Showing papers in "Planta in 1969"

Ultrastructure and functioning of the transport system of the leguminous root nodule.

Abstract: The structure of the vascular tissues of nitrogen-fixing nodules of 27 genera of legumes and some non-legumes has been investigated by light microscopy. Pisum and Trifolium nodules have been examined by electron microscopy. Attention is directed to the presence of a pericycle in the vascular bundles of the nodules. In 7 of the legumes the pericycle cells possess a wall labyrinth consisting of branched filiform protuberances. The ultrastructure of the pericycle cell cytoplasm is described: its most striking feature is its abundant rough endoplasmic reticulum. These cells surround the xylem and phloem of the bundles, and are in turn surrounded by a layer of endodermal cells with Casparian strips. The pericycle cells develop their wall labyrinth in the levels of the nodule at which the bacterial tissue becomes pigmented; in nodule senescence their cytoplasm is disrupted level with the breakdown of the bacterial tissue. A pathway for symplastic lateral transfer of assimilates exists, from the sieve elements through the pericycle, endodermis and cortex to the bacterial tissue. The apoplast within the endodermis consists largely of the pericycle wall labyrinth and the xylem. The ultrastructure of the Casparian strip resembles that of roots. Intact, detached nodules can be induced to bleed a fluid from their severed vascular tissue. This fluid is exceptionally rich in organic nitrogen, particularly amides, but does not appear to contain sugars. Comparison between its amino acid composition and that of other parts of the nodule suggests that an active uptake or secretion of nitrogenous compounds precedes export from the nodule. Special functions are suggested for the nodule endodermis and the pericycle cells in this export process.

An increase in the "inhibitor-β" content of detached wheat leaves following a period of wilting.

Abstract: Wheat seedlings were grown under a 14-hour photoperiod and the first leaves excised at the end of the eighth dark period. The effect of treatments causing wilting on the "inhibitor-β" content of such leaves was studied.When leaves were rapidly wilted (i.e. to a 6% fresh weight loss) and extracted immediately, the amount of "inhibitor-β" per leaf was found to be the same as in fresh turgid leaves. However, when the leaves were maintained in a wilted condition in darkness for a period of 110 minutes, there was a marked increase in "inhibitor-β" content.The greater the degree of wilting (i.e. up to about a 9% loss in fresh weight) the greater the eventual "inhibitor-β" content. Moreover, the increment in "inhibitor-β" was shown to be temperature dependent.The time lapse requirement and the temperature dependency of the "inhibitor-β" formation suggest an enzymic conversion from a precursor.If a similar phenomenon occurs during the wilting of intact plants then the increase in this growth inhibitor might play a role in some of the physiological changes which accompany water stress.

Gibberellic acid and the fine structure of barley aleurone cells

Abstract: This paper describes changes in the fine structure of barley aleurone cells following treatment with gibberellic acid (GA3). Within 2 hr of GA3 treatment the aleurone grains lose the spherical appearance characteristic of aleurone cells incubated in water and buffer alone. This swelling increases with increased exposure of the cells to GA3 and reaches a maximum at about 10 hr. Accompanying this increase in volume of the aleurone grains is an increase in the amount of rough endoplasmic reticulum. The relevance of these GA3-stimulated changes in aleurone-cell fine-structure to GA3-regulated α-amylase production is discussed.

Effects of temperature on the gas exchange of leaves in the light and dark.

Abstract: Evolution of CO2 into CO2-free air was measured in the light and in the dark over a range of temperatures from 15 to 50°. Photosynthetic rates were measured in air and O2-free air over the same range of temperatures. Respiration in the light had a different sensitivity to temperature compared with respiration in the dark. At the lower temperatures the rate of respiration in the light was higher than respiration in the dark, whereas at temperatures above 40° the reverse was observed. For any one species the maximum rates of photosynthesis and photorespiration occur at about the same temperature. The maximum rate for dark respiration generally is found at a temperature about 10° higher. Zea mays and Atriplex nummularia showed no enhancement of photosynthesis in O2-free air nor any evolution of CO2 in CO2-free air at any of the temperatures.

Differences in transpiration rates between tropical and temperate grasses under controlled conditions.

