Effect of root formation on 14C-glycine uptake and incorporation into protein by attached and excised cotyledons of Helianthus annuus

Root formation was found to extend the life-span of excised cotyledons of Helianthus annuus L. markedly. Excised cotyledons of 12-day-old plants attained longer life-span, higher root number and total root length than cotyledons excised before or after 12 days. Protein content of attached cotyledons reached a maximum level 12 days after the commencement of germination followed by a decrease. Cotyledons excised 8 days after sowing showed maximum level of protein content 44 days after excision followed by a decrease. The increase was correlated with the full development of roots. The incorporation of ¹⁴C-glycine into protein followed a pattern similar to the protein content, both in attached and detached cotyledons.     

The Control of Root Initiation and Development in Detached Cotyledons of Sinapis alba L. and Raphanus sativus L.

The initiation and development of root primordia in detachedcotyledons of Sinapis alba (white mustard) and Raphanus sativus(radish) are studied, together with the inhibitory effects ofsucrose and mineral nutrients on these processes. Root primordium initiation on petioles of excised mustard cotyledonscultured in petridishes in water commenced after 3 days andwas completed after 5 days in culture, by which time a numberof the primordia had extended and emerged from the petiole.Both sucrose and mineral nutrient solution had an inhibitoryeffect which was most marked when the cotyledonswere culturedin the solution from the time of excision. The total numberof primordia initiated, their rate of development, and the finaltotal number of emerged roots were all reduced. The later thetime of transfer from water either to sucrose or to nutrient,the less marked the inhibition. Indeed, nutrient solution enhancedroot growth in mustard when cotyledons were transferred after5 days in water when root emergence had just commenced. The effects of sucrose and nutrients in relation to applicationbefore and after initial meristem formation has taken placeare discussed, together with the ways in which these two solutionsmay exert their effect on root initiation and development.     

The effects of light and cotyledon age on growth and root formation in excised cotyledons of Sinapis alba L.

Summary Root formation on excised mustard cotyledons was found to be determined by cotyledon age at excision and by light. Light treatment after excision enhanced root production in cotyledons excised 6 hours to 6 days after the start of imbibition and was essential for root production in cotyledons older than 6 days at excision. Three or more 12 hour light periods after excision were sufficient to induce root production in almost 100% of 7 day old cotyledons. The interposition of up to 5 days of darkness between excision and subsequent culture in the light did not reduce the final rooting percentage but delayed the onset of rooting by a time equivalent to the length of the dark period. The dry weight values of the cotyledons were directly related to the total light energy received after excision.The age and light effects on rooting may be mediated by their effects on the rate of breakdown and on the total levels of available reserves present in the cotyledons.     

CHEMICAL CONTROL OF ADVENTITIOUS ORGAN FORMATION IN LACTUCA SATIVA EXPLANTS

Both kinetin and adenine promote bud initiation in excised cotyledons of Lactuca sativa. Controls lacking these substances form abundant roots but have never formed buds. Indoleacetic acid and certain mineral salts are also necessary for regeneration of shoots. Although bud growth from cotyledons is extensive on a medium containing both indoleacetic acid and kinetin, excised roots display a low propensity toward bud formation and typically develop callus tissue with roots. Growth of hypocotyl sections is intermediate with respect to bud formation. Shoot initiation in lettuce thus varies with the region of the seedling as well as with the culture medium.     

Root Formation by Detached White Mustard (Sinapis alba) Cotyledons

Rooting is shown to occur in excised cotyledons of Sinapis alba when grown in petri dishes on moist filter paper. Cotyledons were excised at intervals from 6 hours after the start of imbibition, when they were yellow, unexpanded and enclosed within the testa, to 27 days after sowing when the cotyledons were green and fully expanded and on plants possessing up to 3 foliage leaves. Rooting generally began 5 or 6 days after excision and was completed dining the following 5 days. The age of cotyledons at t ho time of excision had three effects on rooting: the lag period be-fore rooting began and the period during which rooting took place both increased with age: but the most marked effect was on the total number of cotyledons which were able to form roots, which increased until cotyledon expansion was almost complete, then decreased as the mature cotyledons became older. Optimal rooting was shown by cotyledons detached 8 days alter sowing, when they were half expanded. At this age S5 % of them formed roots between 6 days and 8 days after excision.     

