forstem growth; during both reproductive and vegetative growth,expanded leaves increased their export of labelled carbon tostem, and exported less of their ¹⁴C to roots and sometimesto tillers. In these reproductive and vegetative shoots, grown in a constantexternal environment, the major changes in the pattern of distributionof labelled assimilates appeared to be the result of increasedmeristematic activity in stem internodes; the development ofan inflorescence had no obvious direct effect on the carboneconomy of shoots.     

A Quantitative Analysis of the Uptake of Carbon and of the Supply of 14C-labelled Assimilates to Areas of Meristematic Growth in Lolium temulentum

A quantitative analysis of the ¹⁴C-labelled assimilate suppliedby leaves on the main shoot to terminal meristem, stem, tillers,and roots was conducted during parallel periods of reproductiveand vegetative development in Lolium temulentum. The initial rate of entry of carbon into the shoot varied withthe area and photosynthetic efficiency of the assimilating leaf.Subsequently, respiratory losses of carbon during translocationand incorporation of assimilate at the site of utilization alsovaried. The combined effect of these differences resulted inthe supply of recently assimilated carbon being twofold greaterin reproductive shoots than in vegetative shoots, while withinshoots the carbon supply of the youngest fully expanded leafranged from four-or five-fold greater than the oldest leaf inyoung shoots, to two-or three-fold greater in older shoots.In both reproductive and vegetative shoots, the two or threeyoungest leaves thus dominated the supply of carbon for meristematicgrowth. Meristematic tissue in expanding leaves and leaf primordia atthe terminal meristem of the vegetative shoot received 18–27per cent of the total shoot carbon. This meristem utilized aboutthe same proportion of shoot carbon when it developed into aninflorescence, indicating no major change in the level of meristematicactivity. The proportion of shoot carbon utilized in stem growthincreased as both reproductive and vegetative shoots aged; thisincreased meristematic activity in stem internodes was accompaniedby reduced export of carbon to roots, which received less than10 per cent of the shoot carbon when the experiments ended.The main shoot translocated 20–30 per cent of its recentlyassimilated carbon to developing and rooted tillers, which assinks for carbon were thus as important as the terminal meristemand stem. This outward flow of carbon continued relatively uncheckedwhen donor and receptor shoots developed inflorescences.     

Photosynthesis of plant régénérants. Specificity ofin vitro conditions and plantlet response

Regenerants from tobacco(Nicotiana tabacum L. cv. White Burley) leaf segments cultivatedin vitro in vessels with solid agar medium under usual conditions (plantlets) grew under very low irradiance (I = 40 μxmol m?2 s?1), very high relative humidity (more than 90%) and decreased CO₂ concentration (c_a) during light period. In comparison with seedlings of a similar number of leaves and similar total leaf area grown in sand and nutrient solution, the plantlets had lower dry mass of shoots and roots per plant and thinner leaves almost without trichomes and epicuticular waxes. Due to a low transpiration rate under high relative humidity the water potential of plantlet leaves was higher than that of seedling leaves and the difference in water potential between leaves and medium was lowei. The rate of water loss from leaves detached from plantlets was considerably faster than that from seedlings under the same conditions (I = 110 μrnol m^?2; s^?1, temperature 30 °C, relative humidity 50 %). Net photosynthetie rates (P_n) of leaves of plantlets and seedlings measured under saturating I, natural ca and the leaf temperature 20 °C were similar, nevertheless the shape of curves relating Pn to c» indicated some differences in photosynthetie parameters(e.g. saturation of Pn under lower ca> higher CO2 compensation concentration in plantlets than in seedlings). Similarly compensation and saturating I were lower in plantlets than in seedlings. The shape of transpiration curves as well as the expressive linear phases of P_N(ca) and P_N(I) curves of plantlet leaves indicated ineffective stomatal control of gas exchance. These results were confirmed by microscopic observations of stomatal movementsin situ     

Maize plant growth and accumulation of photosynthetic pigments at short- and long-term exposure to cadmium

