摘要:

The senescence pattern of the three uppermost leaves of four rice (Oryza sativaL.) cultivars viz. Ratna, Jaya, Masuri and Kalojira was analysed in terms of decline of chlorophyll and by measuring [32P]‐phosphate retention and export from leaf to grains during the reproductive development. With the advancement of reproductive development, the cultivars Masuri and Kalojira showed a sequential mode of senescence, but the cultivars Ratna and Jaya showed a non‐sequential mode of leaf senescence where the flag leaf senesced earlier than the older second leaf. Foliar spraying with benzyladenine (0.5 mM) significantly delayed, and abscisic acid (0.1 mM) accelerated, leaf senescence. In untreated control plants, the second leaf had the highest export of labelled phosphate among the leaves at the grain formation stage (0–7 days) in Masuri and Kalojira. This was compensated by the flag leaf at the grain development stage (7–14 days), whereas export of [32P]‐phosphate was highest from the flag leaf of Ratna and Jaya at the grain development stage. Compared with the control, benzyladenine treatment caused higher retention of [32P]‐phosphate in the leaves and also export to the grains, but abscisic acid treatment gave lower retention and export of [32P]‐phosphate to the grains.The amount of [32P]‐phosphate export from a mother to a daughter shoot developed in the axil of the second leaf of plants with the panicle removed, was less than that to panicles remaining on control plants of all cultivars. When the panicle had been excised, the greatest export of [32P]‐phosphate took place from the second leaf to the daughter shoot in all cultivars. Excision of the panicle delayed leaf senescence as compared with intact controls and maintained an age‐related leaf senescence pattern in all the four cultivars. The results presented here demonstrate that mobilization of phosphorus from leaf to grains, regardless of cultivar or age and position of the leaf, correlates well with the sene

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1985.tb02386.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Rhizosheaths (sheaths of sand grains that form around the roots of some grasses) are common in perennial grasses that colonise sandy substrates. It has been hypothesised that rhizosheaths increase water availability by increasing the efficiency of water absorption. Others have suggested that rhizosheaths act as storage reservoirs for water. In either case rhizosheaths undoubtedly play an important role in the water relations of these grasses.In an attempt to evaluate the main function of rhizosheaths, we developed a finite element cylindrical water flow model which enabled us to simulate water uptake byOryzopsis hymenoides(Roem, and Shult.) Ricker. This model allowed us to estimate total water uptake by root systems with and without rhizosheaths and to compare these values to the extra water stored within the rhizosheath. The results of this study suggest that the presence of rhizosheaths is more important in reducing the total resistance to water flow within the rhizosphere than in enhancing water storage.

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1985.tb02387.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

An important physiological feature of chaparral shrubs is the development of low water potentials during periods of drought characteristic of southern Californian summers. Changes in tissue elasticity may be an important characteristic allowing these low water potentials to be reached and maintained without the development of detrimental water deficits. To examine this possibility, seasonal changes in tissue elasticity were measured in 3 species of chaparral shrubs,Arctostaphylos glandulosaEastw.,Quercus dumosaNutt. andCeanothus greggiiGray., by the pressure‐volume method. Tissue elasticity was characterized using graphs of the modulus of elasticity plotted as a function of turgor pressure, and maximum values of the elastic modulus. The moduli of elasticity of the shrubs increased following leaf emergence in the spring, were highest during periods of low soil water potential, and tended to decrease following the summer‐fall drought period. Increases in tissue elasticity facilitate water uptake from drying soils, but result in greater turgor loss during tissue dehydrat

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1985.tb02388.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

