Studies on Extension Growth in Coleptile Sections: III. THE INTERACTION OF TEMPERATURE AND {beta}-INDOLYLACETIC ACID ON SECTION GROWTH

Wheat coleoptile sections were grown at various temperaturesfrom 1–40°C. in water and solutions of the sodiumsalt of ß-indolylacetic acid (NaIAA) ranging fromlow to very high concentrations (0.001 p.p.m. to 10,000 p.p.m.). Growth-time curves are sigmoid, obviously so under conditionsunfavourable to growth, less clearly as conditions either oftemperature or growth-substance supply are improved, the pointof inflection moving nearer to zero time. The growth-rate isreduced by temperatures below the optimum, and although growthcontinues for a longer time, final section length is also reduced.Such reductions are also brought about by sub-optimal levelsof NaIAA and by supra-optimal levels of both factors. In the test method employed, sections are grown in closed tubesof small volume, and after a time lose turgidity and becomewaterlogged; the onset of this condition is accelerated by hightemperature or growth-substance concentration, and greatly delayedby low temperature. Under comparable conditions, but with thetubes uncorked, flaccidity is delayed even at high temperatureor high concentration of NaIAA. If sections are transferred from one temperature to anotherthe change in growth-rate is abrupt; effects of transfer onfinal length are complex. A contour diagram represents the idealized relationships betweensection growth and temperature and NaIAA supply over their wholerange of effectiveness. Relations between temperature and growthin other systems are briefly discussed.     

THE EFFECTS OF TRITIATED THYMIDINE INCORPORATION ON SECONDARY ROOT PRODUCTION BY PISUM SATIVUM

Hummon , Margaret R. (Montana State U., Missoula.) The effects of tritiated thymidine incorporation on secondary root production by Pisum sativum. Amer. Jour. Bot. 49(10): 1038–1046. Illus. 1962.—Most studies of effects of radiation on plants have involved a general exposure of all the cells and tissues of an organ or entire plant. Tritiated thymidine offers a tool for selective irradiation of the nucleus with little effect on the cytoplasm of a cell. Furthermore, differential incorporation due to variation in the pattern of DNA synthesis permits selective irradiation of cells and tissues. In this study, developing primary roots of Pisum sativum were submerged for brief periods in a solution of tritiated thymidine. This resulted in an alteration of the lateral root pattern. In the area corresponding to the region of elongation during treatment, subsequent lateral root production was suppressed. This correlated with the portion of the root in which there was incorporation of tritiated thymidine into a high percentage of pericycle nuclei. Abnormal development of vascular tissues also occurred, with evidence of altered polarity in the xylem. Although incorporation also occurred in the apical meristem, the latter was not affected at this level of exposure. Thus, differential sensitivity as well as differential incorporation may have been involved in producing the temporary alteration of lateral root production.     

EFFECTS OF NEAR ULTRAVIOLET AND VISIBLE RADIATIONS ON CELL CYCLE KINETICS IN EXCISED ROOT MERISTEMS OF PISUM SATIVUM

Near-ultraviolet and visible radiations increased the duration of the mitotic cycle in excised pea root meristems primarily by lengthening the duration of the pre-DNA synthetic period (G₁). All radiations tested shortened the duration of the post-DNA synthetic period (G₂). The most pronounced effects were exhibited by green radiation, which lengthened the duration of the cell cycle, G₁, DNA synthesis (S), and mitosis (M), and shortened the duration of G₂. Progression of cells arrested by starvation in G₁ and G₂ into DNA synthesis and mitosis was also affected by light treatments. Green radiation appeared to arrest a group of cells in DNA synthesis as well as in G₁ and G₂. Meristems receiving green and near-ultraviolet radiations exhibited the most rapid progression of G₁ cells through S and G₂.     

THE EFFECT OF CO2 ENRICHMENT ON ROOT NODULE DEVELOPMENT AND SYMBIOTIC N2 REDUCTION IN PISUM SATIVUM L.

