| By using light microscopy, autoradiography, radioisotope technique and froze-etching, the transportation of exogenous jasmonic acid in relation to its effect on the induction of the secondary laticifer differentiation in Hevea brasiliensis Mull. Arg. clone ZY7-33-97 was studied.The shoots were fed with 3H-JA and the bark with xylem of the treated sites were excised and fixed in 2% EDC+4 % glutaraldehyde in 0.1 mol/L phosphate buffer at PH 7.2 at room temperature. Paraffin blocks were prepared after dehydration through graded series of alcohol. With the liquid-emulsion procedure, autoradiograph was made. The radioactive material was determined by the detection of the black silver grains in the sections. In the autoradiograph, a large amount of silver grains were detected. Their distribution pattern in paraffin sections was similar to that in the froze-eching autoradiograph. Thus, the paraffin section autoradiography founded by us could be used to analyze the transportation of exogenous 3H-JA in Hevea brasiliensis .Based on the data that exogenous JA was not metabolized within five days, the black silver grain should be associated directly with JA itself, not its derivatives. 3H-JA could transport rapidly in plant. It was detected in xylem of the treated site after being fed for 1 min. Five minutes later, 3H-JA was present in the bark and xylem of the upper part and that of the lower part 10 cm far from the treated site respectively. In the cross-section of the samples from treated site, a lot of 3H-JA was detected in the sieve tubles, the secondary phloem parenchyma cells, the secondary phloem ray parenchyma cells, cambia regions, vessel wall, the secondary xylem parenchyma cells and the secondary xylem ray parenchyma cells, especially in the phloem and xylem ray parenchyma cells, suggesting that transportation of JA from phloem to xylem occurred mainly through ray parenchyma cells. In the cross-sections of the samples from the upper part as well as the lower part 5 cm and 10 cm far from the treated site respectively, 3H-JA was present exclusively in the secondary phloem and xylem, and no 3H-JA was found in epidermis and cortex five minutes and thirty minutes after feeding, indicating that JA could be transported upwards and downwards through vessel tuble and sieve tuble.Radioisotope showed that exogenous JA sustained mainly in the treated site afterentering. The CPM in the treated site was significantly higher than that in the other parts (P<0.01). The radioactivity in the samples from the treated site of wounded shoot was obviously lower than the radioactivity in the samples from the corresponding site of unwounded shoot ten minutes after feeding (P<0.0l), suggesting that localized mechanical wounding reduced the entrance of exogenous JA. Sixty minutes later, however, there were no obvious changes in the radioactivity in the samples of wounded shoot, suggesting that mechanical wounding held back the entered J A to the regions around wounded site. Meanwhile, similar case occurred for the unwounded shoot although the radioactivity reduced to much extent (P>0.05), suggesting that most of the entered JA was bounded to the treated site for a long time. The radioactivity in the samples of extending new shoot was significantly higher than the other four sites CP<0.05), but obviously lower than that of the treated site (P<0.05). Mechanical wounding reduced the radioactivity in the samples of new shoot although there was no significant difference comparing to the case of unwounded shoot. Low radioactivity was detected in the samples of the upper and lower stems 5 cm and 10 cm far from the treated site respectively, but there was no significant difference in the radioactivity among these four sites (P>0.05). This result showed that 3H-JA could transport upwards and downwards. In the treated site, most radioactivity of 3H-JA was detected in bark and xylem and moreover, the radioactivity was much higher in bark than that in xylem (P<0.01).When the first extending unit (EU1) was applied with 0.07% non-radioactive JA,... |
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