UsingAvena sativaL. cv. Victory oat seedlings and excised p‐1 stem segments (including the p‐1 and p‐2 internodes) the effect of exogenously supplied ethylene and the removal of ethylene on internodal extension and gravitropic bending was assessed. Similarly, the ability of the excised system to respond to gravistimulation was assessed in the presence of inhibitors of ethylene action (AgNO3) and ethylene synthesis (3,5‐diiodo‐4‐hydroxybenzoic acid and benzyl isothiocyanate; BITC). The production of ethylene from both intact and excised systems was also measured from 0 to 48 h after gravistimulation, relative to vertical controls.Although gravitropic curvature is initiated, and indeed enters the most rapid phase of upward bending during the first 6 h, there is no difference in ethylene production between vertical and geostimulated plants during this period. The ethylene production of gravistimulated plants rises sharply to a maximum at 24 h, then decreases steeply to almost the control level by 48 h, at which time the rate of upward curvature is diminishing. Neither the addition nor removal of ethylene, nor the addition of inhibitors affecting ethylene‐action (AgNO3) or synthesis (DIHB) influence gravitropic bending or internodal extension in excised segments. Although the ethylene synthesis inhibitor BITC showed down the rate of upward bending, this effect could not be reversed by addition of ethylene. We conclude that the burst in ethylene production that develops in leaf‐sheath bases (pulvini) after they have started to curve upwards is not primary to the induction of curvature. We further suggest that ethylene has no major effect or role in the induction of upward bending after gravistimulation.The metabolism of high specific activity gibberellin A1([3H]‐GA1) in the excised system was assessed during 1, 2 and 4 h of gravistimulation. Changes in endogenous GAs and GA metabolism have been shown previously to be correlated (at the later stages) with gravistimulated bending in intactAvenashoots. The excised segments ‘leaked’ free [3H]‐GAs and [3H]‐GA glucosyl conjugate‐like substances into the bathing medium, and this was a confounding factor. Nevertheless, gravistimulated stem segments, and especially the bottom half of the segment, were significantly less leaky then vertical segments. Thus, just 1 h after gravistimulation, bottom segment halves retained 22% more precursor [3H]‐GA1, 36% more free [3H]‐GA‐like metabolites, and 48% more [3H]‐GA glucosyl conjugate‐like metabolites than vertical segments. In contrast, the 1 h gravistimulated top halves retained slightly less (1–4%) precursor [3H]‐GA and free [3H]‐GA metabolites, but 21% more [3H]‐GA glucosyl conjug

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1985.tb02389.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Investigations of Al phytotoxicity, including the identification of the Al species responsible for toxicity, require a rapid assay procedure employing very low concentrations of Al and a chemically simple rooting medium. Root elongation in newly germinated red clover (Trifolium pratenseL. cv. Kenland) was inhibited by submicromolar concentrations of Al. Ca2+at concentrations of at least 0.2 mMwas essential for optimal elongation in control seedlings. Ca2+also relieved Al toxicity with the net effect that maximum reduction of elongation by 1 μMAl was achieved at 0.2 mMCa2+. Elongation in control seedlings was at least 90% of maximum from pH 4.5 to 5.7. Increases in pH relieved Al toxicity so that maximum sensitivity to 1 μMAl occurred at pH 4.7. As a consequence of these experiments and other considerations we chose for our basic assay a medium composed of 0.2 mMCaSO4adjusted to pH 4.5 with H2SO4, variously supplemented with Al2(SO4)3.Day‐old seedlings were incubated in this aerated medium in the dark at 23°C for one day. No additions of other solutes increased the sensitivity of the assay, but amelioration of Al toxicity was effected by Mg2+, F‐, phosphate and citrate. Increases in ionic strength per se had comparatively little effect on the toxic effects of Al. Two barley cultivars (Hordeum vulgareL. cv. Dayton and Kearney) and two wheat cultivars (Triticum aestivumL. cv. Hart and Thorne) known to differ in sensitivity to Al were reliably separated at submicromolar Al concentrations by the assay procedure, which was slightly modified. Suggestions for the improvement of the assay and for applications to future research are o

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1985.tb02390.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Leaf mesophyll cells were isolated from developing first trifoliate leaves ofGlycine max(L.) Merr cv. Fiskeby V using a mechanical isolation procedure combined with low speed centrifugation. Cell yields of 17 ± 1.7% were routinely obtained with 55–75% intactness, as assessed by staining techniques, fluorescence transients and the ability of cells to convert to protoplasts after enzyme treatment. Rates of leaf photosynthesis were maximal in 27‐day‐old plants [280 μmol O2evolved (mg chlorophyll)‐1h‐1], from which isolated cells and protoplasts gave rates of up to 140 μmol O2evolved (mg chlorophyll)‐1h‐1. Results are discussed in relation to leaf development and cell status during the attainment of photosynt

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1985.tb02391.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

