Final Leaf Size Research Articles

Delayed Budbreak: A Defensive Response of Mountain Birch to Early-Season Defoliation?

Delayed budbreak has been suggested to be a potentially defensive characteristic of deciduous trees against early-feeding lepidopteran larvae. We therefore tested the effects of early (in June) and late (in August) manual defoliations on leaf development in mountain birch. Early defoliation induced a significant delay in budbreak, whereas late defoliation influenced only slightly leaf flush during the next growing season. This supports the defense hypothesis. However, the responding units were separate branches rather than entire birch trees, since leaf growth was delayed on defoliated branches relative to untreated branches on the same trees. Furthermore, as artificial defoliation induced the delay in leaf flush, the presence of larvae is not necessary for triggering these localized responses in mountain birch. The fact that both early and late defoliation reduced final leaf size may suggest that the observed defoliation effects were associated with localized resource deficiencies suppressing leaf growth. Still, a delay in budbreak on previously defoliated branches, due to resource shortage or other causes, could be expected to adversely affect immobile early-feeding larvae. Mobile larvae, on the other hand, should be generally capable of overcoming within-tree variation in the predictability of their food resources.

Effects of harvesting programme and sowing date on leaf growth in forage barley in Cyprus

SummaryAll combinations of four harvesting treatments and two sowing dates were compared in each of 2 years in field experiments near Nicosia. In one of the years, two levels of applied nitrogen were compared. The harvesting treatments were: (1) a milk-stage cut, (2) a boot-stage cut and a regrowth cut, (3) a grazing-stage cut and a regrowth cut, and (4) three grazing-stage cuts and a regrowth cut. The sowing dates were (1) normal (12 November) and (2) early (15 October), with sufficient irrigation to ensure establishment.Applied nitrogen had virtually no effect on leaf growth, evidently because of high reserves of available nitrogen in the soil. Early sowing increased the rates of leaf emergence, extension and expansion up to the time of the first ‘grazing’ cut (when the first node was showing) and reduced the number of leaves which died in that period. Where growth was uninterrupted to the milk stage, early sowing did not affect the number of leaves produced by a main stem or primary tiller, but increased the longevity of the later leaves. Where there were three ‘grazing’ cuts, early sowing allowed time for the production of more and larger leaf blades, with longer sheaths, between the third 'grazing’ cut and the final harvest.The ‘grazing’ cuts considerably reduced the rates of extension and expansion and the final size of the leaves which emerged soon after a cut. There was good recovery subsequently, however, in rates of extension and expansion and final leaf size, particularly with October sowing.During almost all the period of leaf production on a main stem or primary tiller, several leaves (up to six) were expanding at the same time. The stage, during the period between emergence and death, at which a leaf blade reached its full length was typically half-way between emergence and death. Where growth was uninterrupted, area per leaf blade was positively correlated with both the number of days between the emergence of successive leaves and the number of days between emergence and death.

The influence of photosynthetically‐active radiation and simulated shadelight on the control of leaf growth of Betula and Acer

SUMMARYThe primary aim of the study was to quantify the effects of photosynthetically‐active radiation (PAR) on extension of leaves of silver birch (Betula pendula Roth.) and sycamore (Acer pseudoplatanus L.). Plants grown at 250 μmol m−2 s−1 were exposed to a range of fluence rates (0·680 μmol m− s−1) whilst enclosed in Perspex chambers in which temperature, vapour pressure deficit and photoenvironment were all controlled. Measurements of leaf extension, water relations, and cell wall extensibility (VVEX) were made at the end of a 3 h exposure period.For leaves of birch, reducing the fluence rate resulted in reduced leaf extension and a lowering of WEX. Exposure of sycamore seedlings for 3 h to different values of PAR had little effect on the growth of leaves and WEX remained constant. The characteristics of net photosynthesis also differed for the two species and photosynthesis and wall loosening may be linked.Since natural woodland shadelight, in addition to reduced PAR, also has a reduced R/FR ratio, a second group of seedlings were placed in a photoenvironment which simulated shadelight (low PAR, R/FR) for 28 d. This treatment reduced extension rate and final leaf size for both species. Measurements of extension, water relations and WEX made when seedlings were exposed to shadelight whilst held in the Perspex chambers revealed differences in the control of leaf growth for the two species.It is confirmed that leaves of birch are highly responsive to changes in PAR with cell wall loosening the most likely process controlling this response.

