Growth of Populus euramericana

Growth curves of successive leaves of Populus euramericana (Dode) Guinier 'Robusta' have been determined. With ample supply of water and nutrients the growth of a poplar shoot follows a fixed pattern: an initial logarithmic acceleration phase followed by a stationary phase in which leaves of equal size are produced at a constant rate. Analysis of growth curves of leaves enabled the growth curves of leaf primordia to be predicted. These primordial growth curves are compared to the indirectly determined growth curves of primordia by measuring the lengths of successive leaf primordia in the apex during the stationary phase of growth. The increase in length of successive leaves in the acceleration phase of growth continues for a longer period at high than at low irradiace. The relative growth rates of leaf primordia, leaves and internodes are discussed in terms of shoot growth and phyllotaxis.     

Relation between the diameter of the growing shoot and the mature size of leaves and flower head of sunflower

Helianthus annuus L. cv. INRA 6501 plants were cultivated at irradiances of 15, 30 and 60 W m⁻² (400–700 nm) at 20°C and a relative humidity of 60% on a gravel culture subirrigated with Hoagland's nutrient solution. From 10 days after the opening of the cotyledons the diameter of the growing shoot increased linearly with time at a rate dependent on the irradiance. These measurements were continued until the flower bud became visible. By extrapolation of this linear growth to the day of anthesis the diameter of the stem below the flower head was predicted. This stem diameter had a constant ratio (9.7) to the measured diameter of the flower head. In the early stages of development of the plant it is proposed that the diameter of the growing shoot, supported by its vascular system, is a determinant of the size of the mature leaves. Later in the development the diameter of the growing shoot is a determinant of the diameter of the flower head. This change of function is caused by localised activity of the cambial cells which results in tangential growth in the vascular cylinder and ultimately in a hollow stem.     

Carbon and nitrogen economy of 24 wild species differing in relative growth rate

The relation between interspecific variation in relative growth rate and carbon and nitrogen economy was investigated. Twentyfour wild species were grown in a growth chamber with a nonlimiting nutrient supply and growth, whole plant photosynthesis, shoot respiration, and root respiration were determined. No correlation was found between the relative growth rate of these species and their rate of photosynthesis expressed on a leaf area basis. There was a positive correlation, however, with the rate of photosynthesis expressed per unit leaf dry weight. Also the rates of shoot and root respiration per unit dry weight correlated positively with relative growth rate. Due to a higher ratio between leaf area and plant weight (leaf area ratio) fast growing species were able to fix relatively more carbon per unit plant weight and used proportionally less of the total amount of assimilates in respiration. Fast growing species had a higher total organic nitrogen concentration per unit plant weight, allocated more nitrogen to the leaves and had a higher photosynthetic nitrogen-use efficiency, i.e. a higher rate of photosynthesis per unit organic nitrogen in the leaves. Consequently, their nitrogen productivity, the growth rate per unit organic nitrogen in the plant and per day, was higher compared with that of slow growing species.     

Effects of light on the growth and clonal reproduction of Ligularia virgaurea

Ligularia virgaurea is a perennial herb that is widely distributed in the alpine meadow on the eastern Qinghai-Tibet plateau.We investigated the patterns of growth and reproduction of L.virgaurea under two contrasting levels of light conditions for two continuous growing seasons.Our results showed that the light affects on the maximum relative growth rate,the shoot weight ratio and the root weight ratio differed between the two growing seasons.L.virgaurea reproduced initially through rhizome in the second growing season,rather than sexual reproduction.The proportion of genets with clonal reproduction decreased under shaded conditions.A minimum genet size should be attained for clonal reproduction to begin under the shaded conditions.There was a positive linear relationship between clonal reproduction and genet size.Light level affected the allocation of total biomass to clonal structures,with less allocation under the full natural irradiance than under the shaded conditions.There seemed to be a trade-off between vegetative growth and clonal reproduction under the full natural irradiance,in terms of smaller relative growth rates of genets with clonal reproduction than those without clonal reproduction.L.virgaurea emphasized clonal reproduction under the full natural irradiance,while the plant emphasized vegetative growth under the shaded conditions.     

