THE ONTOGENY OF THE PRIMARY THICKENING MERISTEM OF ATRIPLEX HORTENSIS L. (CHENOPODIACEAE)

Seedlings of Atriplex hortensis were studied to ascertain; 1) in which organ the primary thickening meristem (PTM) first differentiates; 2) the direction of differentiation of the PTM, and 3) the pattern of differentiation of conjunctive tissue. The PTM initially differentiates in pericycle of the primary root base 11 days after emergence of the primary root. It then differentiates in the transition region of the hypocotyl, mostly in cells of pericycle between pairs of vascular bundles. In the upper hypocotyl, PTM differentiates by day 20 in the inner layer of cortical parenchyma. In the epicotyl, PTM apparently differentiates in the inner layer of cortex, by day 24. Desmogic xylem differentiates from radial files of internal conjunctive tissue cells and desmogic phloem differentiates opposite desmogic xylem strands from newly formed cells of external conjunctive tissue. No interfascicular cambium differentiates in the root, hypocotyl, or epicotyl.     

THE DEVELOPMENT OF THE SEED OF ABUTILON THEOPHRASTI I. OVULE AND EMBRYO

Winter , Dorothy M. (Iowa State U., Ames.) The development of the seed of Abutilon theophrasti. I. Ovule and embryo. Amer. Jour. Bot. 47(1): 8–14. Illus. 1960.—Abutilon theophrasti Medic, is a widespread annual weed which produces an abundance of seed in capsules which mature within 20 days after pollination. Ovule differentiation may be observed at least 8 days before anthesis when a sporogenous cell becomes evident and 2 integuments are initiated. An 8-nucleate embryo sac is produced from the chalazal megaspore approximately 2 days before anthesis. The outer integument of the mature campylotropous ovule consists of 2 cell layers, the inner integument has 6 to 15 cell layers. The initially free-nucleate endosperm becomes cellular betwen 3 and 7 days after pollination. At maturity a thin layer of gelatinous endosperm encases the embryo. The Asterad-type proembryo of Abutilon has a stout suspensor and develops rapidly. Four days after pollination cotyledons are initiated; 4 days later a leaf primordium is evident. Fifteen days after pollination the embryo, which has essentially completed its growth, consists of a large hypocotyl with root promeristem and root cap at its basal end, and 2 flat, folded, leaflike cotyledons enclosing a small epicotyl at its upper end. The epicotyl consists of an embryonic leaf and a stem apex.     

Brassinolide, a growth-promoting steroidal lactone

Brassinolide (BR), a naturally-occurring-steroidal lactone from rape ( Brassica napus L.) pollen, was compared with auxin for activity in a number of bioassay systems. Responses similar to IAA were elicited by BR in bioassays based upon bean hypocotyl hook opening, elongation of maize mesocotyl, pea epicotyl and azuki bean epicotyl sections, and fresh weight increase in Jerusalem artichoke (2,4-D used) and pea epicotyl sections. The azuki bean and dwarf pea epicotyl bioassays were much more responsive to BR than IAA (at 10 μ M ). Responses approximately two-fold greater in magnitude were elicited by IAA in the maize mesocotyl, bean hypocotyl hook and Jerusalem artichoke bioassays. Little or no response was elicited by BR (0.01 to μ M ) in the cress root or decapitated pea-lateral bud bioassays. A powerful synergism between BR and IAA was observed in the azuki bean, pea epicotyl and bean hypocotyl hook bioassays. Although, as previously reported, other steroidal substances are active in some of the bioassay systems tested, none compared with BR in magnitude and diversity of elicited responses.     

Auxin Activity of Glucobrassicin

The indole-glucosinolate, glucobrassicin, which is found in large amounts in members of the genus Brassica, was subjected to tests in the standard Avena curvature bioassay. Both the tetramethylammonium salt of glucobrassicin and the non-crystallizted material induced curvature at a concentration of 5 × l0^?4M. The curvature from the salt was, however, only half of that induced by the acid form. Bioassays of chromatograms of fresh methanolic extracts of savoy cabbage indicated the presence of indole-3-acetic acid as well as indole-3-acetonitrile in small amounts along with large amounts of glucobrassicin. Segments of green hypocotyl tissue of savoy cabbage respond with limited growth to high concentrations of glucobrassicin. Segments of etiolated hypocotyls or green epicotyls give no growth response to glucobrassicin. Pea stem segments which do not respond to indoleacetonitrile responded with similar growth to glucobrassicin and indoleacetic acid. Nitrilase activity was found in savoy hypocotyl and epicotyl tissue by chromatography of incubation media. The growth regulation in savoy cabbage in conjunction with data on the distribution of glucobrassicin in the plant, leads to the conclusion that glucobrassicin is a special, inactive storage and transport form of the active auxin in cabbage.     