Abstract: Two experiments were conducted to determine the transpiration rates of tropical and temperate grasses under a range of environmental conditions. In dense populations, three temperate grasses lost considerably more water per unit leaf area than did four tropical grasses, though tropical grasses tended to produce more dry matter per unit leaf area. The efficiency of production in relation to water use was thus greater in tropical than in temperate grasses. Wheat, a temperate grass, lost water at an average rate 2.25 times that of sorghum, a tropical grass, on a unit leaf area basis when single leaves were exposed to temperatures from 17 to 32° and light intensities from 1.7 to 4.4×10(4) ergs cm(-2) sec(-1) at 0.55 μ (1,100 to 2,800 ft.-c.). The measurement of transpiration and leaf temperature indicated that latent heat loss was much more important in wheat, and sensible heat loss was more important in sorghum as means of dissipating excess energy absorbed. These findings were attributed to the greater resistance to gas diffusion offered by sorghum than by wheat stomata in each environment.

Carboxydismutase activity in plants with and without β-carboxylation photosynthesis

Abstract: A comparison was made of the activity of carboxydismutase (ribulose-1,5-diphosphate carboxylase) between higher plant species which possess the β-carboxylation (C4-dicarboxylic acid) pathway for photosynthesis and species which lack this pathway. Contrary to earlier findings no marked difference in the level of this enzyme was found between the two groups of species. Chloroplast-containing vascular-bundle-sheath cells which seem to be present only in plants with β-carboxylation apparently contain relatively high carboxydismutase activity.

Increase in femaleness of three cucurbits by treatment with Ethrel, an ethylene releasing compound

Abstract: The application of Ethrel (2-chloroethane phosphonic acid), an ethylene-releasing compound, to monoecious cultivars of cucumber and squash and an andromonoecious cultivar of muskmelon, caused a shift towards femaleness in all three species. The increase in femaleness manifested itself in several symptoms: a decrease in the number of staminate (male) flowers, an increase in the number of pistillate (female) or hermaphrodite (perfect) flowers, and a change in flowering pattern, namely, formation of female flowers at lower nodes in cucumber and squash, and formation of hermaphrodite flowers on the main axis in muskmelon where normally only male flowers are formed in this cultivar.

Time relationships of sporopollenin synthesis associated with tapetum and microspores in Lilium.

Abstract: The development of the sporopollenin orbicules (Ubisch bodies) on the tapetal cells of Lilium begins while the spores are still enclosed in the meiotic tetrads. Spherosome-like structures, the pro-orbicular bodies, accumulate in the vicinity of the plasmalemma early in the tetrad period, and are extruded into the space within the degenerating inner walls of the tapetal cells. There they acquire a coating of sporopollenin, the accretion continuing until after the release of the spores from the tetrads. Some orbicules remain attached to the plasmalemma by stalks. Synthesis of a material of the general class of sporopollenin begins in the primexine of the young spore in the mid-tetrad period, again outside of the cell membrane, but within the callose tetrad wall.

Gibberellic acid and the fine structure of barley aleurone cells : II. Changes during the synthesis and secretion of α-amylase.

Abstract: This paper describes the ultrastructural changes in barley aleurone cells following exposure to gibberollic acid (GA3) for 10-12 hr and longer. These changes involve a further proliferation of the endoplasmic reticulum (ER), distention of the endoplasmic reticulum (ER) cisternae (12-16 hr of GA3) and proliferation of vesicles from the ER and dictyosomes (14-22 hr). Accompanying these changes is a reduction in the size of the aleurone grains and a decrease in the number of spherosomes. Plastids and microbodies however appear to increase in number during this period of GA3 treatment. The relevance of these ultrastructural changes to GA3-stimulated synthesis of hydrolases is discussed.

Changes in Chloroplast Number per Cell during Leaf Development in Spinach

Abstract: The amounts of chlorophyll and nitrogen and the numbers of cells per unit area change as the green leaves of spinach plants grow and increase in size in the light. The changes in the numbers of chloroplasts per cell were measured by a new method. A 5-fold increase in the numbers of chloroplasts per cell took place in both palisade and mesophyll cells over a growing period of 10 days during which time the area of the leaves increased from 1 to 50 cm2. Proplastids were not present in the young green leaves but electron-microscope and phase-contrast observations showed the presence of grana-containing chloroplasts, many of which appeared to be undergoing division by constriction. It is suggested that the large increase in chloroplast numbers as leaf cells grow and expand in the light is from the division of differentiated chloroplasts containing grana.

The fine structure of barley aleurone cells.

Abstract: The ultrastructural morphology of both dry and water-imbibed barley aleurone cells is described. The aleurone cell is characterized by the presence of numerous aleurone grains and spherosomes. In addition, it contains organelles typical of other plant cells including structures similar to microbodies, and rough endoplasmic reticulum characterized by the presence of numerous polyribosomes. It is inferred that the morphological specialization of aleurone cells is related to their biochemical specialization.

