CYTOKININ- AND GIBBERELLIC ACID-INDUCED EFFECTS ON THE STRUCTURE AND METABOLISM OF SHOOT APICAL MERISTEMS IN OPUNTIA POLYACANTHA (CACTACEAE)

The dormant axillary buds of Opuntia polyacantha can be activated by either cytokinins or gibberellic acid. Under the influence of benzylaminopurine (BAP), the axillary bud meristem increases greatly in size and becomes mitotically active. The primordia produced by the meristem develop as normal photosynthetic leaves. Gibberellic acid (GA) also causes the meristem to become mitotically active, but the meristem does not increase in size. The primordia produced under the influence of GA develop as normal cactus spines. Leaf-producing meristems and spine-producing meristems have the same zonation, despite the differences in size. The meristems are composed of a uniseriate tunica, a central mother cell zone, peripheral zone, and a pith rib meristem. The mitotic activity of each of the zones in the leaf-producing meristem differs significantly from the mitotic activity of the corresponding zones in the spine-producing meristem.     

HORMONAL CONTROL OF ORGANOGENESIS IN OPUNTIA POLYACANTHA (CACTACEAE)

An axillary bud (areole) of Opuntia polyacantha is composed of an extremely short axis which bears highly modified leaves (spines). After producing the spines, the bud apical meristem becomes quiescent. When the axillary bud is excised and cultured with benzylaminopurine (BAP), the apical meristem increases in complexity and produces leaves on an elongated axis. Gibberellic acid (GA) induces spine production with no elongation of the axis. Naphthaleneacetic acid (NAA) causes no structural change in the meristem but induces root formation in adjacent tissue. The initiation of roots, spines, or leaves is visible within three days. Explants on medium lacking hormones show no structural change, but by the tenth day are insensitive to BAP or NAA. These aged explants can be made to respond to BAP or NAA by merely rewounding them at the time of hormone application. With concentrations previously found to be optimal for single hormone responses, NAA in combination with BAP prevents shoot formation, or in combination with GA prevents spine production. When all three hormones are combined, spines are produced, indicating that GA is active morphologically while BAP and NAA counteract each other. If the level of NAA is decreased, BAP counteracts the NAA and also overrides the GA and leafy shoots are produced. By varying the proportions of BAP and GA, in the absence of NAA, four types of lateral appendage can be produced: leaves, mildly altered leaves, leaf-spine transition forms, and spines.     

EFFECT OF GROWTH RATE,MORPHOGENIC ACTIVITY,AND PHYLOGENY ON SHOOT APICAL ULTRASTRUCTURE IN OPUNTIA POLYACANTHA (CACTACEAE)

Dormant short shoot apices of Opuntia polyacantha were cultured under three conditions: cytokinin and high sucrose to stimulate the formation and rapid growth of a leafy long shoot; cytokinin and no sucrose (slow growth of a leafy long shoot); gibberellic acid and high sucrose (rapid growth of a spiny short shoot). These meristems, and also dormant (uncultured) ones, were analyzed by stereological, ultrastructural techniques. By comparing meristems growing with cytokinin but with or without sucrose, correlations between metabolic rate and apical ultrastructure were studied; comparison of leaf-producing and spine-producing meristems permitted examination of correlations with morphogenic role; comparison with published data for four other species permitted study of phylogenetic effects, and comparison with dormant apices revealed information about meristem activation. Ultrastructure varied according to each condition: metabolic rate, morphogenic activity and species can be distinguished by quantitative methods. Apical ultrastructure is most strongly correlated with rate of growth such that apices of differing species resemble each other if growing at similar rates, whereas apices of a single species differ markedly if growing at differing rates or if performing different morphogenic activities. Hyaloplasm is an excellent indicator of metabolic rate; mitochondria, nuclei, and vacuoles are not.     

THE FUNCTION OF EXTRAFLORAL NECTARIES IN OPUNTIA ACANTHOCARPA (CACTACEAE)

Opuntia acanthocarpa (Cactaceae) possesses extrafloral nectaries embedded in the areoles of new reproductive and vegetative growth. The nectar secreted by these glands attracts ants and is a nutritional food source. Members of one attracted ant species, Crematogaster opuntiae (Myrmicinae), are aggressive and efficient defenders of the plants against cactus-feeding insects. The results of our study are consistent with the ant-guard hypothesis for the role of extrafloral nectaries in O. acanthocarpa. Additionally, individuals of O. acanthocarpa are well protected in comparison with those of O. phaeacantha. The latter generally possess ephemeral extrafloral nectaries and consistently maintain fewer ants.     