PLASTOCHRON2 regulates leaf initiation and maturation in rice

In higher plants, leaves initiate in constant spatial and temporal patterns. Although the pattern of leaf initiation is a key element of plant shoot architecture, little is known about how the time interval between initiation events, termed plastochron, is regulated. Here, we present a detailed analysis of plastochron2 (pla2), a rice (Oryza sativa) mutant that exhibits shortened plastochron and precocious maturation of leaves during the vegetative phase and ectopic shoot formation during the reproductive phase. The corresponding PLA2 gene is revealed to be an orthologue of terminal ear1, a maize (Zea mays) gene that encodes a MEI2-like RNA binding protein. PLA2 is expressed predominantly in young leaf primordia. We show that PLA2 normally acts to retard the rate of leaf maturation but does so independently of PLA1, which encodes a member of the P450 family. Based on these analyses, we propose a model in which plastochron is determined by signals from immature leaves that act non-cell-autonomously in the shoot apical meristem to inhibit the initiation of new leaves.     

Effect of irradiance on shoot development in vitro

The growth of Disanthus cercidifolius and Rhododendron cultivars, and to a lesser extent Crataegus oxyacantha cv. Paul's Scarlet, was modified by altering either the spectral quality or the level of irradiance received by shoot cultures; which were otherwise maintained under uniform medium and plant growth regulator (PGR) conditions in vitro. When the spectrum of Philips colour 84 (white) fluorescent lamps was modified by coloured cellulose acetate filters, red light promoted shoot extension and axillary branching, whereas blue light inhibited shoot growth and reduced leaf chlorophyll content in the sensitive cultivar R. cv. Dopey. By using single or multiple layers of neutral density filters, or moving cultures nearer to the light source, irradiance from white light was varied. All cultures grew well at low levels of irradiance (c. 11 µmol m^–2 s^–1), but the growth and leaf chlorophyll content of cultures of Disanthus and Rhododendron cultivars were suppressed by increasing irradiance. In three related Rhododendron cultivars, increased irradiance promoted the development of adventitious shoots. Crataegus shoots were tolerant of a wide range of irradiances and only shoot extension was inhibited at the highest level tested; leaf chlorophyll content was unaffected. These results are discussed in terms of the differential perception of light relative to the natural habitats of these plants, and of the possible direct effect of irradiance upon PGRs in the culture system.     

Productivity-independent initial growth of individual leaves in sunflower (Helianthus annuus L.)

Growth rates of individual leaves attached to sunflower (Helianthus annuus) plants were measured experimentally under different levels of environmental productivity, modified by irradiance and nutrient conditions. The unfolding rate and final area of an individual leaf increased with increasing environmental productivity. The final area of an individual leaf also varied according to differences in leaf order. The declining pattern of relative leaf area growth rate (RLGR) varied with environmental productivity; leaves in a productive environment had a longer period of high sustained initial RLGR than leaves in a less productive environment. However, maximum RLGR was hardly influenced by leaf order or environmental factors such as irradiance and mineral nutrition. This article is dedicated to Prof. Emeritus Toshiro Saeki in recognition of his fruitful career in plant ecology.     

QUANTITATIVE PHENOLOGY AND LEAF SURVIVORSHIP OF RHODODENDRON MAXIMUM IN CONTRASTING IRRADIANCE ENVIRONMENTS OF THE SOUTHERN APPALACHIAN MOUNTAINS

Seasonal plant growth patterns were compared for Rhododendron maximum L. in two contrasting subcanopy environments. The two subcanopy, above ground environments differed only in their quantity of irradiance by virtue of the relative dominance of evergreen or deciduous trees in the canopy. A third site had no canopy influence. Overall growth (shoot elongation, woody increment, leaf production) was maximized under the open (BMO) and deciduous dominated canopy (PCD). The leaf pool was significantly smaller under the evergreen dominated canopy (PCE) but average leaf area per leaf was slightly larger at PCE. Individual age-specific leaf cohorts, identified from shoot morphology, indicated increased leaf survivorship with a decreased irradiance environment. Leaf production was synchronous and rapid (1 week), followed by three weeks of leaf expansion, which created the even-aged leaf cohorts. Wood growth (diameter increment), in contrast, continued through the beginning of the winter. Reproductive effort increased with increasing irradiance environment. Significant variation in growth was observed between canopy shoot types at all three research sites. The significance of these phenological patterns is discussed in view of the variable subcanopy environment of southwestern Virginia.     