The transport and metabolism of (14)C-labelled indoleacetic acid in intact pea seedlings.

Abstract: Part of the IAA-I- or IAA-2-14C applied at low concentrations to the apices of intact, light-grown dwarf pea seedling was transported unchanged to the root system The calculated velocity of transport in the stem was 11 mm per hour. In the root the label accumulated in the developing lateral root primordia. A large proportion of the applied IAA was converted by tissues of the apical bud, stem and root to indole-3-acetyl-aspartic acid (IAAsp). This compound was not transported. In addition evidence was obtained for the formation of IAA-protein complexes in the apex and roots, but not in the fully-expanded internodes. Large quantities of a decarboxylation product of IAA, tentatively indentified as indole-3-aldehyde (IAld), and several minor metabolites of IAA, were detected in extracts of the roots and first internodes, but not in the above-ground organs exposed to light. These compounds were readily transported through stem and root tissues. Together, the decarboxylation of IAA and the formation of IAAsp operated to maintain a relatively constant level of free IAA-14C in the root system.

A comparative study of translocation of assimilated14C from leaves of different species

Abstract: Translocation of assimilated14C from the leaves of different species varied both in the rate of export and in the total percentage moved out. Those species which are known to have high photosynthetic rates, such as the tropical grasses sorghum and millet, exported 70% or more of the assimilated14C during the first 6 h after assimilation, compared to values of 45 to 50% for tomato, castor bean,Nicotiana affinis and soybean.

Studies on abscisic acid in apple seeds

Abstract: Abscisic acid (AbA) was found to be present in non-stratified apple seeds. The evidence is based on chromatographic behaviour, fluorescence, UV-spectrum and growth inhibition in a wheat-coleoptile straight-growth test. The AbA level, as measured by this bioassay, falls considerably with progressing stratification; after 3 weeks of after-ripening no AbA could be detected in the seeds. The longer the period of stratification, the higher was the concentration of synthetic AbA necessary to inhibit germination.

Retardation of leaf senescence by benzyladenine in intact bean plants.

Abstract: Benzyladenine (BA) applied to primary leaves of intact bean plants delayed the senescence of both the leaves and the entire shoot. The retardation of senescence was manifested in higher levels of chlorophyll, protein, RNA and ribonuclease activity at all stages of development. Also, the levels of incorporation of labelled precursors into protein and RNA were enhanced. The effect of BA was largely independent of light intensity and the compound did not act merely as a nitrogen source.

Evidence against induction of protein synthesis during auxin-induced initial elongation of Avena coleoptiles.

Abstract: The timing of the response of cell elongation of oat coleoptiles to auxin was studied using a flow chamber. The lag period before a steadystate rate of growth is reached is dependent on the hormone concentration. By increasing the temperature and application of high concentrations of indoleacetic acid (IAA) the lag of the growth response can be gradually shortened, down to zero. All these data indicate that auxins do not induce or promote protein synthesis, whether at the transcriptional or at the translational level. Free (nonbound) IAA seems to be the regulator of the growth response; no metabolite of the oxindole pathway could be detected. There is no indication for an induced uptake of IAA which could explain the lag. The longitudinal distribution of IAA within the coleoptile is unequal which may add to the lag. The maximal initial growth rate is constant over a concentration range of 10-8 to 10-3 M IAA at 21°; the dose-response curve has a sigmoid shape. Under the conditions of the standard Avena section test (conducted for 24 hr) 80–90% of the initial IAA (10-5 to 10-8M) are destroyed mainly by epiphytic bacteria.

Nutrition and organ differentiation in tissue cultures of sugarcane, a monocotyledon.

Abstract: Sugarcane tissues subcultured for over 4 years had lost the capability to differentiate shoots. In freshly isolated tissues from 3 cultivars, we readily obtained shoot differentiation on Murashige-Skoog medium, but shoot differentiation was lost, apparently irreversibly, after more than one subculture on a modified White's medium. Tissue from a fourth cultivar produced only roots. The tissue cultures of all cultivars studied have the capability to form roots regardless of the length of time in culture; root formation was enhanced by treatment with dalapon (2,2-dichloropropionic acid).

The distribution of plasmodesmata in the root tip of maize.

