Induction of hydrotropism in clinorotated seedling roots of Alaska pea,Pisum sativum L.

Roots of the agravitropic pea (Pisum sativum L.) mutantageotropum show positive hydrotropism, whereas roots of Alaska peas are hydrotropically almost non-responsive. When the gravitropic response was nullified by rotation on clinostats, however, roots of Alaska peas showed unequivocal positive hydrotropism in response to a water potential gradlent. These results suggest that roots of Alaska peas possess normal ability to respond hydrotropically and their weak hydrotropic response results from a counteracting effect of gravitropism.     

Grafting and gibberellin effects on the growth of tall and dwarf peas

Tall peas var. Alaska and dwarf peas var. Progress No. 9 were grafted onto their own roots or reciprocally grafted to determine the rootstock effect on the growth of the stem. In all cases the grafted stems grew the same as their ungrafted controls regardless of which rootstock they were grown on. When similarly grafted plants were supplied with gibberellic acid, good graft unions did not inhibit its translocation. This evidence supports the thesis that the mechanism controlling stem growth in peas is located in the stem and that the roots have no direct control over this mechanism.     

Root hydrotropism of an agravitropic pea mutant, ageotropum

We have partially characterized root hydrotropism of an agravitropic pea mutant, ageotropum (from Pisum sativum L. cv. Weibull's Weitor), without interference of gravitropism. Lowering the atmospheric air humidity inhibited root elongation and caused root curvature toward the moisture-saturated substrate in ageotropum pea. Removal of root tips approximately 1.5 mm in length blocked the hydrotropic response. A computer-assisted image analysis showed that the hydrotropic curvature in the roots of ageotropum pea was chiefly due to a greater inhibition of elongation on the humid side than the dry side of the roots. Similarly, gravitropic curvature of Alaska pea roots resulted from inhibition of elongation on the lower side of the horizontally placed roots, while the upper side of the roots maintained a normal growth rate. Gravitropic bending of Alaska pea roots was apparent 30 min after stimulation, whereas differential growth as well as curvature in positive root hydrotropism of ageotropum pea became visible 4–5 h after the continuous hydrostimulation. Application of 2,3,5-triiodobenzoic acid or ethyleneglycol-bis-( β -aminoethylether)-N,N,N',N'-tetraacetic acid was inhibitory to both root hydrotropism of ageotropum pea and root gravitropism of Alaska pea. Some mutual response mechanism for both hydrotropism and gravitropism may exist in roots, although the stimulusperception mechanisms differ from one another.     

Control of the formation of amylases and proteases in the cotyledons of germinating peas

Protease activity increased in attached cotyledons of germinated peas (Pisum sativum L. cv. Alaska) as the stored proteins declined but did not increase in excised cotyledons incubated for the same length of time. Cotyledons of seeds germinated in the presence of a casein hydrolysate solution developed less protease activity than did those germinated on water. These results suggest that accumulation of amino acids regulates the protease level in the cotyledons of germinating peas.     

Putrescine and Spermidine in Peas: Effeets on Nitrogen Source and Potassium Supply

Free and total putrescine and, to a lesser extent, spemidine accumulate in both roots and shoots of peas in response to potas stum deficiency and ammomnium supply. Free putrescine responds more sensitively than total putreseine to variatioin of nutrients. Accumulation of putrescine is more pronounced in the roots than in the shoots.     

Response of lupins (Lupinus angustifolius L.) and peas (Pisum sativum L.) to Fe deficiency induced by low concentrations of Fe in solution or by addition of HCO3 -

