ULTRASTRUCTURE OF NECTARIES IN RELATION TO NECTAR SECRETION

In the last 15–20 years, ultrastructural studies have added new important cytological information to the relatively rich literature on the morphology and light microscopy of nectaries. On the basis of these studies, the following main conclusions can be drawn regarding the relation between the ultrastructure of nectaries and the process of nectar secretion: (1) the transport of the pre-nectar in the nectariferous tissue is mainly via the symplast; (2) the ER alone or the ER and the Golgi apparatus are involved in the process of secretion; (3) the elimination of nectar from the protoplast of the secretory cells is by reverse pinocytosis; (4) the outer walls of the secretory cells of nectaries in many plants possess wall ingrowths.     

抗氧化剂对苜蓿原生质体早期培养的影响

研究发现,分离原生质体的酶解脱壁处理可以诱导苜蓿细胞产生活性氧。培养基中添加抗氧化剂,有助于提高培养原生质体的分裂频率,缓解褐化现象的出现。经紫外照射处理的培养基不利于苜蓿原生质体的生长和分裂,添加抗氧化剂后,紫外辐射所引起的不良效应则被抵消。因而,通过抗氧化剂对活性氧的清除,有助于早期原生质体的培养。     

FLORAL NECTARIES AND TRICHOMES IN RELATION TO POLLINATION IN SOME SPECIES OF THEOBROMA AND HERRANIA (STERCULIACEAE)

Floral surfaces of two Theobroma spp. and one species of the allied genus Herrania (Sterculiaceae) were examined using scanning electron microscopy for reward system information of the pollinator-adaptation syndrome. These flowers are structurally complex and have sheltered reproductive parts indicating an elaborate insect-mediated pollination mechanism. Analysis of anther dehiscence, anthesis and pollen tube growth suggests a crepuscular pollination strategy. Suspected pollinators have been observed on floral parts of theobromas possessing stomate type nectaries and various shaped trichomes (blade of petal ligule and adaxial surface of petal hood). H. purpurea has elongate ligules devoid of stomates. Glandular clublike structures are found on the ovaries of all three spp. In numerous spp. of theobromas, except T. cacao, and two species of Herrania, a conspicuous ring of multicellular trichomes occurs at the adaxial base of the sepals. A possible function for the ring may be fragrance production because of its greatly reduced condition in the faintly scented T. cacao and the prevalence of pronounced fragrances in these other species.     

FINE STRUCTURE OF THE DORMANT EMBRYO OF MEDICAGO SATIVA

The subcellular organization of epidermal and parenchymatous cells of various embryo parts of naturally desiccated Medicago sativa seeds was examined by electron microscopy. Both epidermal and parenchymatous cells were filled with reserve protein and lipid bodies, which varied somewhat in structure, size, and abundance among different embryo parts and between epidermal and cortical cells of the same part. Variations in wall thickness, nuclear conformation, and clarity of organelle membranes were noted. Mitochondria and plastids were recognizable but were poorly differentiated. The endoplasmic reticulum was sparse and not well defined, microtubules were rarely encountered, while dictyosomes appeared to be absent. Polyribosomic configurations were lacking although the cytoplasm of most cells contained large concentrations of ribosomes.     

ULTRASTRUCTURE OF THE SUBGLANDULAR CELLS FROM THE FOLIAR NECTARIES OF COTTON IN RELATION TO THE DISTRIBUTION OF PLASMODESMATA AND THE SYMPLASTIC TRANSPORT OF NECTAR

Foliar nectaries on the midveins of 7-cm leaves from cotton (Gossypium hirsutum L., cv. Stoneville 213) were examined by light and electron microscopy. The nectaries consist of external multicellular papillae and internal subglandular tissue that extends from the bases of the papillae to the vascular tissue of the midveins. The subglandular tissue is composed of small parenchyma cells; it does not contain sieve elements or xylem vessels. The parenchyma cells are rich in mitochondria, and their walls contain numerous pit fields having a high concentration of plasmodesmata. The absence of vascular tissue and the significance of the pit fields in the subglandular tissue are discussed in relation to symplastic transport of nectar secretions.     

Hormonal Regulation of Morphogenesis and Cold-resistance: I. MODIFICATIONS BY ABSCISIC ACID AND BY GIBBERELLIC ACID IN ALFALFA (MEDICAGO SATIVA L.) SEEDLINGS.