A very significant increase in N₂(C₂H₂) reduction by Visum sativum L. infected with Rhizobium leguminosarum occurred when plants were grown in the light with 6 hr of CO₂ enrichment (0.00120 atm). Plants grown for 4 wk under 0.00120 atm CO₂ showed significant increases over control plants at 0.00032 atm CO₂ in plant dry weight, N content, root nodule mass, number of nodules, and mean nodule dry weight. Acetylene-reduction assays, however, revealed no reproducible increase in nitrogenase activity/mg nodule in plants subjected to long-term CO₂ enrichment. Both control and CO₂-enriched plants optimized the sink/source ratio between the mass of nodules and the extranodular plant mass. The optimum ratio for N₂ reduction by 4-week-old peas was 0.05. Long-term CO₂ enrichment did not promote root nodule formation to a greater degree than total plant development, and increases in N content were directly proportional to increases in nodule mass. Morphological data revealed significantly greater deposits of starch in root nodules of plants grown under CO₂-enriched conditions. The results are interpreted as showing that short-term increases in CO₂ levels promote N₂ reduction by affecting root nodule functioning, whereas long-term CO₂ enrichment promotes N₂ reduction by increasing total plant and root nodule development.     

Studies on the Geotropism of Roots: III. EFFECTS OF GEOTROPIC STIMULATION ON GROWTH-SUBSTANCE CONCENTRATIONS IN VICIA FABA ROOT TIPS

The auxins contained in 5-mm. tips of horizontal Vicia fabaroots have been compared with those in tips of vertical rootsafter cold ethanol extraction, paper-chromatographic separation,and Avena mesocotyl bioassay. At about the time curvature commencesin horizontal roots there is a marked increase in the contentof an auxin corresponding to ‘AP(ii)’ of pea roots(Rf 0.35–0.65 in isobutanol/methanol/water). There areindications that this is not due to its release from an inactivebound state but that it is either synthesized de novo or maybe converted from another auxin corresponding to ‘AP(iii)’of pea roots (Rf 0.75–1.0). The literature dealing with the auxins of geotropically stimulatedorgans is reassessed and it is concluded that, with the exceptionof the Avena coleoptile, there is very little evidence favouringa simple transport redistribution of auxin under gravity; themajority of the data favour an effect of gravity on auxin metabolism.     

THE ROLE OF LIGHT IN HISTOGENESIS AND DIFFERENTIATION IN THE SHOOT OF PISUM SATIVUM. I. THE APICAL REGION

Thomson , B. F., and P. M. Miller . (Connecticut Coll., New London.) The role of light in histogenesis and differentiation in the shoot of Pisum sativum. I. The apical region. Amer. Jour. Bot. 49(3): 303–310. Illus. 1962.—Seedlings of Pisum sativum grown under constant conditions and kept in total darkness or exposed daily to red or white light were harvested at the same plastochron age and examined histologically to determine what specific aspects of histogenesis and differentiation are affected by light. The tissue organization of the shoot apex is the same in all light conditions to a point below the 2 youngest leaf primordia. The first detectable difference is a slight thickening of the internode in light due to more and larger cells. The first effect on longitudinal growth appears below the fourth youngest primordium and consists of an increase of internode length in light-grown plants. This is associated with a greater distance between the apex and the first mature protoxylem. The distance from apex to the first pith, provascular strands, and protophloem and the distances between the 4 youngest leaf primordia are not affected by light.     

Chelation in Auxin Action: I. A STUDY OF THE INTERACTIONS OF 3-INDOLYLACETIC ACID AND SYNTHETIC CHELATING AGENTS AS AFFECTING THE GROWTH OF WHEAT ROOTS AND COLEOPTILE SECTIONS

