Effects of Constant and Variable Nitrogen Supply on Sunflower (Helianthus annuus L.) Leaf Cell Number and Size

The effects of nitrogen (N) availability on cell number andcell size, and the contribution of these determinants to thefinal area of fully expanded leaves of sunflower (Helianthusannuus L.) were investigated in glasshouse experiments. Plantswere given a high (N =315 ppm) or low (N=21 ppm) N supply andwere transferred between N levels at different developmentalstages (5 to 60% of final size) of target leaves. The dynamicsof cell number in unemerged (< 0.01 m in length) leaves ofplants growing at high and low levels of N supply were alsofollowed. Maximum leaf area (LA_max) was strongly (up to two-fold)and significantly modified by N availability and the timingof transfer between N supplies, through effects on leaf expansionrate. Rate of cell production was significantly (P<0.05)reduced in unemerged target leaves under N stress, but therewas no evidence of a change in primordium size or in the durationof the leaf differentiation–emergence phase. In fullyexpanded leaves, number of cells per leaf (N_cell), leaf areaper cell (LA_cell) and cell area (A_cell) were significantly reducedby N stress. WhileLA_cell and A_cellresponded to changeover treatmentsirrespective of leaf size, significant (P<0.05) changes inN_cellonly occurred when the changeover occurred before the leafreached approx. 10% of LA_max. There were no differential effectsof N on numbers of epidermal vs. mesophyll cells. The resultsshow that the effects of N on leaf size are largely due to effectson cell production in the unemerged leaf and on both cell productionand expansion during the first phase of expansion of the emergedleaf. During the rest of the expansion period N mainly affectsthe expansion of existing cells. Cell area plasticity permitteda response to changes in N supply even at advanced stages ofleaf expansion. Increased cell expansion can compensate forlow N_cellif N stress is relieved early in the expansion of emergedleaves, but in later phases N_cellsets a limit to this response.Copyright 1999 Annals of Botany Company Helianthus annuus, leaf expansion, leaf cell number, leaf cell size, nitrogen, leaf growth, sunflower.     

Diagnostic associations of p53 immunostaining in fine needle aspiration cytology of the breast

Duplicate cytospin preparations were made from 46 symptomatic breast fine needle aspirates. One of each pair was assigned to benign or malignant categories by one experienced observer as part of the 'triple approach'patient assessment. the other was immunostained with DO7, a monoclonal antibody to recombinant p53 protein, and rated by another observer as positive or negative for nuclear staining, unaware of the cytodiagnosis. Positive controls included carcinomas known to have mutant p53, while negative controls were of the reagent substitution type. of the 26 aspirates with a benign cytodiagnosis (verified by the triple approach), 23 were p53 protein-negative and three positive. of the 20 with a malignant cytodiagnosis (histologically confirmed), six were p53 protein-negative and 14 positive (exact P <0.0001). As a diagnostic test this would give 70% sensitivity and 88% specificity.     

RNAi-mediated resistance to Potato spindle tuber viroid in transgenic tomato expressing a viroid hairpin RNA construct

Because of their highly ordered structure, mature viroid RNA molecules are assumed to be resistant to degradation by RNA interference (RNAi). In this article, we report that transgenic tomato plants expressing a hairpin RNA (hpRNA) construct derived from Potato spindle tuber viroid (PSTVd) sequences exhibit resistance to PSTVd infection. Resistance seems to be correlated with high-level accumulation of hpRNA-derived short interfering RNAs (siRNAs) in the plant. Thus, although small RNAs produced by infecting viroids [small RNAs of PSTVd (srPSTVds)] do not silence viroid RNAs efficiently to prevent their replication, hpRNA-derived siRNAs (hp-siRNAs) appear to effectively target the mature viroid RNA. Genomic mapping of the hp-siRNAs revealed an unequal distribution of 21- and 24-nucleotide siRNAs of both (+)- and (–)-strand polarities along the PSTVd genome. These data suggest that RNAi can be employed to engineer plants for viroid resistance, as has been well established for viruses.     

Hemolymph Proteins and Molting in Crustaceans and Insects

The exoskeleton of crustaceans and insects is formed by cellsof the hypodermis, but several hemolymph proteins contributeto the synthesis of the new exoskeleton. These hemolymph proteinsshare a surprising degree of sequence similarity and are membersof the hemocyanin gene family. Copper-containing prophenoloxidasesof crustaceans and insects are directly involved in cross-linkingand hardening of the exoskeleton during molting and repair.Crustacean cryptocyanin and insect hexamerins lack copper andhave probably evolved from a copper-free product of an earlyhemocyanin gene duplication. These proteins have been implicatedin transport of hormones and phenols, and may be used directlyas structural components of the new exoskeleton. They are synthesizedelsewhere in the body, transported in the hemolymph, and probablytaken up by the hypodermis via specific receptors. Hemocyaninshave some residual phenoloxidase activity, in addition to theirprimary role of supplying oxygen to the metabolizing tissues.Thus multiple members of the hemocyanin gene family play vitalroles during molting, and a molecular phytogeny of these proteinswill contribute to our understanding of the evolution of formand function of these molecules from oxygen transport to molt-relatedactivities. Further studies on the expression of prophenoloxidase,cryptocyanin, hexamerins and hemocyanin, potential marker proteins,may extend our understanding of the relationship between othermolting animals in the proposed clade, Ecdysozoa.     

