PHOSFON-INHIBITION OF GERMINATION AS AFFECTED BY TEMPERATURE AND RADIATION

Inhibition of radiation-induced germination in Verbascum thapsusL. by low concentrations of the growth retardant Phosfon isincreased by maintenance temperature of 30 or higher. The germinationprocess is most sensitive to combined supraoptimal temperatureand Phosfon treatments during the time when root protrusionor processes preparatory to it occur in control seeds. At 25,inhibition of induced germination by Phosfon is relieved bycontinuous irradiation, with effective wavebands centered onwave-lengths of 430, 535, 600 and 650 mµ. The bands at485 and 735 mµ reduce germination to or below the levelof briefly red-irradiated seeds. (Received November 22, 1965; )     

GROWTH OF MAIZE SEEDLINGS AS AFFECTED BY GLUCOKININ AND INSULIN

1. Solutions of glucokinin and insulin, particularly those from which the easily dialyzable substances had been removed, increased the growth of roots and tops of young maize seedlings, as shown by comparisons with untreated seedlings grown in distilled water. 2. Strong solutions of crude glucokinin or of crude insulin repressed growth. 3. Seedlings from which the tips of the primary roots had been removed just before placing the plants in the test solutions made greater gains in both top growth and root growth than seedlings with uncut roots treated with solutions of the same strength. Control experiments showed that this difference in growth was not the result of cutting the roots, and that crude glucokinin and crude insulin contained several substances some of which were more readily absorbed by the plant than others. 4. Purification of crude glucokinin and crude insulin by dialysis showed that the residue of relatively non-dialyzable substance was the growth-promoting fraction. 5. The dialysate of crude glucokinin contained at least three types of material, one of which repressed growth. 6. Ammonium sulfate, one of the possible impurities of glucokinin, repressed the growth of seedlings but did not produce the other changes in metabolism shown by seedlings treated with dialysate of onion glucokinin. 7. The endosperm of plants treated with growth-promoting solutions of purified insulin did not lose weight as rapidly as the endosperms of untreated plants, indicating that the treated plants made their greater gains in growth by more efficient utilization of the endosperm, or as a result of greater photosynthetic activity, or by a combination of these. 8. Experiments with albino seedlings suggested that the greater gain in weight made by plants treated with insulin was the result in part of increased photosynthetic activity.     

REGULATION OF GROWTH AND CELLULAR DIFFERENTIATION IN DEVELOPING AVENA INTERNODES BY GIBBERELLIC ACID AND INDOLE-3-ACETIC ACID

Auxin (IAA) at physiological concentrations causes significant reduction of GA₃-promoted growth in excised Avena stem segments. IAA is thus considered to be a gibberellin antagonist in this system. It was found to act non-competitively in repressing GA₃-augmented growth in these segments. In intercalary meristem cells at the base of the elongating internode, GA₃ blocks cell division activity and causes a marked increase in cell lengthening. IAA substantially promotes lateral expansion in comparable intercalary meristem cells, particularly in the vicinity of vascular bundles underlying the epidermis. It also alters the plane of cell division in differentiating stomata. IAA at high concentrations (10⁻³, 10⁻⁴ m ), in combination with GA₃, overrides the effects of GA₃ on cell lengthening, while with low concentrations of IAA (10⁻⁹, 10⁻¹⁰m ), the effects of GA₃ are clearly dominant. At intermediate concentrations of IAA (10⁻⁶, 10⁻⁷m ), in the presence of GA₃, the effects of this treatment on cell differentiation closely parallel the pattern of differentiation in untreated tissue. It is postulated that a lateral gradient of auxin and gibberellin could control cell expansion in long epidermal cells during intercalary growth of the internode.     

LONG-TERM DEVELOPMENTAL CHANGES IN XANTHIUM INDUCED BY GIBBERELLIC ACID

One application of gibberellic acid (GA₃) to Xanthium shoots resulted in an initial large stimulation, followed by inhibition, of internode elongation. After presumed translocation of the hormone from the locus of its application to the stem apex several morphological changes were observed. There was a significant increase in number of mitotic figures in the apical meristem and a twofold increase in volume of the apical dome. With time, the rate of leaf production was accelerated about 1.8 times. The phyllotaxis of leaf primordia initiated under the influence of GA:, changed from a (2, 3) contact parastichy pattern in control shoot to a (3, 5) pattern. Final petiole length was smaller than the control, and the absolute rate of lamina expansion decreased under prolonged treatment. Gibberellic acid had a pronounced effect on leaf morphology. GA_a induced the development of lanceolate leaves instead of typical deltoid leaves. The reduction in leaf area coincided with a 32% reduction in the average area of epidermal cells. Plastochron changes were correlated with anatomical and morphological changes during the course of leaf development.     