Factorial experiments have been carried out on the effects,upon growth of roots of intact wheat seedlings and growth ofwheat coleoptile sections, of different concentrations of 3-indolylaceticacid (IAA) and various known chelating agents. These have demonstrateda similar mutual antagonism between pairs of agents whetherthese are IAA and a single known chelating agent or two knownchelating agents. This interaction takes the form that eitheragent alone in ‘high’ concentration severely inhibitsgrowth but this inhibitory effect is almost or entirely removedby the presence of one-millionth the concentration of the otheragent; when both agents are present in ‘high’ concentrationthe inhibition is again severe. The substitution of a non-chelatinganalogue for one of the agents either destroys the mutual characterof the antagonism or entirely prevents either agent at low concentrationfrom reducing measurably the inhibition caused by high concentrationof the other. The fact that IAA interacts with known chelatingagents, in controlling the growth both of roots and coleoptilesections, in the same unexpected and symmetrical way that theseinteract with each other, is held strongly to support the hypothesisthat it is here itself acting as a chelating or complexing agent;the absence of such interactions with a non-chelating analoguemakes this the more convincing. These results are concernedwith the removal of growth inhibition, due to supra-optimalconcentrations of one agent, by minute proportions of another;it cannot be regarded as proven that the promotion of growthby IAA in the absence of another agent is also due to chelationor complex formation. This seems probable, however, when thefindings here presented are taken in conjunction with the accumulatingevidence that IAA and other auxins can form complexes or chelateswith metals in vitro, and with the finding already publishedin detail that the eight chelating agents tried promoted growthin the wheat coleoptile test. The main criticisms to which this hypothesis has been subjectedhave been concerned with the relative magnitudes of effectsof IAA and chelating agents upon growth, with the low stabilityconstants of metal complexes with IAA and other auxins, withthe lack of parallelism between stability constants and growth-promotingactivity, and with the fact that one chelating agent (ethylenediamine-tetraaceticacid; EDTA) has been found inactive in certain growth tests.A series of factorial experiments comparing the authors' techniques(which are here described in detail), chemicals, and strainof wheat with those used by Fawcett et al. (1956) demonstratethat the discrepancies found, both as regards magnitudes ofeffects of IAA and EDTA and optimal concentrations, were partlydue to differences in strain but mainly to differences of technique.It is considered that ‘foreign’ molecules such asEDTA are likely to have side effects, which may well differin different strains or tests; competition with internal chelators(Burstrom and Tullin, 1957) is also likely to differ; differencesin rate of penetration and steric hindrance may also be involved.For these reasons effective chelating activity in vivo may bevery different from that in vitro and in the first instancethe magnitudes of growth-promoting effects of chelating agents(which may indeed be the net result of stimulatory and inhibitoryprocesses) seem less important than the fact that they are foundin so many instances. Possible ways in which IAA and other growth substances may regulategrowth by chelation or complex-formation are discussed.     

氮源及其浓度对三角褐指藻生长和脂肪酸组成的影响

为了研究氮源的类型和浓度对微藻脂肪酸组成的影响 ,用含有不同浓度NO3 -、NH4 、NH2 CONH2 的培养基 ,对三角褐指藻 (Phaeodactylumtricornutum)进行了培养 ,并测定了其生长和脂肪酸组成。结果表明 ,培养基中不添加氮源时 ,三角褐指藻生长缓慢 ,但多不饱和脂肪酸 (PUFAs)和C18脂肪酸 (C18∶0 ,C18∶2 (n -6) ,C18∶3 (n -6) )占总脂肪酸的比例较高 ;氮浓度较低 (<1 8mmol/L)时 ,三角褐指藻以NH4 为氮源 ,生长较快 ;氮浓度较高 (>3 5mmol/L)时 ,以NH2 CONH2 为氮源 ,生长较快。以NH4 或NH2 CONH2 为氮源时 ,EPA(Eicosapentaenoicacid)和PUFAs占总脂肪酸的比例随着其浓度的增加而上升 ;而以NO3 -为氮源时 ,EPA和PUFAs随着NO3 -浓度增加先上升后下降 ,最适NO3 -浓度为 1 8mmol/L ,此时的EPA占总脂肪酸的比例为 16 7%。EPA占干重 (w/w)的比例 ,不管是哪种氮源 ,均随着氮浓度的增加而升高 ,但是在 0 9— 3 5mmol/L之间 ,3种氮源间EPA含量差异不显著。当氮源浓度为 7 0mmol/L时 ,以NH2 CONH2 为氮源 ,EPA和PUFAs含量最高 ,分别为 2 6 %和 4 4 %。PUFAs占干重的比例随着NO3 -浓度增加而下降 ,随NH2 CONH2 浓度增加而升高 ,而受NH4 浓度变化的影响不显著。     

Studies on the Geotropism of Roots:II.THE EFFECTS OF THE AUXIN ANTAGONIST {alpha}-(I-NAPHTHYLMETHYLSULPHIDE)PROPIONIC ACID (NMSP) AND ITS INTERACTIONS WITH APPLIED AUXINS

