SURFACE CHARACTERS OF DIVIDING CELLS IV. ALLOTMENT OF THE CORTEX AND PARTITIONING OF THE CYTOPLASM IN UNEQUAL DIVISION OF GRASSHOPPER SPERMATOCYTE UNDER THE TEMPERATURE GRADIENT

The allotment of cell surface and the allotment of cell volume between two daughter cells were observed in unequal division of spermatocytes of the grasshopper, Acrida lata, caused by steep temperature gradient. In applying a temperature gradient through the cell division, coincidence in position between the provisional division plane indicated by the tongue of mitochondria, and the actually formed furrow, has been established (i) by markers attached to cell surface and (ii) by calculated volumes of cytoplasm on the two sides of the planes. On removing a temperature gradient while a cell is dividing, equality is regained as far as the volume of the incipient daughter cells are concerned but territories of the surface once allotted are strictly observed. Unequal division, therefore, involves two different meanings; allocation of the surface, and apportionment of the cytoplasm both of which are dependent upon the development of asters.     

Biological activities of rishitin, an antifungal compound isolated from diseased potato tubers, and its derivatives

Rishitin, a norsesquiterpene alcohol, found in infected, resistantpotato-tuber tissue completely inhibited zoospore germinationand germtube elongation of Phytophthora infestans (MONT.) DEBARY at 10^–3M. There was little difference in sensitivityto rishitin among races of Phytophthora infestans. IAA-inducedelongation of Avcna coleoptile sections and GA₃-induced elongationof wheat leaf sections were also inhibited by rishitin. Theinhibition of IAA-induced elongation of Avena coleoptiles wasrelieved to some extent by increasing IAA concentration. However,little relief of the inhibition of GA₃-induced elongation ofwheat leaf sections was obtained by increasing GA₃ concentration.No plant injury was observed at this concentration of rishitin(10^–3M). Examination of a series of rishitin derivatives indicated thatthe hydroxyl group at C-3 is indispensable for antifungal activity.This activity was intensified by saturating the double bondbetween the rings of rishitin and/or that of the isopropenylgroup at C-7, though activity decreased when oxygenated functionalgroups were introduced into the side chain. Aromatization of the A ring did not lower biological activities.The antifungal activities of most rishitin derivatives almostparalleled their activities as plant growth retardants. However,some compounds without antifungal activity were active as growthretardants. ¹Studies on the phytoalexins (5). (Received August 14, 1968; )     

SURFACE CHARACTERS OF DIVIDING CELLS III. UNEQUAL DIVISION CAUSED BY STEEP TEMPERATURE GRADIENT IN GRASSHOPPER SPERMATOCYTE

Division of the spermatocytes of the grasshopper, Acrida lata, was studied under a steep temperature gradient. When a temperature gradient is applied along the spindle, the development of the aster on the warmer side is accelerated which, in turn, pushes the spindle toward the cooler side of the cell and the division becomes unequal. A condition to obtain such an unequal division is to shift the spindle by the temperature gradient and hold it eccentric during anaphase. Future cleavage plane is foreshadowed by the tongue of the mitochondria at anaphase before the cell departs from sphericity. If a temperature gradient is applied across the spindle, the spindle slides towards the cooler side sideways and the furrow is formed earlier, on the farther side of the cells from the spindle on the warmer side, although the size of the daughter cell is equal. The result indicates that the advance of the furrow is endothermically accelerated.