Leaf gas exchange capacity in relation to leaf position on the stem in field grown teak (Tectona grandis L.f.)

Leaf gas exchange patterns in relation to leaf positions on stems were studied in field grown forest tree, teak (Tectona grandis L.f.) during first year growth under intensive culture plantation. Net photosynthetic rates (PN) were low in immature leaves (1-2 from shoot apices), increased basipetally on shoot, peaked in leaves (3rd or 4th leaves from shoot apices) which had recently reached full expansion, and thereafter declined in lower crown leaves. High PN found in fully expanded young leaves was associated with increased dark respiration rate (RD) and high radiation saturation as well as compensating irradiance for PN when compared to those of aged leaves. Intercellular CO2 concentrations (Ci) determined at ambient CO2 concentration and saturating irradiance were apparently low for leaves exhibiting high PN when compared to those of aged leaves. Differences in stomatal conductance (gs) and the rate of transpiration (E) were not apparent between leaves after full expansion. The relationship of PN with Ci recorded for leaves at different positions on stems and under natural ambient CO2 concentrations showed a linear decrease in PN with marked increasing Ci and suggested that increase in mesophyll limitations could cause decline in PN during aging of teak leaves after full expansion. Highly significant positive linear correlation was found between PN and Ci determined at below ambient CO2 concentrations and saturating irradiance for both fully expanded young and aged leaves. The estimate of linear relationship between PN and Ci, often considered as carboxylation efficiency, was higher for fully expanded young leaves characterised by high PN than for aged leaves exhibiting low PN. Hence, the increase in mesophyll limitations or decrease in carboxylation efficiency could explain gradual reduction in photosynthetic potential with leaf age after maturation in teak.     

Leaf gas exchange capacity in relation to leaf position on the stem in field grown teak (Tectona grandis L.f.)

Leaf gas exchange patterns in relation to leaf positions on stems were studied in field grown forest tree, teak (Tectona grandis L.f.) during first year growth under intensive culture plantation. Net photosynthetic rates (PN) were low in immature leaves (1-2 from shoot apices), increased basipetally on shoot, peaked in leaves (3rd or 4th leaves from shoot apices) which had recently reached full expansion, and thereafter declined in lower crown leaves. High PN found in fully expanded young leaves was associated with increased dark respiration rate (RD) and high radiation saturation as well as compensating irradiance for PN when compared to those of aged leaves. Intercellular CO2 concentrations (Ci) determined at ambient CO2 concentration and saturating irradiance were apparently low for leaves exhibiting high PN when compared to those of aged leaves. Differences in stomatal conductance (gs) and the rate of transpiration (E) were not apparent between leaves after full expansion. The relationship of PN with Ci recorded for leaves at different positions on stems and under natural ambient CO2 concentrations showed a linear decrease in PN with marked increasing Ci and suggested that increase in mesophyll limitations could cause decline in PN during aging of teak leaves after full expansion. Highly significant positive linear correlation was found between PN and Ci determined at below ambient CO2 concentrations and saturating irradiance for both fully expanded young and aged leaves. The estimate of linear relationship between PN and Ci, often considered as carboxylation efficiency, was higher for fully expanded young leaves characterised by high PN than for aged leaves exhibiting low PN. Hence, the increase in mesophyll limitations or decrease in carboxylation efficiency could explain gradual reduction in photosynthetic potential with leaf age after maturation in teak. This revised version was published online in June 2006 with corrections to the Cover Date.     

DEVELOPMENTAL POTENTIAL OF EXCISED PRIMORDIAL AND EXPANDING LEAVES OF COLEUS BLUMEI BENTH.