Host-tissue differences in transformation of pumpkin (Cucurbita pepo L.) by Agrobacterium rhizogenes

Agrobacterium rhizogenes (wild-type strains 8196 and 15834) transformation of pumpkin (Cucurbita pepo L.) intact seedlings grown in vivo, and 6–8-day-old excised cotyledons cultured in axenic conditions was investigated. Transformed (hairy) roots were successfully induced only on the excised cotyledons with the strain 8196, while intact seedlings failed to form hairy roots with either of the two different bacterial strains. Axenic hairy-root cultures established on MS medium without hormones grew vigorously. Mannopine was detected in all transgenic root clones examined. The peroxidase activity in transformed roots was higher compared with normal roots. Electrophoretic analyses of soluble proteins and isoperoxidases showed substantial differences between transformed and normal pumpkin roots.     

Change in Size and Cell Number during the Development of Lateral Root Primordia in Zea mays L.

Increase in cell number, anlage volume and length have beeninvestigated during the overall period of lateral root primordiumdevelopment in excised primaries and in attached roots of Zeamays L. Each of these aspects of anlage growth was found toincrease more or less exponentially during the interval betweenprimordium initiation and subsequent emergence as a lateralin both batches of roots. Values were then determined for celldoubling time (Td), the size of the proliferative fraction (Pf),and for anlage volume (Tv) and length (Tt) doubling times duringthe overall period of primordium development and at intervalsduring this period in both the excised and attached roots. Thepattern of change which took place in Td, Tv, Tl and Pf duringlateral primordium development was found to be similar in bothbatches of roots. However, the overall period of anlage developmentwas shorter in the excised roots than in the attached ones.Moreover, when laterals grew out of the excised roots they didso with fewer cells than comparable laterals emerging from theattached roots. Zea mays L., maize, root primordia, lateral emergence, cell doubling time     

The Effects of Benzylaminopurine on Growth and 14Carbon Translocation in Excised Mustard Cotyledons

When localized areas of blades of recently excised mustard cotyledons were fed with ¹⁴CO₂ it was found that the fixation products passed rapidly into the veins and then were translocated to the petiole. Since other cotyledons similarly treated subsequently rooted at the petiole base, this suggested that it acted as a sink for assimilates. Treatment of excised cotyledons with benzylaminopurine (BAP) resulted in the enhancement of blade growth and the suppression of root initiation and development. Quantitative determinations of labelled assimilate in both the cotyledon blade and the terminal 2 mm portion of the petiole were made. It was found that cotyledons treated with BAP at a concentration high enough to suppress completely root initiation had a higher level of radioactivity in the petiole base than the terminal segments in untreated petioles, whether expressed as specific activity or as a percentage of the total radiocarbon fixed. BAP-treated cotyledons also fixed consistently higher levels of ¹⁴CO₂, probably due to an increase in photosynthetic area. The results suggest that BAP alters the pattern of differentiation at the base of the petiole rather than the polarity of movement of assimilates to the petiole base.     

Hormonal factors controlling the initiation and development of lateral roots

The decapitated primary root of 3-day-old Alaska pea seedlings has been used as a test system to determine the activities on lateral root formation of six auxins, six cytokinins and several other naturally-occurring compounds. Their effects were assessed on (1) the initiation of lateral root primordia, (2) the emergence of visible lateral roots, and (3) the elongation of these laterals. All the auxins, at the optimum concentration of 10^-4M, promoted the initiation of lateral root primordia, and all except 3-indolylpropionic acid inhibited the elongation of the resulting lateral roots. Their effects on the emergence of laterals were small and varied. All the cytokinins, at 10^-6M and above, inhibited both the initiation and the emergence of lateral roots, zeatin being the most powerful inhibitor. The emergence process was about twice as sensitive as the initiation of primordia to the presence of cytokinins. The cytokinin ribosides were generally less active than the free bases. Abscisic acid and xanthoxin inhibited both emergence and elongation, the concentration for 50% decrease of emergence being about 10^-4M. Gibberellic acid had little clear effect on any of the three criteria. Nicotinic acid and thiamine at 10^-3M promoted both the initiation of primordia and their emergence: pyridoxal phosphate stimulated both emergence and elongation but did not influence the initiation of primordia. Adenine and guanine had little effect but decreased root elongation some 25%. The strong inhibiting effect of the cytokinins may well be the basis for the marked inhibition exerted by the root-tip on lateral root formation, while the promoting effects of auxins may explain the previously observed promotion of lateral root formation by the young shoot and cotyledons.     

