Effect of Sink Region Cooling on Translocation of Photosynthate

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ABSTRA(CTTran-slocation rate, ATP level, and CO2 production of a developinig leaf (sink leaf) were studied in stugar beet (Beta vulgaris) planits prior to and duiiig aniaerobic treatment of the sink leaf. W/ithini 3 to 5 mintutes after oniset of treatmienit with a N2 atmosphere, translocationi inito tile sink leaf decreased to near zero and th-eni recovered to a level of about .;0% of the control over the next 2 lours. A decline in CO2 output and ATP levels coincided photoperiod with a 24-C day temperature and 17-C night temperature. Light intensity at leaf level was about 1200 ft-c during the 30-to 35-day growth period and during the labeling period. Leaves of the experimental plants were removed except for a source leaf with a 10-cm-long blade and a sink leaf with a 3-to 4-cm-long blade. The latter was held against a Geiger Mueller detector to follow the arrival of labeled translocate.Measuring Systems. The methods used for steady-state labeling with "4CO, and for continuously monitoring the arrival of labeled translocate were described previously (5). The sink leaf was enclosed in a light-tight, sealed chamber which was part of a closed gas-flow system containing a nondispersive, infrared gas analyzer.

“…The 50% inhibition of translocation under anaerobiosis corresponded to the 30 to 50%,, decrease observed when the sink was cooled to near zero (4).…”

Section: Resultsmentioning

confidence: 84%

mentioning

confidence: 99%

Effect of Sink Region Anoxia on Translocation Rate

Geiger

Christy

1971

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“…Low temperatures have been shown to retard translocation in other plants (4,6,16). In the greenhouse studv the minimun night tenmperature was 200.…”

Section: Discussionmentioning

confidence: 97%

Carbon-14 Distribution in Carbohydrates of Immature Zea mays. Kernels Following ¹⁴CO₂ Treatment of Intact Plants

Shannon¹

1968

Shortly after Zea mays L. plants were exposed to (14)CO(2), most of the radioactivity in the kernel occurred in the free monosaccharides, glucose and fructose. Later the proportion of (14)C in sucrose increased and that in the monosaccharides declined. These data have been interpreted as showing that the translocated sugar is hydrolyzed prior to or during its movement into the storage cells of the endosperm. This hydrolysis appears to occur in the "pedicel region" of the kernel. After entry into the endosperm tissue, sucrose was rapidly resynthesized from the monosaccharides prior to its utilization in starch synthesis.

“…It was considered that root cooling may reduce translocation more drastically (3,19). Roots were cooled by passing ice water through the pots.…”

Section: Methodsmentioning

confidence: 99%

An Explanation for the Difference in Photosynthetic Capabilities of Healthy and Beet Yellows Virus-infected Sugar Beets (Beta vulgaris L.)

Hall

Loomis

1972

Sugar beets (Beta vulgaris L) infected with the Beet Yellows Virus exhibit lower rates of net photosynthesis at light saturation than do healthy plants. These Pn reductions were correlated with increases in leaf resistance to water vapor loss. Theoretical analyses demonstrated that, although the leaf resistance to water vapor loss increases could account for a major part of the net photosynthesis decreases, some other aspect of leaf functioning also was debilitated by infection. Both the levels and the activities of ribulose-l, 5-diP carboxylase were less on a leaf area basis in extracts from infected leaves than from healthy ones. Soluble carbohydrates accumulate in Beet Yellows Virus-infected leaves, but inhibiting translocation in several ways provided no evidence in support of the hypothesis that the accumulation of photosynthates in leaves has a direct, short term, feed-back effect upon the photosynthetic rate.Sugar beets (Beta vulgaris L.) exhibit reductions in net photosynthesis at light saturation when infected with the Beet Yellows Virus (6). The physiological explanation for this Pn8 reduction has practical significance in that (a) it might be useful in selecting genotypes for tolerance to the virus (4), and (b) it may also provide an evaluation of the physical and biochemical factors that control net photosynthesis at light saturation in healthy plants. It has already been shown that differences in photorespiration (estimated from the inhibition by oxygen of CO2 uptake in normal air) and differences in respiration (estimated from rates of CO2 evolution in the dark) could not account for the reduction in infected leaf Pn (6). There are indications that the physical resistance to the entry of CO2 into the leaf may be greater in infected plants 1This investigation was partially supported by a grant from a cooperative agreement with the United States Department of (6, 21), and it has also been reported that soluble and insoluble carbohydrates accumulate to high levels in leaves of BYVinfected sugar beets (18, 23). Thus, it was possible that the frequently postulated feed-back effect of photosynthate accumulation in leaves on photosynthesis might also be present. No unequivocal, direct evidence has been reported which supports this postulate (15), yet it is a potentially important aspect of plant functioning. If a feed-back mechanism of this type does exist, then photosynthetic rates may reflect translocation capacity, growth, and sink activity, as well as climatic factors and the inherent photosynthetic capabilities of both chloroplast and leaf. MATERIALS AND METHODSA uniform hybrid of Beta vulgaris L. (MS NB1 X NB4) was grown in pots in a mixture of peat moss and sand in different environments. The plants were thinned for uniformity to one plant per pot, and half the plants were inoculated with the Brawley strain of BYV supplied by C. W. Bennett, United States Department of Agriculture, Salinas, California. Four plant replicates were used in most of the treatments. In experiments I and II, the p...