Coleus blumei Benth. primordial leaves 1 through 4 and expanding leaves 5 to 8 were isolated and cultured to examine the effects of auxin and kinetin on development. Without the plant growth regulators in the medium, expanding leaves 7 and 8 developed as leaves; younger leaf primordia did not develop. With 0.01 to 5.0 mg/1 IAA, 2–7% of the youngest pair of primordial leaves (1 and 2) developed as roots. Small leaf blade development occurred on IAA at 0.5 to 5.0 mg/1 with 10–12% of the explants, and shoots developed from 2% of the youngest primordia explants at 3 mg/1 IAA. With 2–28% of the second set of primordial leaves (3 and 4), a leaf with a root developed with 0.01 to 5.0 mg/1 IAA. At 3.0 mg/1 IAA, in addition to leaf formation, 2% of the explants formed a rosette of leaves and 1% formed a shoot. With the highest level of IAA (5 mg/1), 2% of the explants formed a root. Expanding leaves 5 through 8 developed mostly into leaves without petioles on IAA and kinetin. Plant development occurred from 2% of the youngest primordial leaves on 0.03 mg/1 kinetin; otherwise, these primordia on 0.003 to 2 mg/1 kinetin developed into abnormal leaves. Primordia 3 and 4 developed into normal appearing leaves at levels of kinetin between 0.03 and 2 mg/1. At lower levels the leaves were abnormal.     

Sun Shade Acclimation and Nitrogen Nutrition of

Growth, sun/shade acclimation and nitrogen nutrition were examined in Tradescantia fluminensis to gain greater understanding of why this species is so successful in New Zealand native forest remnants. Over a two year period, the rate of shoot extension of T. fluminensis in a New Zealand mixed mahoe (Melicytus ramiflorus) coastal forest remnant showed a similar pattern to monthly mean values for mean daily air temperature and day length. Growth at the shoot apex was balanced by death at the shoot base. During the first year, nitrate (NO3-)content of the plant in the field was always > 250 mu mol per g dry weight. On high NO3- supply in pot experiments, in a glasshouse or outdoors, total plant dry weight increased with increased relative irradiance from 1 to 30-50% (open ground photosynthetically active radiation = 100% relative irradiance). Changes in shoot to root dry weight ratio (S:R), specific leaf area (SLA) and leaf chlorophyll, carotenoid and protein content associated with decreased irradiance from 50 to 1% were similar to those associated with increased distance into the forest remnant and are discussed in relation to shade acclimation. Values for S:R (>30.1) and SLA (approximate to 900 cm(2) per g dry weight) were extremely high at low irradiance. These results support earlier conclusions that irradiance level is likely to be the primary factor limiting the extent of colonisation of forest remnants by T. fluminensis. Under glasshouse conditions, the growth response of T. fluminensis to different ammonium and NOS concentrations was similar to that previously reported for herbaceous species capable of rapid growth. Leaf nitrate reductase activity was within the range previously reported for fast growing species. Tradescantia fluminensis accumulated substantial amounts of NO3- in shoots with no depression in growth. This NO3- was utilised when nitrogen became limiting to growth. An 'invasion strategy' of T. fluminensis into N.Z. native forest remnants is proposed.     

Distribution of assimilate during the flush cycle of growth in Theobroma cacao L.

The growth of the shoot and roots of seedling plants of cocoa (Theobroma cacao L.) under constant glasshouse conditions showed a rhythmic cycle, with the maximum growth stages of each alternating in a regular sequence. When the growth cycle of the shoot was upset by removing all new leaves immediately after unfolding, the roots showed a high constant growth rate during this period, suggesting that normally the rapidly expanding leaves exert an inhibitory influence on the roots. Conversely removal of portions of the root delayed the production of new leaves in the shoot. The level of soluble and starch carbohydrate in the mature leaves, roots and stem declined during the period of expansion of the flush leaves, but accumulated again at the end of the leaf expansion stage. It is likely that this reserve carbohydrate was remobilised and translocated to the flush leaves during their period of expansion. A large proportion of newly formed photoassimilate, as shown by the distribution of ¹⁴C radioactivity from different source leaves, was also translocated to the young leaves during expansion. The large sink created by these leaves may cause photoassimilate and reserve carbohydrate to be diverted from the roots, thereby inhibiting root growth during the stage of leaf expansion. It is suggested that the rhythmic leaf production at the apex may control the growth cycle of the roots.     