Abstract: The distribution of plasmodesmata in different regions of the root apex of Zea mays has been analysed from electron micrographs. There are many more plasmodesmata traversing transverse walls than across longitudinal walls in all the regions studied. When the number of plasmodesmata per unit cell volume is calculated, cells in non-dividing tissue have a considerably lower value than cells in dividing tissue. Evidence for the transport of materials between cells via plasmodesmata is summarised. If it is accepted that plasmodesmata do act as channels for intercellular communication then we believe that their pattern of distribution may be a contributory factor to the process of cell differentiation.

The absorption and translocation of sodium by maize seedlings.

Abstract: The absorption and subsequent distribution of sodium and potassium has been examined in maize seedlings in short-term experiments using sodium-22 and potassium-42. The absorption and translocation of sodium by different segments of intact seedlings was also investigated. Although absorption of potassium exceeded that of sodium by a factor of about 50, there was no evidence that the entry of sodium was confined to a small region of the root. Determinations of the relative quantities of sodium and potassium in the xylem exudate of detached roots showed that the ratio of sodium to potassium decreased with increasing length of the root. These results suggested that upward movement of sodium in the xylem vessels was progressively reduced towards the basal part of the root. This conclusion was supported by microautoradiographs, which showed that although the concentration of sodium within the endodermis was greater than that in the cortex, there was an apparent decrease in the sodium content of the major xylem vessels at the basal end of the root.

Photocontrol of germination in Amaranthus caudatus.

Abstract: Germination of Amaranthus caudatus is inhibited by light, far-red being the most effective part of the spectrum. At temperatures of 25° and below there is a low final germination percentage under continuous far-red whereas above 25° there is only a delaying effect. In the presence of a saturating concentration of gibberellic acid (GA3) at 25° seeds germinate under continuous far-red although they are delayed. At 25° seeds exposed to 48 hr far-red fail to germinate when transferred to darkness. This induced dormancy can be broken by a single short exposure to red light given at any time after the far-red illumination. This effect of short red can be reversed by a subsequent short period of far-red indicating that the seeds are phytochrome controlled. Although most seeds have escaped from the reversing effect of short far-red after an intervening dark period of 5 hours, germination is greatly reduced by continuous far-red at this time. Results of exposing seeds to varying periods of far-red before and after dark imbibition are interpreted in terms of a continual production of phytochrome in its active P fr form and a requirement for P fr action over a long period of time. Effects of intermittent and continuous low intensity far-red on the inhibition of germination provides further evidence for a low energy photoreaction involving phytochrome. Effects on Germination Index of continuous illumination with various light sources maintaining different P fr /P total ratios have been investigated. The results suggest that the proportion of phytochrome in the P fr form is the most important factor in the regulation of germination. A scheme for the phytochrome control of germination in Amaranthus caudatus is presented and possible explanations for the dependence on P fr /P total ratio are discussed.

Cell-wall-hydrolysing enzymes in wall formation as measured by pollen-tube extension.

Abstract: Cell-wall-softening enzymes affect the plasticity of the tip wall of pollen tubes and modity tube elongation. Length of pear pollen tubes is increased by the addition of β-1,3-glucanase at the beginning of in-vitro germination. The longer tubes after 3 hours are primarily the result of earlier germination. Application of β-1,4-glucanase or pectinase to germinating pollen does not affect germination but enhances the growth rate of 1-hour-old pollen tubes. The stimulating effects of β-1,4-glucanase and pectinase are additive. Denatured enzymes had no effect. Proteinase, pectin esterase, acid phosphatase and α-amylase only inhibited growth and germination. Replacing the medium 1 hour after germination begins stops pollen-tube growth; growth can be restored by adding cellulase-pectinase mixtures to the replacement medium. These results provide evidence that cellulase and pectinase are important in pollen-wall extension, and that callose-hydrolyzing enzymes are involved in pollen germination but not wall extension.

Prolonged reduction of acetylene by detached soybean nodules.

Abstract: Detached soybean nodules reduce acetylene at a constant rate for at least 8 hours provided that (1) only small quantities of nodules per unit volume of gas are used, (2) when incubated in aqueous media they are given sufficient oxygen and shaken, (3) they are not allowed to dry out.

Phytochrome in seeds of Amaranthus caudatus.