A MORPHOMETRIC STUDY OF THE ULTRASTRUCTURE OF ECHINOCEREUS ENGELMANNII (CACTACEAE). IV. LEAF AND SPINE PRIMORDIA

A stereological morphometric study of leaf primordia (P1 and P2) of Echinocereus engelmannii indicated that primordia are significantly different ultrastructurally from the shoot apical meristem tissues (tunica and peripheral zone) that produce the primordia. Leaf initiation involves readjustments of rates of synthesis and growth of cytoplasm, vacuoles, mitochondria, chloroplasts, and dictyosomes, such that leaf initiation must be a complex process in which different cell components are affected individually. Furthermore, leaf primordia are ultrastructurally distinct from spine primordia. Leaf and spine primordia as young as these are not yet irrevocably determined, thus different types of primordia, from the time of their inception and before their determination, have distinctly unique metabolisms; primordia are not merely generalized, uncommitted outgrowths whose developmental fate is set at some time later than inception.     

CYTOKININ-ELICITED FORMATION OF THE PITH-RIB MERISTEM AND OTHER EFFECTS OF GROWTH REGULATORS ON THE MORPHOGENESIS OF ECHINOCEREUS (CACTACEAE) SEEDLING SHOOT APICAL MERISTEMS

Shoot apical meristems of Echinocereus engelmannii have only a tunica-corpus organization at germination, but the corpus rapidly develops central mother cells, a peripheral zone and a pith-rib meristem. The manner in which nutrition, darkness and various growth regulators at several concentrations and in several combinations affect the development of zonation was examined by growing derooted seedlings on agar which contained the nutrients or growth regulators. Benzylaminopurine was able to elicit the formation of the pith-rib meristem in an otherwise non-zonate corpus. Also, the rate of leaf initiation was greatly increased. Gibberellic acid severely inhibited the formation of corpus zones but had little effect on leaf initiation. Indoleacetic acid had no effects other than mild inhibition of zonation and a slight retardation of leaf initiation. Abscisic acid was strongly inhibitory. Sucrose only slightly increased the rate of leaf formation and did not affect apex size or zonation. To more closely examine the cytokinin-induced effects on the apical meristem, several growth regulators were applied in combination with the most effective concentration of cytokinin. Certain combinations were able to interfere with several of the cytokinin-induced responses, while other cytokinin-induced responses occurred even in the presence of high concentrations of these other growth regulators. Leaf initiation and meristem morphogenesis appeared to be remarkably stable and insensitive to the presence of most hormones except cytokinin and gibberellin.     

ROOT GLOCHIDS AND ROOT SPURS OF OPUNTIA ARENARIA (CACTACEAE)

Root glochids of Opuntia arenaria Engelm. are produced by adventitious buds (areoles) that arise endogenously on fleshy roots. If they remain active, root areoles become dwarf shoots that initiate only glochids and trichomes unless the roots are uncovered or the shoots bearing the roots are removed. Then they will expand, producing aerial shoot joints. Root spurs are formed in great numbers on the profusely branched system of small roots. They consist of clusters of rootlets about one mm long that are initiated in sympodial sequence, each new rootlet arising endogenously near the base of the preceding one. On older spurs this results in the formation of a short axial peg. Rootlet primordia lack a root cap from the beginning and appear to mature quickly, losing all their meristematic characteristics and becoming completely covered with root hairs, even over the tip. They may represent a mechanism for the rapid production of root hairs during the infrequent periods when moisture is available. In any case, they seem to be transitory structures because cork soon forms beneath the older ones on a spur.     

SEEDLING DEVELOPMENT OF OPUNTIA BRADTIANA (CACTACEAE)

Seedling development in Opuntia bradtiana, a north-central Mexican endemic, is similar to that of other opuntias, except for the absence of glochids and the fact that germination is extremely slow and germination percentage low. Hypocotyl and root elongation and epicotyl development are rapid for two weeks after rupture of the seed coat. However at this point hypocotyl elongation nearly ceases, while stem and root development continue at a reduced rate. An eight-month seedling is usually not more than 25 mm tall but has numerous areoles with spines and occasionally one subtending leaf. At this time tubercles have begun to coalesce into the vertical rows of ribs characteristic of the section Grusonia.     

