Diffusible and Extractable Gibberellins in Bean Cotyledons in Relation to Dwarfisni

Dwarfism in bean plants (Phaseolus vulgaris L.) is investigated in relation to the diffusible and extractable gibberel-lins in cotyledonary tissues. These gibberellins were partitioned into four parts prior to thin layer chromatograplty: non-acidic and acidic ethyl acetate fractions, and non-acidic and acidic butanol fractions. Cotyledonary segments from a tall plant (cv. Kentucky Wonder) seem to diffuse, preferentially acropetally, more gibberellins in each fraction than those from a dwarf plant (cv. Masterpiece). The diffusion increases with the length of the segments and decreases with period after sowing. From experiments on extraetable gibberellins, however, it is concluded that these phenomena actually result from differences in the gibbereliin contents of the tall and the dwarf plants, from differences in the gibberellin contents of the distal and proximal parts of cotyledons, and from the gibberellin contents before and after imbibition. Ten kinds of gibberellin-Iike substances are detectable in the diffusates, exudates and extracts from the cotyledons of both the plants; two in the non-acidic ethyl acetate, three in the acidic ethyl acetate (GA₁, GA₆ and another), two in the non-acidic butanol, and three in the acidic butanol frac—tion. They are almost identical in quality in the dwarf and tall plants, but in the latter they are more abundant in the cotyledons, particularly in their distal part. With respect to the change in content during the period after sowing, the gibberellin-Iike substances are classified in three groups; unchanging, decreasing (GA₁, GA₆, others) and increasing (butanol soluble glucosyl esters and glucosides of gibberellins)-. The increase of glucose-bound gibberellins and the decrease of free gibberellins during the sowing period suggest the occurrence of conversion. This is obvious only in the tall plants. The gibberellin content in cotyledons is higher in the tall plant than in the dwarf plant. Thus, the marked hypocotyl growth in the tall plants may be dependent on the higher content of gibberellins in their cotyledons and on the higner rate of conversion from free to bound forms.     

Nodulation in Light- and Dark-grown Macrozamia communis L. Johnson Seedlings in Sterile Culture

The ability of aseptically cultured Macrozamia communis seedlingsto form apogeotropic root nodules in light and darkness wasexamined. In darkness, apogeotropic root nodules developed atthe junction of the primary-root and the cotyledonary node.More acropetally formed lateral-roots were not nodular and weretypical ageotropic or plagiotropic secondary-roots. When thesecultures were exposed to light, all of the roots became typical,apogeotropic cycad root nodules. Light stimulated dichotomousbranching of nodules previously formed in the dark. Nodulesexposed to light were more papillose than those maintained indarkness. Light also inhibited primary and secondary-root elongation. Macrozamia communis, cycad apogeotropism, dichotomous branching, light induction, root nodulation sterile culture     

The Effect of Red Irradiation on Plastid Ribosomal RNA Synthesis in Dark-grown Pea Seedlings

Dark-grown pea seedlings (Pisum sativum L.) were irradiated for a short period each day with low intensity red light (662 nm), red light immediately followed by far red light (730 nm), or far red light alone. Other plants were transferred to a white light regime (14 hours light/10 hours dark). There was no change in the amount of RNA in the tissue on a fresh weight basis after the various treatments. However, compared with dark-grown seedlings, those plants irradiated with red light showed an increase in the net RNA content per stem apex. In addition there was a two- to three-fold increase in ribosomal RNA of the etioplasts relative to the total ribosomal RNA. These increases were comparable to those found in plants grown in the white light regime. The changes were much smaller if the dark-grown plants were irradiated either with red light followed by far red light, or with far red light alone. Thus continuous light is not essential for the production of ribosomal RNA in plastids, and the levels of ribosomal RNA found in chloroplasts can also be attained in etioplasts of pea leaves in the dark provided the leaf phytochrome is maintained in its active form.     

Appearance of Three Chloroplast Isoenzymes in Dark-grown Pea Plants and Pea Seeds

Activity peaks characteristic of the chloroplastic Calvin cycle enzymes triose-phosphate isomerase, ribose 5-phosphate isomerase, and fructose 1,6-diphosphate aldolase are found in isoelectric focusing patterns of dark-grown pea (Pisum sativum) seedlings and seeds. Apparently, in this higher plant these three chloroplastic isoenzymes can be formed in the absence of light and of chloroplast formation.     

