STUDIES ON SUBMICROSCOPIC ASPECTS OF MINERAL DEFICIENCIES. I. CALCIUM DEFICIENCY IN THE SHOOT APEX OF BARLEY

Marinos , Nicos G. (Waite Agric. Res. Inst., Adelaide, S.A., Australia.) Studies on submicroscopic aspects of mineral deficiencies. I. Calcium deficiency in the shoot apex of barley. Amer Jour. Bot. 49(8): 834–841. Illus. 1962.—The apical dome of the shoot apex of barley, or other cereals, is suitable for the study of submicroscopic cytological changes induced by specific mineral deficiencies because of the many uniform cells available. Also, the well-defined stages of development of the entire apex make possible, in certain cases, the correlation between growth responses and changes in cell structure. The ultrastructure of shoot apex meristematic cells, after KMnO₄ fixation, is fundamentally similar to that of root meristems. The effects of Ca deficiency on cell ultrastructure appear rather suddenly and it has not been possible to reveal unequivocably the initial sequence of events. The first indisputable signs of structural abnormalities appear when the nuclear envelope and the plasma and vacuolar membranes break up and “structureless areas” appear in the cells, followed by the disorganization of other structures like mitochondria and Golgi apparatus, while plastids are more persistent although eventually they also disintegrate. With the progress of Ca deficiency, the cell walls stain darker and gaps may appear, indicating a weakening of their structure. This evidence suggests that Ca is essential for the maintenance and probably for the formation of cell-membrane systems on which the functional integrity of cell metabolism is dependent; Ca effects on cell walls are probably secondary to those changes already described.     

DEVELOPMENTAL STUDIES IN SMILAX (LILIACEAE). I. ORGANOGRAPHY AND THE SHOOT APEX

The ontogeny of the shoot and the tendril-bearing leaf was studied in four species of Smilax which differ considerably in growth habit. Growth is indeterminate in S. bona-nox, S. rotundifolia, S. laurifolia and determinate in S. pumila. Shoot apical organization in all four species is consistent with the tunica-corpus concept. The number of tunica layers varies from 2 in S. bona-nox, S. pumila, and S. rotundifolia to 3 (2–4) in S. laurifolia. A primary thickening meristem was observed in 5. laurifolia. Shoot tip abortion involving a cessation of vegetative growth resembling that found in many woody plants occurs in S. pumila. Even though there are distinct differences in growth habit, vigor, and anatomy, the four species share many developmental similarities. Hence, subtle changes in apical ontogeny may be associated with marked differences in habit.     

STRUCTURE OF THE SHOOT APEX IN LACTUCA SATIVA

Histological observations of the leaf lettuce ‘Black Seeded Simpson’ showed the dormant embryo to possess two visible leaves and a flkat to slightly depressed plumular apex. Observations conducted over a 12-day period of germination and growth showed the development of L₁ and L₂, emergence of L₃ and L₄, and periodic changes in size of the apex which were associated with leaf emergence. Thus the dormant embryo of Lactuca appears to be considerably more advanced in development than was previously believed. The shoot apex appeared flat to slightly depressed at all developmental stages studied.     

THE INDUCTION OF FLOWERING IN NICOTIANA. I. MORPHOLOGICAL DEVELOPMENT OF THE APEX

The morphological changes which the stem apex undergoes in the course of photoperiodic induction are described and presented photographically in order to provide a basis for subsequent physiological investigations. In both a short-day Nicotiana (N. tabacum cultivar ‘Maryland Mammoth') and a long-day one (N. sylvestris), the vegetative meristem is narrow and flat. It becomes wider and dome-shaped when flower induction has become irreversible. The speed at which the various morphological steps succeed each other varies with the intensity of light during the day, especially in the case of N. sylvestris.     

AN ELECTROPHORETIC INVESTIGATION OF INTRAGAMETOPHYTIC SELFING IN EQUISETUM ARVENSE

Because homosporous pteridophytes (Psilotophyta, Arthrophyta, most Microphyllophyta and Pteridophyta) produce bisexual gametophytes, it was maintained that high levels of inbreeding would characterize these plants. Electrophoretic evidence was used to estimate the frequency of intragametophytic selfing in Equisetum arvense (Arthrophyta). A total of 669 samples from 17 populations was examined from western North America. Although some populations exhibited as many as seven or eight genotypes, 10 populations were each characterized by only a single genotype; eight of these populations were heterozygous for one or more loci. For most populations, estimates of intragametophytic self-fertilization are 0.000, indicating that virtually all matings involve different gametophytes. Genetic data corroborate predictions based on earlier field and laboratory investigations of Equisetum gametophytes. These detailed studies demonstrated that in many species, including E. arvense, gametophytes are initially either male or female; only later and in the absence of fertilization do some gametophytes become bisexual. Our findings join a growing electrophoretic data base which demonstrates that homosporous pteridophytes are not highly inbreeding as previously suggested.     

香榧营养苗端的结构及淀粉动态的研究

香榧（Torreya grandis Fort ex Lindl)成熟植株营养芽的季节生长可分四个时期,休眠期,叶扩展期,芽鳞形成期和新的顶芽形成期,在整个生长周期中,苗端始终保持一定的分区形式,但各区繁简在不同发育阶段不尽相同,淀粉在苗端的分布及消长也具有分区特性,与细胞组织学分区完全一致。     

FATE MAP OF THE ORGANIZING SHOOT APEX IN GOSSYPIUM

Chimeral seedlings from a “semigametic” strain of cotton were used as the basis for a clonal analysis of events in the progressive organization of the nascent shoot apex. At the time the proembryo becomes a globular stage embryo with a distinct dermatogen, the surface of the embryo contains an eight-celled compartment for each cotyledon, a two-celled compartment for the first leaf, a one-celled compartment for the second leaf, and a three-celled compartment for the apical initials and all subsequent leaves and aerial structures. The developmental history of the first two leaves differs in a fundamental way from that of all the other leaves.