A wide range of cadmium concentrations (from 4 to 200 μM for seedlings and up to 2 mM for germinating kernels) was used to assess Cd toxic effects on maize (Zea mays L.) plants at the different developmental stages: germinating kernels, seedlings (4–9 days), and juvenile plants (34 days). Cd accumulation in plant organs was followed, and its lethal concentration was elucidated. In maize, cadmium was accumulated predominantly in roots; in shoots it was mainly accumulated in the lower leaves, and the higher was leaf position the lower was Cd content in it. At high concentrations (80 and 200 μM), kernels became the substantial cadmium depot. Germinating kernels manifested the lowest sensitivity to cadmium; seedlings were more sensitive; the inhibition of juvenile plant growth attained 90% and more. In the tested range of concentrations, cadmium suppressed shoot mass accumulation harder than that of roots. In 34-day-old plants, water content in shoots was stronger reduced than in roots. Plant death was also manifested earlier in shoots. It was concluded that maize plant sensitivity to cadmium increases with plant growing and that, under conditions of normal mineral nutrition, cadmium inhibits shoot growth more severe than root growth.     

Resistance of Cotton to the Root-Knot Nematode, Meloidogyne incognita

Cotton plants resistant to Meloidogyne incognita had roots characterized by fewer and smaller galls, and females that produced fewer egg masses containing fewer eggs than did susceptible plants. Many galls on resistant roots contained no nematodes at the time of examination. Penetration of the resistant cultivar was equal to that of the susceptible cultivar and independent of the number of nematodes in the inoculum. Fewer nematodes penetrated resistant or susceptible plants with eight leaves than those with fewer leaves. Reciprocal grafts of resistant and susceptible plants failed to confer resistance or susceptibility to the rootstock.     

Distribution of labelled assimilates within a young apple tree after supplying14CO2to a leaf or shoot

Labelled carbon dioxide was supplied for 22 hrs to a leaf of the leader or to the lateral shoot in two-year-old apple seedlings. The distribution of radioactive assimilates within the plant following this treatment was investigated by using radioautography. The transport of labelled assimilates from the young leaf of the leader was very meagre and affected only parts of the stem and the leaves situated in the close vicinity of the treated leaf. The¹⁴C-labelled assimilates from the mature leaf of the leader were transported in a considerable amount to the apex and to the other leaves of the leader. They were also found in an appreciable amount in the stem and the roots, as well as in some lateral shoots. After supplying¹⁴CO₂ to the lateral shoot remarkable transport of labelled assimilates was observed. Radioactivity was detected in the tip and in the youngest leaves of the leader, as well as in the roots. Their path in the stem was studied by dissecting the plant and examining the cross section from each internode. This method revealed that the assimilates from the treated leaf or shoot were transported downward only on one side of the stem in a helical pattern. The lateral shoots situated on the radioactive side of the stem were also labelled, whereas those situated on the opposite (non-radioactive) side were not labelled.     

Abscisic acid root and leaf concentration in relation to biomass partitioning in salinized tomato plants

Salinization is one of the most important causes of crop productivity reduction in many areas of the world. Mechanisms that control leaf growth and shoot development under the osmotic phase of salinity are still obscure, and opinions differ regarding the Abscisic acid (ABA) role in regulation of biomass allocation under salt stress. ABA concentration in roots and leaves was analyzed in a genotype of processing tomato under two increasing levels of salinity stress for five weeks: 100 mM NaCl (S10) and 150 mM NaCl (S15), to study the effect of ABA changes on leaf gas exchange and dry matter partitioning of this crop under salinity conditions. In S15, salinization decreased dry matter by 78% and induced significant increases of Na⁺ and Cl⁻ in both leaves and roots. Dry matter allocated in different parts of plant was significantly different in salt-stressed treatments, as salinization increased root/shoot ratio 2-fold in S15 and 3-fold in S15 compared to the control. Total leaf water potential (Ψ_w) decreased from an average value of approximately −1.0 MPa, measured on control plants and S10, to −1.17 MPa in S15. In S15, photosynthesis was reduced by 23% and stomatal conductance decreased by 61%. Moreover, salinity induced ABA accumulation both in tomato leaves and roots of the more stressed treatment (S15), where ABA level was higher in roots than in leaves (550 and 312 ng g⁻¹ fresh weight, respectively). Our results suggest that the dynamics of ABA and ion accumulation in tomato leaves significantly affected both growth and gas exchange-related parameters in tomato. In particular, ABA appeared to be involved in the tomato salinity response and could play an important role in dry matter partitioning between roots and shoots of tomato plants subjected to salt stress.     

