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

Abstract

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...

Effects of Phosphorus Deficiency on the Photosynthesis and Respiration of Leaves of Sugar Beet

“…Under conditions of light saturation, 25 CO2 cm-2 sec'I (68 mg CO2 dM-2 hr-') in oxygen-free air. Similar high rates for sugar beet were obtained by Hall (11) and Elmore (8). Respiration rates in the dark, RD, (measured 15 hr after the dark period commenced) in our experiments were about 5 ng CO2 cm-2 sec-', and agreed closely with those of Hall (11).…”

Expression of a luteoviral movement protein in transgenic plants leads to carbohydrate accumulation and reduced photosynthetic capacity in source leaves

“…In many cases the rate of photosynthesis was reduced and chloroplast function altered (Hall and Loomis, 1972;T~csi et aL, 1994;T~csi et al, 1996;Zaitlin and Hull, 1987). In a few instances ribosomal RNA and protein synthesis were found to decrease in infected plants (Hirai and Wildman, 1969;Wang and Maule, 1995).…”

Systemic Acquired Resistance Mediated by the Ectopic Expression of Invertase: Possible Hexose Sensing in the Secretory Pathway.

“…lnfection of leaf tissues by viruses and pathogens may result in elevated carbohydrate levels (Watson and Watson, 1951;Steudel and Heiling, 1954;Hall and Loomis, 1972). Thus, local accumulation of sugars caused by the pathogen may in turn be exploited by the plant cell in the way described above.…”