Microbodies (Glyoxysomes and Peroxisomes) in Cucumber Cotyledons: Correlative Biochemical and Ultrastructural Study in Light- and Dark-grown Seedlings

The changes in activities of glyoxysomal and peroxisomal enzymes have been correlated with the fine structure of microbodies in cotyledons of the cucumber (Cucumis sativus L.) during the transition from fat degradation to photosynthesis in light-grown plants, and in plants grown in the dark and then exposed to light. During early periods of development in the light (days 2 through 4), the microbodies (glyoxysomes) are interspersed among lipid bodies and contain relatively high activities of glyoxylate cycle enzymes involved in lipid degradation. Thereafter, these activities decrease rapidly as the cotyledons expand and become photosynthetic, and the activity of glycolate oxidase rises to a peak (day 7); concomitantly the microbodies (peroxisomes) become preferentially associated with chloroplasts.     

Some Properties of Phytochrome Isolated From Dark-grown Oat Seedlings (Avena sativa L.)

Phytochrome was partially purified from etiolated seedlings of Avena sativa L. Several properties of the red-absorbing (P_R) and far-red absorbing (P_FR) forms of the pigment were compared. The 2 forms could not be shown to differ with respect to their sedimentation velocity in sucrose density gradients, elution volume from Sephadex G-200 columns, binding properties on calcium phosphate, or electrophoretic mobility. P_FR, however, was more labile than P_R during precipitation with 50% ammonium sulfate. Sephadex G-200 elution diagrams obtained with fresh phytochrome preparations revealed 2 components of different molecular weights, 1 roughly 180,000, and 1 roughly 80,000. Native phytochrome had an absorption spectrum in vivo showing an absorption maximum for P_R of 667 nm. Both the large and small forms of phytochrome mentioned above can be maintained with an absorption maximum for P_R of 667 nm. However, allowing them to remain for several hours as P_FR, even at 4°, shifted this peak to 660 nm. The protein conformational change during phytochrome transformation may be quite small, though the various comparative techniques used do not strictly rule out a fairly large one. The need for maintaining the pigment as P_R during all steps of purification, but particularly during ammonium sulfate precipitation is underscored.     

Photoactivation of Oxygen-evolving System in Dark-grown Spruce Seedlings

Plastids prepared from dark-grown spruce seedlings showed a negligible activity of photosystem II, and no fluorescence variation was observed during actinic illumination. The photosystem II reaction centre, however, was present in primary thylakoids. Exposure of such seedlings to continuous light induced the development of photosystem II activity via three stages (rapid, lagged and gradual), and the variable fluorescence appeared. The rapid development of photosystem II may be attributed to the activation of the oxygen-evolving system, possibly the manganese-catalyzing site, and the lagged and gradual developments may be closely related to the formation of thylakoid membranes and their assembly to grana.     

Calcium Deficiency of Dark-grown Seedlings of Phaseolus vulgaris L

Hypocotyl collapse in dark-grown seedlings of Phaseolus vulgaris cv. Pinto was due to calcium deficiency. There was no evidence of an associated pathogen. The number of seedlings with hypocotyl collapse decreased and the mean hypocotyl length increased when increasing levels of calcium (0-100 micrograms per gram) were supplied in an external nutrient solution to seedlings grown under sterile conditions.     

莲胚芽暗萌发过程中的光合系统发育研究

被子植物在黑暗中萌发生长不能合成叶绿素和建成光合系统,但是将莲（Nelumbo nucifera Geartn.)胚芽置于黑暗中萌发生长时,却可以清楚地观察到它的光合系统进行发育;首先,在原位低温荧光光谱上,LHCⅡ的荧光发射逐步红移变成典型的PSⅡ荧光发射,同时随着萌蝗延长,PSⅠ的荧光发射也从无到有,逐渐增强;其次,对暗萌发10d莲苗的叶绿体进行部分变性凝胶电泳分析也得到了PSⅠ的叶绿素蛋白复合物条带。通过Western blots的蛋白免疫检测,在暗萌发莲苗中也证实了LHCⅠ组分中有Lhca1的存在;最后,对暗萌发莲苗叶绿体的PSⅡ和PSⅠ电子传递活性测量结果表明,在暗中发育形成的PSⅡ和PSⅠ核心都是有光化学活性的。章讨论了莲胚芽暗萌发过程中进行光合系统发育的原因。     

Effects of Auxin Transport Inhibitors on Gibberellins in Pea

The effects of the auxin transport inhibitors 2,3,5-triiodobenzoic acid (TIBA), 9-hydroxyfluorene-9-carboxylic acid (HFCA), and 1-N-naphthylphthalamic acid (NPA) on gibberellins (GAs) in the garden pea (Pisum sativum L.) were studied. Application of these compounds to elongating internodes of intact wild type plants reduced markedly the endogenous level of the bioactive gibberellin A₁ (GA₁) below the application site. Indole-3-acetic acid (IAA) levels were also reduced, as was internode elongation. The auxin transport inhibitors did not affect the level of endogenous GA₁ above the application site markedly, nor that of GA₁ precursors above or below it. When plants were treated with [¹³C,³H]GA₂₀, TIBA reduced dramatically the level of [¹³C,³H]GA₁ recovered below the TIBA application site. The internodes treated with auxin transport inhibitors appeared to be still in the phase where endogenous GA₁ affects elongation, as indicated by the strong response to applied GA₁ by internodes of a GA₁-deficient line at the same stage of expansion. On the basis of the present results it is suggested that caution be exercised when attributing the developmental effects of auxin transport inhibitors to changes in IAA level alone. Received April 13, 1998; accepted April 14, 1998     