Regulation of alpha-amylase activity in bean stem tissues

α-Amylase activity was assayed in 1-centimeter sections taken from bean (Phaseolus vulgaris var. Kentucky Wonder) hypocotyls and epicotyls at measured distances from the cotyledons. The activity was low throughout the hypocotyl for the first 7 days. An increase was first observed with etiolated hypocotyls in the basal region, becoming higher in the more central regions by 14 to 17 days. By 21 days the activity was highest in the upper region, but had decreased in the lower regions. A comparable pattern was observed for the epicotyl from etiolated seedlings, the activity increasing first in the region closest to the cotyledons. These increases were associated with loss of cells from the pith in the hypocotyl and epicotyl of both dark- and light-grown plants. Since the changes were observed in tissues virtually devoid of starch, it is hypothesized that the control mechanism is related to the cellular disassembly associated with the mobilization of materials released during senescence rather than to a regulation by the enzyme's substrate or products.     

宁夏枸杞的胚胎发生和胚乳发育

宁夏枸杞的胚胎发生属茄型,由顶细胞参与胚体的形成,基细胞仅形成六细胞胚柄。胚乳发育为细胞型,但也观察到少数核型胚乳的现象。初步探讨了核型胚乳与细胞型胚乳的关系。     

STUDIES ON THE SEED OF BANANA. II. THE ANATOMY AND MORPHOLOGY OF THE SEEDLING OF MUSA BALBISIANA

Mc Gahan , Merritt W. (Central Research Labs., United Fruit Co., Norwood, Massachusetts.) Studies on the seed of banana. II. The anatomy and morphology of the seedling of Musa balbisiana. Amer. Jour. Bot. 48(7): 630–637. Illus. 1961.—The first external evidence of germination of the seed of Musa balbisiana is the displacement of the micropylar plug by the elongation of the hypocotyl-radicle axis. As the hypocotyl and epicotyl emerge from the micropylar collar, the seminal adventitious roots become apparent and the cotyledonary sheath surrounding the epicotyl emerges as a coleoptile-like structure. Subsequent growth results in the elongation of the first leaves beyond the cotyledonary sheath and the rapid elongation of the adventitious root system. The vascular transition occurs between the cotyledon and the radicle. The sheath is considered to be only analogous to the coleoptile of the grasses.     

THE EFFECTS OF AUXINS AND KINETIN ON XYLEM DIFFERENTIATION IN THE PEA EPICOTYL

Sorokin , Helen P., S. N. Mathur , and Kenneth V. Thimann . (Harvard U., Cambridge, Mass.) The effects of auxins and kinetin on xylem differentiation in the pea epicotyl. Amer. Jour. Bot. 49(5): 444–454. Illus. 1962.—Treatment of isolated segments from the second internode of etiolated ‘Alaska’ pea epicotyls with indoleacetic acid or 2,4-D results in: (1) activation of fascicular cambium, and initiation of some interfascicular cambium, resulting in abundant production of secondary xylem, and in formation of hyperplastic tissue; (2) partial or even total occlusion of proto- and metaxylem. The secondary xylem formed consists of short vessel members with scalariformly reticulate or pitted walls, which often lack vertical connection with each other, being interrupted by unlignified cells. When IAA is used, the hyperplastic growth mainly takes the form of root primordia, whereas 2,4-D initiates the formation of callus, but not of root primordia. The growth of this callus causes a characteristic split at the base of the internode. Treatment with kinetin, alone or in combination with the auxin, changes the above structure markedly. It leads to the initiation, over the entire circumference of the core of the internode, of a still more active cambium, which forms several layers of secondary xylem; this consists mainly of long vessel members with pitted walls. Hyperplastic growth is completely absent, and the xylem does not become occluded. Thus the effect of kinetin is to make the xylem more normal and to alter the epicotyl structure from herbaceous to more-or-less woody.     

Growth, anatomy and morphology of the mesocotyl and the growth of appendages of the wild oat (Avena fatua L.) seedling

Morphological and histological studies were made on the mesocotyl and the emergence of seedlings of a nondormant strain (CS40) of wild oats (Avena fatua L.). The elongation of the mesocotyl was primarily responsible for the emergence of seedlings from deeper levels of soil. The mesocotyl of the seedling is here interpreted as the hypocotyl. The functionally suctorial scutellum together with coleoptile constitutes the first cotyledon and the first true-leaf is regarded as the second cotyledon. The development of tillers from scutellar and first-leaf buds depends on the depth at which level the seeds (caryopses) germinated and the seedlings emerged above the soil surface. The first-leaf axillary buds, regradless of depths, develop into dominant tillers. The scutellar buds, especially at greater depths, remain inhibited. At shallower levels, however, they develop into tillers. The scutellar buds, at deeper levels, behave as reserve ramets which feature adds to the success of the species as a weed in the agricultural prairies.     