Individual leaf development in Arabidopsis thaliana: a stable thermal-time-based programme

In crop species, the impact of temperature on plant development is classically modelled using thermal time. We examined whether this method could be used in a non-crop species, Arabidopsis thaliana, to analyse the response to temperature of leaf initiation rate and of the development of two leaves of the rosette. The results confirmed the large plant-to-plant variability in the studied isogenic line of the Columbia ecotype: 100-fold differences in leaf area among plants sown on the same date were commonly observed at a given date. These differences disappeared in mature leaves, suggesting that they were due to a variability in plant developmental stage. The whole population could therefore be represented by any group of synchronous plants labelled at the two-leaf stage and followed during their development. Leaf initiation rate, duration of leaf expansion and maximal relative leaf expansion rate varied considerably among experiments performed at different temperatures (from 6 to 26 degrees C) but they were linearly related to temperature in the range 6-26 degrees C, with a common x-intercept of 3 degrees C. Expressing time in thermal time with a threshold temperature of 3 degrees C unified the time courses of leaf initiation and of individual leaf development for plants grown at different temperatures and experimental conditions. The two leaves studied (leaf 2 and leaf 6) had a two-phase development, with an exponential phase followed by a phase with decreasing relative elongation rate. Both phases had constant durations for a given leaf position if expressed in thermal time. Changes in temperature caused changes in both the rate of development and in the expansion rate which mutually compensated such that they had no consequence on leaf area at a given thermal time. The resulting model of leaf development was applied to ten experiments carried out in a glasshouse or in a growth chamber, with plants grown in soil or hydroponically. Because it predicts accurately the stage of development and the relative expansion rate of any leaf of the rosette, this model facilitates precise planning of sampling procedures and the comparison of treatments in growth analyses.     

Optimal allocation of resources in response to shading and neighbours in the heteroblastic species, Acacia implexa

BACKGROUND AND AIMS: Heteroblasty is an encompassing term referring to ontogenetic changes in the plant shoot. A shaded environment is known to affect the process of heteroblastic development; however, it is not known whether crowded or high density growing conditions can also alter heteroblasty. Compound leaves of the shade-intolerant Acacia implexa allocate less biomass per unit photosynthetic area than transitional leaves or phyllodes and it is hypothesized that this trait will convey an advantage in a crowded environment. Compound leaves also have larger photosynthetic capture area - a trait known to be advantageous in shade. This studied tested the hypothesis that more compound leaves will be developed under shade and crowded environments. Furthermore, this species should undergo optimal allocation of biomass to shoots and roots given shaded and crowded environments. METHODS: A full factorial design of irradiance (high and low) and density levels (high, medium and low) on three populations sourced from varying rainfall regions (high, medium and low) was established under controlled glasshouse conditions. Traits measured include the number of nodes expressing a compound leaf, biomass allocation to shoots and roots, and growth traits. Key Results A higher number of nodes expressed a compound leaf under low irradiance and in high density treatments; however, there were no significant interactions across treatments. Phenotypes strongly associated with the shade avoidance syndrome were developed under low irradiance; however, this was not observed under high density. There was no significant difference in relative growth rates across light treatments, but growth was significantly slower in a crowded environment. Conclusions Heteroblastic development in Acacia can be altered by shade and crowded environments. In this experiment, light was clearly the most limiting factor to growth in a shaded environment; however, in a crowded environment there were additional limiting resources to growth.     

PRIMORDIAL LEAF AND PHYTOHORMONE EFFECTS ON EXCISED SHOOT APICAL MERISTEMS OF COLEUS BLUMEI BENTH.