Seasonal Accumulation of Starch by Components of the Kiwifruit Vine

The accumulation of starch by various components of 6-year-oldkiwifruit vines (Actinidia deliciosa var dehciosa cv Hayward)was recorded over one season Twenty vines were harvested periodicallythroughout the year and separated into perennial components(fibrous roots, structural roots, stump, stem, cordon, laterals)and current season's growth (shoots, leaves, and fruit) The concentration of starch in the fibrous roots followed asinusoidal trend Minimum concentrations occurred 98 d afterbudbreak, while the maximum concentrations occurred 182 d laterCorresponding times in the structural roots were approximately42 d earlier In the above-ground perennial components, elevatedconcentrations of starch in the cordon, fruiting wood and barkof the stem were evident at budbreak and fruit harvest (approx220 d later) In the case of the stem, concentrations were greatestat fruit harvest Because the biomass of the perennial componentswas found to be relatively constant throughout the year, starchconcentrations and contents were directly proportional in thesetissues For current season's growth, peak concentrations and contentsin leaves and shoots were observed at fruitset and fruit harvest,respectively For fruit, starch increased continuously untilharvest Approximately 30% of the total starch content accumulated inthe perennial components by leaf abscission was lost duringwinter and early summer Quantitative losses were greatest forthe roots Regeneration of the starch pools in the perennialcomponents of the vine occurred from midseason until leaf abscissionAt the same time, approximately five times more starch was accumulatedby the current season's growth, in particular the fruit, thanby the perennial components As a result of the difference inthe rate of accumulation, the starch content of the currentseason's growth increased from less than 10% midseason to nearly60% of the total starch content of the vine by fruit harvest The results were discussed in relation to the carbon economyof the kiwifruit vine, and compared with seasonal trends instarch concentrations found for other deciduous crops Actinidia deliciosa, kiwifruit, seasonal changes, starch content, whole plant     

Interorgan photosynthate partitioning in alfalfa

The net partitioning of current photosynthate among vegetative organs of nodulated alfalfa (Medicago sativa L.) was investigated by determining radiolabel distribution from upper and lower source leaves, at different times of day, and during successively longer chase periods. Photosynthate was exported sooner and more completely by a fully expanded lower than by a fully expanded upper source leaf. The radiolabel pulse from the lower source leaf peaked in the main stem within 1.5 hours, in the crown and nodules after 3 hours, in the unexpanded leaves and apex of the main stem after 6 hours, and in the shoots growing from leaf axils on the main stem after 24 hours. The results suggest that the crown, apex, axillary shoots, and nodules both imported and mobilized photosynthate originating at a lower source leaf, while roots and shoots growing from the crown showed net accumulation. The pulse from the upper source leaf was initially rapidly exported by the main stem and imported by the root between 1.5 and 3 hours, but there was no net change of label content of these organs during the ensuing 21 hours. Rapidly growing organs had the highest concentrations, and the largest organs had the highest content of radiolabel. These results provide new information about the accumulation and circulation of photosynthate within the alfalfa plant.     

In vitro morphogenesis in Selaginella microphylla (Kunth.) Spring

Selaginella, an extant genus of primitive vascular plants, has survived over 400 million years of evolution. In vitro morphogenesis in Selaginella microphylla is considered for the first time to establish a well-documented aseptic culture on half- strength Murashige and Skoog’s basal medium with 2ip (4.92–49.21 μM), or Kn (4.65–46.47 μM) or GA₃ (2.89–28.90 μM) for shoot multiplication, and with different concentrations of IBA (4.9–49 μm) to initiate root cultures. GA₃ was instrumental for shoot multiplication as well as induction of reproductive structures in each and every leaf axil. On the other hand, it is observed that IBA alone in S. microphylla can act as signal molecules for induction of enormous numbers of root masses from a few existing roots. An interesting pattern of re-differentiation has also been observed where apical portions of large numbers of roots were converted to green shoot apical meristems. Further differentiation produced tiny green shoots. Distinct bipolarity was noted in shoots when they were isolated from root masses and appeared as embryo-like structures. Chromosome analysis from in vitro sporophytic plants revealed 2n = 16 chromosomes, indicating chromosomal stability. The interesting in vitro pattern of morphogenesis obtained in S. microphylla may provide new insights into totipotency of plants.