Importance of Photosynthetic Cotyledons for Early Growth of Woody Angiosperms

At various times after seed germination, epigeous cotyledons were excised or treated with DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) to inhibit cotyledon photosynthesis of seedlings of Acer negundo L., Ailanthus altissima (Mill.) Swingle, Eucalyptus globulus Labill., Fraxinus pennsylvanica Marsh., Robinia pseudacacia L., and Ulmus americana L. In all species, DCMU inhibited expansion of cotyledons, elongation of roots, initiation of lateral roots, and expansion of foliage leaves. During the first 10 days after radicle emergence decotylization also variously inhibited growth of plant parts. Photosynthetic rates per cotyledon varied among species in the following order: Robinia pseudacacia > Ailanthus altissima≥Fraxinus pennsylvanica > Ulmus americana. The length of time that cotyledon photosynthesis contributed to growth of axial parts varied widely among species.     

Sulphate uptake and xylem loading of young pea (Pisum sativum L.) seedlings

Sulphate uptake and xylem loading was analysed in young pea (Pisum sativum) seedlings. The rate of sulphate uptake into intact 8-days-old pea seedlings (determined by a 1 h exposure to radiolabelled sulphate in the nutrient solution) was 585 nmol sulphate g^–1 root fresh weight h^–1. When the cotyledons were removed on day 6 the 8-days-old seedlings took up only 7% of the controls. Interruption of the phloem transport by steam girdling of the stem or the root (1 h before incubation with radiolabelled sulphate) diminished sulphate uptake by approximately 50%. The addition of sucrose to the nutrient solution during incubation did not restore sulphate uptake rates indicating that the decrease was not due to a lack of energy. Apparently, a signal from the shoot and/or the cotyledons is necessary to stimulate sulphate uptake into the roots of pea seedlings. Glutathione fed to the roots for 3 h prior to incubation with radiolabelled sulphate diminished sulphate uptake by approximately 50%. The relative proportion of the sulphate taken up that was loaded into the xylem remained unchanged (between 7 and 9% of total uptake), even when the stem was girdled above the cotyledons or when the seedlings were pre-exposed to glutathione. Only removal of the cotyledons or girdling of the root below the cotyledons increased the proportion of sulphate loaded into the xylem to 13–15% of total uptake upon exposure to glutathione. Apparently, a signal from the cotyledons represses xylem loading to some extent.     

Inter-organ Control of Greening in Etiolated Cucumber Cotyledons

Inter-organ control of greening in etiolated cucumber (Cucumis sativus L. cv. Aonagajibae) cotyledons was investigated. Four- or six-day-old excised or intact etiolated cucumber cotyledons were illuminated under aerobic conditions. Excised cotyledons without hypocotyl hooks produced chlorophyll without a prolonged lag phase and the rate of chlorophyll formation was not depressed if they were illuminated immediately after excision. If the excised cotyledons were incubated in the dark before illumination, chlorophyll accumulation at the end of 6 h of continuous illumination was remarkably lowered as the dark period lengthened, especially in 6-day-old cotyledons. The rapid loss of chlorophyll-forming capacity of excised cotyledons during dark preincubation suggests a stimulatory effect of hypocotyls on the greening in cotyledons. The treatment of excised cotyledons with bleeding sap in the dark for 18 h resulted in the promotion of chlorophyll formation during subsequent continuous illumination. Partial fractionation of bleeding sap with organic solvents and paper chromatography indicates that the active substances showed the same behavior as cytokinins. These facts add weight to the hypothesis that cytokinins from roots flow into cotyledons and stimulate greening.     

