ORGANIZATION OF THE ADVENTITIOUS ROOT APEX IN TAMARIX APHYLLA

Adventitious roots on branches of Tamarix aphylla (L.) Karst. develop in hyperhydric outgrowths of the lenticels. The following stages could be distinguished in the formation of the apices of these roots: (1) initiation, (2) a stage of random divisions, (3) a stage of transverse divisions, with respect to the longitudinal axis of the primordium, (4) formation of the procolumella, (5) differentiation of the procambium, the cortical meristem and the protoderm, (6) enlargement of the promeristem, and (7) emergence.     

SOLUTE CONCENTRATIONS IN THE PHLOEM AND APEX OF THE ROOT OF ZEA MAYS

Plasmolytic studies utilizing a graded series of mannitol solutions (0.1–1.4 M in 0.1 M increments) were conducted on adventitious roots of Zea mays to determine solute concentrations of cell types at various locations in the root. Results indicated that mature sieve-tube members had the highest solute concentration as determined by their C₅₀ (the estimated mannitol concentration plasmolyzing an average of 50% of a given cell type) of any cell type in the root. In tissue 12 cm from the tip, C₅₀ values calculated for proto- and metaphloem sieve-tube members were 1.15 and 1.19 M, respectively, while in tissue 0.5 cm from the root tip, values for the same cell types were 0.68 and 0.46 M, respectively. The C₅₀ values for sieve elements in tissue 5 cm from the tip were intermediate (1.08 and 1.11 M). Although the companion cells generally plasmolyzed at nearly the same concentrations of mannitol as the sieve elements, their C₅₀ values were slightly lower than adjacent mature sieve elements. The lowest C₅₀ (0.35 M) for any cell type examined was associated with meristematic cells in tissue 0.1 cm from the root tip. Taken collectively, the results indicate that positive concentration gradients exist between mature sieve tubes and meristematic cells of the root apex of maize.     

THE ROOT APEX OF MALVA SYLVESTRIS. III. LATERAL ROOT DEVELOPMENT AND THE QUIESCENT CENTER

Both histological and autoradiographic procedures were used to follow lateral root initiation and development. Lateral roots of M. sylvestris were initiated in the pericycle, and although the endodermis became multiseriate, endodermal derivatives were not incorporated into the lateral root primordium. Apical organization of pre-emergent roots, characterized by two tiers of cortical initials, did not change with growth. During pre-emergent development there was no evidence of cortical lysogeny or quiescent center formation. Quiescent centers were present in both secondary and tertiary roots longer than 0.5 cm.     

THE ROOT APEX OF MALVA SYLVESTRIS. I. STRUCTURAL DEVELOPMENT

The apical organization of the primary root of Malva sylvestris was analyzed at several growth stages, beginning with the embryo, to determine the structural changes that occurred during growth. Seeds were germinated, and plants were grown under controlled conditions. There were three discrete groups of initials in the embryonic root: those of the central cylinder, cortex, and secondary columella. The secondary columella initials consisted of a plate of cells flanked by a ring of cortical initials. The lateral portion of the rootcap shared a common origin with the epidermis. During growth both the initials of the secondary columella and outer cortex produced rootcap cells. The first indication of the outer cortical initials participating in rootcap formation was observed in roots 3 cm long. In 6-, 9-, and 16-cm roots the cellular continuity between the outer cortex and rootcap was marked, but in 23- and 33-cm roots the histogenic continuity between the outer cortex and rootcap was not evident. In all growth stages the initials of the central cylinder and inner cortex retained their histogenic integrity.     

外源胆固醇对水稻根端线粒体ATP酶活力的影响

外源胆固醇无论是通过根系吸收或是直接与离体线粒体一起温育的方式,在试验浓度范围内均能提高水稻根端线粒体ATP酶的活力,同时观察到外源胆固醇能明显降低ATP酶表现活化能(Apparent activation energy,AEa)在Arrhenius图上的折点温度。其中通过根系吸收进入线粒体膜内后,其线粒体ATP酶AEa的两个折点温度由对照的27.7℃和15.5℃分别降低到24.5℃和12.7℃;直接与离体线粒体一起温育的两个折点温度分别降低到18.8℃和9.6℃。试验结果证明,适量的外源胆固醇不仅对水稻根端线粒体ATP酶活力具有明显的促进作用,而且对降低线粒体膜脂的相变温度也有明显的调节作用。     

外源胆固醇对水稻根端线粒体膜流动性的影响

应用荧光探剂 1,6-二苯基-1,3,5-己三烯(DPH)观察外源胆固醇对水稻极端线粒体膜流动性的影响。结果表明,无论外源胆固醇通过水培根系吸收或是直接添加给予水稻根端线粒体,都能使DPH与线粒体结合后的荧光强度减弱,使荧光偏振度和微粘度降低,增加水稻根端线粒体膜流动性。     

MITOTIC ACTIVITY IN THE ROOT APEX OF THE WATER FERN MARSILEA VESTITA HOOK. AND GREV.

