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Effects of Boron on the Physiology and Nutritional Status of Papays(Carica papaya L.) seedling
不完全，有中空斷裂現象。而 8 ppm處理植株老葉葉尖及葉緣呈現黃化壞疽現象。石
In Taiwan, an aggregate of 6300 hectares has been allocated for the cultivation of papaya. The plant, however, is devastated by ring spot virus diseases on the ond hand and plaqued occasionally by boron deficiency, which leading to the decreases in fruit quality and yields, on the other. In order to probe the effects of boron on the physiology of papaya, endeavors have been made to investigate the changes that boron deficiency could bring to metabolism, and inorganic nutritional status of the crop.
The results showed, when papaya was subjeted to boron deficiency for 21 days, symptoms such as yellowing of new leaves, tissues texture turning hard and brittle, growth retardation and the formation of brown, coralshaped roots were evident. Paraffin method demonstrated the primodia, in addition to being undergrown, were hollow and broken. At 8 ppm of boron, the tips and edges of the old leaves were yellow and necrosis. The development of primodia, as revealed by paraffin method, had taken place but not reached the stage of ompletion. Phloroglucin stain indicated lignin content in 0 ppm boron treated papaya was high and dense, which also showed a tendency of penetrating into the inward of the tissues. The growth of the boron-starvated plants was stunted. Their surface areas were around 520 cm2 and stopped to grow any larger. The fresh and the dry weight of their roots and the parts of plant above ground were lighter than that of their normal counter-parts. The same is true with their water content; the boron deficient plants contained less water.
In the course of boron deficiency, nitrogen in the form of ammonia rose sharply after 14 days of treatment whereas soluble proteins on the other hand decreased after 21 days of incubation. The amounts of free amino acids in the plant were higher as the deficiency proceeded to the 28th and 35th days. However, there was no perceptible change in nitrate level in plants which under went different treatments. The soluble carbohydrates in leaf surged drastically beginning with the 7th day of the treatment and remained high for the rest experimental period. However, the concentrations of reducing sugars did not show any sign of increase until the 14-21 day period was reached. Low boron regime inhibited glutamine synthetase and acid phosphatase activities but stimulated the activity of peroxidase. Interextingly, it had no effect whatsoever on nitrate reductase.
An assay of mineral elements in papaya leaf indicated that low boron uptake had led to the drop of N, P, Ca, Cu, Fe, B contents but not the levels of K, Mg, Mn and Zn. Furthermore, the conditions were harmful not only to growth but also to nitrogen and carbon metabolisms, enzyme activities and ion composition of papaya.
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