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  • Author or Editor: Hening Hu x
  • Journal of the American Society for Horticultural Science x
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Seedlings of pecan [Carya illinoensis (Wangenh.) C. Koch] grown in perlite culture were treated with N and S in a 5 × 5 factorial in a randomized complete block design to determine the effect of N, S, and N × S interaction on vegetative growth and photosynthesis. Nitrogen and S deficiency symptoms occurred when leaf N and S were < 25 and 1.4 mg·g-1 dry weight, respectively. Photosynthesis was reduced when combined leaf N and S exceeded 35 and 3.7 mg·g-1 dry weight, respectively; growth was reduced when leaf N and S were > 34 and 3.7 mg·g-1 dry weight, respectively. Photosynthesis and growth increased with N supply, but depended on leaf N: S ratio. In plants without visible N or S deficiency, a N: S ratio of ≈9. is proposed to be near the optimum for maximum growth. Comparison of leaf N, S, and the N: S ratio with similar analyses in selected orchards suggests that pecan productivity will increase from S application under field conditions. We conclude that the interaction” of N and S imposes stringent controls on leaf N and S, photosynthesis, and growth.

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The activities of catalase and of glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH), the two key enzymes in the pentose phosphate pathway (ppp), were measured in the seeds of Prunus persica (L.) Batsch var. nectarina Maxim `Nectarine 7'. The seeds were subjected to three imbibition treatments: 1) continuous 24C; 2) continuous 4C; and 3) application of thiourea (TU)/gibberellic acid (GA) at various concentrations to seed held at 24C then subsequently chilled at 4C. Treatments of continuous 24 or 4C indicated that catalase, G6PDH, and 6PGDH exhibited significant activity increases only when the seeds obtained germination potential, which occurred in the seeds chilled for 7 weeks at 4C. Seeds held at 24C did not germinate and showed little change with time in G6PDH and 6PGDH activity. There was only a slight increase in catalase activity beginning 3 weeks following treatment initiation and a decrease in activity following 13 weeks of treatment. Thiourea treatment resulted in an inhibition of catalase activity and a stimulation of G6PDH, but had no effect on 6PGDH activity. However, no correlation between enzymic activity and seed germination was found. The results strongly questioned the role of the ppp and catalase activity in dormancy control as previously hypothesized.

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Greenhouse-grown pecan [Carya illinoensis (Wangenh.) C. Koch] seedlings were treated with S as SO4 -2 (0 to 4 mm) to determine the effect of S on its vegetative growth, chlorophyll concentration, nutrition, and free and protein amino acid content. Sulfur deficiency symptoms occurred when leaf S was ≈1.5 mg·g-1 dry weight or less. Chlorophyll concentration and growth increased curvilinearly with leaf S and had not peaked when leaf S was 2.7 mg·g-1 dry weight. The N : S ratio in the leaf and leaf S were equally reliable indicators of the S status of the plant, but the optimum ratio was less than the value of 15 found in other plant species. Calcium and Mg decreased with S application, suggesting a direct SO4 -2 or NH4 + effect. The concentration of all other elements determined was elevated, in one or more plant parts, when S deficiency symptoms were visible. The most conspicuous effect of S deficiency on N metabolism was a greatly expanded free amino acid pool, mainly arginine. The concentration of free amino acids decreased exponentially with leaf S. Conversely, protein amino acid was inhibited by S deficiency and increased with leaf S concentration or, perhaps more specifically, with methiouine.

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The influence of B and salinity [3 Na2SO4 : 1 CaCl2, (molar ratio)] on B toxicity and the accumulation of B, sodium, and SO4 in six Prunus rootstocks was evaluated. High salinity reduced B uptake, stem B concentrations, and the severity of toxicity symptoms in five of the six rootstocks. Forward and backward stepwise regression analyses suggested that stem death (the major symptom observed) was related solely to the accumulation of B in the stem tissue in all rootstocks. The accumulation of B and the expression of toxicity symptoms increased with time and affected rootstock survival. No symptoms of B toxicity were observed in leaf tissue. The Prunus rootstocks studied differed greatly in stem B accumulation and sensitivity to B. The plum rootstock `Myrobalan' and the peach-almond hybrid `Bright's Hybrid' were the most tolerant of high B and salinity, whereas the peach rootstock `Nemared' was very sensitive to high B and salinity. In all rootstocks, adding B to the growth medium greatly depressed stem SO4 concentrations. In every rootstock except `Nemared' peach, adding salt significantly depressed tissue B concentrations. A strong negative correlation between tissue SO4 and B was observed. Grafting experiments, in which almond was grafted onto `Nemared' peach or `Bright's Hybrid', demonstrated the ability of rootstocks to influence B accumulation and scion survival.

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The phloem mobility of boron (B) in plants varies dramatically among species. Variations in phloem B mobility occur as a consequence of the presence of sugar alcohols (polyols) in some species but not in others, and these differences in phloem B mobility profoundly affect the expression of B toxicity symptoms. Twenty-four species including common ornamental species varying in sugar alcohol content, were selected to test their response to B toxicity. Species that do not produce sugar alcohols exhibited previously described B toxicity symptoms that include accumulation of high concentrations of B in, and burning of, the tip and margin of old leaves. In the sugar-alcohol-producing species these symptoms were absent, and B toxicity was expressed as meristematic dieback and an accumulation of B in apical tissues. These symptoms have not previously been associated with B toxicity in these species and hence may have been frequently misdiagnosed.

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Boron (B) remobilization, mannitol and glucose concentrations, and the effect of B application on changes in soluble carbohydrates were investigated in various organs of bearing `Manzanillo' olive trees (Olea europaea L. `Manzanillo'). Following foliar 10B application to leaves of various ages, there was significant 10B export out of the treated leaves, and significant 10B enrichment in nontreated adjacent organs, including inflorescences and fruit. Results demonstrated that B can be remobilized from leaves of various ages, and that foliar-applied B is phloem mobile in olive. Soluble carbohydrate analysis determined that mannitol and glucose are the predominant sugars in all organs analyzed and that the mannitol concentration in the leaves is adequate to account for all B transport. This is consistent with observations in other species, where the presence of mannitol is known to facilitate phloem B transport through formation of a mannitol-B complex. Previous reports have indicated that B application can alter carbohydrate metabolism. In the present study, foliar B application significantly suppressed glucose concentration in the leaf petioles of all ages and increased mannitol in petioles of the current-year-developed leaves.

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