Translocation through plant tissue

In this type of activation, which occurs in both animal and plant tissues, the original insecticide is relatively stable and can be translocated through plant tissues without destmctive hydrolysis until the oxidation has occurred, which then makes the insecticide both highly toxic and relatively unstable so that it rapidly is hydroly2ed to nontoxic products. 

Difficulty in Translocating Brassinolide through Plant Tissue. The navel orange experiments revealed that brassinolide was only effective when polyethyleneglycol was added to the spray solution to prevent quick evaporation. Brassinosteroid is active at very low concentrations, such as 0.1 ppm. When such a low concentration was sprayed in solution on the plants with surfactant, the solution dried up immediately and did not be penetrated into the plant tissue. Thus, addition of chemicals to avoid quick evaporation is necessary for a successful treatment. 

Sodium chlorate is strongly phytotoxic to all green plant tissues, hence it is used as a total contact herbicide on soil and folia. It is also absorbed through the roots and is rapidly translocated into the parts of the plant above the soil. 

Only the D-isomer of these compounds shows strong herbicidal activity, while the L-isomer is inactive, and any additional substituents on the benzene ring significantly decrease the activity (6). Thus we speculated that the phenoxypropanoic acid part of the structure is the essential moiety, which interacts with a receptor in plant tissues. And if this is so, the pyridinyloxy moiety may serve to optimize the hydrophobicity of the whole molecule for maximum herbicidal activity, enhancing the translocation of the molecule through the plant. 

Following spray treatment, using a [ C]-labeled radioactive compound, most of the antibiotic remained as residue on the surface of the rice plants and only a small portion was taken up and translocated in the host tissue. In contrast, the compound was easily taken up through wounds of infected plant parts and translocated to the apexes [9]. 

In blue lupin, a rapid lateral movement of pH]-[9R]Z and [ H]-(diH)(9R]Z from xylem to bark was observed using girdled stems with leaves removed. This movement was somewhat more pronounced in the two main lateral stems which develop just below the primary inflorescence. Thus, when pM]-[9R]Z (2 /xM) was supplied to derooted plants via the xylem stream, for 1.5 h followed by a water chase for 3.5 h, 24% of the total [ H] extracted from the stem was derived from the bark. Kinetic studies of metabolites in xylem plus pith and in bark following pH]-[9R]Z and [ H]-(diH)[9R]Z uptake through the xylem of de-rooted lupin plants, together with studies of the metabolism of these ribosides in excised stem tissues, indicated that (1) the supplied ribosides were translocated to bark per se and possibly as the nucleotides (2) U-Ri and DU-Ri were formed exclusively in the bark and were probably the precursors of U-NT and DU-NT, respectively (3) ribose cleavage and sidechain reduction were largely confined to bark. 

---