STEM ELONGATION OF XANTHIUM PLANTS PRESENTED IN TERMS OF RELATIVE ELEMENTAL RATES

Vegetative Xanthium plants grown under noninductive conditions were marked along the stem with India ink and photographed during three successive days. The relative elemental rates of stem elongation [d(dX/dt)/dX] were estimated for 18 plants between 15 and 18 plastochrons. On the average, only the 8.0 cm terminal part of the stem was elongating in this group of plants. Young internodes were elongating at constant relative elemental rates ([d(dX/dt)/dX] was about 0.2 days^–1); nodal portions of the stem beteween two young internodes were not elongating. Internodes longer than 2 cm displayed an acropetal pattern of elongation in which the basal part of an internode stopped elongating and matured first and the apical portion last. The pattern of elongation of the stem could be best approximated to a set of cascading waterfalls with declining plateaus in the direction of the water flow. The acropetal pattern of individual internode elongation observed in Xanthium was similar to those reported for Helianthus and Phaseolus internode growth.     

AN ANALYSIS OF LEAF ELONGATION IN XANTHIUM PENSYLVANICUM PRESENTED IN RELATIVE ELEMENTAL RATES

Maksymowych , Roman . (Villanova U., Villanova, Pa.) An analysis of leaf elongation in Xanthium pensylvanicum presented in relative elemental rates . Amer. Jour. Bot. 49(1): 7–13. Illus. 1962.—Xanthium plants were grown vegetatively, and leaves, whose developmental stages were specified by a previously described leaf plastochron index (L.P.I.), were marked with India ink along the midrib and photographed during 3 successive days. The relative elemental rates of elongation, d(dX/dpl)/dX were estimated during the whole course of development. The pattern of elongation was not constant but was changing with increasing plastochron age of the leaf. The elements of a young leaf of L.P.I. 0.75 elongated with a constant relative rate. In older leaves, the d(dX/dpl)/dX values were progressively declining toward the tip of the lamina. After L.P.I. 6.3 the only increment in length was due to the elongation of the elements of the petiole. The pattern of growth distribution is discussed in terms of relative elemental rates with respect to cell division and cell elongation in various portions of the lamina and is correlated with the basipetal trend of tissue differentiation in the developing Xanthium leaf.     

INTERNODE ELONGATION IN XANTHIUM PLANTS TREATED WITH GIBBERELLIC ACID PRESENTED IN TERMS OF RELATIVE ELEMENTAL RATES

Xanthium plants were grown vegetatively and their developmental stages were designated by a previously described plastochron index (PI). Internodes of plants, both treated with gibberellic acid (GA₃) and untreated, were marked with India ink and photographed during 3 successive days. The relative elemental rates of elongation d(dX/dt)/dX were estimated between 15.7 and 19.0 plastochrons. The rate of growth of the GA₃-treated internodes was at least twice that of the control. The emerging pattern of acropetal internode elongation was similar in both GA₃-treated and control plants. Only rates of growth were significantly higher in the GA₃-treated plants. The acropetal pattern of internode elongation was the opposite of the basipetal pattern observed in Xanthium leaves but followed the acropetal pattern observed in Helianthus and Phaseolus internode growth.     

EFFECTS OF RED AND FAR-RED RADIATION ON CELL DIVISION AND ELONGATION IN THE STEM OF PINTO BEAN SEEDLINGS

Nine-day-old Pinto bean seedlings, Phaseolus vulgaris L., were treated daily for 12 days with supplementary red or far-red radiation following daily exposure to 8 hr of daylight. Stem elongation was nearly exponential from the 4th to the 12th day of treatment and was about 2.9 times greater under far-red radiation. Cell division and cell elongation were promoted essentially equally by far-red radiation. There was virtually no difference in either the rate of leaf initiation or the duration of growth of internodes under the supplementary radiation.     

PHOTOINHIBITION OF ELONGATION GROWTH OF ROOTS IN RICE SEEDLINGS

Effects of white, blue, red and far-red lights on the elongationgrowth of intact primary roots in rice seedlings were investigated.White light inhibited elongation of root cells. Blue light inhibitedboth cell elongation and cell multiplication, but red lightinhibited only cell elongation. The effect of far-red lightwas almost the same as that of the red. The lights exerted;the same effects on the growth of primary roots irrespectiveof age of the seedlings. The inhibitory effects of the lightswere also observed when the root of the deshooted seedlingswas irradiated, but not when only the shoot of the seedlingswas irradiated. It was inferred that it is not the shoot butthe root which responds to the light in this phenomenon. DCMUhardly affected root growth at a concentration so high as toinhibit strongly photosynthesis in the shoot. The possibilitythat photosynthesis participates directly in the photoinhibitionof root growth in rice seedlings was excluded. ¹ Present address: Tohoku National Agricultural Experiment Station,Morioka     