Growth and Photosynthesis of Mutant Pea Seedlings

The recessive of gene, producing tendrils in place of leaves,and the recessive st gene, reducing stipule size, produce phenotypesof pea that are termed leafless (afafstst) and semi-leafless(afafStSt). Photosynthesis and growth of these two types werecompared with the conventional phenotype (AfAfStSt) during thefirst 9 days of post-emergent growth. The conventional seedlingshowed faster net photosynthesis per unit dry weight than theleafless phenotype, whilst the semi-leafless seedlings wereintermediate. Differences in dark respiration were small butleafless seedlings had significantly higher rates soon afteremergence. Where the three phenotypes used were isogenic, except for ofand st, the rates of shoot growth were in the same ranking orderas net CO₂ uptake. With three other genotypes, representingthe three phenotypes, more similar shoot growth was found betweenthe conventional and semi-leafless phenotype, possibly becauseof compensating differences in embryonic axis size. The ratesof growth of roots and the rates of dry weight loss from thecotyledons showed no consistent differences between phenotypes. The results are discussed in relation to the potential for thesemi-leafless phenotype as an alternative to the conventionalphenotype for the dried pea crop. Pea seedling, Pisum sativum, leafless pea, photosynthesis, seedling growth     

Temperature and Anoxic Injury in Pea Seedlings

Anaerobic incubation of newly germinated pea seedlings understerile conditions on moist filter paper was used to distinguishbetween the physical effects of excess moisture on soaking injuryand the metabolic consequences of prolonged anoxia. Over a 4d incubation period seedling death after anoxia fell as temperaturewas reduced from 25 to 5 °C. Internal ethanol concentrationsincreased with length of anaerobic incubation but fell withdecrease in temperature. For all combinations of temperaturewith length of anaerobic incubation, seedling survival was alwaysinversely related to ethanol concentration. An internal ethanolconcentration of 60 µM appeared to be a threshold valuefor seedling survival as anoxic death occurred only when thisconcentration was exceeded.     

Nitrate Uptake by Dark-grown Corn Seedlings: Some Characteristics of Apparent Induction

Five-or six-day old seedlings of corn (Zea mays L.) were exposed to 0.25 mm Ca(NO₃)₂, 1.0 mm sodium 2-[N-morpholino]-ethanesulfonate, 5 μg Mo per liter and 50 μg of chloramphenicol per ml at pH 6. Nitrate uptake was determined from depletion of the ambient solution. The pattern of nitrate uptake was characterized, after the first 20 minutes, by a low rate which increased steadily to a maximal rate by 3 to 4 hours. Transfer of nitrate to the xylem did not totally account for the increase. Development of the maximal accelerated rate did not occur at 3 C with excised roots nor with seedlings whose endosperm had been removed. Use of CaCl₂ rather than Ca(NO₃)₂ resulted in a linear rate of chloride uptake during the first 4 hours, and chloride uptake was not as restricted by endosperm removal as was nitrate uptake.     

Activation of 80S Maize Ribosomes by Red Light Treatment of Dark-grown Seedlings

The in vitro protein synthetic activity of 80S ribosomes from leaves of dark-grown corn seedlings was enhanced (at low Mg²⁺ levels) by a 5-minute red light treatment applied 2 hours prior to tissue harvest. The effect was completely reversed by an immediate brief far red treatment, suggesting that ribosome activation is controlled by the phytochrome system. Experiments in which the interval between light treatment and tissue harvest was shortened indicate that the response was quite rapid. The initial increase in activity was detected within 30 minutes, followed by a rapid increase during the next 1.5 hours. No further increase occurred after 2 to 3 hours.     

Isoxazolin-5-ones and Amino Acids in Root Exudates of Pea and Sweet Pea Seedlings

Seeds of Pisum sativum L. cv Finale and Lathyrus odoratus L. cv Spencer were germinated aseptically in moistened sand in the dark. At several stages, the amino acid composition of the exudate and of the corresponding roots was analyzed. A number of common amino acids, including homoserine, were exuded by the growing seedling root in an early stage and were partly reabsorbed later. A number of uncommon amino acids, including several isoxazolin-5-one derivatives, uracil alanines, l-γ-glutamyl-d-alanine, and α-aminoadipic acid were exuded at different rates.