Lupins appear to be more sensitive than peas to Fe deficiency. However, when grown in nutrient solutions between pH 5–6, little difference existed between them in their ability to acidify the solution or to release Fe^III reducing compounds. This experiment was aimed at determining whether differences between species which occurred when Fe deficiency was induced by withholding Fe from an acid solution, are maintained when Fe deficiency is induced by addition of HCO₃ ^-. Lupins and peas were grown in nutrient solutions at 0, 2 and 6 μM of Fe^III EDDHA and either with or without HCO₃ ^- (6 mM). Bicarbonate induced symptoms of Fe deficiency (chlorosis) in both lupins and peas, and markedly decreased the growth of shoots. Symptoms appeared sooner and were more severe in lupins than in peas. Growing plants without HCO₃ ^-, but at the lowest Fe level, decreased the growth and Fe concentration of shoots of lupins but did not induce chlorosis. Growing peas in this treatment, decreased Fe concentrations, but to a lesser extent than in lupins, and did not decrease growth. H⁺-ion extrusion and release of Fe^III reducing compounds was greater in lupins than in peas. Bicarbonate also decreased the growth of roots of lupins but increased the growth of roots of peas. Results indicate that when Fe deficiency is induced by HCO₃ ^-, then the response of lupins and peas are similar to their response in acid solution culture. Differences between species therefore could not be explained by their relative abilities to acidify or release Fe^III reducing compounds. Greater control of the distribution of Fe within the shoots, the presence of a pool of Fe within the roots, a lower threshold for Fe uptake, or a higher content of seed-Fe, may therefore be the reason for the lower sensitivity of peas than lupins to Fe deficiency.     

Light-controlled Leaf Expansion in Peas Grown under Different Light Conditions

Several photosystems control leaf expansion in Alaska peas (Pisum sativum). Phytochrome is known to control expansion in dark-grown peas. But plants exposed briefly to red light are insensitive to phytochrome, an insensitivity that is itself phytochrome-produced. Leaf expansion in these plants is promoted by 440 or 630 nm of light (probably mediated by protochlorophyll). Plants grown in white fluorescent light required simultaneous exposure to high intensity blue and yellow light for promotion of leaf expansion. Since these results parallel studies on light-controlled inhibition of stem elongation, shoot growth as a whole is coordinated by these photosystems. Such coordination might be a mechanism of plant competition for light.     

Correlations of Growth Rate and De-etiolation with Rate of Ent-Kaurene Biosynthesis in Pea (Pisum sativum L.)

Biosynthesis of the gibberellin precursor ent-kaurene-¹⁴C from mevalonic acid-2-¹⁴C was assayed in cell-free extracts of shoot tips of etiolated and light-grown Alaska (normal) and Progress No. 9 (dwarf) peas (Pisum sativum L.). During ontogeny of light-grown Alaska peas, kaurene-synthesizing activity increased from an undectectable level in 3-day-old epicotyls to a maximum in shoot tips of 9-day-old plants and remained relatively constant thereafter until postanthesis. The capacity for kaurene synthesis in extracts from shoot tips of 10-day-old etiolated Alaska seedlings increased approximately exponentially during the first 12 hr of de-etiolation in continuous high intensity white light and remained relatively constant during the succeeding 24 hr of irradiation. Extracts from light-grown Alaska (normal) shoot tips possessed greater capacity for kaurene synthesis than did extracts from light-grown Progress No. 9 (dwarf) shoot tips. Extracts from shoot tips of either light-grown cultivar displayed greater kaurene-synthesizing capacity than was observed in extracts from their dark-grown counterparts. It is concluded that gibberellin biosynthesis in pea shoot tips is subject to partial regulation by factors controlling the rate of biosynthesis of kaurene.     

Hydrotropism and its interaction with gravitropism in roots

We have studied hydrotropism and its interaction with gravitropism in agravitropic roots of a pea mutant and normal roots of peas (Pisum sativum L.) and maize (Zea mays L.). The interaction between hydrotropism and gravitropism in normal roots of peas or maize were also examined by nullifying the gravitropic response on a clinostat and by changing the stimulus-angle for gravistimulation. Depending on the intensity of both hydrostimulation and gravistimulation, hydrotropism and gravitropism of seedling roots strongly interact with one another. When the gravitropic response was reduced, either genetically or physiologically, the hydrotropic response of roots became more unequivocal. Also, roots more sensitive to gravity appear to require a greater moisture gradient for the induction of hydrotropism. Positive hydrotropism of roots occurred due to a differential growth in the elongation zone; the elongation was much more inhibited on the moistened side than on the dry side of the roots. It was suggested that the site of sensory perception for hydrotropism resides in the root cap, as does the sensory site for gravitropism. Furthermore, an auxin inhibitor, 2,3,5-triiodobenzoic acid (TIBA), and a calcium chelator, ethyleneglycol-bis-(-aminoethylether)-N,N,N,N- tetraacetic acid (EGTA), inhibited both hydrotropism and gravitropism in roots. These results suggest that the two tropisms share a common mechanism in the signal transduction step.     