Lateral root formation in pine seedlings

The role of assimilates in lateral root development was studied in Pinus pinea seedlings grown in a nutrient solution. Seedlings were treated with ¹⁴CO₂ for 2 h following removal of the tap root tip at various times prior to the application of ¹⁴CO₂ or removal of a different number of cotyledons at one time. In seedlings with intact root systems most of the radioactivity accumulated in the lower section of the root containing the tap root apex. When the tap root tip was removed, the pattern of radioactivity accumulation along the root was affected by the presence and the stage of lateral root development. Removing the tap root tip of young seedlings (with no lateral roots) resulted in an almost equal distribution of radioactivity along the root. About 50% of the total radioactivity was found in the section showing the highest lateral root growth. Removing the tap root tip of mature seedlings (with lateral roots in the upper section) resulted in an immediate increase in the radioactivity accumulation in the upper section. When lateral roots appeared in the middle section, the pattern of radioactivity distribution was similar to that found in root decapitated young seedlings. Removal of cotyledons of mature seedlings somewhat increased the transport of radioactivity to the lower root section at the expense of the radioactivity in the lateral roots of the upper section. The present study suggests that competition within the root system between the tap root apex and the lateral roots may play an important role in determining the morphology of the root system.     

Lateral Root Development in Attached and Excised Roots of Zea mays L. Cultivated in the Presence or Absence of Indol-3-yl Acetic Acid

The initiation of lateral root primordia and their subsequentemergence as secondary roots have been examined in attachedand excised roots of Zea mays grown in the presence or absenceof indol-3-yl acetic acid (IAA). Exposure to IAA enhanced anlageinception in both batches of roots. In the attached roots, theIAA-induced stimulation of primordium initiation was followedby a similar increase in lateral emergence. IAA treatment, however,had no effect on the number of laterals produced, per centimetreof root, in the excised primaries. Thus, exposure to IAA didnot directly enhance lateral emergence in the attached rootsnor did it stimulate such emergence in the excised ones. Nocorrelation was found between proliferative activity in themeristem at the apex of the primary or the rate of root elongationon the one hand, and either the number of primordia initiated,or the number of laterals produced, per centimetre of primary,on the other. Zea mays, maize, root, primordium, lateral, indol-3-yl acetic acid, meristematic activity     

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.     

水曲柳和落叶松不同根序之间细根直径的变异研究

细根直径大小和根序高低对细根寿命和周转估计具有重要的影响,研究不同根序之间的直径变异对认识细根直径与根序的关系具有重要意义。该文根据Pregitzer等(2002)提供的方法,研究了位于东北林业大学帽儿山实验林场尖砬沟森林培育实验站17年生水曲柳(Fraxinus mandshurica)和落叶松(Larix gmelinii)人工林细根1~5级根序的平均直径的变化、直径的最小值和最大值范围、直径的变异系数。结果表明,水曲柳和落叶松细根直径<2 mm时,包含5个根序,随着根序由小到大的增加,细根直径也在增大。各根序平均直径之间,存在较大的差异。在同一根序内,细根直径范围很大,水曲柳和落叶松一级根最小直径均<0.20 mm,最大直径分别<0.50 mm(水曲柳)和<0.70 mm(落叶松)左右。2~3级根序直径最小值在0.20~0.30 mm之间,最大值≤1.0 mm。5级根直径最小值<1.0 mm,最大值超过2.0 mm。随着根序等级增加,直径变异系数增大。一级根序的直径平均变异系数<10%,2~3级根序直径平均变异系数在10%~15%左右,4~5级根序直径的平均变异系数在20%~30%之间。因此,在细根寿命与周转研究过程中,必须同时考虑直径和根序对细根的寿命估计的影响。     

IS TRIGONELLINE A PLANT HORMONE?