THE COMPARATIVE AND DEVELOPMENTAL MORPHOLOGY OF THE ROOT SYSTEM OF SELAGINELLA SELAGINOIDES (L.) LINK

All of the roots of Selaginella selaginoides are attached laterally to the base of the shoot, which has monopolar growth as is characteristic of Selaginella. The first three roots are produced by meristematic activity in the cortex of the hypocotyl as in several other species of Selaginella. The fourth root is produced in the same way as the first three, except that not all of the cortical cells which become meristematic mature into root tissue. Some of the meristematic tissue remains undifferentiated and continues to produce additional roots. Potentially an unlimited number of roots could be produced, but no plant was found to have more than eight. There is some secondary growth in the cortex of the basal swelling on the hypocotyl, but no secondary vascular tissue is produced and no cambium of any sort is ever organized. On the basis of comparisons with other living species of Selaginella. the centralized root system of S. selaginoides is interpreted as having been modified from a noncentralized type of root system by the persistence of the juvenile mode of root production.     

Slow wave potentials in cucumber differ in form and growth effect from those in pea seedlings

A positive hydraulic signal in the form of a xylem pressure step was applied to the roots of intact seedlings of Cucumis sativus L. and Pisum sativum L. Surface electrodes at three positions along the epicotyl/hypocotyl recorded a propagating depolarization which appeared first in the basal, then the central and sometimes the apical electrode positions and fitted the characteristics of a slow wave potential (SWP). This depolarization differed between pea and cucumber. It was transient in cells of pea epicotyls but sustained in cucumber hypocotyls. It was not associated with a change in cell input resistance in pea epicotyls but preceded an increase in the input resistance of cucumber hypocotyl cells. With the increased xylem pressure the growth rate (GR) of cucumber hypocotyls and pea epicotyls underwent a transient increase, peaking after 5 min. If the depolarization reached the growing upper region, it preceded a sustained decrease in the GR of cucumber hypocotyls but only a transient decrease in the GR of pea epicotyls. A temperature jump in the root medium (heat treatment) induced a steep pressure spike in the xylem of the cucumber hypocotyl which showed similar electric and growth effects as the previously applied, non-injurious pressure steps. We suggest that the observed differences in the electric and growth responses between the species were caused by the closure of ion channels in depolarized cells of cucumber but not pea seedlings.     

Gibberellic-acid-induced cell elongation in pea epicotyls: Effect on polyploidy and DNA content

In gibberellic-acid(GA₃)-treated epicotyls of dwarf peas (Pisum sativum L.) grown in the light, DNA (per cell and per epicotyl) is followed. Histofluorometric DNA determinations show that GA₃-promoted cell elongation is not accompanied by increased endomitosis, but chemical estimations show an increased DNA content per epicotyl. This difference must therefore be the result of increased mitotic activity in the GA₃-treated tissue. Epicotyls of seedlings grown with or without cotyledons under continuous light with GA₃ are tetraploid, as are those of ecotylized embryos grown in darkness. These epicotyls reach no more than half the length of octaploid epicotyls of seedlings grown in darkness. This result provides evidence for a relationship between polyploidy and final possible cell length.     

DEVELOPMENTAL MORPHOLOGY OF THE EMBRYO AND SEEDLING OF RHIZOPHORA MANGLE L. (RHIZOPHORACEAE)

The embryo of Rhizophora mangle L. is initially attached to the integument by a long multiseriate suspensor. Its basal cells lyse, and intrusive growth of the endosperm envelops the embryo, forces the micropyle open, and often carries the embryo out of the integument. Thus, “germination” is effected by growth of the endosperm rather than of the embryo. The surface of the endosperm differentiates into a layer of peculiar transfer cells. The cotyledonary body initiates as a toroidal primordium, which later becomes lobed; most of the free portions ultimately fuse. After “germination,” the axis of the viviparous seedling grows by a diffuse intercalary meristem below the cotyledonary node. Before seedling abscission, the shoot apex produces three pairs of leaves, the first of which aborts, leaving the rest of the plumule protected by their stipules. The (immersed) radicle apex is nearly inactive, but lateral roots arise early in seedling development; these are usually the first or only roots to grow during establishment. Ten provascular strands “differentiate” in the cotyledons; a hollow provascular cylinder develops in the hypocotyl. Initial vascular differentiation in the latter is of many alternate poles of xylem and phloem; later, de novo differentiation of metaxylem opposite the protophloem poles, and vice versa, produces collateral bundles. Xylem maturation is endarch over most of the length of the hypocotyl, but tangential and random series of metaxylem vessels occur in the radicle end.     