THE INDEPENDENT ACTION OF MORPHACTINS AND GIBBERELLIC ACID ON HIGHER PLANTS

The comparative activity of three morphactins, n-butyl-9-hydroxyfluorene-9-carboxylate (IT 3233), 9-hydroxy-fluorene-9-carboxylicacid (IT 3235) and methyl-2-chloro-9-hydroxy fluorene-9-carboxylate(IT 3456) on the action of gibberellic acid (GA₃) were examinedutilizing dwarf pea (Progress No. 9), dwarf corn (strain d-5),CCC dwarfed Alaska pea, and embryoless barley half-seeds. When applied either prior to or simultaneously with GA₃ themorphactins were without effect in reducing the response ofthe dwarf peas to the gibberellin. In fact IT 3233 and IT 3235in combination with GA₃ produced taller plants than the GA₃controls. Similar results were observed using CCC dwarfed Alaskapeas. The morphactins did, however, produce several morphologicaleffects on the peas. In addition, they were effective in breakingapical dominance in the peas. The morphactins were also withouteffect on the dwarf corn bioassay and no morphological changeswere observed. In the embryoless barley half-seeds the morphactins did notinhibit the response of the tissue to the GA₃. Also, the morphactinsdid not exhibit gibberellin-like properties. The results suggest that morphactins do not compete with gibberellinfor similar sites of action. ¹Published with the approval of the Director of the MichiganAgricultural Experiment Station as Journal Article Number 3917.     

Characterization of hydrotropism: the timing of perception and signal movement from the root cap in the agravitropic pea mutant ageotropum.

In recent years, experiments have demonstrated that the gravity response of roots can be separated from the hydrotropic response by using the agravitropic pea mutant ageotropum. Though this mutant has been a useful tool for demonstrating the existence of the hydrotropic response of roots, little is known about how perception, transduction, transmission, and the growth response is accomplished. In this study, we have used the ageotropum mutant to investigate both the threshold time for perception of an osmotic stimulation and the minimum time required for signal transduction and transmission in roots following an osmotic stimulation at the root cap. In addition, we have compared the threshold times and signal transmission times of hydrotropism in the ageotropum roots to the gravity response of Alaska pea roots.     

Multilocus Sequence Typing Confirms Wild Birds as the Source of a Campylobacter Outbreak Associated with the Consumption of Raw Peas

From August to September 2008, the Centers for Disease Control and Prevention (CDC) assisted the Alaska Division of Public Health with an outbreak investigation of campylobacteriosis occurring among the residents of Southcentral Alaska. During the investigation, pulsed-field gel electrophoresis (PFGE) of Campylobacter jejuni isolates from human, raw pea, and wild bird fecal samples confirmed the epidemiologic link between illness and the consumption of raw peas contaminated by sandhill cranes for 15 of 43 epidemiologically linked human isolates. However, an association between the remaining epidemiologically linked human infections and the pea and wild bird isolates was not established. To better understand the molecular epidemiology of the outbreak, C. jejuni isolates (n = 130; 59 from humans, 40 from peas, and 31 from wild birds) were further characterized by multilocus sequence typing (MLST). Here we present the molecular evidence to demonstrate the association of many more human C. jejuni infections associated with the outbreak with raw peas and wild bird feces. Among all sequence types (STs) identified, 26 of 39 (67%) were novel and exclusive to the outbreak. Five clusters of overlapping STs (n = 32 isolates; 17 from humans, 2 from peas, and 13 from wild birds) were identified. In particular, cluster E (n = 7 isolates; ST-5049) consisted of isolates from humans, peas, and wild birds. Novel STs clustered closely with isolates typically associated with wild birds and the environment but distinct from lineages commonly seen in human infections. Novel STs and alleles recovered from human outbreak isolates allowed additional infections caused by these rare genotypes to be attributed to the contaminated raw peas.     

