Leaf Extension Research Articles

Leaf Water Potential and Relative Water Content Variation in Creeping Bentgrass Clones

Creeping bentgrass (Agrostis palustris Huds.) often requires daily irrigation and syringing to persist in turf areas in warmer environments with high evapotranspiration rates. Turfgrass performance could be enhanced if turgor maintenance under decreasing soil moisture levels could be incorporated into new bentgrass cultivars. The objectives of this study were to determine: (i) if genetic variation in leaf water potential (LWP) existed among creeping bentgrass clones under declining soil moisture, (ii) if LWP was associated with maintenance of growth under declining soil moisture levels, and (iii) if genotypic variation existed in water‐relation characteristics, including components of LWP, as determined by a hydraulic press. The LWP was measured on four field‐grown creeping bentgrass clones twice per day with a hydraulic press. Leaf water potential and soil moisture levels were determined in a growth room study on five creeping bentgrass clones grown in pots, 17 by 13 cm, during a 17‐d period. Waterrelation characteristics were determined on five creeping bentgrass clones grown in a greenhouse using a hydraulic press. Genetic variation existed among clones in LWP in both field and growth room studies. The most negative LWP was not associated with the greatest leaf firing or decrease in leaf extension. The relative water content at zero turgor represented a substantial difference in the degree of hydration at zero turgor. This study illustrated that genetic variation exists for LWP and relative water content in creeping bentgrass.

Diurnal pattern of leaf extension in Salix viminalis relates to the difference in leaf turgor before and after stress relaxation.

Diurnal variations in leaf extension and turgor relaxation were measured in young willow leaves (Salix viminalis L.). Turgor relaxation was calculated from measurements of xylem water potential and osmotic potential of whole, detached leaves that were incubated, without loss of water, under controlled conditions. There were clear diurnal variations in leaf extension and in leaf turgor relaxation and the diurnal pattern of the difference in leaf turgor before and after relaxation was in phase with that of leaf extension. The extent to which leaf turgor after relaxation may be related to threshold turgors for growth and the possible importance of leaf turgor during leaf extension are discussed.

Gibberellin status and responsiveness in shoots of tall and dwarf genotypes of diploid rye (Secale cereale)

The recessive dwarfing alleles of rye (Secale cereale L.), ct1 and ct2, caused a 35–55% reduction in the length of leaf 2 compared with corresponding tall lines grown at both 10°C and 20°C. The dwarf lines were 45–50% as responsive to applied GA3 as the tall lines at 20°C but the absolute GA‐responsiveness of the dwarfs was greater at 10°C than at 20°C. There was no significant difference in the contents of GA19, GA20, GA29, GA1, GA3 and GA8 in the leaf extension zone of tall and dwarf seedlings grown at 20°C. It was concluded that the mechanism whereby GA homeostasis is maintained is functional in both tall and dwarf lines despite marked differences in leaf extension rate. The recessive rye mutations may cause loss of function late in the GA‐cell elongation pathway or, alternatively, indirectly affect GA‐responsiveness in vegetative tissues. The genetic and physiological evidence indicates that ct1 and ct2 are unrelated to the GA‐insensitive Rht genes in hexaploid bread wheat.

Effects of cutting height on the growth of leaves and stolons in perennial ryegrass–white clover swards

SUMMARYAll combinations of five cutting heights (2, 4, 6, 8 and 10 cm) were compared, for 3 years (1986–88), on field plots sown with a mixture of perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) in Wales. The plots were cut at 4-week intervals from April to October each year.A reduction in cutting height reduced the length, width and weight of clover leaflets, petiole length, stolon diameter, the length of stolon internodes and the height of stolons above ground level, but increased the length of clover stolon/m2, the number of stolon nodes/m2 and the proportion of stolon nodes which produced branches. The latter factors out-weighed the former, leading to the inverse relationship between cutting height and the proportion of clover in the sward previously reported (Acuñia & Wilman 1993).A reduction in cutting height reduced the following attributes of ryegrass: the height of the shoot apex, the length and width of leaf blades, sheath length, leaf extension rate, the death rate of leaves and the net gain in blade length.Cutting height had little effect on either the thickness of clover leaflets or the rates of leaf emergence in clover and ryegrass.