In vitro organogenesis of Citrus volkameriana and Citrus aurantium

In vitro organogenesis of Citrus volkameriana and C. aurantium was studied considering three explant types: epicotyl segment, internodal segment, and hypocotyl segment with attached cotyledon fragment. The explants were cultured in medium according to Grosser and Gmitter (EME) supplemented with 0, 0.5, 1.0, 1.5, and 2.0 mg dm^{− 3} 6-benzyl-aminopurine (BAP), incubated firstly in darkness for 4 weeks, and then transferred to 16-h photoperiod for 2 weeks. Comparing epicotyl and internodal segments, a higher percentage of responsive explants and a higher number of shoots per explant were obtained with epicotyl segments, regardless of the BAP concentration. For C. volkameriana the highest percentage of responsive epicotyl segments (42 %) was obtained in EME with 1.0 mg dm⁻³ BAP, while for C. aurantium (59 %) in EME with 0.5 mg dm⁻³ BAP. The organogenesis efficiency was the best with the use of the hypocotyl segment with attached cotyledon fragment (77 % for C. volkameriana and to 75 % for C. aurantium). With this explant the morphogenesis occurred only in the hypocotyl region. The in vitro organogenesis was characterized by histological analyses showing that the morphogenic process started in the cambium region near the explant cut end.     

影响四季桔器官发生的因素

对四季桔胚轴直接出芽、愈伤组织诱导及植株再生能力的研究表明：上、下胚轴在含有BA的MT培养基上,均能直接出芽,但上胚轴出芽能力明显高于下胚轴,最高出芽率为96．9％。外植体在培养基上的接种方式,对出芽也有一定影响,上胚轴切段以形态学下端垂直插入,出芽率高,且在培养前期表现尤为突出。胚轴愈伤诱导的适宜培养基为MT＋IBA0．5mg-1＋BAgmg-1。愈伤组织分化时,上、下胚轴愈伤组织所要求的BA浓度分别为4mgL-1及2mgL-1。在根的诱导中,附加的生长素种类,不仅影响生根率的高低,而且影响上部茎叶的生长,其中以加入lmgL-1IBA的效果最好,生根率达84．4％。     

PROLIFERATION AND PLANT REGENERATION FROM THE NODAL REGION OF ZEA MAYS L. (MAIZE,GRAMINEAE) EMBRYOS

Immature embryos of Zea mays L. (maize), cultured on Murashige and Skoog's medium containing 2,4-dichlorophenoxyacetic acid (2,4-D, 0.25–1.0 mg/l) and sucrose (3, 6 and 12%), produced a narrow ridge of tissue in the nodal region of the embryo axis, opposite the scutellum. Only those embryos which were placed with the scutellum in contact with medium showed such a response. The ridge of tissue further proliferated and formed a compact and opaque callus that appeared similar to the scutellar callus. Morphogenesis took place on media containing low concentrations of both 2,4-D and sucrose. Plant regeneration was achieved and is interpreted to take place by the precocious germination of somatic embryos. It is suggested that the ridge of tissue formed at the node may represent an evolutionarily extinct epiblast of the maize embryo and may be cotyledonary in nature.     

Physiology of gibberellin-induced elongation of epicotyl explants from Vigna sinensis

The physiological characteristics of the response of excised cowpea (Vigna sinensis cv Blackeye pea No. 5) epicotyls to gibberellins (GAs) were studied. Epicotyl explants, retaining the petioles and a 2-cm portion of hypocotyl, were placed upright in small vials containing water. Plant growth substances were injected into the subapical tissues as ethanol solutions.Epicotyl elongation resulting from treatment with 0.5 g of GA ranged between 5 and 13 times that of the control, depending on the GA applied. With GA₁, no differences were obtained with explants prepared from 5 to 9-day-old seedlings. The increase in elongation could be detected within 6 h of treatment, and the stimulus of a single application lasted at least 4 days. Final elongation was proportional to the logarithm of the amount of GA, applied, 0.01 to lug. The response to GA treatment was limited to the upper part, the most sensitive zone being located between 2 to 4 mm below the apex of the epicotyl; this effect was entirely due to cell elongation.The induction of epicotyl elongation by GAs seems to be specific and independent of the effect of auxin. IAA had no effect on elongation and 4-chloro-phenoxyisobutyric acid (PCIB) did not affect the response to GA₁ Abbreviations ABA abscisic acid - GA gibberellin - IAA Indole-3-acetic acid - TIBA 2,3,5-triiodobenzoic acid - PCIB 4-chloro-phenoxyisobutyric acid