GIBBERELLIN RELATIONSHIPS IN THE ‘ALASKA’ PEA (PISUM SATIVUM)

'Alaska’ peas (Pisum sativum L.) grown under a 16-hr photoperiod at 20 ± 1 C and an 8-hr dark period at 16 ± 1 C in their ontogeny exhibit two periods of sensitivity to applied gibberellin (GA), namely, prior to and subsequent to but not during the linear phase of stem elongation. This paper describes experiments conducted primarily with seedlings. Growth-saturating doses of GA, applied to dry seeds before planting (10⁻³ m) and to the shoot tips of 3-day-old seedlings (10 μg), evoked growth rates equal to the growth rate of etiolated seedlings. Sensitivity of seedlings to applied GA decreased with age through the first 2 to 3 weeks of development; by the time seedlings were about 14 days of age and had four elongating internodes they no longer responded to applied GA. As endogenous growth rate diminished late in ontogeny, the plants again became sensitive to applied GA. Growth response was used as a criterion for determining apparent translocation of applied GA. ‘Alaska’ pea seedlings appeared to transport GA, both acropetally from the cotyledons and basipetally from the shoot tip, to all internodes with remaining extension potential. Excision of both cotyledons at any time during the first 9 days of development caused a significant reduction of growth rate, and applied GA did not restore normal growth rate. No evidence was found that the cotyledons supply endogenous GA to the shoot axis in normal seedling development. It is suggested that the normal growth rate of light-grown ‘Alaska’ peas is correlated with the rate of synthesis of GA and that GA is rate-limiting for stem elongation during early seedling development and during the period of decreasing growth rate and onset of apex senescence.     

A potent inhibitor of ethylene action in plants

Ag(I), applied foliarly as AgNO(3), effectively blocked the ability of exogenously applied ethylene to elicit the classical "triple" response in intact etiolated peas (Pisum sativumcv. Alaska); stimulate leaf, flower, and fruit abscission in cotton (Gossypium hirsutumcv. Stoneville 213); and induce senescence of orchids (Hybrid white Cattleya, Louise Georgeianna). This property of Ag(I) surpasses that of the well known ethylene antagonist, CO(2), and its persistence, specificity, and lack of phytotoxicity at effective concentrations should prove useful in defining further the role of ethylene in plant growth.     

The control of damping-off in Pisum sativum L. by cycioheximide

Experiments on the effect of cycioheximide (Acti-dione) in controlling damping-off disease of peas confirmed that phytotoxicity would preclude its use despite its high toxicity to Pythium spp. The antibiotic did not inhibit germination of peas, but retarded growth of the shoot; the tap root was apparently unaffected, but the lateral roots were stunted.     

Does salinity induce early ageing of pea root tissue?

Summary The effect of salinity on ageing of pea roots was studied. The distance from the apex at which differentiation of xylem elements occurred and the relative increase in the function of pentose phosphate pathways were taken as parameters for maturation or ageing.Pea seeds (Pisum stivum L.) of the varieties Alaska and Dan were used in these experiments. The seeds were germinated and grown in vermiculite moistened with Hoagland's solution or Hoagland's solution containing either 96 or 120 mM NaCl. In Alaska roots salinity induced differentiation in a lower section of the root than in controls, and the increase in the function of the pentose phosphate pathway paralleled the advance of maturation. Salinity apparently induces earlier ageing in Alaska roots. This is not the case in Dan roots which tolerate slightly higher salinity levels than Alaska.This paper is dedicated to Professor Michael Evenari for his 75th birthday, in admiration and friendshipThis research was supported by a grant from The Hebrew University's Central Research Fund     

The Biosynthesis of Indole-3-acetic Acid from D-tryptophan in Alaska Pea Plastids