The application of gibberellic acid (GA3,10 μM) as a root drench to 16‐day‐old plants ofPhaseolus vulgarisL. cv. Masterpiece stimulated growth of the stem internodes and reduced root growth. GA3treatment did not affect the export of14C from a primary leaf to which [14C]‐sucrose was applied, but greatly increased upward translocation to the elongation region of the stem at the expense of transport to the hypocotyl and root system. The observed changes in the patterns of growth and [14C]‐labelled assimilate distribution were correlated with an increase in the specific activity of acid invertase in the elongating stem internodes and a decrease in invertase activity in the hypocotyl and root. Sucrose concentration in the elongating internodes fell substantially after treatment with GA3while the concentration of hexose sugars increased. We suggest that by stimulating acid invertase synthesis in the elongating internodes, GA3acts to establish a more favourable sucrose gradient between these sinks and source leaves. Under source‐limiting conditions this, in turn, will lead to a reduced rate of assimilate translocation to competing sinks in the r

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1985.tb02392.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Sunflower,Helianthus annuusL. cv. INRA 6501, plants were grown in a gravel culture subirrigated with Hoagland nutrient solution, at photosynthetically active radiation levels of 15, 30 and 60 W m‐2at a daylength of 16 h, a temperature of 20°C and a relative humidity of 60% throughout. Development of the plant and growth of the leaves were measured. High irradiance accelerated development proportionally in all phases from germination, through leaf initiation, primordial flower formation and the maturation of all plant organs until anthesis. High irradiance levels stimulated the expansion of the growing shoot, which produced more and larger primordia. Under constant conditions the ratio between leaf initiation rate and mature length of a leaf remained constant, although the growth patterns [relationship between relative growth rate (RGR) and organ age] of successive leaves were not similar. Consequently, it may be assumed that, as in poplar, the increasing size of the growing shoot reflects the increase of the vascular system of sunflower. The growth patterns of the leaves depend on the developmental stage of the plant and, in the young primordial stage, also on irradiance level. In the linear phase of growth the growth pattern is independent of irradiance lev

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1985.tb02393.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Cell wall preparations of the ectohydric forest mosses,Pleurozium schreberi(Brid.) Mitt. andHylocomium splendens(Hedw.) B. S. G. contain polymerized lipids consisting of hydroxy acids, dicarboxylic acids, fatty acids, fatty alcohols and unidentified components. The finding of polymerized lipids in ectohydric mosses, which have highly permeable cell walls, indicates that the polymers do not form an effective barrier against water and nutrients, at least not in the cell walls of these mosses. The youngest parts ofP. schreberiandH. splendenscontained 2.0 and 1.6 mg polymerized lipids, respectively, on a dry cell wall weight basis. In the senescent, greyish‐green parts ofP. schreberiand in the one‐year‐old shoot tissue ofH. splendensthe corresponding amounts were about 1.5‐fold. In both species the increase was due to increases in hydroxy acids, particularly dihydroxyhexadecanoic acids, dicarboxylic acids, unknown components and, in the case ofH. splendens, also an increase in fatty acids. The increase may be related to the maturation of the cell walls. In still older shoot parts the amounts of polymerized lipids decreased in both species, and remained low until final decay of the tissues into small particles. A slight increase in the amount of the polymerized lipid monomers was found in the oldest and most decomposed parts ofH. splendens, probably indicating a better resistance to decay than for other cell wall components. These findings are discussed in relation to what is known from the ectohydric peat‐formingSphag

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1985.tb02394.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Sucrose synthase (EC 2.4.1.13) activity in young growing leaves was highest in the leaf base in eggplants (Solanum melongenaL.), cassava (Manihot esculentaCrantz), grapevine (Vitis viniferaL.), and in the leaf sheath of sugar cane (Saccharum of ficinarumL.) and maize (Zea maysL.). In addition, increasing sucrose synthase activity was measured towards the edge of growing eggplant leaves while the activity in mature leaves was highest in the midrib. The activity of acid and alkaline invertase was very low in the midrib but higher in the blade of fully expanded eggplant leaves. Highest invertase activities were found in younger growing leaves. It was concluded that in growing leaves a close relationship might exist between the activity of sucrose synthase and the import of sucrose from source leaves.Detachment of mature eggplant leaves led to a 2‐ to 3‐fold increase of sucrose synthase activity in blade and midrib of these leaves. In contrast, invertase activity decreased after detachment in both leaf blade and midrib. It was concluded that the rise in sucrose synthase activity might have been caused by the observed increase of sucrose concentration in detached leaves and that sucrose synthase might have an important role in the regulation of sucrose content of the conducting tis

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1985.tb02395.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY