FLEXIBILITY IN ONTOGENY AS SHOWN BY THE CONTRIBUTION OF THE SHOOT APICAL LAYERS TO LEAVES OF PERICLINAL CHIMERAS

The development of leaves on apically stable, periclinal chimeras was studied in a number of dicot genera. The mutant cell layers of the shoot apex and the tissues derived from them were as active developmentally as the normal layers. Ontogeny was the same in these chimeras as in nonchimeras, and growth of their leaves can be outlined as follows. Formation of the buttress, the axis, and the lamina of simple dicot leaves were independent events. In each the first growth included derivatives of the apical layers, usually three in number, found in the apex of the shoot and the lateral buds. Most cell divisions in the outer layers (L-I and L-II) were anticlinal relative to the new structures. Therefore, in the proximal regions of the buttress, axis (petiole and midrib), and lamina, the derivative cells of L-I and L-II were usually present in single layers. The rest of the internal tissue was from L-III. As formation of the axis and the lamina proceeded, derivatives of L-II replaced L-III internally in the distal and marginal regions leaving cells of L-III behind. Both the determinate growth of leaves and the pattern of cell divisions at and near the leading edges of growth meant that no cells in the leaf were comparable to the initial cells of the shoot apex. As the lamina extended, there were extensive intercalary cell divisions, both anticlinal and periclinal, so that in any given region of a leaf the layers of internal cells were from either L-II or L-III. At any point along the axis, L-III participated or did not participate in laminar extension. At any given stage in laminar growth either of two sister cells in any internal layer divided either a few times or extensively. The extreme variability in direction and frequency of cell division during leaf development was under an overriding genetic control, which resulted in the normal or typical size, shape and thickness of leaves.     

人胎儿早中期肠壁肌层发育分化的研究

目的探讨人胚早中期肠壁肌层的发育分化过程.方法采用形态学及免疫组织化学方法对24例4-28周胎儿空肠、回肠、结肠肠壁肌层进行形态学及免疫组化观察.结果α-SMA阳性的环行肌层与纵行肌层在10周胎儿已形成完整环形,空肠、回肠的黏膜肌层在10周时刚开始形成,13周时才刚刚形成完整环形,而结肠的黏膜肌层迟至15周才形成完整环形,此时细胞均呈圆形或卵圆形,绒毛中央α-SMA阳性的细胞在13周胎儿各段肠已出现,但结肠较空肠、回肠少.此后,随着胎龄的增大,各肌层均明显增厚,细胞形态也逐渐由卵圆形变为梭形.结论环行肌层与纵行肌层的发育分化早于黏膜肌层;空肠、回肠各肌层的发育分化早于结肠.     

内源吲哚乙酸、脱落酸和赤霉酸与棉铃发育及脱落的关系

气相色谱分析的结果表明,开花后5～6天,不受精即将脱落棉铃里IAA和ABA的含量显著高于对照;GA_3处理的铃中IAA和ABA的含量则明显低于对照。IAA和GA_3含量在开花后第10天达到高峰,以后迅速下降,至第30天。又出现第二峰胚珠和纤维里尤为明显。ABA含量在开花后第15天达得高峰,以后下降,到第30天,又逐渐上升。棉纤维伸长及干重增加的最快速率与这三种激素的含量高峰密切相关。     

GENETIC BLOCKS IN THE THIAMINE SYNTHESIS OF THE ANGIOSPERM ARABIDOPSIS,,

Five thiamine-requiring mutants were obtained at two loci. Two are blocked in the synthesis of the pyrimidine part of the vitamin, the other three have lost the ability to make the thiazole moiety. None of the tested substances suggested as possible or likely precursors of the pyrimidine or the thiazole components of thiamine displayed any activity in the mutants. These conditional lethals responded to remarkably small supplements of thiamine. The pyrimidine-requiring mutants utilized to some extent the anti-vitamin neopyrithiamine. The thiazole-less mutants grew on basal media supplemented only with the analog, oxythiamine. Thiamine deficiency, irrespective of the position of the genetic block in the synthesis, results in a characteristic anomaly of pigmentation. The position of the py locus in the second linkage group has been determined. Allelic complementation has not been detected. The frequency of mutations affecting thiamine synthesis appears about the same in Arabidopsis as in fungi. The general frequency of reparable genetic lesions is, however, one to two orders of magnitude lower in Arabidopsis than that in fungi or bacteria.     

银杏叶的研究开发概况

本文对银杏叶的化学、药理、临床和制剂等进行了综述。     

EFFECT OF CARBON DIOXIDE ENRICHMENT ON DEVELOPMENT OF THE FIRST SIX MAINSTEM LEAVES IN SOYBEAN

Many conclusions concerning plant responses to CO₂ enrichment have been based on assumptions of increased leaf size derived from observations of average leaf area measured at some time well into the growth period. The objectives of this study were to study the effect of elevated CO₂ on 1) the timing of mainstem leaflet appearance, 2) the rate and duration of leaflet expansion, and 3) the final area of individual leaflets of soybeans (Glycine max [L.] Merr. cv. Bragg) grown from seed at 348, 502, and 645 μl 1^–1 CO₂ concentrations. Central leaflet areas from mainstem trifoliolates 1–6 were measured every two days from time of appearance to full expansion. Leaflets tended to appear earlier in elevated CO₂ treatments; leaflets 2 through 6 appeared an average of 0.4 days earlier in the 502 μl 1^–1 treatment and 1.2 days earlier in the 645 μl 1^–1 treatment than in the 349 μl 1^–1 treatment. Relative rates of expansion were different among leaflets in their response to elevated CO₂; expansion rates of leaflets 1 and 4 were significantly higher at the highest CO₂ concentration. However, final area of leaflets was not affected by CO₂, or (in leaflet 5 only) was slightly smaller at the highest CO₂ treatment. Apparently, higher expansion rates of leaflets 1 and 4 at high CO₂ were offset by a tendency for decreased duration of expansion. It appears that there are morphological constraints on final leaflet area in soybean seedlings which limit the effects of elevated CO₂ on the early development of mainstem leaf area.