IAA biosynthesis in Alaska peas is shown to be plastid localized.D-tryptophan is a much better substrate than is L-tryptophan,and IAA production is dependent on a keto acid. In line withthis, a plastid localized D-tryptophan aminotransferase hasbeen found and purified 1,500 fold. The enzyme has no activitywith L-tryptophan and prefers pyruvic or oxaloacetic acid asan amino group acceptor. Activities are much higher in darkthan in light grown tissues. Some possible physiological ramificationsare discussed. (Received May 15, 1989; Accepted July 25, 1989)     

THE ETCHING OF MARBLE BY ROOTS IN THE PRESENCE AND ABSENCE OF BACTERIA

In a study of the effect of soil bacteria upon the etching power of the roots of Canada field peas upon polished marble, it has been shown that the presence of the bacteria increases the etching power of the roots.     

Magnitude and Kinetics of Stem Elongation Induced by Exogenous Indole-3-Acetic Acid in Intact Light-Grown Pea Seedlings

Exogenously applied indole-3-acetic acid (IAA) strongly promoted stem elongation over the long term in intact light-grown seedlings of both dwarf (cv Progress No. 9) and tall (cv Alaska) peas (Pisum sativum L.), with the relative promotion being far greater in dwarf plants. In dwarf seedlings, solutions of IAA (between 10-4 and 10-3 M), when continuously applied to the uppermost two internodes via a cotton wick, increased whole-stem growth by at least 6-fold over the first 24 h. The magnitude of growth promotion correlated with the applied IAA concentration from 10-6 to 10-3 M, particularly over the first 6 h of application. IAA applied only to the apical bud or the uppermost internode of the seedling stimulated a biphasic growth response in the uppermost internode and the immediately lower internode, with the response in the latter being greatly delayed. This demonstrates that exogenous IAA effectively promotes growth as it is transported through intact stems. IAA withdrawal and reapplication at various times enabled the separation of the initial growth response (IGR) and prolonged growth response (PGR) induced by auxin. The IGR was inducible by at least 1 order of magnitude lower IAA concentrations than the PGR, suggesting that the process underlying the IGR is more sensitive to auxin induction. In contrast to the magnitude of the IAA effect in dwarf seedlings, applied IAA only doubled the growth in tall seedlings. These results suggest that endogenous IAA is more growth limiting in dwarf plants than in tall plants, and that auxin promotes stem elongation in the intact plant probably by the same mechanism of action as in isolated stem segments. However, since dwarf plants to which IAA was applied failed to reach the growth rate of tall plants, auxin cannot be the only limiting factor for stem growth in peas.     

Electrotropism of Maize Roots : Role of the Root Cap and Relationship to Gravitropism

We examined the kinetics of electrotropic curvature in solutions of low electrolyte concentration using primary roots of maize (Zea mays L., variety Merit). When submerged in oxygenated solution across which an electric field was applied, the roots curved rapidly and strongly toward the positive electrode (anode). The strength of the electrotropic response increased and the latent period decreased with increasing field strength. At a field strength of 7.5 volts per centimeter the latent period was 6.6 minutes and curvature reached 60 degrees in about 1 hour. For electric fields greater than 10 volts per centimeter the latent period was less than 1 minute. There was no response to electric fields less than 2.8 volts per centimeter. Both electrotropism and growth were inhibited when indoleacetic acid (10 micromolar) was included in the medium. The auxin transport inhibitor pyrenoylbenzoic acid strongly inhibited electrotropism without inhibiting growth. Electrotropism was enhanced by treatments that interfere with gravitropism, e.g. decapping the roots or pretreating them with ethyleneglycol-bis-[β-ethylether]-N,N,N′,N′-tetraacetic acid. Similarly, roots of agravitropic pea (Pisum sativum, variety Ageotropum) seedlings were more responsive to electrotropic stimulation than roots of normal (variety Alaska) seedlings. The data indicate that the early steps of gravitropism and electrotropism occur by independent mechanisms. However, the motor mechanisms of the two responses may have features in common since auxin and auxin transport inhibitors reduced both gravitropism and electrotropism.