Adaptations to soil drying in woody seedlings of African locust bean, (Parkia biglobosa (Jacq.) Benth.).

Stomatal conductance, transpiration and xylem pressure potential of African locust bean (Parkia biglobosa (Jacq.) Benth.) seedlings subjected from the sixth week after emergence to four weeks of continuous soil drought did not differ from those of well-watered, control plants until two-thirds of the available soil water had been used. In both well-watered and drought-treated plants, stomatal conductance was highest early in the day when vapor pressure deficits were low, but decreased sharply by midday when evaporative demand reached its highest value. There was no increase in stomatal conductance later in the day as vapor pressure deficit declined. The relationship between transpiration rate and xylem pressure potential showed non-linearity and hysteresis in both control and drought-treated plants, which seems to indicate that the plants had a substantial capacity to store water. The rate of leaf extension in African locust bean seedlings subjected to six consecutive 2-week cycles of soil drought declined relative to that of well-watered, control plants, whereas relative root extension increased. It appears that African locust bean seedlings minimized the impact of drought by: (1) restricting transpiration to the early part of the day when a high ratio of carbon gain to water loss can be achieved; (2) utilizing internally stored water during periods of rapid transpiration; (3) reducing the rate of leaf expansion and final leaf size in response to soil drought without reducing the rate of root extension, thereby reducing the ratio of transpiring leaf surface area to absorbing root surface area.

The Control of the Light Acclimation of Photosynthesis inGlycine max: Dependence on Import as Modified by Intraplant Shading

Ward, D. A. and Bunce, J. A. 1986. The control of the light acclimation of photosynthesis in Glycine max: Dependence on import as modified by intraplant shading.—J. exp. Bot. 37: 615-624. The dependence of photosynthetic capacity on imported and locally-assimilated supplies of carbon during leaf development under different irradiances was investigated in Glycine max. The potential export of carbon to the developing, mainstem trifoliate leaf (source-potential) was restricted non-destructively by shading all lower, source leaves (source-shading), while local photosynthesis was modified concurrently by exposing the young leaf to different light levels during development. When source-shading was applied below the 2nd mainstem trifoliate leaf at the bud stage of development, photosynthetic capacity was unaffected in leaves which had developed under moderate and low irradiances (500 and 250 /?mol PAR m~2 s1, respectively), but was reduced significantly in leaves developed under a high irradiance (900 /?mol PAR m~2 s~'). If source-shading was applied beneath the 2nd leaf at unfolding, the reduction of photosynthetic capacity under the high irradiance was relatively minor. The photosynthetic capacity attained by the 2nd leaf during development under different irradiances was influenced by the previous light environment of the whole plant. In contrast to the 2nd leaf, the photosynthetic capacities of the 1st and 4th mainstem leaves were relatively unaffected by source-shading, even under the highest light regime. While photosynthetic capacity showed a widespread insensitivity to the light level of the lower region of the canopy, source-shading reduced final leaf size irrespective of node position or local irradiance during leaf development. These effects were not related to differences in daily photosynthesis by the expanding leaf, and are discussed

The Influence of (2-Chloroethyl)trimethylammoniumchloride (CCC) on Growth and Photosynthetic Metabolism of Young Wheat Plants ( Triticum aestivum L.)