THE EFFECT OF GIBBERELLIC ACID ON LEAF AREA AND DRY-MATTER PRODUCTION IN MAJESTIC POTATO

When gibberellic acid (50 p.p.m. in aqueous solution) was sprayed twice or six times at weekly intervals on potato plants (var. Majestic) with a low or high nitrogen supply it did not affect rate of leaf production on the main axis, but caused earlier senescence of leaves, especially with the more frequent spraying, and inhibited leaf production and growth on laterals of the high-nitrogen plants at nodes 10 and 11 but not at other nodes. This central region of the stem appears to have a low growth potential, probably because it lies midway between two zones of active growth, viz. the basal branches and the younger leaves on the main stem. Competition between these is increased by gibberellic acid. Gibberellic acid increased leaf area even when lack of nitrogen was restricting growth but this did not produce extra dry matter. Tuber weight was increased more in high-nitrogen plants by two sprayings than by six sprayings. The net assimilation rate of low-nitrogen plants was halved by spraying but was not changed in high-nitrogen plants where the value was similar to that of low-nitrogen control plants. The high-nitrogen plants had absorbed nearly all the available nitrogen between the second and third harvests, but plants treated with gibberellic acid, nevertheless, had more total dry weight and tuber dry weight than the controls. The nitrogen content of the leaves expressed on an area basis was lower in sprayed plants and, with continued spraying, fell at the third harvest to equal that of low-nitrogen plants. Evidently, the effect of gibberellic acid depended on the interaction between the rate of application and the nitrogen supply, but further work is necessary to define the conditions that give the maximal effect on dry-matter production.     

BIOMECHANICS OF CLADODES AND CLADODE-CLADODE JUNCTIONS FOR OPUNTIA FICUS-INDICA (CACTACEAE)

Shoots of Opuntia ficus-indica (L.) Miller consist of a sequence of flattened stem segments (cladodes) in contact over only a small portion of their periphery. The maximum angular deflection for an upper terminal cladode under a weight equal to its own fresh mass applied perpendicular to its face increased from 5° to 9° as cladode length increased from 20 cm to 60 cm, consistent with an increase in mass proportional to length^2.83. Just over half of the angular deflection of an upper cladode represented flexure of the cladode-cladode junction; the angular deflections averaged fourfold more for mass loadings perpendicular to the cladode face compared with those parallel to it. Compared with such static loading by mass, dynamic loading by wind for a 31-cm-long cladode led to a maximum angular deflection of only 0.13° at a wind speed of 1 m sec⁻¹ and 2.3° at 10 m sec⁻¹. Drought caused the angular deflections to increase 9% for 21-cm-long cladodes over a 90-day period and to decrease 45% for 44-cm-long cladodes. Increases in stem temperature from 0 C to 20 C increased angular deflections of a 27-cm-long cladode about 10%, with little further increase up to 50 C. Even though the cladodes were thin compared with stems of many perennials and the cladode-cladode junction comprised only about 3.5% of their peripheral area, the shoots of O. ficus-indica proved to be quite rigid, as angular deflections of cladodes were only slightly influenced by temperature and wind, were not markedly enhanced by drought, and were less than 10° under loading by a cladode's mass.     

PHYSIOLOGICAL RESPONSES TO RAINFALL IN OPUNTIA BASILARIS (CACTACEAE)

An immediate, marked response to small amounts of rainfall occurs in Opuntia basilaris, despite previous drought conditions. The effect of rainfall is upon plant water potential, which is the single most important parameter influencing stomatal opening, CO₂ assimilation, and organic acid synthesis. Nocturnal stomatal opening is initiated following rainfall, and stomata remain open during the daytime. Decreasing stomatal and mesophyll resistances correlate with increasing rates of nocturnal assimilation of ¹⁴CO₂. Photosynthetic rates of ¹⁴CO₂ assimilation are low, despite high plant water potentials and low stomatal diffusion resistances. The decreased mesophyll resistances and increased rates of nocturnal ¹⁴CO₂ assimilation correlate with the increases of nocturnal efficiency of water use and CO₂ assimilation. The diurnal efficiency of water use and CO₂ assimilation is lower than the nocturnal gas exchange efficiency values.     