Roots of Marsilea vestita ranging from 1–120 mm in length, as well as root primordia, were analyzed to determine mitotic activity and ploidy levels in the apical cell, five well-defined regions of the root proper, and two regions in the root cap. The mitotic index of the apical cell tended to be above the overall mean mitotic index for the entire apical meristem. No diurnal rhythm in mitotic index was apparent. The cell-cycle duration of the apical cell ranged from 12.1–25.2 hr, that of other regions of the root from 16.1–41.5 hr. There was no indication of polyploidy in any part of the apical meristem except in a few procambial cells. Thus, the results support the classical concept that the apical cell is the ultimate source of cells in the root.     

大豆根尖维管组织分化和静止中心

用~3H-胸腺嘧啶核苷标记的自显影方法测定了大豆根尖的静止中心。结果表明在萌发后24小时产生,其高度为最大值,随着天数增加静止中心的高度逐渐减小。静止中心的高度与根的直径显著相关(r=0.94,p=0.01)。用显微光度计测定了静止中心细胞核的DNA 含量,大部分细胞在2c 水平,处在 G_1期。大豆根尖的静止中心与维管组织分化水平不相关,静止中心不直接控制维管组织的分化。     

THE SHOOT APEX OF BOUGAINVILLEA SPECTABILIS

The shoot apex of Bougainvillea spectabilis consists of five zones: A two- or occasionally three-layered tunica, a central mother cell zone, a cambium-like zone, a rib meristem (central meristem), and a peripheral meristem. The presence of a cambium-like zone is somewhat unusual in the apex of vascular plants, having only been reported for a few taxa. In B. spectabilis the cambium-like zone is consistently present throughout the plastochron and all yearly seasonal periods.     

ONTOGENY OF THE FLORAL APEX OF MICHELIA FUSCATA

Tucker , Shirley C. (u . Minnesota, Minneapolis.) Ontogeny of the floral apex of Michelia fuscata. Amer. Jour. Bot. 47(4): 266—277. Illus. 1960.–The floral apex of Michelia fuscata, although determinate, has a prolonged period of activity. It undergoes an increase in average height and diameter through the time of initiation of stamens, followed by a decrease in average size during initiation of successive carpels. The floral apex also shows periodic or plastochronic fluctuation in size and configuration between initiation of tiers of appendages at nearly the same level and time. Plastochrons of different duration alternate in an orderly sequence in the floral meristem.     

THE ONTOGENY OF CARBONIFEROUS ARTICULATES: THE APEX OF SPHENOPHYLLUM

Twig apices of Sphenophyllum lescurianum, S. constrictum, and two new Sphenophyllum taxa are described in transverse and longitudinal section from middle and upper Pennsylvanian age specimens. In all of the species the single apical cell has the shape of a tetrahedron, with a triangular upper surface and three internal cutting faces. Segment cells are produced from each of the cutting surfaces in a dextrorse or sinistrorse direction, depending upon the species. The central portion of each segment cell contributes to the initiation of the procambium, while the remaining outer portion undergoes a vertical and subsequent horizontal division to form segment cells. Segment cells are aligned in vertical tiers beneath the respective apical cell cutting faces, with the individual leaves positioned directly beneath a tier of segment cells. Leaf primordia are first observed as a series of surface undulations below the apex, with an intercalary meristem located directly beneath each primordium. The vegetative apical organization of Sphenophyllum is demonstrated to be very similar to the type of organization found at the stem tips of Catamites and Equisetum.     

ONTOGENY OF THE SHOOT APEX OF SEEDLINGS OF PINUS PONDEROSA

Dormant seeds of ponderosa pine (Pinus ponderosa) were stratified and then planted in the greenhouse. Changes occurring in the shoot apex during germination and growth of the seedlings were observed and are described. Cell divisions in germinating embryos are first noted on the flanks of the apex near the cotyledons. From these loci, mitotic reactivation proceeds up the flanks of the apex and inward toward cells of the rib meristem. Cells are dividing actively in all regions of the shoot apex of seedlings 12 days after planting, but no cytohistological zonation is evident due to differences in staining intensity and in cell and nuclear size. In 64-day-old seedlings the mitotic rate is reduced and the characteristic zonation of pine apices begins to appear. Zonation is even more evident in older seedlings. These observations are discussed in relation to the concept of initials and to theories concerning factors which regulate growth in the shoot apex.