Seedlings of alfalfa (Medicago saliva L.) cv. Ranger and cv.Hairy Peruvian were grown under conditions of long day and hightemperatures or short day and low temperatures. Under long daysand high temperatures, both varieties developed an elongatedshoot and exhibited relatively low cold-resistance, as measuredby the extent of leakage of cellular substances, after beingexposed to sub-zero temperature. Under short days and low temperatures,Ranger seedlings developed a rosette growth and exhibited animproved response to sub-zero temperature. In contrast, HairyPeruvian seedlings developed an elongated shoot and did notacquire cold-resistance. Hairy Peruvian grown in a nutrientsolution containing abscisic acid, however, developed a rosetteand acquired an improved response to sub-zero temperature, likecv. Ranger under short days and low temperatures. Addition ofgibberellic acid to Ranger seedlings grown under these conditionsnullified the environmental effects, since they developed anelongated shoot and did not acquire cold-resistance. It is concludedthat abscisic acid and gibberellic acid are involved in theinterrelationship between morphogenesis and cold-resistancein the seedlings of the two alfalfa cultivars.     

THE HORMONAL CONTROL OF ORGAN FORMATION IN CALLUS OF MEDICAGO SATIVA L. CULTURED IN VITRO

Organogenesis in alfalfa callus (Medicago sativa L. cv. ‘Regen S’) has been obtained by the transfer of callus from an induction medium containing growth regulators to a regeneration medium lacking growth regulators. The transfer of callus from induction medium containing high levels of 2,4-D and low levels of kinetin to regeneration medium resulted in the formation of shoots. Conversely, the transfer of callus from induction medium containing low levels of 2,4-D and high levels of kinetin resulted in the formation of roots. The pattern of organogenesis on regeneration medium was modified by the nutritional composition of that medium. When Blaydes medium supplemented with inositol and yeast extract was employed as regeneration medium, root organogenesis was inhibited. Root organogenesis was not inhibited by either Shenk and Hildebrandt medium or Gamborg's B5 medium. Shoot formation occurred on all of these media. A survey of the in vitro organ-forming capacity of 14 genotypic clones from the cv. ‘Regen S’ was conducted. The capacity to form organs differed quantitatively among the clones analyzed. A more detailed analysis of a highly responsive clone (RA3) and a poorly responsive clone (RA5) revealed no significant qualitative difference in their organogenic responses.     

THE FOLIAR AND FLORAL NECTARIES OF TURNERA ULMIFOLIA L.

The floral and foliar nectaries of Turnera ulmifolia are specialized and are representative of others found in the Turneraceae. The foliar and floral nectary systems must be treated independently. Foliar nectaries are organized into a definite structure (composed of a base, rim, secretory tissue, modified epidermis) and are supplied with vascular tissue composed of both xylem and phloem. Nectar from foliar nectaries contained equal concentrations of glucose, fructose, and sucrose. Floral nectaries are an integral part of the basal portion of each filament. The nectariferous tissue is not supplied with vascular tissue and secretion lasts only a few hours. Nectar from these staminal nectaries yielded a sucrose-dominant nectar containing also fructose, glucose, an unknown, and a trace amount of melezitose. Observations of flowering confirmed the reported short duration of the individual flowers.     

苜蓿胚状体的分离及其发育过程中三种同工酶酶谱分析(简报)

目前,对胚状体发生过程中的生理生化研究表明,这一过程伴随有核酸、蛋白质等大分子物质合成速度的增加及与胚胎发生有关的特异性蛋白的合成;一些同工酶,如过氧化物酶、脂酶、细胞色素氧化酶和谷氨酸脱氢酶     

GROWTH REGULATOR EFFECTS ON BUD INITIATION IN CALLUS CULTURES OF MEDICAGO SATIVA

Influence of growth regulators on bud initiation in callus of alfalfa (Medicago sativa L.) was studied by varying levels and combinations in the first medium of a two-medium sequence used to obtain whole plants. Callus of tetraploid clone S-4 (cv. ‘Saranac‘) was initiated from immature ovaries on a modified Blaydes' basal medium containing all combinations of six concentrations (0–36 μM) of kinetin (K), six concentrations (0–44 μM) of naphthaleneacetic acid (NAA), and seven concentrations (0–36 μM) of 2,4-dichlorophenoxyacetic acid (2,4-D). After 28 days the callus was challenged to form buds by transfer to the modified Blaydes' medium containing 2.0 g/liter yeast extract and 0.57 mM inositol. No buds were produced in the absence of 2,4-D in the first medium, and the frequency of bud formation on the second medium was directly proportional to the 2,4-D concentration in the range 2.3–54 μM in the preceding medium. Buds were produced in the absence of kinetin in the first medium, but its presence in the range 2.3–36 μM markedly increased bud formation. NAA was not required for bud formation, and the budding frequency increased only slightly with increasing NAA concentration in the first medium. Budding of callus of two other alfalfa clones was also influenced by the 2,4-D concentration in the initial medium. There were several indications that many of the buds were initiated on the first medium and completed development on the second medium. These included the differential effect on budding of combinations of 2,4-D, NAA and kinetin in the callus initiation medium, the specific media sequence required, and the presence of embryoids on the callus which after transfer to the yeast extract-inositol medium produced buds.