抗氧化剂对农杆菌介导的大豆下胚轴GUS基因瞬时表达的影响

大豆(Glycine max)下胚轴作为大豆遗传转化的外植体材料,能快速高频再生不定芽。然而,在遗传转化过程中褐化影响基因转化效率。在该研究中,我们用含有GUS染色基因和hpt II(Hygromycin phosphotransferase II)筛选基因的农杆菌(Agrobacterium tumefaciens) LBA4404侵染大豆下胚轴,并用组织化学定位法测定了GUS基因的瞬时表达,以确定大豆的优化基因转化条件。结果显示,在共培养基中加入硫代硫酸钠、L_半胱氨酸以及二硫苏糖醇等抗氧化剂,可以有效地抑制大豆下胚轴在组培过程中褐化的发生,并大幅度提高农杆菌在下胚轴的瞬时表达率。这些结果说明抗氧化剂可以降低这种影响并有效提高基因转化效率。     

SEASONAL TRENDS IN RATES OF PHOTOSYNTHESIS AND RESPIRATION OF LOBLOLLY PINE AND WHITE PINE SEEDLINGS

Mc Gregor , William H. Davis (Clemson Coll., Clemson, S.C.), and Paul J. Kramer . Seasonal trends in rates of photosynthesis and respiration of loblolly pine and white pine seedlings. Amer. Jour. Bot. 50(8): 760–765. Illus. 1963.—Seasonal trends in the rates of photosynthesis and respiration of potted loblolly and white pine seedlings were studied by measuring CO₂ exchange with an infra-red gas analyzer at intervals during a year. The seedlings were kept out-of-doors, but measurements were made indoors at 25 C and 4000 ft-c of light. Beginning in February, the rate of photosynthesis per plant of both species increased, reaching a peak in mid-September for loblolly pine and in mid-July for white pine and then declining rapidly after mid-September for both species. The spring increase began before new needles emerged and the autumn decline was not accompanied by appreciable loss of foliage. The respiration rate of loblolly pine increased steadily throughout the year. Respiration of white pine increased until mid-May and then remained fairly constant through the remainder of the year. Maximum rate of photosynthesis per unit of fascicle length occurred in July for the white pine and in May for the loblolly pine, and rates declined after September in both species. Respiration rate per unit of fascicle length showed a marked increase as spring growth began in April, then decreased to a minimum in September and increased during the winter in both species. Total chlorophyll per seedling reached a maximum in September for both species and declined slightly during winter. Total chlorophyll per unit of fascicle length increased in the spring, declined slightly in midseason, and increased again in September. Photosynthesis per unit of chlorophyll reached a maximum in May for loblolly pine and in July for white pine. Stem elongation of white pine was 88% completed by May 15. On the same date, stem elongation of loblolly pine was only 42% completed.     

THE INITIATION AND ELONGATION OF RHIZOID CLUSTERS IN CAULERPA PROLIFERA

Under improved environmental conditions the average rate of elongation of the rhizoid cluster was 5.2 mm/day in the first 3 days. The rate decreases thereafter and is close to zero around 5–6 days after initiation. The elongation, like that of the rhizome, is chiefly by means of “tip-growth.” The presumptive site of the initiation is 1.3–1.7 mm from the rhizome tip. Under present experimental environment, the presumptive time of the initiation was mainly at 1 to 3 hr after the beginning of the light period. Initiation in the dark period was less frequent, and little or no initiation in the middle and later parts of the light period was observed. The average plastochron of the cluster was 0.91 day. The rate of elongation of the rhizoid cluster was less variable than that of the rhizome. Hence, the slope of calculated regression line from the plot, the cluster length vs. its distance from the rhizome tip, is steeper when the rhizome grows slower (4.9–5.8 mm/day) and less steep when the rhizome grows faster (7.3–8.9 mm/day). In spite of some variation in the slope of the regression line, the intersection between the line and X-axis remains about the same. The application of information on the presumptive site and presumptive time of the rhizoid cluster initiation to a developmental study of micro-events taking place prior to the morphological differentiation is proposed.     

THE TRANSITION FROM FILAMENTOUS TO TWO-DIMENSIONAL GROWTH IN FERN GAMETOPHYTES. III. INTERACTION OF CELL ELONGATION AND CELL DIVISION

Periodic cell divisions were induced in gametophytes of Pteridium aquilinum by daily irradiation with white light. In white-dark cycles, the rate of cell division was promoted by increased time in white light; cell elongation was not affected. The time of transition to two-dimensional growth (days to 5% 2-D) was closely associated with the mitotic rate. For white-red cycles, the rate of elongation was controlled by the intensity of red light (wavelengths over 550 nm). This increased elongation delayed the initiation of 2-D development. In both cases the rate of transition to 2-D growth was correlated with the amount of elongation per division.