Previous experiments on the effects of auxins on the geotropicresponses of seedling pea roots (Audus and Brownbridge, 1957)have been extended using the ‘anti-auxin’ -(I-naphthylmethylsulphide)propionicacid (NMSP) alone and in combination with indole-3-acetic acid(IAA) and 2:4-dichlorophenoxyacetic acid (2:4-D). NMSP action differs from that of the auxins in that it reducesthe rate of curvature progressively as the concentration isincreased, irrespective of whether the overall extension growthof the roots is being stimulated (10 and 30 p.p.m.) or inhibited(100 p.p.m.). Correspondingly the reaction time is lengthenedby 25–50 per cent. in all concentrations. Studies of responsesin mixtures of growth-stimulating concentrations of NMSP (30p.p.m.) and growth-inhibiting concentrations of IAA (10^–8)and 2:4-D (3 x 10^–8) show that auxins and ‘antiauxins’are mutually antagonistic in most, if not all, their actionson growth and curvature. The results suggest that the anti-auxin NMSP may stimulate rootgrowth and inhibit curvature by interfering with the synthesisor distribution of a natural endogenous inhibitor, which isnot IAA. NMSP inhibition of root growth in high concentrationsmust, however, be exerted independently of this natural inhibitor.The mutual antagonisms shown between the auxins and NMSP arebest explained in terms of an interference with access to thegrowth centres; competitive action at the growth centres themselvesseems not to be involved.     

Studies on Plant-Growth Hormones: VI. THE NATURE OF INHIBITOR-{beta} IN POTATO

1. The chemical nature of a plant growth inhibitor in potato tuberpeel, the ‘Inhibitor-ß’ which commonlyoccurs on chromatograms of many plant extracts, has been examined.
2. The inhibition, as indicated by bioassays using wheat coleoptilesections, could not be associated with any particular compound,but was partly or entirely due to a complex mixture of aliphaticacids.
3. . Azelaic acid and the coumarin, acopoletin, were isolatedtogetherwith a new substance, Acid A; degradative evidenceis not sufficientto enable a complete structure to be proposedfor this acid,but it appears to be an unsaturated polyhydroxyfatty acid.
4. The growth of coleoptile sections in solutionsof ßat several concentrations was examined over thefirst 7 hoursof growth. Inhibition did not occur until 4 hours;visible damageto the cells of the tissues appeared after thisperiod. Whenß was examined in a mixture with 3-indolylaceticacid,inhibition was evident after 1 hour. These results areinterpretedand the chemical system in which ß mayoperate ingrowth is briefly considered.

     

Studies on the Geotropism of Roots: I.GROWTH-RATE DISTRIBUTION DURING RESPONSE AND THE EFFECTS OF APPLIED AUXINSI

Experiments are described in which the normal geotropic responsesof the roots of Pisum sativum seedlings have been compared withthose obtained in the presence of auxins (indole-3-acetic acidand 2:4-dichlorophenoxyacetic acid) in the external medium.The courses of positive curvature resulting from short exposures(40 minutes) and also subsequent recovery phenomena on a horizontalklinostat have been followed. A photographic recording techniqueallowed the determination of absolute growth-rates of both upperand lower sides of the root during the course of each experiment. Positive curvature started at its maximum rate (0.30–0.32deg./min.) after a reaction time of 11.5 minutes and continuedconstant at that rate for about 60 minutes after stimulationceased. Recovery took place at a similar rate of curvature andwas complete after a further 150–200 minutes. During thephase of positive curvature overall root growth-rates were considerablyreduced and were slowly restored to normal during recovery. Low concentrations (1 part in 10¹¹) of both auxins increasedthe rate of positive curvature by 30–40 per cent. andshortened the reaction time roughly in proportion. The growth-ratesof both sides of the root were increased to the same extentduring both curvature and recovery. High concentrations (10^–8IAA and 3.10^–8 2: 4-D)reduced the rates of curvature by 50 per cent., lengthened thereaction time, and inhibited the growth of both sides of theroot during both curvature and recovery. Neither concentration of either auxin otherwise affected thetime course of response and recovery. It is suggested that geotropic response is due to the de novoproduction of an endogenous inhibitor in the extending cellsof the lower side of the root whence it may later spread tothe upper side. The complete independence of the growth actionsof this inhibitor and of the applied auxins suggests that itis not indole-3-acetic acid or any similar compound. Recoverymay be very largely independent of both inhibitor and auxinsand due to the action of another growth factor limiting celllength. The implications of these findings and of the attendant theoriesare fully discussed.