Translocation of 14C-assimilates in Canada Thistle and Leafy Spurge

Download or read book Translocation of 14C-assimilates in Canada Thistle and Leafy Spurge written by Alan S. MacDonald and published by . This book was released on 1977 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Greenhouse and field studies were concerned with the translocation of 14 C-assimilates in Canada thistle ( Cirsium arvense (L.) Scop.) and leafy spurge ( Euphorbia esula L.). The pattern of distribution of 14 C-assimi1ates was the same for both species. When individual shoots were supplied with 14 C0 2 , most of the fixed carbon was retained in the treated shoot but some 14 C was exported to the other parts of the plant. The principal sink was the root system. Translocation of 14 C to the roots was rapid; it was faster for Canada thistle than for leafy spurge but the distribution over time was the same. It was not until thistles were 30 days and leafy spurge plants 60 days old that the shoots sent significantly more 14 C-assimil- ates to the rapidly growing areas of the root system than they did at early stages of shoot growth. In Canada thistle, the export of assimilates to the roots was greater from a mature leaf occupying a middle position on the shoot than from leaves situated either above or below that portion. There was no evidence to support the hypothesis that lower leaves tend to supply the roots with assimilates. The translocation and subsequent distribution within the plant was highly sensitive to temperature. Less 14 C was retained in the shoot of plants treated at 10°C than in plants which had received treatment at either 20 or 27°C. Again the principal sink was the root system. The translocation of assimilates from a primary shoot to a number of secondary shoots present on the root was studied for both species. Of the 14 C not retained in the treated shoot, most was found in the roots and the remainder in the secondary shoots. All secondary shoots received some 14 C from the treated primary shoot. The 14 C was distributed evenly among the secondary shoots. The transfer of 14 C-assimilates between a secondary shoot or shoots and the primary shoot was examined in Canada thistle plants. Quantitative data are presented and it is concluded that the existence of a reciprocal exchange of assimilates between shoots means that each must simultaneously be both a source and a sink. Shoots and portions of the roots closest to the treated shoot contained slightly more 14 C than those more distal. Root buds were noted as major sinks. In the field, rosettes of Canada thistles were able to export assimilates to a limited extent after exposure to 14 C0 2 . The sink areas were the roots, regrowth shoots and other rosettes to which the fed rosette was connected. In the greenhouse, the presence of secondary shoots did not alter the distribution of 14 C-assimilates to the roots. Sectioned material and cleared whole tissues indicate that the connections between the vascular systems of the shoot and the root for Canada thistle and leafy spurge are in many respects similar. The anatomical feature which appears to be significant with respect to the junction is the uninterrupted extension of two collateral bundles from the root stele to the shoot. There is no real evidence of an anatomical block at the site of the junction although accumulation and metabolism of 14 C-assimi1ates in the area of procambial cells could prevent the movement of assimilates or herbicides to a shoot. The procambial cells constitute a "constriction" to assimilate flow rather than an actual block.