油菜幼苗对硼的吸收与运转及钙的影响

硼促进油菜幼苗生长和对N、P、K、Ca 营养元素的吸收.当油菜生长介质中钙浓度增大时,植株吸硼量和硼在新叶中的积累减少,老叶中积累增加。硼在油菜体内的运转系数在低硼条件下较大,并随钙处理水平的增加而下降.结果表明,在硼素供应有限的条件下,油菜体内硼仍具一定的移动性,钙则使硼的吸收和移动性下降.     

GROWTH AND DEVELOPMENT OF LITCHI CHINENSIS AS AFFECTED BY SOIL-MOISTURE STRESS

The effects of soil-moisture tension on growth and floral development of field-grown Litchi chinensis, a woody subtropical fruit tree, were investigated. Floral initiation and fruit set were promoted by a high soil-moisture tension for 6 months, beginning with June, 1967, or for 4 months, beginning with October, 1967. The normal floral-initiation period in Hawaii is during the period November to January. The apical meristematic tissue, judged from the number of branches flowering, was apparently not adversely affected by a soil-moisture stress, provided adequate water was available during the floral-bud development period. Low soil-moisture tension (0.3 bar) throughout the experimental period was inhibitory for floral bud initiation. High soil-moisture tension inhibited growth of the trunk and the emergence of flush-growths. Flowering was correlated significantly, and negatively, with growth. Leaf nitrogen and potassium levels were unaffected by water stress, but the phosphorus levels in leaf and stem were lowered by high-moisture tension. Hydrolysis of starch under moisture stress, reported for some species, was not evident in the Litchi. No correlation between trophic constituents and flowering was observed.     

CONTROL OF INTERCALARY GROWTH IN THE SCAPE OF GERBERA BY AUXIN AND GIBBERELLIC ACID

With the inflorescence removed, intercalary growth can be maintained in the scape of Gerbera jamesonii by application of gibberellic acid (GA, gibberellin A₃) or indole-3-acetic acid (IAA); the latter usually promotes more rapid and greater elongation than the former because of a greater effect on older tissues. Simultaneous application of the two substances, even when both are at optimal levels, promotes more rapid elongation than either substance alone; in fact, the rate of elongation may equal that of the intact scape. In decapitated scapes (receptacle and involucral bracts removed with the inflorescence), GA and IAA promote cell elongation with reduced or no cell division. In deflowered scapes (receptacle and involucral bracts intact) both GA and IAA promote cell division, as well as cell elongation, so that the pattern of scape elongation is nearly the same as that for intact scapes. Apparently the bracts and receptacle contribute something required for cell division which acts in concert with GA and IAA. Deflowered and decapitated scapes elongate at nearly the same rates initially; thus the rate of elongation does not depend on cell division. The ultimate length of the scape is dependent on cell number and, hence, cell division, since deflowered scapes attain greater lengths than those that are decapitated.     

INDUCTION OF MORPHOGENETIC CHANGES AND ACCELERATION OF LEAF INITIATION BY GIBBERELLIC ACID IN XANTHIUM PENNSYLVANICUM

One application of gibberellic acid (GA₃) to young internodes significantly accelerated the rate of leaf initiation and caused an increase in the number of internodes in shoots of Xanthium pennsylvanicum. The average duration of one plastochron was reduced from 3.3 to 1.9 days. The rate of growth of the GA₃-treated internodes, and also of those positioned above and below, was at least twice that of the control. It appeared that the growth substance was translocated both acropetally and basipetally from the locus of application and that it significantly accelerated the rate of stem elongation. Gibberellic acid also had a pronounced morphogenetic effect on the leaves. It induced the development of lanceolate leaves instead of typical deltoid leaves. The area and the leaf length of the treated plants were both significantly reduced. Each response may be regulated by increasing or decreasing the concentration of gibberellic acid. The induced morphogenetic changes were not permanent. A reversion to the original condition was noticeable about 8 wk after treatment.