Coleus blumei Benth. apical meristems and apical meristems +1, +2, +3 primordial leaf pairs were cultured to examine phytohormone influences on development and correlative effects of developing primordial leaves on in vitro responses. The meristem with no phytohormones or low levels of IAA could not develop in vitro. At least 0.1 mg/l IAA and optimumly 1-2 mg/l IAA were required for development into complete plants. IAA from 0.1 to 3 mg/l also resulted in root development with no apparent leaf or shoot formation. Levels of IAA higher than 3 mg/l were inhibitory to development. Kinetin, as a substitute for naturally occurring cytokinins, alone (0.0003 to 3 mg/l) resulted in development of rosettes of leaves. In the presence of IAA (***1 mg/l) and kinetin (0.003 mg/l) plants, rosettes, individual leaves with roots, and roots developed from isolated meristems. Glutamine and adenine sulfate both appeared inhibitory to meristem development. With +1, +2, +3 developing primordial leaf pairs left attached to the apical dome, three pairs were required for plant formation in the absence of phytohormones. In the presence of IAA, two pairs of primordial leaves resulted in plant formation; whereas, with IAA and low levels of kinetin one pair of primordial leaves was enough. Higher levels of kinetin were inhibitory to plant development with primordial leaves present. ABA appeared to be inhibitory to development of meristems and meristems +1, +3 primordial leaves at low concentrations and resulted in death at ***1 mg/l. Developing primordial leaves appear to supply the apical meristem with a balance of phytohormones during growth. Meristem development into a plant first involved formation of leaf primordia. Establishment of a bipolar axis with root formation followed.     

Endogenous ABA maintains shoot growth in tomato independently of effects on plant water balance: evidence for an interaction with ethylene

To examine whether the reduced shoot growth of abscisic acid (ABA)-deficient mutants of tomato is independent of effects on plant water balance, flacca and notabilis were grown under controlled-humidity conditions so that their leaf water potentials were equal to or higher than those of well-watered wild-type plants throughout development. Most parameters of shoot growth remained markedly impaired and root growth was also greatly reduced. Additional experiments with flacca showed that shoot growth substantially recovered when wild-type levels of ABA were restored by treatment with exogenous ABA, even though improvement in leaf water potential was prevented. The ability of applied ABA to increase growth was greatest for leaf expansion, which was restored by 75%. The ethylene evolution rate of growing leaves was doubled in flacca compared to the wild type and treatment with silver thiosulphate to inhibit ethylene action partially restored shoot growth. The results demonstrate that normal levels of endogenous ABA are required to maintain shoot development, particularly leaf expansion, in well-watered tomato plants, independently of effects on plant water balance. The impairment of shoot growth caused by ABA deficiency is at least partly attributable to ethylene.     

Effect of irradiance and plant age on the dimensions of the growing shoot of poplar

Populus euramericana (Dode) Guinier cv. Robusta plants were cultivated at irradiances of 7.5, 15 and 30 W m⁻² (32.5, 65 and 130 μmol m² s⁻¹), 400–700 nm at 22°C and a relative humidity between 40 and 60% on a gravel culture subirrigated with Hoagland's nutrient solution. The basal diameter of the growing shoot, a measure of the number of apical cells participating in growth, increased proportionally to irradiance and was correlated with mature leaf length. The development of the length of the growing shoot (L_gs) depended also on the nutritional status of the (young) shoot. L_gs was strongly correlated with the rate of height growth.     

Leaf habit influences nitrogen remobilization in Vaccinium species.

The effect of N supply on plant growth and leaf demography of a deciduous and an evergreen Ericaceae was studied in relation to their internal cycling of N. Mature ramets of Vaccinium myrtillus (deciduous) and Vaccinium vitis-idaea (evergreen) were established in sand culture for 1 year with an adequate supply of a balanced nutrient solution. During one growing season, the plants were given two levels of N supply enriched with 15N and eight sequential destructive harvests were taken. Recovery of unlabelled N in the new shoot was used to determine the remobilization of N from storage. Initially, growth was unaffected by N supply. After May, High N enhanced growth for both species but the nature of their growth response differed. For both species, new shoot biomass and leaf number increased but root biomass production was affected for V. myrtillus only. Whole plant biomass production was similar for both species under High N, but was greater for V. vitis-idaea under Low N. The amount of N remobilized to support new shoot growth was similar for the two species and was independent of N current supply. N was remobilized predominantly from previous year leaves for V. vitis-idaea and from previous year stems and roots for V. myrtillus. The contribution of remobilization to new shoot N was similar for the two species, but depended on N supply. Remobilization was faster in V. myrtillus, but lasted longer in V. vitis-idaea. The results are discussed in relation to species growth in N-poor environments, focusing on the extent to which species-differences in the dynamic of N remobilization and growth may explain their adaptation to constant and/or changeable N supply.