The influence of (2-chloroethyl)trimethylammoniumchloride on growth and cell metabolism of Triticum aestivum var. Kolibri was investigated. CCC was added to the nutrient solution on the 11th day of development with a final concentration of 10(-2) mol·1(-1). It immediately stopped root growth and showed a strong inhibitory influence on the growth of the leaves. Smaller and fewer cells accounted for the reduction in final leaf size of about 40 %. The content of soluble proteins and soluble reducing sugars were significantly increased in the treated leaves. CCC also exhibited a stimulating effect on the synthesis of RubPc-ase protein and the in vitro activity of this enzyme. In contrast to this, the dry weight remained unchanged and the maximum CO(2)-fixation was even decreased. This result is briefly discussed in connection with a possible involvement of water stress induced by CCC.

Proline accumulation: A parameter for evaluation of sensitivity of tomato varieties to drought stress?

The pattern of proline accumulation and the growth response were followed in several tomato (Lycopersicon esculentum Mill.) varieties which were exposed to 7 days of drought stress followed by a 15‐day period of rewatering. During dehydration, water potential and leaf elongation rates decreased more in var. ‘Hosen’ and ‘S‐5’ than in ‘LX‐11’, ‘1970’, ‘Pakmor’, ‘Faculty‐16’, ‘Alcobaca’ and ‘475’. Proline accumulation during stress was greatest in the first two varieties. In ‘Hosen’ and ‘S‐5’ rewatering resulted in a decrease of proline to control levels, whereas in the other varieties accumulation of proline continued long after turgor had been regained. The extent of this continued accumulation was not correlated with the degree to which each variety was dehydrated. Upon rewatering of the plants the rate of leaf elongation was increased, but the final leaf size as well as whole shoot and root fresh weight of the recovered plants were not colated with the degree of “suffering” that each variety experienced during the drought period. Incubation of detached young tomato leaves in polyethylene glycol solution for 48 h resulted in a substantial accumulation of proline. The varietal differences observed under these conditions were reminiscent of the differential responses in proline accumulation obtained in the intact plants. It is concluded that proline accumulation at the time of dehydration signals drought stress in tomato plants but does not correlate with the overall varietal sensitivity to transient dehydration in recovered plants.

Mild phosphorus stress in barley and a related low‐phosphorus‐adapted barleygrass: Phosphorus fractions and phosphate absorption in relation to growth

Barleygrass (Hordeum leporinum) from Australian low‐P (phosphorus) soils and commercial barley (H. vulgare) with high fertilizer requirements were grown in solution culture at 3 levels of P supply. The high‐P‐adapted barley produced more biomass at all levels of P supply and was more responsive to added P in terms of rate of tillering, rate of leaf production, final leaf size, and therefore total shoot weight compared to barleygrass. In both species root: shoot ratio decreased in response to improved tissue P status, even at P levels where total biomass did not respond to P supply. Removal of endosperm reserves of barley reduced total biomass to a greater extent than it altered phosphate absorption rate, thus increasing tissue P status and making plants less responsive to added P. Similarly, barleygrass had a slower growth rate but a comparable P absorption rate to that of barley. Thus barleygrass also accumulated tissue P and was unresponsive to added P. All phosphorus chemical fractions increased in response to improved tissue P status, but to differing extents (inorganic‐P > nucleic acid‐P > lipid‐P > ester‐P), suggesting that all P fractions (particularly inorganic P) serve, in part, a storage function. Both barleygrass and barley without endosperm had higher concentrations of all P fractions (particularly inorganic P) than did unaltered barley, but this was due entirely to their higher P status (due to slow growth) rather than to any major difference in P metabolism between species. We conclude that slow growth is more important than interspecific differences in P metabolism, P absorption, or efficiency of P utilization in explaining the success of barleygrass and other low‐P‐adapted species on infertile soils.