MYCORRHIZAE AND NONHYDRAULIC SIGNALLING IN SORGHUM EXPOSED TO PARTIAL SOIL DRYING OR ROOT EXCISION

Our objectives were to determine (a) if mycorrhizal (VAM) fungi can alter drought-induced, nonhydraulic regulation of shoot growth, and (b) how much of a root system can be dried or severed before hydraulic effects on shoot responses become evident. Sorghum was grown with roots equally divided among four pots. The 2×2×4 factorial design had two levels of mycorrhizae (± Glomus intraradix), two levels of root treatment (dried or severed) and four levels of amount of roots treated (0, 1, 2 or 3 pots dried or severed). Neither leaf water potential (Ψ) nor Cs were affected by drying 1 or 2 pots, and reductions in leaf area in these plants were therefore attributed to nonhydraulic signalling. When 2 pots were dried, leaf growth was reduced less in VAM than in nonVAM plants, despite lower P in VAM leaves and despite quicker soil drying by VAM roots. Drying or severing roots of 3 pots did result in drops in leaf Ψ and Cs, indicating a likely hydraulic effect on leaf water status in those plants. Leaf P declined progressively as more roots were dried or severed, possibly also affecting growth in plants with roots in 3 pots dried or severed. Leaf extension rates (LER) declined with only slight drops in soil Ψ, and LER declines were related to volume of soil drying. In VAM plants, leaf area reductions were correlated with length of time roots were exposed to soil Ψ between -0.02 and -0.50 MPa.

Growth and Development of Uniculm and Conventional‐Tillering Barley Lines

AbstractBarley (Hordeum vulgare L.) producers in northern regions require genotypes that develop and mature rapidly. Although the phenological development of barley has been studied extensively, the effect of the uniculm character on rate of growth and development has not been investigated. The objective of this study was to compare the growth and development of uniculm and conventional‐tillering near‐isogenic barley lines. Three pairs of near‐isogenic lines that differed by the presence of the uc2 (uniculm) gene were evaluated at Palmer and Fairbanks, AK during the 1990 and 1991 growing seasons. Averaged over four environments, uniculm genotypes required more growing degree days (GDD) to reach double ridge formation, but there were no differences for GDD to terminal spikelet formation (P < 0.01). Uniculm genotypes had 0.3 more leaves per main culm, required 12 fewer GDD to reach full flag leaf extension, and had a leaf appearance rate that was 0.12 leaves (100 GDD)−1 faster than conventional genotypes (P < 0.01). Uniculm genotypes matured 23 GDD earlier and were 10.9 cm taller than their conventional counterparts (P < 0.01). The restriction of a single culm per plant decreased kernels per spike by 2.2 kernels and increased kernel weight by 8.4 mg (P < 0.01). Our results suggest that the uniculm phenotype results in several favorable modifications of phenological development, which may be of practical value in regions where early maturity is important.

Tillering, Leaf Expansion and Growth of Plants of Two Cultivars of Perennial Ryegrass Grown using Hydroponics at Two Water Potentials