Melanocytes in Human Embryonic and Fetal Skin: A Review and New Findings

Melanocytes account for approximately 5–10% percent of the cells in adult epidermis. Unlike the ectodermally derived keratinocytes, they originate in the neural crest and migrate into the epidermis early in development. There has been an interest in melanocytes in developing human skin since the late 1800s, when concentrated pigmented cells were identified in the sacro-coccygeal skin of Japanese fetuses. This observation led to speculation and subsequent investigation about the racial nature of the melanocytes in this site (the Mongolian spot), the presence of melanocytes in fetuses of other races, the timing of appearance of these cells in both the dermis and epidermis, and their origin. The early investigators relied primarily on histochemical methods that stained either the premelanosome or the pigmented melanosome, or relied upon the activity of tyrosinase within the melanosome to effect the DOPA reaction. Studies by electron microscopy added further documentation to the presence of melanocytes in the skin by resolving the structure of the melanosome regardless of its state of pigmentation. All of these methods recognized, however, only differentiated melanocytes. The thorough investigations of melanocytes in the skin from a large number of black embryos and fetuses by Zimmerman and colleagues between 1948 and 1955 provided insight into the time of appearance of melanocytes in the dermis (10–11 weeks' menstrual age) and the epidermis (11–12 weeks) and revealed the density of these cells in both zones of the skin of several regions of the body. The precise localization of the melanocytes in the developing hair follicles was contributed by the studies of Mishima and Widlan (J Invest Dermatol 1966; 46:263–277). More recently, monoclonal antibodies have been developed that recognize common oncofetal or oncodifferentiation antigens on the surface or in the cytoplasm of melanoma cells and developing melanocytes (but not normal adult melanocytes). These antibodies recognize the cells irrespective of the presence or absence of melanosomes or their activity in the synthesis of pigment and therefore are valuable tools for re-examining the presence, density, and distribution patterns of melanocytes in developing human skin. Using one of these antibodies (HMB-45), it was found that dendritic melanocytes are present in the epidermis between 40 and 50 days estimated gestational age in a density comparable with that of newborn epidermis and are distributed in relatively non-random patterns. A number of questions about the influx of cells into the epidermis, potential reservoirs of melanoblasts retained within the dermis, division of epidermal melanocytes, and the interaction of melanocytes and keratinocytes during development remain unresolved. The tools now appear to be available, however, to begin to explore many of these questions.     

Association between smoking behaviour and genetic variants of glial cell line-derived neurotrophic factor

Glial cell line-derived neurotrophic factor (GDNF) promotes development and differentiation of dopaminergic neurons, thus it has an important role in dopamine-related neuropsychiatric disorders. Since the role of dopamine system in smoking is well established, we hypothesized that GDNF gene variants may affect smoking behaviour. Self-reported data on smoking behaviour (never smoked, quit, occasional, or regular smokers) and level of nicotine addiction (Hooked on Nicotine Checklist and Fagerstrom Nicotine Addiction Scale), anxiety, as well as buccal samples were obtained from 930 Hungarian young adults (18–35 years). Genetic analysis involved eight GDNF single-nucleotide polymorphisms (SNP) (rs1981844, rs3812047, rs3096140, rs2973041, rs2910702, rs1549250, rs2973050 and rs11111). Allele-wise association analyses of the eight GDNF SNPs provided a significant association between smoking behaviour and rs3096140 (P = 0.0039). The minor allele (C) was more frequent in those groups who smoked in some form (quit, occasional or regular smokers) as compared to those who never smoked (P = 0.0046). This result remained significant after Bonferroni correction for multiple testing. In the ever smoking group, no significant differences were found in the level of nicotine addiction by the alleles of these polymorphisms. Also, no significant interaction of rs3096140 and smoking categories were observed on anxiety mean scores. Although previous data demonstrated an association between GDNF rs2910704 and severity of methamphetamine use to the best of our knowledge, this is the first study on the role of GDNF genetic variations in smoking behaviour. Our results suggest that GDNF rs3096140 might be involved in the genetic background of smoking, independent of anxiety characteristics.