Leaf expansion of four sunflower (Helianthus annuus L) cultivars in relation to water deficits. I. Patterns during plant development

Abstract. The influence of a slow stress and recovery cycle on the pattern of leaf expansion in four diverse sunflower cultivars (Helianthus annuus L. cvs. Hysun 31, Havasupai, Hopi and Seneca) was studied in a glasshouse. Stress had no significant effect on the time of flower bud emergence and anthesis, or on final leaf number, but delayed the appearance of leaves at high insertions in all cultivars except Hysun 31.Leaf expansion was markedly reduced as the predawn leaf water potential decreased from −0.35 to −0.60 MPa, and the predawn turgor pressure decreased from 0.3 to 0.2 MPa, and expansion ceased at a predawn leaf water potential of about −1.0 MPa, i.e. when the predawn turgor pressure reached zero.The leaves most reduced in final size when water was withheld were those at the insertions which grew the most rapidly in unstressed plants. The maximum reduction in final leaf size of 25–35% was similar in all cultivars and was due to retardation of the rate of leaf expansion: the duration of leaf expansion was actually increased by stress. However, leaves that were initiated during stress, but emerged after rewatering, had final leaf areas at least equal to those in the unstressed plants: in the cultivar Seneca, the final size of leaves of high insertion was significantly greater in stressed than unstressed plants, whereas in the three other cultivars the final leaf sizes were similar in both treatments. All four cultivars examined adjusted osmotically to the same degree, but leaf water potentials in one, Seneca, increased more rapidly after rewatering than in the other three, and this may have contributed to the greater relative leaf size in the leaves of high insertion in this cultivar.

Plastochron Indices in Cantaloupe Grown on an Irrigation Line Source

Cantaloupes were grown on an irrigation line source so that one row received 65 cm water (wet plants) and another row received 21 cm water (dry plants) during the growing season. In wet plants, plastochron indices (PIs) advanced more rapidly with time, and final leaf size was greater. Diminished water supply appears to affect the rate of development more than the sequence of developmental events, as evidenced from the similarity for wet and dry plants of plots of branch plastochron index versus main stem plastochron index. It is concluded that the PI is a better scale than chronological time for studies of the effect of water availability on cantaloupe development.

The growth and development of cowpeas (Vigna unguiculata) under tropical field conditions: 1. Leaf area

SUMMARYThe pattern of leaf growth and death was followed in stands of cowpea grown in the field at Ibadan, Nigeria. Temperature affected this pattern. Leaf area index increased quicker and leaf death started sooner during warm seasons. Individual leaves died while pods at the same node were filling. The rate of leaf appearance increased with temperature and the duration of expansion of individual leaves decreased so that a constant number of leaves were expanding at one time. The mean rate of expansion of individual leaves increased with temperature proportionately more than the duration decreased, hence final leaf size increased with temperature. Base temperatures for leaf appearance and leaf expansion were 16 and 20 °C respectively.

Vegetative development of soybeans grown on different soil types

Nine soybean (Glycine max (L.) Merrill) genotypes, three from each of Maturity Groups V, VI, and VII, were grown on Dubbs silt loam (Typic Hapludalf, fine-silty, mixed, thermic) and Sharkey clay (Vertic Haplaquept, very fine montmorillonitic, thermic) soils to evaluate the effect of soil environment on vegetative development. Leaf enlargement rate (cm2 leaf−1 day−1), final leaf size, internode length, plant height, and number of nodes per plant were all significantly greater on the silt loam for each genotype. The lowered leaf enlargement rate on the clay may have been due to the lower hydraulic conductivity of the clay, and thus fewer hours during the night conducive to leaf enlargement. A highly significant correlation (R2 = 0.96) was found between leaf enlargement rate and final leaf size, indicating that number of days to the different maximum leaf sizes is nearly identical regardless of soil environment. These results indicate that the soil environment and its related physical and textural properties are important factors in determining canopy development of soybeans.