Tillering and growth parameters of perennial ryegrass cultivars Wendy (diploid) and Condesa (tetraploid) were determined in a glasshouse experiment using hydroponics at low (−1·3 MPa) and normal water potential (0 MPa). At −1·3 MPa, leaf extension rate was reduced by 36%. Final plant tiller number was 20% lower at −1·3 MPa because of a 12% reduction in the leaf appearance rate in the first weeks after the start of the treatments. Site filling, the relative increase in tiller number per leaf appearance interval, was high (0.61)-but still lower than theoretically possible-and was only slightly affected by water potential. Site filling was shown to be strictly related to the number of inhibited plus unemerged tiller buds. Dry matter production was 64% lower at −1·3 MPa. Relative growth rate (RGR) was, on average, 17% lower at −1·3 MPa, but the reduction was greater just after the treatments started. Also, net assimilation rate (NAR) was reduced more by low water potential just after the start of the treatments. Specific leaf area (SLA) was 13 % lower at −1·3 MPa for Wendy, but not significantly reduced for Condesa. Contrary to expectations based on the theory of the functional balance between root and shoot, leaf weight ratio was slightly higher at −1·3 MPa. From comparison of the results of this study with published data, it is concluded that effects of drought in the field on tillering cannot be attributed only to low water potential.

A Model of the Leaf Extension Rate of Tall Fescue in Response to Nitrogen and Temperature

The leaf extension rate (LER) of tall fescue (Festuca arundinacea Schreb.) was studied in the field under various nitrogen and temperature regimes. The LER was closely related to temperature when N was not limiting plant growth. Two distinct relationships between the LER and the temperature were obtained, one for vegetative growth and one for the reproductive period. These relationships, described by a Gompertz function, were exponential at temperatures below 8 °C and linear at temperatures above 8 °C. They made possible the calculation of an optimal LER corresponding to non-limiting N conditions for plant growth. The strong influence of the temperature on the LER was still observed under N limiting conditions. The N status of the swards was described by the ratio between the actual N content (Nactual) and the optimal N content (Noptimal). The Noptimal was defined as the N content experienced at a non-limiting level of N nutrition but without N luxury consumption. The Noptimal, expressed as a function of dry matter yield, declined during growth. The effect of the N status of the swards on the LER was analysed by calculating the ratio between the actual LER and the optimal LER, and relating it to the ratio between Nactual and Noptimal. It was shown that these two ratios were highly correlated.

Leaf development in Lolium temulentum L.: characterization of a slow-to-green mutant.

A nuclear-gene mutation of the C3 grass Lolium temulentum L., which arose following cell suspension culture and plant regeneration, is manifested as delayed and incomplete greening, which occurs from the leaf tip downwards. Many plastids in the mutant exhibit abnormal morphology when examined by transmission electron microscopy; the plastid outer envelope lacks integrity and thylakoids, while still stacked, are spread over a wide area surrounded by diffuse stromal contents. These aberrant plastids can coexist with apparently normal chloroplasts in the same cell of mutant plants. Levels of chlorophyll a and b, and carotenoids, are all lower in the mutants than in normal Lolium temulentum. Leaf length, absolute growth rate, and number of cells per unit length at the leaf base, are greatly reduced (20-30% the normal values) in slow-to-green plants, but relative growth rate, duration of leaf growth, length of cell division zone and proportion of cells dividing are little affected. This novel mutant is a potentially valuable resource for studying interrelationships between photosynthetic function and leaf extension growth in grasses.

Diurnal variation in the temperature response of leaf extension of two bunchgrass species in the field

ABSTRACTThe effect of temperature on short‐term leaf extension rates was studied for two cool‐season tussok grasses, Agropyron desertorum and Pseudoroegneria spicata, growing in the field under a variety of water stress and defoliation conditions. Leaf extension rates and air temperatures were monitored every half hour during numerous 12‐ to 65‐h periods in three growing seasons using auxanometers constructed of precision resistors. For both species, a three‐phase relationship between leaf extension rate and temperature was observed during diurnal cycles. Leaf extension rate increased linearly with temperature from dawn until midday (phase 1). Leaf extension then increased rapidly, reaching maximum rates in the early evening (approximately 1900h), despite decreasing temperatures during this period (phase 2). Finally, leaf extension rate declined with temperature from evening until dawn (phase 3). This diurnal cycle was described by linear (phase 1) and quadratic (phases 2 and 3 combined) regression models. Although the rate of leaf extension and daily integrals were affected by the water stress and defoliation treatments, the diurnal pattern was consistently observed. Temperature was probably a major factor governing leaf extension rates at night (phase 3), but it appeared unimportant in controlling leaf extension between dawn and midday. The relative importance of physiological and environmental factors controlling leaf extension rate appears to shift during the day in these species under field conditions.

