Photosynthesis, nitrogen metabolism and shoot:root equilibria in leeks infected with the rust Puccinia allii Rud

Various aspects of the physiology of rust-infected leeks were studied. Rates of net photosynthesis of healthy leaves of leek were very low In comparison with other C3 species. However, rust Infection led to substantial reductions In photosynthetic rates In Infected leaves. This was linked to large stimulations In dark respiration and reductions In photorespiration, coupled with reductions In the activity of a variety of photosynthetic enzymes. Including RuBPcase, PePcase and 3-phosphoglycerate kinase. Rust Infection also led to reductions In total soluble protein and chlorophyll, and chloroplast preparations from Infected leaves exhibited much reduced rates of oxygen evolution compared to healthy controls. Rates of net photosynthesis were markedly Increased In uninfected leaves of otherwise rusted leeks. Such leaves also exhibited decreased rates of photorespiration, although dark respiration was not affected. An examination of enzyme activity In uninfected leek leaves revealed that RuBPcase, 3-phosphoglycerate kinase, NADP-glyceraldehyde-3-P-dehydrogenase and NADP malic enzyme activities were all significantly stimulated. Infection of the lower leaves had no effect on the activity of PePcase and NAD malic enzyme in upper, uninfected leaves, nor were protein and chlorophyll content altered. Construction of a carbon budget revealed that rust infection led to a substantial reduction in assimilate production in all but the two upper, uninfected leaves of infected leeks. Disease also led to reductions in the translocation of assimilates out of all rusted leaves, although stimulations in assimilate translocation were noted in uninfected fourth leaves. Although photosynthesis was stimulated in upper, uninfected leaves of rusted leeks, assimilate production by these leaves was slightly lower than controls. Since reductions in photosynthesis by infected leaves appeared to account for reductions in dry weight, the observed stimulations in photosynthesis in uninfected leaves may only have served to alleviate the effects of rust infection. A detailed examination was made of photosynthesis in localized regions of infected leek leaves. Oxygen evolution, expressed on both a chlorophyll and an area basis, was significantly reduced in pustule regions, coupled with an increase in dark respiration, for the duration of the experiment. The activity of RuBPcase was lower in pustule areas, and losses in total soluble protein and chlorophyll were observed. Areas between pustules exhibited photosynthetic rates near to control values, on a chlorophyll basis, and dark respiration was reduced for at least part of the experiment. No significant alteration in RuBPcase activity, nor in protein or chlorophyll levels, was detected in inter-pustule areas. Rates of photosynthesis were significantly stimulated in tissue from uninfected leaves of rusted plants, coupled with a lowering of dark respiration. RuBPcase activity was significantly stimulated in uninfected leaves towards the end of the experiment, while protein and chlorophyll levels were unaltered. Phosphate did not appear to limit photosynthesis in any tissue type, since the addition of exogenous phosphate had no appreciable effect on rates of photosynthesis. Stomatal resistance was also measured, revealing that infection led to reductions in stomatal resistance in pustule regions, while areas between pustules remained unchanged. By the end of the experiment, i.e. 21 days after inoculation, stomatal resistance was considerably higher in uninfected leaves of otherwise rusted leeks, compared to controls. Cytokinin concentrations were higher in pustule areas at 14 days after inoculation, although trans-zeatin (t-ZR) concentration returned to near control values in pustules by the end of the experiment. Abscisic acid (ABA) concentrations were significantly higher in both infected regions and in uninfected leaves by 14 days after inoculation. However, the concentration of ABA was significantly less in Infected regions by 21 days after inoculation, and there was almost eight times more ABA present in uninfected leaves by this time. The concentration of dihydrozeatin (DHZR) was slightly Increased in all tissue types compared to healthy controls, by the end of the experiment. ABA and cytokinin concentrations were always consistently lower in roots of infected plants than in healthy ones at 21 days after inoculation, and with the exception of DHZR, at 14 days after inoculation also. (Abstract shortened by ProQuest.)