THE EFFECT OF SUGARS AND APPLIED CHEMICALS ON HETEROBLASTIC DEVELOPMENT IN IPOMOEA PURPUREA GROWN IN ASEPTIC CULTURE

Seedlings of Ipomoea purpurea were grown in aseptic culture in order to investigate more directly than had been possible in pot culture the effect of carbohydrate and protein nutrition on heteroblastic development which in this species involves a change from entire juvenile to lobed adult leaves. The effect of sugars was to accelerate the development of the adult leaf form while casein hydrolysate retarded it. The growth retardants, AMO-1618 and CCC, also promoted the formation of the adult leaf. These results are discussed in the light of current views on the factors controlling heteroblastic development.     

EFFECT OF SEED SIZE ON SEEDLING SUCCESS IN THREE SPECIES OF SESBANIA (FABACEAE)

Variation in seed size may produce variation in seedling fitness, but the relationship is not simple. Differences in seed size within and among species may not have the same effects. We examined effects of differences in seed size within and among three species of Sesbania, S. macrocarpa, S. drummondii, and S. vesicaria, on seedling emergence and growth in the greenhouse and the field. Of the three species, the largest-seeded species, S. vesicaria, produced the largest, longest-lived seedlings in both the greenhouse and the field. Even though plant size differed, annual S. macrocarpa produced the same seed mass as annual S. vesicaria in the greenhouse. Within-species effects were less clear. In the greenhouse, S. vesicaria seedlings grown from large seeds remained largest until maturity, but the other species did not exhibit this effect. Some persistent within-species effects of seed size differences on height were observed in the field in 1981, but not in 1980, suggesting that field conditions increase the importance of seed size differences. Unscarified S. drummondii seeds germinated before seeds of the two annual species. Within species, larger seeds of the annuals and smaller seeds of the perennial germinated first. Differences among the species in the importance of seed size to seedling fitness may allow the species to have different patterns of regulation of reproduction in response to stress. Sesbania vesicaria showed the largest within-species effects of seed size and has the lowest plasticity in seed size, suggesting that patterns of plasticity have been selected such that the most important component of yield varies least.     

EFFECT OF 4'-CHLOROGLUTARANILIC ACID ON GROWTH AND DEVELOPMENT OF SUNFLOWER SEEDLINGS

The potential growth-regulating properties of 4'-chloroglutaranilic acid (CGA) as well as oxygen and nitrogen isosteres were examined in whole-plant bioassay systems utilizing sunflower seedling (Helianthus annuus L.). Test systems included both soil-grown plants and hydroponic studies. Foliar applications of CGA produced growth inhibition which was detectable within 24 hr and which persisted for at least 30 days. Direct application to roots produced a growth inhibition which was 15% greater than foliar applications. Foliar or root application at 10^-5 m or greater concentrations produced gross changes in leaf morphology. Total plant-height inhibition was principally associated with stem growth in an area located between primary leaves and the shoot meristem. CGA was found to be 32 % less active than IAA as a growth promoter, but was 76 % more active than IAA as a growth inhibitor; the most severely affected organ was the leaf and the least affected was the root system. Leaves from soil-grown plants treated wth a 10^-3 m foliar application of CGA possessed several abnormalities. These included an increase in thickness and dry weight, a reduction in chloroplast starch vacuoles, extractable starch, soluble hexoses, and soluble proteins.     

THE EFFECT OF GENETICALLY BASED DIFFERENCES IN SEED SIZE ON SEEDLING SURVIVAL IN ARABIDOPSIS THALIANA (BRASSICACEAE)

The relationship between genetically different seed sizes and seedling survival under severe nutrient deprivation was determined by comparing ten inbred lines of Arabidopsis thaliana. Seedlings were supplied with only sterile distilled water, and the number of days between germination and death (complete chlorosis) was recorded. Seedlings from genotypes with larger seeds survived longer than seedlings from genotypes with smaller seeds. These results suggest a genetically based adaptive significance of larger seed size resulting from a greater seedling tolerance of nutrient deprivation. This may confer a potentially important selective advantage when nutrient deprivation is the result of a low resource supply in the environment, or the result of nutrient depletion by neighbors.     

EFFECT OF ETHYLENE ON CELLULAR DIFFERENTIATION IN ETIOLATED PEA SEEDLINGS

Ethylene (50 ppm) and 2,4-D (1 mm ) inhibit xylogenesis and completely prevent fiber lignification in the third internode of etiolated pea seedlings (Pisum sativum var. Alaska) during 96–240 hr of treatment. When ethylene is removed after 72 hr, normal differentiation resumes; thus the gas causes no irreversible damage to the cells. A combined treatment with 50 ppm ethylene and 50 μm 2,4-D or treatment with 1 mm 2,4-D alone causes inhibition similar to that observed with 50 ppm ethylene, and 50 μm 2,4-D is partially effective. The inhibition of xylogenesis and fiber lignification caused by 2,4-D is partly or wholly due to auxin-induced ethylene production.     