Diurnal variation in extension growth of leaves of Salix viminalis

Diurnal variation in leaf extension and biophysical parameters of leaf growth were measured in young leaves from a stand of Salix viminalis L. in southern Sweden over a two-day period of clear skies during late July. Leaf growth rate (irreversible extension) was greatest during the late afternoon and early evening, falling to negligible values during the night and early morning.Leaf water potential and leaf osmotic potential showed declining values in the morning with subsequent recovery in the late afternoon. Diurnal variation in osmotic potential (-1.3 to -1.7 MPa) was small compared with that of leaf water potential (-0.1 to -1.2 MPa). Calculated values of leaf turgor pressure during the night (1.2 MPa) were double the midday values. Growth rate correlated poorly with turgor, which (except on one occasion) was always above a calculated value of yield turgor at 0.53 MPa.Diurnal variation in extension growth rate was large compared with that in plastic extensibility of leaf tissue as measured by an Instron technique. Values of extensibility were low and showed little diurnal variation, which is consistent with a proposed negative feedback of expansive growth rate on extensibility. Extension growth rate correlated well with air temperature, suggesting that the rate of leaf expansion may have been limited by a temperature-dependent rate of cell wall loosening.

Evapotranspiration and Leaf Extension Rates of 24 Well-watered, Turf-type Cynodon Genotypes

Cultivar selection is one method used for the conservation of irrigation water. The primary objective of this research was to evaluate the evapotranspiration (ET) rates of 24 well-watered, turf-type bermudagrass (Cynodon spp.) genotypes under field conditions and established on a fritted clay root zone contained in plastic minilysimeter pots. A secondary objective was to correlate ET rate to leaf extension rate, a potential rapidly assessed predictor of the amount of leaf surface area present for ET. ET rates were determined by the water-balance method. Both the overall ET and leaf extension rate differed significantly among genotypes. ET rates were not correlated with leaf extension rates in individual years. Our data indicated a potential for water savings based on bermudagrass cultivar selection that was similar to the reported potential water savings based on warm-season turfgrass species selection.

The influence of temperature on leaf development and growth in potatoes in controlled environments

SummaryThree controlled environment experiments were conducted at different temperatures to determine the relation between temperature and leaf development and growth in the potato (cv. Maris Piper). Developmental stages are defined for the appearance and duration of leaf extension in the potato and comparisons made with other temperate zone crops.The rate of leaf appearance was linear over the temperature range (9–25°C) and above 25°C there was no further increase in the rate. The temperature coefficient for the rate of appearance of leaves was 0.032 leaves (degree days)‐1 using a base temperature of 0°C. The duration of extension of an individual leaf decreased with increase in temperature up to 25°C such that the thermal duration was constant at 170 degree days using a base temperature of 0°C for leaf positions 4–10 on the main stem. At higher leaf positions the thermal duration was similar or greater. The advantages and limitations of controlled environment work as a parallel to field experimentation are discussed.

MODELING INFLORESCENCE DEVELOPMENT OF AFRICAN VIOLETS

The effects of temperature and irradiance on flower initiation and development were quantified to provide a basis for an inflorescence development model. The percentage of leaf axils forming an inflorescence increased as the daily integrated PPF increased from 1 to 4 mol m-2 d-1, while the rate of inflorescence development was a linear function of temperature from 18 to 26C. The appearance of a visible flower bud in the leaf axil was correlated with leaf blade length of the subtending leaf. Mathematical functions were used to describe leaf blade length at the time of visible flower bud as a function of temperature and irradiance, and also to describe the influence of temperature on the rate of leaf extension. The time of visible flower bud in the leaf axil was then predicted by measuring the current length of the subtending leaf blade and estimating the time required for the leaf blade to extend to the length required for visible flower bud appearance. A phasic development scale was used to describe the developmental status of an inflorescence from visible flower bud to anthesis. A model was then created which predicted time to anthesis based upon temperature and the current stage of inflorescence development.

