The photoreaction controlling seed germination in Eragrostis curvula

This study reexamines the nature of the previously reportedphotoreaction (7) that controls simultaneous promotion and inhibitionof germination of Eragrostis curvula (SCHRAD.) NEES seeds bya light-interruption of the dark-imbibition period. As the intensity of the illumination that interrupts the dark-imbibitionperiod is increased many fold, the promotion of germinationincreases slightly; but the percent of seed apparently inhibitedincreases appreciably. As the intensity of the illuminationof the main light period following an interrupted dark periodis increased, the inhibitory effects of the interrupting lightare increasingly counteracted. Thus, an interaction occurs betweenthe interruption and the main light period; the higher the energyof the interrupting light, the higher must be the energy oflight during the main period to overcome the apparent inhibition. The reversibility of the separate promotive and inhibitory effectsof light that interrupts the dark-imbibition period and thepromotive effects in the main light period indicate that allare phytochrome controlled. Both promotive and inhibitory effectsare produced at the time of the interruption by the formationof the P_fr form. A physical analogy is used to suggest an explanationfor the inhibitory effects. Thus, only one photoreaction, that of phytochrome, is thoughtto account for all the results. This conclusion is supportedby the finding that both promotive and inhibitory responsesare energy dependent over wide reciprocal variations of timeand intensity of irradiation. (Received December 15, 1967; )     

In vitro Inhibition of Oocyte and Follicular Maturation and Spawning in Starfish (Asterias forbesi) by 2-4-Dinitrophenol

The in vitro effects of 2-4-dinitrophenol (DNP) on spawning and follicular and oocyte maturation in starfish ovaries and its various cellular components were investigated. Spawning and oocyte and follicular maturation induced by starfish gonadotropin radial nerve factor (RNF) in isolated ovarian fragments were all inhibited by appropriate doses of DNP. DNP inhibits processes which occur shortly after addition of the gonadotropin; in ovarian fragments insensitivity to DNP inhibition occurred shortly after addition of RNF but prior to initiation of spawning. Spontaneous follicular and oocyte maturation which occurred following release of ovarian follicles into sea water was prevented by DNP. In non-spontaneously maturing follicles released from the ovary, DNP inhibited both follicle and oocyte maturation induced by the secondary stimulator of spawning and maturation, 1-methyladenine (1-MA). DNP also inhibited 1-MA induced meiotic maturation in isolated immature oocytes incubated in the absence of follicle cells. Inhibition of oocyte maturation was not associated with inhibition of ³H-1-MA incorporation by isolated oocytes. Immature oocytes incubated in the presence of DNP underwent maturation following washing and subsequent exposure to 1-MA. Immature oocytes initially exposed to both 1-MA and DNP, however, showed decreased maturation responsiveness following washing and re-exposure to 1-MA. The results suggest that the inhibitory effects of DNP on spawning and oocyte maturation are the result of direct effects on the oocytes and possibly other cells and tissues within the ovary.     

Hyaluronate and Hyaluronidase in Morphogenesis and Differentiation

Hyaluronate turnover is correlated with morphogenetic eventsduring chondrogenesis in the regenerating newt limb and in thechick embryo limb and axial preskeleton and during developmentof the chick embryo cornea. In vitro hyaluronate, in concentrationsas low as 1 ng/ml, blocks the formation of cartilage—likeaggregates in high density stationary cultures of stage 26 chickembryo somite cells. This inhibition is prevented by hormonesknown to promote skeletal development and by adenosine 3',5'cyclicmonophosphate. An hypothesis is discussed in which (1) hyaluronate may interferewith cell interactions leading to aggregation, encapsulationby matrix and consequent immobilization and (2) hyaluronateturnover could provide a means of timing of morphogenetic eventssuch as cell migrations, allowing sufficient accumulation ofcells prior to overt differentiated tissue formation.