Field Studies of Cereal Leaf Growth

Throughout winter and early spring, rule and auxanometer measurements showed that leaf extension rate (RE) was directly related to temperature and stopped at about 0°C. During this period, both night and day time RE responded similarly to temperature. Bright sunshine in late April and May caused fast transpiration which was associated with low leaf water potential (Ψ) and slow RE. When bright sun was obscured by cloud, RE increased but this did not compensate for previous slow RE. Leaf turgor potential, calculated as the difference between Ψ and leaf osmotic potential, was large (0.6–1.8 MPa) and bore little relation to RE. Low Ψ was associated with slower RE than would have been expected without water stress, but the relation was not unique. On a bright day in May, adaptation to low Ψ occurred and during the afternoon RE was faster than at similar values of Ψ and meristem temperatures before noon. The response of RE and duration of leaf extension to temperature suggested that for any particular leaf grown under field conditions, variation in mean growing temperature would affect final leaf length only slightly. Because severe water stress slows RE without affecting the duration of leaf extension markedly, it decreases final leaf size.

An Exploration of the Carbon Economy of the Tobacco Plant. II. Patterns of Leaf Growth and Dry Matter Partitioning

As a sequel to calculations made in Part I about the carbon economy of the tobacco plant, a short-day variety of tobacco (Nicotiana tabacum L. cv. Mammoth 17L) was grown at controlled temperatures in two contrasting photoperiods (13 and 9 h) and the growth and gas exchange of the plants were determined as frequently as possible during the period 30–100 days from sowing. This paper describes aspects of the leaf emergence, leaf expansion, floral development, and dry matter partitioning in these plants. Part III will present the gas-exchange data. The most striking finding from the growth data concerned leaf expansion. The application of curve-fitting techniques showed that the expansion of each leaf studied could be accurately described by the Gompertz growth function, which implied that the maximum absolute rate of expansion had been achieved quite early in the leaf's development, at about 37% of full expansion. Furthermore, in all but the juvenile leaves, the time-spread of expansion was similar, despite up to 10-fold differences in the final area of the leaves due to photoperiod and position on the stem. Other relationships observed in the data seemed of fundamental interest. Attention is drawn (1) to the smooth progression in final leaf size with progress up the stem, and (2) to the changes with time in the ratio of the relative growth rates of the major plant parts, but whether these relationships, and those between leaf expansion and time, are typical of tobacco will remain uncertain until comparable studies are performed. * Part I, Aust. J. Biol. Sci., 1973, 26, 1057–71.

葉の生長におよぼす物質生産の影響

1. The growth courses of individual leaves were pursued in green gram plants under field conditions, and in tobacco plants under continuous illuminationand at constant temperature of a growth cabinet. 2. In each of successive leaves on the main stem of a green gram plant, comparison was made between the amount of dry matter produced by photosynthesisand the amount of dry weight increased during the same time interval (Fig. 1-b). The comparison indicates that for the growth of younger leaves supplementary material must be imported from older leaves.3. It was postulated that an expanding leaf has an 'internal force' whereby the leaf attracts raw materials for its own growth. The curve that shows the time trend of the internal force resembles the 'normal probability curve', and is quite of the same shape for every leaf along the main stem.4. In the tobacco plants as exposed to continuous illumination, constant temperature and sufficient nutrient condition, plastochrone appears to be influenced only by dry matter production of the whole plant.5. Final leaf size depends upon the magnitudes, at the time when the leaf expands, of the following three major factors: i) dry matter productivity of the whole plant; ii) proportion of the total foliage growth in dry matter to the total dry matter production; iii) plastochrone. The first and the second determine the absolute quantity of dry matter in total foliage growth of the whole plant, and the third determines the amount of dry matter incorporated into each of the expanding leaves. 6. In plants devoid of branching, individual leaf size at any insertion at any time can be given in Equation (1), if daily increase of the total leaf amount (ΔF) or of the total leaf area (ΔF) is given beforehand. The change of ΔF with time is shown in Fig. 8, which was drawn on the basis of the data in a previous paper15), and the leaf amounts at different days were calculated thereby from Equation (1), the resultbeing illustrated in Fig. 9.