Short‐ and Long‐Term Responses of Corn to a Pre‐Anthesis Soil Water Deficit

AbstractIrrigation should be scheduled in order to minimize water application while maximizing crop yield, and such judicious watering requires better understanding of how crops respond to water supply. This field study was initiated to determine the influence of water deficits prior to anthesis on growth and yield of corn (Zea mays L.) grown in a sandy soil. A rain shelter was employed to provide periods without water of 21 d in 1988 and 18 d in 1989. Water deficit treatments were begun as the eighth or ninth leaf emerged from the whorl of plants for two corn hybrids. Control plots were irrigated to maintain plant available water (PAW) at 80% or greater throughout the growing season. A correlation between leaf extension and PAW revealed relative growth of deficit plants declined linearly beginning at 85% PAW, and approached zero at 25% PAW. Short‐term effects of the water deficits were delayed leaf tip emergence and decreased production of leaf area. Long‐term consequences were manifested in the form of reduced final sizes of certain leaves and internodes; delays of tassel emergence, silk emergence, the onset of grain filling by 2 to 3 d; and yield losses of 15 to 25%. Decreased yield of deficit plants was attributed to a reduction in the number of well‐developed kernels.

Forage potential of wild populations of perennial ryegrass collected from southern New Zealand farms

A ryegrass breeding programme to improve the cool season activity and summer quality of perennial ryegrass (Lolium perenne L,) in southern regions was initiated in 1986. One of the strategies assessed wild ryegrass populations from 50 dairy and sheep farms in Southland, West Otago and Westland. The plants were collected and evaluated as spaced plants in a high and low fertility site at DSIR Grasslands Gore in comparison with current ryegrass cultivars. Principal Component Analysis was used to order the performance of the ryegrass populations in relation to the observed characters of seasonal growth, tillering, crown rust infection, recurrent ear emergence and endophyte presence. Ihe collection consisted of many short-leaved densely tillered prostrate plants with high levels of crown rust infection and recurrent flowering. In comparison the cultivars had fewer, but larger tillers, rapid leaf extension and good rust tolerance. There were no strong distinguishing features between plants from dairy and sheep farms and 30% of plants had no endophyte. Selected ecotypes hybridised with New Zealand and European cultivars produced plants with better cool season growth and summer quality than standard cultivars. The ecotype germplasm is an important source in the development of new cultivars suited to the southern region. Keywords plant evaluation, Lolium perenne, ryegrass hybrids, southern New Zealand ecotypes

Winter temperatures and reproductive development affect the productivity and growth components of white clover and phalaris growing in a mixed pasture

The effects of low winter temperatures (means down to 5�C, daily air minimums to 3�C and 82 potential frost days), frost damage and reproductive development on productivity and growth components of white clover ( Trifolium repens cv. Haifa) and phalaris (Phalaris aquatica cv. Australian Commercial) growing together in a mixed pasture were studied during winter and spring. Initially there was a higher proportion of white clover in the pasture which was maintained throughout winter and early spring. Leaf appearance rates were similar for both species, but petiole extension rates of white clover were significantly less than leaf extension rates of phalaris. Growth rates were higher per tiller for phalaris than per stolon for white clover. Larger sward yields of white clover were only maintained because of the higher density of white clover growing points. The lower extension rates of white clover were due to a different temperature response curve to phalaris. Below 10�C there was little growth of white clover leaves whereas phalaris had some leaf growth down to below 5�C. There was evidence that leaf extension rates of both white clover and phalaris were stimulated by reproductive development. This had a larger effect on phalaris, but also resulted in greater susceptibility to frost damage, though the damage to phalaris was not enough to reduce leaf growth to the same level as white clover. Leaf damage from frost/low temperatures was generally marginal.