滇紫草Onosma paniculatum愈伤组织中主要成分的抑菌作用

从诱导形成的滇紫草愈伤组织中分离得到四种单体.其中两种单体:β、β-二甲基丙烯酰阿卡宁(β,β-dimethyacrylalkannin,)和乙酰阿卡宁(Acetylalkannin,)的愈伤组织混合色素,对金黄色葡萄球菌和假单孢杆菌都有比较明显的抑制作用.尤其是乙酰阿卡宁抑制效果格外显著.然而对大肠杆菌却表现不出抑制效应.     

除草剂拿草特对菟丝子幼苗茎尖分生区有丝分裂的影响

酰胺类除草剂拿草特对菟丝子幼苗生长具有强烈的抑制作用。采用石蜡切片法和细胞扫描分光光度法,通过测定对照及处理幼苗茎尖分生区的细胞分裂指数和核DNA含量,发现拿草特对菟丝子幼苗生长的抑制是由于它对分生区细胞有丝分裂的双重抑制作用:间期抑制和中期抑制。即它既可阻止有丝分裂的启动,又可象秋水仙素一样通过影响纺锤丝的功能而将细胞分裂阻止于中期,引起分生区细胞的多倍体化和径向膨大。这种生长受到抑制且茎尖粗肿的幼苗不能够在农作物上寄生。     

ON THE DEVELOPMENT OF MACROSCLEREIDS IN SEED COATS OF PISUM SATIVUM L.

Macrosclereid differentiation was investigated by light and electron microscopy in pea testae during the transformation of protodermal precursors to the mature sclereids. The protodermal cells divide anticlinally and elongate into the macrosclereid layer during seed coat development. Young sclereids have elongate nuclei, plastids become somewhat granal during cellular maturation, vacuolation appears to be an autolytic process, and the cells have dense arrays of endoplasmic reticulum and ribosomes. Considerable dictyosome activity and microtubule development is observed as the secondary wall is produced. Many coated vesicles are associated with and fuse with the plasmalemma. During development, the outer tangential wall area of the macrosclereids acquires a definite cuticle and subcuticular layer. Also, at this time the sclereid walls under the subcuticular layer display semicircular microfibril orientation. The sclereid walls adjacent to the hypodermis become multilayered. As the macrosclereids near maturity, the “light line” becomes discernable in the light microscope at the junction of the cellulosic tips of the macrosclereids and the subcuticular layer. This “light line” is prominent using interference optics and is an osmiophilic layer in the electron microscope. This layer may represent the suberin “caps” reported by earlier workers.     

PRODUCTION AND EFFECT OF SEED SIZE IN A GRASSLAND ANNUAL (ERODIUM BRACHYCARPUM,GERANIACEAE)

Over its fruit maturation period in the field, Erodium brachycarpum (Geraniaceae) exhibited a striking decrease in average seed mass; seeds produced in the 1st week of fruiting were twice the size of those produced 6 weeks later at the time of drought-induced plant senescence. Individuals with earliest fruit maturation produced the most seeds with the widest range of sizes and over a longer period than the others. In a greenhouse experiment, a similar decline in mean seed weight was generated by inducing drought conditions. Large seeds remained dormant longer and, once the seed coat was scarified, took longer to germinate than small seeds. This study indicates that small E. brachycarpum seeds (36% of the seed pool) produced late in the fruiting period are likely to germinate in the year of seed production, approximately 4–8 months after seed maturation. In contrast, the large seeds (23% of the seed pool), most of which are produced early in the fruiting period, are more likely to germinate in subsequent years (i.e., 15 months or more after seed maturation).     

PLEIOTROPIC EFFECTS ON SEED DEVELOPMENT OF THE INDETERMINATE GAMETOPHYTE GENE IN MAIZE

Not more than half the seeds borne by maize plants of the W23 inbred strain, homozygous for a mutant gene termed “indeterminate gametophyte” (ig), develop normally. The remainder exhibit polyembryony (6 %), heterofertilization (7 %), elevated ploidy level of the endosperm (45 %), or other less frequent anomalies. The ig effects were identified and characterized by chromosome counts and genetic tests. Twins were regularly found to be diploid and concordant for heterozygous marker genes introduced maternally. When the marker genes were introduced paternally, twins frequently were non-concordant, or the embryo and endosperm phenotypes did not correspond. The proportion of the various types and the absence of conjoined embryos indicated that, although identical in their maternal inheritance, the twins were regularly dizygotic. Those twins identical in paternal inheritance probably originate from the fertilization of two genetically identical eggs by the two sperm of one male gametophyte. When ig ig compared to normal diploid plants were pollinated by tetraploids, the proportion of plump seed formed was markedly increased. Evidently this result is the consequence of elevation of the endosperm ploidy level by the ig gene. The ig gene thus appears to interfere with differentiation of the components of the female gametophyte so that the number of eggs and polar nuclei, instead of being one and two, is indeterminate.     

低温胁迫对水稻幼苗抗坏血酸含量的影响

随着低温时间的延长,水稻幼苗抗坏血酸和GSH的含量均平行地下降,抗坏血酸含量与电解质渗出率之间呈负相关。增强低温胁迫程度,随着抗坏血酸含量逐渐减少,MDA含量则逐渐增加。经低温处理后在不同光强下恢复时,抗坏血酸和MDA含量的变化不同。抗氧化剂(GSH、半胱氨酸和巯基乙醇)的预处理可抑制低温引起的抗坏血酸含量的下降。