烟草叶组织培养中光与激素对形态发生的调节作用

我们在烟草叶的组织培养中,研究了光与激素对形态发生所起调节作用的相互关系。在培养基中细胞分裂素与生长素的浓度比例都取得最佳值,而浓度绝对值则取两组不同数值。在这两组实验条件下,分别考察了不同波段,不同强度的光照射对于不定芽的发生和愈伤组织增重的影响。用不同波段的光照射,改变光强,光促进生长的效应都有一极大值。用蓝光照射,极大值的数值最高。激素浓度低时光的效应较大;浓度高时,除蓝光外,其他波段的光效应都很微弱。     

THE EFFECTS OF GIBBERELLIC ACID AND KINETIN ON THE GROWTH OF MAJESTIC POTATO

The effects of spraying potato plants (var. Majestic) with gibberellic acid and kinetin were investigated. Gibberellic acid increased both leaf area and dry-matter production over the short period of the experiment, but there were indications that this would not persist at maturity. Kinetin alone depressed leaf area and dry-matter production, but this did not occur in the presence of gibberellic acid. The mean net assimilation rate measured over a 2-week period was not significantly reduced by gibberellic acid.     

EFFECTS OF CARBON DIOXIDE ON THE GROWTH AND MORPHOGENESIS OF MARSILEA

Increased concentrations of CO₂ in air (1–50%) cause young plants of Marsilea vestita to exhibit many characteristics of the water form when they are grown on a solid substrate under sterile conditions. Thus these plants have longer internodes, shorter petioles, more rectangular-shaped epidermal cells and fewer stomata on the lower leaf epidermis than controls grown in 0.03% CO₂. Over a 2-week period, dry weight increase is considerably greater in 12.5% and 25% CO₂ than in 0.03% CO₂. Fifty percent CO₂ is inhibitory to growth. CO₂-enriched air has the same morphogenetic effect when supplied in the light or the dark. Possible explanations for this effect are discussed.     

INTERACTIVE EFFECTS OF GIBBERELLIC ACID AND SALINITY ON THE GROWTH OF BEANS

Nieman , R. H., and Leon Bernstein . (U. S. Salinity Laboratory, Riverside, Calif.) Interactive effects of gibberellic acid and salinity on the growth of beans. Amer. Jour. Bot. 46(9): 667–670. 1959.—Dwarf red kidney bean plants, grown from the primary leaf stage to maturity on a graded salt series (0, 1.5, 3.0 and 4.5 atm. O.P. NaCl added to a base nutrient solution), showed a progressive and highly significant growth depression with increasing concentration of NaCl. At low levels of salinity (0 and 1.5 atm. O.P.), gibberellic acid applied as a spray to primary leaves, in concentrations of 10 and 100 p.p.m. in distilled water, increased the stem length, fresh and dry wt. of both the top and the root, the yield of green beans, area per leaf, and the total leaf area per plant. At high levels of salinity (3.0 and 4.5 atm. O.P.) growth was so severely suppressed that the expression of all gibberellin effects, except the increase in stem length, was essentially prevented. Gibberellin was, therefore, ineffective in overcoming the salt-induced suppression of growth. An increased rate of water use per unit leaf area was quite consistently observed with the gibberellin-treated plants. This may be simply the result of the increased exposure to light and to air movement of leaves on an elongated stem.     

DEVELOPMENT OF FLORAL ORGANS IN THE SITES OF LEAF PRIMORDIA IN PINGUICULA VULGARIS

Plants of Pinguicula vulgaris L. have either clockwise or counterclockwise spiral phyllotaxy. The inception of floral primordia occurs in leaf sites as a normal sequence of development. Only two leaf primordia initiated late in the season develop into floral primordia in the following year. They do not represent a direct modification of the apical meristem nor of the detached meristem. The apical meristem continues to produce leaves in the vegetative phase and flowers in the reproductive phase, and thus the plants show a monopodial growth. Axillary buds are not developed in this perennial species and instead additional buds of adventitious ontogeny appear. Such buds are produced on the older leaves of larger plants, and they are extremely useful in the vegetative propagation of the species.     

器官间关系对叶片衰老的影响

叶片衰老是整个植株生理特性的敏感表现,受根系、茎、生殖器官和其他叶片等器官的影响。器官间关系影响叶片衰老可能是通过竞争体内营养、水分等物质、竞争环境因子、源库关系、激素等信息系统调节等机制实现的。从整株水平上加强叶片衰老的生理机制和控制技术研究,将为生产上控制衰老、减少叶片异常衰老造成的产量和品质损失提供有效的技术途径。