Root to shoot translocation of macronutrients in relation to shoot demand in maize (Zea mays L.) grown at different root zone temperatures

AbstractRoot growth and nutrient uptake rates of maize (Zea mays L.) are decreased at low root zone temperatures (RZT) and thus, shoot growth may be limited by nutrient deficiency. The objectives of this research were to characterize the shoot demand for nutrients per unit root at suboptimal RZT and to relate net translocation rates of N, P, K, and Ca from the roots to the shoot to shoot demand. Maize plants were grown for 11 days in soil or 8 days in nutrient solution at uniform shoot (24°/20°C, day/night) but different RZT (12°, 18°, and 24°C). The shoot base of the plants (apical shoot meristem and zone of leaf extension) was either kept within or above the cooled root zone.Shoot and root growth were significantly reduced at suboptimal RZT (12°, 18°). Lifting the shoot base above the cooling zone increased shoot growth markedly, whereas root growth was not significantly influenced. Thus, the shoot fresh weight increment day−1 g−1 root fresh weight (i.e. the shoot demand per unit root) was increased by a factor of up to 9 for plants with their shoot base above as compared to within the cooling zone.At suboptimal RZT, translocation rates of N, K, and Ca to the shoot remained low in plants with the shoot base in the cooling zone but were higher than in 24°C‐grown plants, when the shoot base was above the cooling zone. In both nutrient solution‐ and soil‐grown plants translocation rates of N, K, and Ca were closely correlated with the shoot demand per unit root but less to RZT. In contrast, the translocation rate of P was mainly affected by RZT but insensitive to shoot demand and, therefore, was always higher at a RZT of 24° than of 12°C.From these results it is suggested, that at low RZT the root‐to‐shoot translocation rates of N, K, and Ca are mainly determined by the shoot demand, whereas the translocation rate of P, regardless of the shoot demand, is reduced by a direct effect of low temperature on the roots.

Growth and water relations of simulated swards ofLolium perenneL. selection lines with contrasting leaf osmotic potentials

AbstractTwo selection lines ofLolium perenne, which had different leaf lamina osmotic potential (Ψs) when droughted in controlled environments, were grown as vegetative simulated swards in containers of soil 1·0 × 1·3 × 0·9 m deep in the glasshouse. Water was withheld during July, August and September.Under irrigation the low‐ψsline had leaf lamina and leaf base ψs0·06 MPa lower than the high‐ψsline. Under drought, the two lines did not differ significantly in lamina ψsbut leaf base ψswas 0·16 MPa lower in the low line than in the high line. Upon rewatering, most of the osmotic adjustment in the leaf bases was lost within 2 d, but that in the laminae was more stable.Herbage growth under irrigation was similar in the two lines until September, when it was greater in the highψsline. Drought reduced herbage growth, and also regrowth rates following rewatering, but the two lines did not differ in their sensitivity to drought.Selection for low ψsalso increased leaf extension rates, and reduced tillering and leaf water conductance of irrigated plants.The results are discussed in relation to selecting for improved drought resistance on the basis of physiological characters.

Evapotranspiration Rates and Growth Characteristics of Ten St. Augustinegrass Genotypes

The primary objective of this research was to determine the evapotranspiration (ET) rates of 10 well-watered St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] genotypes under field conditions and in a controlled-environment chamber with a high evaporative potential. A secondary objective was to correlate ET rate to leaf extension rate, shoot density, and abaxial and adaxial leaf blade stomatal densities. Overall ET rates among genotypes were not significantly different in the field study, but they were significantly different under the higher evaporative potential of the chamber study. ET rates under field conditions were not correlated to ET rates under chamber conditions. ET rates were not correlated to leaf extension rates in the field or chamber. ET rates in the chamber were correlated neither with shoot nor with stomatal densities. Overall ET rates in the field study were not correlated to stomatal densities, but were correlated to shoot density (r = 0.77).