Effects of gibberellic acid and chlormequat chloride on the proportion of phloem and xylem parenchyma in the storage root of carrot (Daucus carota L.)

A foliar application of gibberellic acid (GA) (100 mg/l) 5 weeks after emergence increased the shoot/storage root ratios, measured 4 weeks later, of 9 cultivars representing a range of types of carrot. Chlormequat chloride (CCC) (2000 mg/l) decreased the ratio for seven of the cultivars. Assessment 8 weeks after treatment showed fewer significant effects of both growth regulators.At the first harvest, GA decreased the phloem/xylem ratio and significantly reduced the amount of secondary phloem produced in the storage root of all cultivars. CCC had no comparable effect except for an increase in the phloem/xylem ratio for one cultivar at both harvests. The significance of these results is discussed in relation to secondary vascular tissue production in storage roots as affected by assimilate partitioning in the whole plant.     

ADP-ribosyl transferase,rearrangement of DNA,and cell differentiation

Cell differentiation is the process by which genetic information is selectively expressed to produce cells with various morphologies and functions. The integrated changes necessary for this fundamentally important process have recently been the subject of intense study. This review will summarize data from several laboratories correlating differentiation with the activity of the enzyme ADP-ribosyl transferase and with changes in single-strand DNA breaks in various diverse eukaryotic systems. We will then discuss the implications of these observations for differentiation in general, including the possibility that rearrangement of genetic material is a widespread mechanism for controlling gene expression.     

Tail Autotomy in the Central American Spiny Rat,Proechimys semispinosus

We studied the effects of sex, age, density and island size and isolation on tail autotomy within twelve island populations of the Central American spiny rat (Proechimys semispinosus, Rodentia: Echimyidae). The proportion of individuals losing their tail differed among islands but not between sexes. Most P. semispinosus lost their tail as adults. Population density and island size and isolation did not influence tail autotomy. Overall tail loss (8.0%) was lower than that previously reported in other populations of P. semispinosus. We suggest that low frequencies of tail loss were due to low rates of attack by mammalian predators typical of small, isolated islands and that differences among islands were due largely to the occasional appearance of transient predators such as coatis (Nasua narica). However, we caution against using tail loss as an index of predation because such a link has not been established yet.     

The Politics of the Plane: On Fatimah Tuggar's Working Woman

In her digital photomontage Working Woman (1997), U.S.-based Nigerian artist Fatimah Tuggar stages a disjunctive encounter between the aesthetic procedures of the historical avant-garde and a postcolonial feminist critique of the visual imagery of the “Afro-optimism” that became prominent in the late 1990s. Treating the “modern African woman” as a mediatic phantom rather than a taken-for-granted subject-position, Tuggar's work evokes the universal “right to communicate” increasingly claimed by anti-neo-liberal activists in the Global South over the past decade.