We report on the fourth in a series of studies on the reliability of application programs in the face of random input. Over the previous 15 years, we have studied the reliability of UNIX command line and X-Window based (GUI) applications and Windows applications. In this study, we apply our fuzz testing techniques to applications running on the Mac OS X operating system. We continue to use a simple, or even simplistic technique: unstructured black-box random testing, considering a failure to be a crash or hang. As in the previous three studies, the technique is crude but seems to be effective in locating bugs in real programs.We tested the reliability of 135 command-line UNIX utilities and thirty graphical applications on Mac OS X by feeding random input to each. We report on application failures -crashes (dumps core) or hangs (loops indefinitely) -and, where source code is available, we identify the causes of these failures and categorize them.Our testing crashed only 7% of the command-line utilities, a considerably lower rate of failure than observed in almost all cases of previous studies. We found the GUI-based applications to be less reliable: of the thirty that we tested, only eight did not crash or hang. Twenty others crashed, and two hung. These GUI results were noticeably worse than either of the previous Windows (Win32) or UNIX (X-Windows) studies.

We report on the fourth in a series of studies on the reliability of application programs in the face of random input. Over the previous 15 years, we have studied the reliability of UNIX command line and X-Window based (GUI) applications and Windows applications. In this study, we apply our fuzz testing techniques to applications running on the Mac OS X operating system. We continue to use a simple, or even simplistic technique: unstructured black-box random testing, considering a failure to be a crash or hang. As in the previous three studies, the technique is crude but seems to be effective in locating bugs in real programs.We tested the reliability of 135 command-line UNIX utilities and thirty graphical applications on Mac OS X by feeding random input to each. We report on application failures - crashes (dumps core) or hangs (loops indefinitely) - and, where source code is available, we identify the causes of these failures and categorize them.Our testing crashed only 7% of the command-line utilities, a considerably lower rate of failure than observed in almost all cases of previous studies. We found the GUI-based applications to be less reliable: of the thirty that we tested, only eight did not crash or hang. Twenty others crashed, and two hung. These GUI results were noticeably worse than either of the previous Windows (Win32) or UNIX (X-Windows) studies.

MATERIALS AND METHODSDuring its response to low cytokinin concentrations, a tissue might be expected to bind the incoming hormone rather tenaciously. High affinity binding sites could sequester the hormone, transport it, enzymically modify it, or provide the first step in the hormonal response. These functions need not be mutually exclusive, but a number of physiologically important cytokinin-binding sites could exist in a single tissue or cell type. Study of binding sites could clarify the cytokinin economy and could lead to a molecular understanding of the cellular response to cytokinin.The first demonstration of cytokinin binding to a subcellular component was provided by Berridge et al. (2), who described low affinity binding to Chinese cabbage ribosomes. Fox and Erion (8) found such activity in wheat germ ribosome preparations, but also noted high affinity bzl6Ade4-binding sites that could be solubilized from the ribosomes with 0.5 M KCI. The same laboratory has since reported on several aspects of the purification and properties of this high affinity binding moiety (4,5,7,9). Recently, Polya and Davis (24) have published their work on a wheat germ protein that is apparently identical to that under investigation by Fox's group.In addition, Sussman and Kende (28) have reported heat-labile high affinity binding of cytokinins by the 80,000g pellet from suspension-cultured tobacco cells. The nature and intracellular location of these sites are, however, unknown.

Four series of azidopurines have been synthesized and tested for cytokinin activity in the tobacco callus bioassay: 2-and 8-azido-N6-benzyladenines, -N -(A2-isopentenyl)adenines, and -zeatins, and N -(2-and 4-azidobenzyl)adenines. The compounds having 2-azido substitution on the adenine ring are as active as the corresponding parent compounds, while those with 8-azido substitution are about 10 or more times as active. The 8-azidozeatin, which is the most active cytokinin observed, exhibited higher than minimal detectable activity at 1.2 x 10-5 micromolar, the lowest concentration tested. The shape of the growth curve indicates that even a concentration as low as 5 x 10-6 micromolar would probably be effective. By comparison, the lowest active concentration ever reported for zeatin has been 5 x 10-5 micromolar, representing a sensitivity rarely attained.All of the azido compbunds have been submitted to photolysis in aqueous ethanol, and the photoproducts have been detected and identified by low and high resolution mass spectrometry. They are rationalized as products of abstraction and insertion reactions of the intermediate nitrenes. The potential of the major released products as cytokinins was also assessed by bioassay. 2-Azido-N6-(A2-isopentenyl)adenine competed with 114CIki-netin for the cytokinin-binding protein isolated from wheat germ. When the azido compound was photolysed in the presence of this protein, its attachment effectively blocked the binding of 114Clkinetin.Extensive studies of structure-activity relationships for cytokinins have led to a well-defined concept of the chemical nature of '