Abstract: Dry seeds of Amaranthus caudatus show little or no photoreversible absorption changes, attributable to phytochrome. During imbibition phytochrome appears in two phases, one immediately after sowing and the second after about 8 hr. Experiments at different temperatures and under continuous illumination with red, far-red and blue light suggest that there are two pools of phytochrome. The first phase in the appearance of phytochrome could be due to the change in optical properties of the sample on hydration or to rehydration of inactive phytochrome, or both. The second phase probably represents phytochrome synthesis. It is absent at 0° and precedes the water uptake associated with germination by some 10 hr. This second pool of phytochrome does not accumulate in red and blue illuminated seeds indicating that the rate of P fr decay is more rapid than the rate of phytochrome synthesis. The difference spectra of phytochrome in both 2 hr imbibed seeds and 72 hr old seedlings show peaks of absorption at 663 and 735 nm. The presence of P fr in dark imbibed seeds and the process of “inverse reversion” of P r to P fr in darkness have been demonstrated. The results are discussed in relation to previous hypotheses for the mechanism of photocontrol of Amaranthus seed germination.

Nitrogen Metabolism of Spirodela oligorrhiza

Abstract: Spirodela oligorrhiza grown in axenic culture was able to use either ammonium, nitrate, or nitrite as sole source of nitrogen, although the morphology of the plants was affected. Plants utilizing ammonium contained higher levels of NH4, arginine, asparagine and glutamine than did those utilizing NO3, whereas concentrations of other amino acids were similar. The utilization of NH4 inhibited that of NO3 by inhibiting, at least partially, NO3 uptake, and by inhibiting almost completely the reduction of NO3 to NO2. NO2 also inhibited the utilization of NO3. NH4 and NO2 were taken up and assimilated simultaneously when they were supplied together in the medium.

Abscisic-acid-stimulated rooting of stem cuttings.

Abstract: Abscisic acid (ABA) has been found to stimulate rooting of stem cuttings of mung beans and English ivy. ABA partially overcame the inhibitory effect of gibberellic acid on root formation of mung bean cuttings but at the concentrations used did not overcome the inhibitory effect of kinetin on root formation.

The effects of flooding on the export of gibberellins from the root to the shoot.

Abstract: Gibberellin (GA)-like substances are shown to be present in the bleeding sap of tomatoes. It is demonstrated that these substances can promote stem elongation in intact tomato plants. Waterlogging of the root system inhibits stem growth and severely reduces the export of GAs from the root to the shoot in the xylem sap. It is suggested that decline in growth rate following waterlogging may, in part, be due to the reduction in the supply of GAs to the shoot.

The specificity of the auxin transport system

Abstract: In an effort to examine the specificity of the auxin transport system, the movement of a variety of growth substances and of auxin analogues through corn coleoptile sections was measured in both the basipetal and acropetal directions. In contrast to the basipetal, polar transport of the auxins indoleacetic acid (IAA) and 2,4-dichlorophenoxyacetic acid, no such movement was found for benzoic acid or for gibberellin A1. A comparison of the α- and β-isomers of naphthaleneacetic acid showed that the growth-active α-form is transported, but not the inactive β-analogue. Both the dextro (+) and leavo (-) isomer of 3-indole-2-methylacetic acid showed the basipetal movement characteristic of IAA, the dextro isomer being more readily transported than the (-)-form. In this instance, too, the transport was roughtly proportional to the growth promoting activity. The antiauxin p-chlorophenoxyisobutyric acid inhibited auxin transport as it inhibited auxin-induced growth. These results agree with the hypothesis that processes involved in auxin transport are closely linked to or even identical with the primary auxin action.

Ethylene and carbon dioxide as mediators in the response of the bean hypocotyl hook to light and auxins

Abstract: Ethylene inhibits hook opening in the bean hypocotyl and at high concentrations induces closure of the hook. Indoleacetic acid and 2,4-dichlorophenoxyacetic acid, whose inhibitory effect on hook opening resembles that of ethylene, stimulate ethylene production from the hook tissue, and this ethylene production is physiologically active in inhibiting hook opening. It is concluded that the inhibition of opening by auxin is due at least in a major part to auxin-induced ethylene production by the hook tissue.

Changes in phenylalanine ammonia-lyase activity during xylem differentiation in Coleus and soybean

Abstract: Xylem differentiation was induced in cultured Coleus internode slices when grown in the light on a simple agar/sucrose/IAA medium and in darkgrown soybean callus tissue when cultured on a complex defined medium containing 5×10-7 M kinetin. In the Coleus system, the activity of phenylalanine ammonialyase followed the same time course as the formation of lignified wound vessel members. The specific activity of PAL was higher in the soybean callus tissues grown on 5×10-7 M kinetin, which produced tracheary elements, than in the soybean tissue grown on 10-8 M kinetin, which did not produce tracheids. These observations suggest that PAL is a “marker enzyme” for xylogenesis and that PAL activity may be a rate limiting step in lignification.