Experimental results are presented so that trigonelline may be evaluated as a plant hormone. Trigonelline promotes preferential cell arrest in G2 of the cell cycle for about 40% of the cell population in root meristems of Pisum sativum. Trigonelline is present in ungerminated seeds and is transported from cotyledons to other tissues during early seedling development. These experimental results show that trigonelline satisfies all six criteria that have been used to establish whether a substance is a hormone. As the seedlings age from day 3 to 10, the concentration of trigonelline in meristems decreases and so does the proportion of cells arrested in G2. Trigonelline may be isolated from excised cotyledons and can be added back to decotyledonized seedlings or excised root meristems to have the same effect as found in intact organisms. Predominant cell arrest in G2 occurs in roots of some plant species, although other species show preponderant cell arrest in G1. Many members of the Preiss-Handler metabolic pathway show some ability to promote cell arrest in G2 but only at concentrations 100 (10^-5 m ) or 1,000 (10^-4 m ) times the concentration of trigonelline (10^-7 m ) necessary for function. The proportion of cells arrested in G2 is highly correlated with the concentration of trigonelline within the root meristem.     

A comparison of the effects of auxin on cluster root initiation and development in Grevillea robusta Cunn. ex R. Br. (Proteaceae) and in the genus Lupinus (Leguminosae)

The effect of NAA (naphthaleneacetic acid) on the development of cluster roots in members of the Proteaceae and Leguminosae was investigated. The exogenous addition of NAA led to initiation of cluster roots in phosphate conditions normally inhibitory for their development, but initiation took place within the limits of the cluster pattern under –P conditions. There was no change in spacing within the cluster root nor between cluster roots in Grevillea robusta Cunn. ex R. Br. or in rootlet length or cluster root length. In Lupinus albus L., change in rootlet length and cluster root length was noted at 10^-10 and 10¹² M NAA. In L. albus, the length of time that roots were exposed to NAA does not appear to be important, with similar levels of cluster root initiation after 48 h and 7 days. Cluster root production in G. robusta differed from that in L. albus in terms of the concentration of NAA needed to induce initiation, and in the effects of extremely low levels of NAA on rootlet numbers and lengths. L. arboreus L. does not produce cluster roots under –P conditions. Furthermore, neither L. arboreus L., L. angustifolius L., L. luteus L. nor L. mutabilis L. were induced to produce cluster roots under –P conditions, nor under +P conditions in the presence of exogenous NAA. Thus, exogenous NAA only leads to the induction of cluster roots, at levels of P normally inhibitive of their development, in species of Lupinus that produce them under –P conditions. Auxin-induced cluster roots develop within the same constraints as those developing under –P conditions. NAA does not induce cluster roots in species of Lupinus that do not produce them under –P conditions.     

Aluminum tolerance measured by root growth and mucilage protection in Urochloa brizantha and Urochloa decumbens

Aluminum toxicity on root systems was analyzed through comparing root growth and evaluating the protective function of mucilage in Urochloa decumbens and Urochloa brizantha. Seedlings were grown in a solution with different concentrations of AlCl₃ and with mucilage removed or present. The root elongation rate, total length, number of roots and presence of aluminum at the root apex were measured. Root development was inhibited by aluminum and the elongation rate was maintained without any difference between the two species. A significant reduction in root length was found in U. brizantha. Aluminum did not influence root branching in either species and accumulated mostly in the rhizosphere of U. brizantha, where the mucilage has less of a protective function. The greatest aluminum tolerance was found in U. decumbens, observed through maintenance of total root system growth from lower to higher aluminum toxicity.     

Zum Einfluß von Pythium ultimum und Cochliobolus sativus auf Wachstum und Wurzelleistung der Wintergerste in Abhängigkeit vom Düngungsniveau

Influence of Pythium ultimum and Cochliobolus sativus on growth and root efficiency of winter barley dependent on fertilizer level The colonization of barley roots by Pythium ultimum and Cochliobolus sativus can be symptomless or cause root rot. Disease severity of the root systems was increased at higher fertilizer level. Since root length growth was much more affected than shoot growth, the undamaged roots of an infected root systems had an increased efficiency per unit root length. Nevertheless the total root systems, when infected, were positively inferior to the healthy ones. Their utilization of additionaln, utrients was less efficient. This indicates the importance of root health in economical and ecological respect.