Ethylene-induced Isocoumarin Formation in Carrot Root Tissue.

The concentrations of 3-methyl-6-methoxy-8-hydroxy-3,4-dihydroisocoumarin (MMHD) formed in carrot roots inoculated with certain fungi or treated with indole-3-acetic acid, 2,4-dichlorophenoxyacetic acid, or 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), were related to the amount of ethylene produced by the root tissue. Ethylene applied exogenously in concentrations above 0.3 ppm induced the formation of MMHD in carrot root discs. Continued production of MMHD required the continued presence of ethylene. The amounts of MMHD in the discs were reduced by CO(2), an inhibitor of ethylene action, and by reduction of the partial pressure of ethylene in fungus-inoculated or 2,4,5-T-treated carrot root discs. The results indicate that ethylene is required for the induction of MMHD formation by carrot root tissue.

2,4,5-trichlorophenoxyacetic Acid: effect on ethylene production by fruits and leaves of fig tree.

Production of ethylene by fruits and leaves of the fig tree was stimulated by the application of 2,4,5 trichlorophenoxyacetic acid (20 parts per million) to levels that apparently were responsible for hastened matura tion of fruit, epinasty, and senescence of leaves.

Effect of gamma radiation on the ripening of bartlett pears.

Gamma radiation at doses of 300 Krad or more inhibits the ripening of Bartlett pears (Pyrus communis L.). Immediately after irradiation there is a transitory burst of C(2)H(4), which subsequently declines in fruits subjected to inhibitory doses. Ethylene production associated with ripening begins at the same time in unirradiated fruits and those subjected to noninhibitory doses, but the latter produces much more C(2)H(4) at the climacteric peak. Fruits subjected to inhibitory doses produce low levels of C(2)H(4) unless subjected to exogenously applied C(2)H(4), whereupon they produce enough of the gas to induce ripening in unirradiated fruits.Pears subjected to 300 and 400 Krad of gamma rays did not ripen even when held in a flowing atmosphere containing 1000 ppm of C(2)H(4) for 8 days at 20 degrees . It is concluded that the action of gamma rays on Bartlett pears involves both an inhibition of C(2)H(4) production and a decreased sensitivity of the fruit to the ripening action of the gas. Ripening of Bartlett pears is inhibited by gamma radiation only when applied to preclimacteric fruit.